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ECG grammar, part 1 understanding the genesis of normal ECG PowerPoint Presentation

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Description : What is grammar ? As defined by Oxford advanced learner dictionary grammar is “A particular theory that is intended to explain the rules in language”. One can learn mother tongue without learning grammar. However one cannot teach his mother tongue without learning grammar. In my experience our residents and paramedics learn cardiology as their mother tongue. They learn by cramming clinical features , ECG and Echocardiography findings, without reasoning and concepts. They end up learning cardiology ( As their mother tongue) without learning the cardiology grammar. This is food for thought for the teachers and students. I wish to emphasize the importance of learning and teaching the concepts in clinical cardiology, which I consider as “ Cardiology grammar”.

Tags : Basic electrophysiology, QRS and T waves vectors,ECG paper, leads and axis

Published on : Aug 14, 2020 | Views : 3883 | Downloads : 105

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Slide 1-

What is grammar ? As defined by Oxford advanced learner dictionary grammar is “A particular theory that is intended to explain the rules in language”. One can learn mother tongue without learning grammar. However one cannot teach his mother tongue without learning grammar. In my experience our residents and paramedics learn cardiology as their mother tongue. They learn by cramming clinical features , ECG and Echocardiography findings, without reasoning and concepts. They end up learning cardiology ( As their mother tongue) without learning the cardiology grammar. This is food for thought for the teachers and students. I wish to emphasize the importance of learning and teaching the concepts in clinical cardiology, which I consider as “ Cardiology grammar”.
Slide 2-

As this a lengthy presentation I have split it into two parts. ECG grammar, part 1. “understanding the genesis of normal ECG”. ECG grammar, part 2. “understanding the genesis of abnormal ECG”.
Slide 3-

Who should download this presentation ? This presentation is for physicians and paramedics with exceptional curiosity to learn with reasoning. For example one who is concerned to know, Why are all ECG waves (P, QRS &T) inverted in aVR lead of normal person? Why is T wave four to five times wider than QRS. Why is T wave upright in ECG leads with upright QRS ,though they are generated by totally opposite electrical process ,repolarization and depolarization respectively.? Why is ST segmented elevated or depressed or T wave inverted in myocardial ischemia ? An unconcerned person is least bothered about such queries. However I believe that curiosity in learning is secret to master a subject. This is very interactive presentation . Please use option of animation as it will highly facilitate the understanding the discussion.
Slide 4-

ECG grammar, part 1. “understanding the genesis of normal ECG”.
Slide 5-

What is Cardiac Cycle? To define this we need to understand changes which occurs when we switch on AC/fan ? When we press switch on button an electric current is generated immediately followed by mechanical activity, (rotation of fan & emission cold air from AC ) .
Slide 6-

6 Thus cardiac cycle is defined as Repeated sequence of electro-mechanical changes in heart resulting in contraction (systole) and active relaxation (Diastole). So we have two types of activities in the heart. Electrical Changes in the heart followed by Mechanical Changes . The electrical changes in heart, represented by PQRST waves is recorded on a paper know as Electrocardiogram, by an instrument called Electrocardiograph.
Slide 7-

Definitions of key words used in basic electrophysiology. Electrophysiology is the study of electrical changes in the body at the cellular level.
Slide 8-

What is Voltage and what is current ?. Voltage the difference in electric charges between two points with opposite charges. It is the force 'push' that causes electrical charges to move in a wire or cell. Current is the rate of flow of electric charge. Voltage is the cause and current is its effect. In the body the electrical charges are carried by ions (atoms with positive or negative charges). What is electric circuit & potential Difference.? An electrical circuit is a path (wire ) through which an electrical current flows. Difference of Voltage (electric charge ) between any two points in a circuit is known as Potential Difference. It is this potential difference which makes current flow. Membrane potential? It is related to cell membrane. Membrane potential is difference in the numbers of ions( electrical charges ) across cell membrane. What is Polarization ? Polarization literally means division into two sharply contrasting groups or sets of opinions. In electrophysiology polarization refers to difference in electrical charge between inside and outside of the cell (Across the cell membrane ).
Slide 9-

Resting membrane potential (Resting Stage). *During resting stage (when cell is not activated ) there is difference of electrical charges across the cell membrane. This is called resting membrane potential. As shown in the figure interior of the cell is negatively charged (-90 mv). As Interior & exterior of cell have opposite charges in resting stage, the cell is in polarized state. −90 mv *Cause of resting membrane potential. Due to variable permeability and active Na - K pump ,these ions are unequally distributed in a intracellular & extra cellular compartment resulting in net negative charge inside the cell. Ions mainly responsible for resting membrane potential are Na ,K & negatively charged intracellular protein. Guyton and Hall Textbook of Medical Physiology 12th edition Resting membrane potential
Slide 10-

What is action potential of muscle . An action potential is a rapid rise and subsequent fall in voltage (membrane potential ) across a cell membrane. It consists of two stages , depolarization and repolarization. Depolarization and repolarization togather consists of four phases . Depolarization has one phase . This by convention is designated as phase “0”. Repolarization has three phases. Designated as phases 1,2 and 3. Polarized phase (Resting state).This is designated as phase 4.
Slide 11-

Action potential has four phases , one phase of depolarization & three phases of repolarization. Depolarization is reduction in the voltage (difference of charges ) across cell membrane. Phase “0”. It is phase of depolarization in which there is rapid influx of Na ions into the cell. Positively charged Na+ ions markedly reduces the negative charge inside the cell. Repolarization . It is process to restore the resting (Polarized ) state of cell membrane . Phase 1 In this phase there is partial restoration of negative charge inside cell caused by outward K+ ions. Phase 2. Plateau phase. Ca++ ions enters the cell & delays repolarization of myocardial cell. Phase 3. During this phase there is large efflux of K+ ions (Out of cell) resulting in negative charge inside the cell and restoration of resting ( polarized ) state. Phase 4. Resting phase. Cell is in polarized state. Na+ ions are pumped out and K+ ions enters the cell restoring the ionic balance. Note. Action potential starts from small excited portion of the myocardial cell membrane. It is self propagating , moves ,across all the parts of the cardiac chambers & surrounding fluids.
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https://www.google.com/url?sa=i&source=images&cd=&ved=2ahUKEwiA9uX6pc3lAhVCzoUKHSbnDI8QjRx6BAgBEAQ&url=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FMyocardial-action-potential-Shown-is-the-action-potential-of-a-ventricular-musclecell_fig3_40022512& K+ 0 1 2 3 Action potential of cardiac muscle consists of four phases. Phase 4 –(From left side of screen) Resting phase cell is in polarized state.(With -90 mV inside the cell). Phase 0 –Depolarization. Na+ ions rapidly diffuse into the interior of the muscle cell neutralizing (Depolarizing) the polarized resting state.(Minimal or no difference inside &outside cell charge). Phase 1. Repolarization that is caused by transient outward K+ channel.(Reduction in +ve inside). Phase 2. Plateau phase is due to influx of positively charged Ca ions.(Repolarization is delayed). Phase 3. During this phase there is large efflux of K ions (Out of cell) resulting in increased negative charge inside the cell and restoration of resting ( polarized ) state.
Slide 13-

What is vector ? Vector is a symbolic representation of a physical force. It has direction and magnitude. By convention it is represented by an arrow. Size & direction of arrow represent magnitude and direction of the vector respectively. Movement of electrically charged particles(ions ) during action potential generate electrical vectors. Multiple vectors are generated during Atrial /ventricular depolarization & repolarization. Electrical vectors spread across heart into the surrounding fluids and skin. These vectors have different magnitude and directions . Moreover , electrodes are placed at different parts of the precordium and limbs to record these electrical vectors. Thus waves generated by different ECG electrodes have different magnitude and shapes. From https://teachpe.com/images/anatomy-physiology/heart-conduction500.jpg *Electrode is a conductive metallic pads for recording the electrical vectors.
Slide 14-

Experiment in physiology laboratory. What is an electrode ? Electrode is a conductive metallic pads for recording electrical activity. A piece of living ventricular muscle is placed in a bath containing a salt solution to conduct electrical currents. Electrodes are placed in the bath on either side of the muscle. Myocardial cell is polarized, resting state (outside of the cells is positive relative to the inside). As whole of out side is positive , both electrode have same (positive )charge therefore, no current flow along the surface of the muscle and the bath. Ventricular muscle in fluid filled jar with electrode on either sides. Figure modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 15-

What is Dipole . It is generally defined as pair of poles with opposite charges ,placed at some distance from each other. In ECG (Cardiac ) dipole refers to a vector of electrical signals with two ends (having opposite charges) which has a specific direction as well as an amplitude (voltage). During depolarization the direction of the dipole (Electrical signals ) is from the most negative to most positive regions of the heart. During repolarization the direction of dipole is reversed , from positive toward negative end . Figure modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 16-

Conductor Principles and ECG Rules of Interpretation. Figure A shows muscle cell in resting condition left and right ends of cell has same (Positive ) charges therefore there is no deflection of the needle. If the left side of the muscle is stimulated electrically it will initiate a self-propagating action potentials, a wave of depolarization would sweep across the muscle from left-to-right (Fig B) Midway through this depolarization process, cells on the left end of cell (depolarized cells) would be negative on the outside while non-depolarized cells on the right end of the muscle would still be polarized (positive on the outside). The head of arrow is positive and tail is negative. There would now exist a potential difference between the positive and negative electrodes recorded by deflection of the needle. After the wave of depolarization sweeps across the entire muscle mass, all the cells on the outside are negative (totally depolarized cell), and once again, no potential difference would exist between the two electrodes.(Figure C) A C B Totally depolarized - - - - - - - - Figure Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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Modified from https://chemistryoftaste.weebly.com/uploads/2/4/5/7/24576351/9821524_orig.jpg - - - + + + Electrical charges of the myocardial cell in different phases of action potential. + - Wave of repolarization From https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 18-

Rules of electrical conduction across myocardial cell. Several important rules of electrical conduction across myocardial cell has been established. A wave of depolarization travelling toward a positive electrode results in a positive (upward ) deflection in the ECG tracing. A wave of depolarization travelling away from a positive electrode results in a negative (downward ) deflection. A wave of repolarization travelling toward a positive electrode results in a negative deflection. A wave of repolarization travelling away from a positive electrode results in a positive deflection. A wave of depolarization or repolarization travelling perpendicular (At 90* ) to an electrode axis results no net (Isoelectric ) deflection. The voltage amplitude is directly related to the mass of tissue undergoing depolarization or repolarization. From https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 19-

+ - Wave of depolarization. + Wave of repolarization QRS T wave + - QRS A wave of depolarization travelling toward a positive electrode results in a positive (upward ) deflection in the ECG tracing .Why ? A wave of repolarization travelling toward a positive electrode results in a negative deflection Why A wave of depolarization travelling away from a positive electrode results in a negative (downward ) deflection. Why ? + - Wave of repolarization A wave of repolarization travelling away from a positive electrode results in a positive deflection,Why? - V + E + E + V - V - E + V + E + V = Vector , E =Electrode
Slide 20-

A wave of depolarization or repolarization travelling perpendicular to an electrode axis results no net (Isoelectric ) deflection .Why ? QRS ? QRS ? QRS? QRS? + - + - + - + - 30* 70* 90* V = Vector , E =Electrode V + E + V + E + V + E + 0* +ve end of all the vectors are directed towards the +ve electrodes & produce Upward deflection. Maximum upward deflection will be recorded when vector is at zero degree. As the angle between the +Ve end of vector & +ve electrode increase height of +ve wave will get reduced. Till at 90* it will generate minimum size or biphasic wave.(equal size positive and negative waves). or
Slide 21-

+ - + - + - + Review .
Slide 22-

Vector end facing the electrode Electrode Direction of wave Summary electrical conduction across myocardial cell. If negative Positive Negative ( Downward deflection). If positive Negative Negative ( Downward deflection). If positive Positive Positve (Upward deflection). Thus for positive deflection of wave , both electrode and the vector end, facing the electrode should have positive charge.
Slide 23-

Applied anatomy of conducting system of the heart.
Slide 24-

Conducting system of the heart It consists of sinoatrial (S-A node), atrioventricular (A-V) node and conducting fibers. SA and AV nodes are located in right atrium(RA). Normal rhythmical impulses are generated in S-A node. Sinus nodal is connected directly with atrial muscle fibers & two types of conducting pathways Internodal (Three ) pathways connecting SA & AV nodes & one interatrial band connect RA with LA (left atrium). In this way, the action potential spreads through the entire atrial muscle mass & the A-V node. AV node is connected with main AV bundle (Bundle of HIS) which divides into right and left bundle branches . Two bundle branches divides terminally into fine fast conducting fibers , purkinje fibers. Thus His bundle ,bundle branches and purkinje fibers transmits cardiac impulse to both ventricles. From https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/1940/2017/05/29213842/hjbdduukq1619wcos44a.png From Guyton and Hall Textbook of Medical Physiology 12th edition
Slide 25-

Note that bundle of His divides into two large branches right and left bundle. Left bundle is larger & and further divides into left anterior branch (Fascicle ) and Left posterior fascicle) Thus ventricles have trifascicular conduction. From. https://www.teachpe.com/anatomy-physiology/the-heart-conduction-system
Slide 26-

Morphology ( Shape ) of the ECG waves.
Slide 27-

Three blind persons visited zoo. They got very different impressions about the shape of elephant . One observer (A)touched the back (Tail) of the elephant. Observer( B ) felt the body. Observer (C )felt the front (trunk). If you wanted the correct description of the shape of elephant whom would you ask ? A B C All three. ECG machine generate waves of muliple shapes and magnitude Thus multiple ECG leads are required for orientation of multiple electrical vectors generated in the heart. Modified from The Only EKG Book You'll Ever Need, 5th Edition Malcolm s. Thaler
Slide 28-

Morphology of the ECG waves. The direction and the magnitude of vector of depolarization changes as it spreads through the different heart chambers. These change in the direction of depolarization waves, in atrium and ventricles are recorded as P and QRS waves, respectively by the ECG by electrodes placed in different position on the chest & limbs. As the multiple electrodes are placed is different location the shape and amplitude of the waves (PQRS ) generated in leads vary.
Slide 29-

From https://www.pr acticalclinicalskills.com/images/ekg-basics What is Electrocardiogram ( ECG ) ? When an electric impulse passes through the heart, electrical current spreads out into the adjacent tissues surrounding the heart & on to skin surface. If electrodes are placed on the skin on two opposite sides of the heart, it will collect electrical activity generated by the vector (Dipole). This is processed and recorded in on ECG paper in different waves wave forms is known as an electrocardiogram ( ECG ). Normal ECG tracings consist of waveform generated from different chambers of the heart during each heart beat. The normal ECG(see Fig.) These waveforms are labeled P, Q, R, S, T and U.
Slide 30-

Electrocardiogram (ECG) waves , segments and intervals. ECG waves (PQRST & U) are positive (upward )or negative (Downward ) deflections long the Y axis. Segments are horizontal lines in the ECG along the X axis without intervening waves. Intervals are horizontal lines along the X axis with one or more ECG waves .
Slide 31-

Total number of waves , segments and intervals of ECG. Four waves . P , QRS, T and u waves. Four segments and intervals . (Two segments and two intervals). Intervals are horizontal lines in the ECG with one or more ECG waves. Segments are horizontal lines in the ECG without waves. PR interval and QT interval. PR and ST segments. By Derivative: RehuaOriginal: Hank van Helvete - This file was derived from: EKG Komplex.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31447187
Slide 32-

Generation of ECG waves. Each cardiac cycle is initiated by spontaneous depolarization of the sinus node (Located in right atrium). This results in mechanical contraction and relaxation not recorded in ECG. Atrial depolarization is recorded as P wave . Atrial repolarization is not commonly recorded in the ECG. The first part of the P wave reflects right atrial(RA) activity; the second part reflects left atrial (LA) activity. There is a brief pause after P wave as the electrical current cross AV node.(Due to slow conduction) The wave of depolarization then spreads along the ventricular conducting system (His bundle, bundle branches, and Purkinje fibers) and out into the ventricular myocardium. Ventricular depolarization is recorded as QRS. Ventricular repolarization is recorded as T wave From https://ecgwaves.com/ecg-topic/ekg-ecg-leads-electrodes-systems-limb-chest-precordial/ Modified from The Only EKG Book You'll Ever Need, 5th Edition Malcolm s. Thaler
Slide 33-

The QRS is wave complex of three waves (some times mentioned as QRS Interval) It represents the time interval of ventricular depolarization. A normal QRS interval, representing the duration of the QRS complex, is 60 to 100 m Sec. Q wave is first downward deflection before R wave. R wave is upward deflection . S wave is downward deflection after R wave. Single downward defection in ECG with no R wave is called QS wave . QS QS QS This is QR This is R Is this Q or S ? https://litfl.com/q-wave-ecg-library From The Only EKG Book You'll Ever Need, 5th Edition Malcolm s. Thaler
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ECG intervals. The PR interval measures the time from the start of atrial depolarization to the start of ventricular depolarization (QRS). QT interval. Measure the tme for both ventricular depolarization and repolarization . It roughly estimates the duration of an average total ventricular action potential. It therefore includes all of the electrical events that take place in the ventricles. The QRS complex (In some books mentioned as interval) measures the time of ventricular depolarization. From https://litfl.com/wp-content/uploads/2018/10/ECG-waves-segments-and-intervals-LITFL-ECG-library-3.jpg By Created by Agateller (Anthony Atkielski), converted to svg by atom. SinusRhythmLabels.png, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1560893
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The J point is a point in time marking the end of the QRS and the onset of the ST segment . Thus it is junction of QRS with ST segment. From https://litfl.com/wp-content/uploads/2018/08/ECG
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U From https://www.slideshare.net/SubhashiniN3/normal-ecg-interpretation From The Only EKG Book You'll Ever Need, 5th Edition Malcolm s. Thaler
Slide 37-

Atrium. Ventricle . From Guyton and Hall Textbook of Medical Physiology 12th edition ( HIS bundle) PR interval in the ECG represents conduction time from the SA node up to end of HIS bundle. Conduction time from SA node up to AV node = 30 msec. + Conduction time from AV node up to main AV (His ) bundle = 90 msec. + Conduction time across bundle of His up to its division into left and right bundle = 30 msec. PR interval time in ECG is 30 + 90 + 40 = 160 msec. QRS interval in the ECG represents conduction time from division of the bundle of His up to epicardial surface of ventricle Time from bundle branches to end of Purkinje fibers (endocardial muscle mass ) =30msec. + Time interval from endocardial surface to the epicardial surface. =30 msec. Normal QRS duration is 60 to 100 mse. These time intervals have a range ,those mentioned above are approximatel values.
Slide 38-

Atrial muscle is separated from the ventricular muscle by a continuous fibrous barrier(Except at the A-V bundle). This barrier normally acts as an insulator to prevent conduction of the cardiac impulse between atrial and ventricular muscle other route besides forward conduction through the A-V bundle. i Conducting fibers transmit action potentials at a velocity of 1.5 to 4.0 m/sec, a velocity about 6 times that in the usual ventricular muscle and 150 times that in some of the A-V nodal fibers. Atrium. Ventricle . ( HIS bundle ) From Guyton and Hall Textbook of Medical Physiology 12th edition
Slide 39-

Clinical importance of Purkinje System in Synchronous Contraction of the Ventricular Muscle. Total time for transmission of the cardiac impulse from the initial bundle branches to the last ventricular muscle fibers (QRS duration ), in the normal heart is about 60 to 90 milli second. Effective pumping by the two ventricular chambers requires synchronous type of contraction. Thus normally the cardiac impulse arrives in almost all portions of the ventricles within a narrow span of time, exciting the whole myocardium within 30 to 60 m sec. This causes all portions of the ventricular muscle of both ventricles to begin contracting at almost the same time. This is known as synchronized myocardial contraction, necessary for effective myocardial pumping. From Guyton and Hall Textbook of Medical Physiology 12th edition
Slide 40-

What is an ECG Lead ? An ECG lead is graphic recording of the electrical activity of the heart generated by combined analysis of multiple electrodes placed on different parts of the body. The overall magnitude of the heart's electrical potential is then measured from twelve different angles. Correct orientation of the electrical activity (electrical vectors) of various cardiac chambers is possible only if we have multi dimensional recording of these activity.
Slide 41-

ECG LEADS
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Fom https://ecgwaves.com/ecg-topic/ekg-ecg-leads-electrodes-systems-limb-chest-precordial/ What is an electrical conductor. An electrical conductor is a substance (Medium) which allows the electricity to conduct (move) readily. Body tissue and fluid are gelectrical conductors. Thus electrical activity (Depolarization and repolarization ) generated in the heart is conducted (spread ) to the body fluids & skin. Electrodes placed on skin transmits the electrical activity to the ECG machine. The information gathered is processed & is displayed in form of waves as different leads.
Slide 43-

What is difference between an ECG electrode and ECG lead? Electrode is a conductive pad attached to the skin for recording electrical activity. Electricity enters or leaves the body surface (skin) through electrodes. As discussed ,electrical currents generated by the heart generate multiple vectors (Dipole ) which are conducted by the body fluids to the skin. Electrodes are placed on the body surface (Skin) to record potential Difference in different parts of the body. Electrocardiogram uses electrodes on the surface of the body to measure the electrical activity of the heart.
Slide 44-

What is difference between an ECG electrode and ECG lead?(Continued What do these electrodes actually measure ? They measure the magnitude of difference between the two ends of electrical vector . Correct orientation of the electrical activity (electrical vectors) of various cardiac chambers is possible only if we have multi dimensional recording of these activity. ECG lead is graphic recording of the electrical activity of the heart generated by combined analysis of multiple electrodes arranged in different groups . These are called ECG leads. Standard ECG is commonly referred to have 12 leads ECG , obtained by10 electrodes.
Slide 45-

From https://www.teachingmedicine.com/Media/case_discuss/images/Planes_axial_chest_v02.png *Electrical plans of the body. 12-lead ECG, provides 12 records of electrical activity of the heart , using various combinations of electrodes placed at different angles . It records electrical signals (Vectors ) in two electrical planes of the body. Frontal plane. It consists of two axis. Superior –Inferior (Y axis) and Right-Left directions ( X axis). Horizontal plane . It consists of two axis. Anterior—Posterior (Z axis) . Right-left directions (X axis). Electrical activity in Frontal plan is recorded by the Limb leads . Electrical activity of the horizontal plan is recorded by Precordial leads (V1 to V6). Superior Inferior Anterior Posterior Right- Left *Body planes are 2-Dimensional flat surfaces of the body derived by section of the body along any two of the three axis.
Slide 46-

From https://ecgwaves.com/ecg-topic/ekg-ecg-leads-electrodes-systems-limb-chest-precordial/ Transverse ( Horizontal )plan (Chest leads). In this, six positive electrodes are place on the surface of the chest over different regions of the heart in order to record electrical activity in horizontal plane. Chest leads V1 to V6 also known as unipolar precordial leads. They explore the electrical activity along horizontal plan. These leads are best for recording vectors moving in Z and X axis . Precordial chest leads are unipolar and requires only a positive electrode. Detail description of the lead connection is mentioned in later slides. Anterior—Posterior . Right-left directions Posterior Horizontal plan . Anterior—Posterior (Z axis) . Right-left (X) axis.
Slide 47-

Frontal Leads(Limb leads). They may be bipolar or unipolar. Bipolar limb leads The term “bipolar” means that the electrocardiogram is recorded from two(negative and positive ) electrodes located on the limbs on different sides of the heart. Lead I ,Lead II , Lead III Unipolar limb leads. Augmented unipolar requires only a positive electrode for monitoring. Augmented Vector Right (aVR), Augmented Vector Left (aVL), Augmented vector foot (aVF). The positive end to the electrode of lead aVR is on right arm, that of aVL on left arm & aVF on the left foot. Detail description of the lead connection is mentioned in later slides. From https://cdn.shopify.com/s/files/1/0059/3992/files/Image_6.png?v=1476241491
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From https://thoracickey.com/wp-content/uploads/2016/12/image00966-1.gif *Polarity of frontal plan (limb) ECG leads Frontal plan consists of two axis . 1. X (Right to left ) 2.Y axis (Superior -inferior). By using combination of 4 limb electrodes, 6 frontal leads are accquired. These leads best record the electrical signals (Vectors) moving along frontal ( coronal ) plan of the body . Superior *Polarity of ECG leads means orientation of positive and negative ends of the ECG leads.
Slide 49-

Location of the Frontal Plane Axis: In order to accurately interpret the 12-lead EKG, you must have an understanding of the electrical activity of the heart. The direction in which the impulses flow in the heart is important. It is also important to understand that 12 different leads pick up those impulses as they travel in many different directions through the heart
Slide 50-

Precordium is the portion of the body over the heart and lower chest, mainly the area of the anterior chest wall. For purpose of ECG leads, the (360 *) circular net work of leads divides the precordium into superior and inferior half . inferior half (Positive electric zone +0* to +180*) Superior half (Negative electric zone - 0* to -180* This is known as hex axial reference system. What is Hex axial reference system ECG leads.? Chapter V The 12-Lead EKG From https://www.nurseslearning.com/courses/nrp/nrp1619/Section%205/index.htm
Slide 51-

Orientation of the lead placement and direction of lead in frontal plan. Fontal plane consists of two axis. X axis. Right to left and left to right. Y axis superior to inferior and inferior to superior Inferior Chapter V The 12-Lead EKG Modified from https://www.nurseslearning.com/courses/nrp/nrp1619/Section%205/index.htm
Slide 52-

Limb leads are of two types 1 .Bipolar limb leads . 2. Unipolar leads (Limb leads). Also known as Augmented unipolar leads.
Slide 53-

The above illustration shows Leads I, II, and III, their placement & the electrical charges of their electrodes. They are summarized as follows: Lead I: Right arm-negative, Left arm-positive (Positive end is at +zero degree ). Records electrical differences (voltage )between the left and right arm electrodes. Lead II: Right arm-negative, Left leg-positive( Positive end is at +60 degree). Records electrical difference (voltage ) between the left leg and right arm electrodes. Lead III: Left arm-negative, Left leg-positive ( Positive end is at +120 degree). Records electrical differences (voltage ) between the left leg and left arm electrode Right leg doesn't come up in ECG readings & is considered as a grounding lead that helps minimize ECG artifact. Lead I Lead II Lead III Bipolar limb leads connections. Chapter V The 12-Lead EKG Modified from https://www.nurseslearning.com/courses/nrp/nrp1619/Section%205/index.htm
Slide 54-

Bipolar Limb Leads lead I has the positive electrode on the left arm, and the negative electrode on the right arm, and therefore measures the voltage difference between the two arms. In the lead II has the positive electrode is on the left leg and the negative electrode is on the right arm. Lead III has the positive electrode on the left &the negative electrode on the left arm. Electrical connection for recording Bipolar limb leads From Goldberger Al: clinical electrocardiography , A simplified approach . 7th ed. St. Louis ,CVMosby.2006 CHAPTER 13Electrocardiography David M. Mirvis and Ary L. Goldberger. http://www.doctor33.it/cont/download-center-files/17519/cap-electrocardiography-x20968allp1.pdf Figure modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 55-

Unipolar ECG leads . We have two types of so called unipolar leads 1.Unipolar Limb leads. Also called Augmented unipolar limb leads. 2.Unipolar chest leads These lead systems apparently measure the absolute potential at specific point on (Limb or chest ), connected to the positive terminal. This is because in these leads the negative terminal is different from the bipolar limb leads. A central terminal is connected to the negative terminal. What is central terminal ?
Slide 56-

Background of unipolar limb leads . What are Wilson and Goldberger central terminal.? What are difference between the two ? Wilson’s Central Terminal and unipolar leads VR , VL and VF. To develop unipolar limb leads ,Wilson ,an American physician , modified the lead arrangement of bipolar leads. He introduced a terminal called Wilson central terminal (WCT ). Three limbs , right arm (RA), left arm LA and left leg LL , were connected to a central terminal through fixed resistances of 5,000 ohms each and named as Wilson Central Terminal (WCT). Wilson's central terminal (WCT) served as the negative pole in unipolar limb leads. The positive electrode were placed one on each limb and named VL for left arm, VR for right arm and VF and left leg. * Terminal is the point at which wires of a circuit terminates (Ends). Commonly it is a screw type fitting for connection of terminal portion of an electric wire.
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*Reference. 1.Madias JE. On recording the unipolar ECG limb leads via the Wilson's vs the Goldberger's terminals: aVR, aVL, and aVF revisited. Indian Pacing Electrophysiol J. 2008;8(4):292-297. 2. Goldberger E. A simple, indifferent, electrocardiographic electrode of zero potential and a technique of obtaining augmented, unipolar, extremity leads. Am Heart J. 1942;23:483–492. [Google Scholar] What are Goldberger’s Augmented Leads aVR, aVL & aVF. *“Goldberger thought that the three 5,000 Ω resistances of the Wilson central terminal (WCT ) were not necessary.” (However he mentioned that as an option they can be used). They were replaced by 3 plain wires to form a terminal for recording of unipolar limb leads, named Goldberger central terminal (GCT). Another modification was he connected wires of only two limbs to Goldberger central terminal (GCT) instead of three limbs as used in the Wilson central terminal (WST) as follows. When aVR is recorded the GCT consists of a connection of left arm and left leg only. When aVL is recorded the GCT consists of a connection of right arm and left leg only. When aVF is recorded the GCT consists of a connection of right arm and left arm only.
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*Reference. Madias JE. On recording the unipolar ECG limb leads via the Wilson's vs the Goldberger's terminals: aVR, aVL, and aVF revisited. Indian Pacing Electrophysiol J. 2008;8(4):292-297. Goldberger E. A simple, indifferent, electrocardiographic electrode of zero potential and a technique of obtaining augmented, unipolar, extremity leads. Am Heart J. 1942;23:483–492. [Google Scholar] What are Goldberger’s Augmented Leads aVR, aVL & aVF (Continued ). This rearrangement of GCT augmented the voltage of ECG wave form by 50%. It means that the machine augmented (increase amplitude ) of the recording by 50%. Thus they were renamed aVR , aVL ,and aVF. The abbreviation ‘a’ refers to augmented, V’ refers to voltage , R, L and F refer to right arm, left arm and left foot respectively.
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*Assumptions about Unipolar ECG leads. The negative terminal Central Terminal (CT) was apparently assumed to have zero charge . Therefore these leads were named as unipolar leads, measuring absolute electric charge at one limb , as compared to the bipolar limb leads. *“The term "unipolar", popularized by Wilson, is a misnomer, since no leads can be truly "unipolar", all requiring positive and negative poles.” *“Thus the term unipolar is used herein in the quasi (apparently )unipolar sense, as when first introduced by Wilson and Goldberger, who also realized that such leads were not truly unipolar” The central terminal records an average of the connected limb leads and not infect zero. *Reference. Madias JE. On recording the unipolar ECG limb leads via the Wilson's vs the Goldberger's terminals: aVR, aVL, and aVF revisited. Indian Pacing Electrophysiol J. 2008;8(4):292-297.
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Goldberger E. A simple, indifferent, electrocardiographic electrode of zero potential and a technique of obtaining augmented, unipolar, extremity leads. Am Heart J. 1942;23:483–492. [Google Scholar] Following figure is from the original article by EmanuelGoldbergerM.D .1942 Note that in GCT the wires are not connected to 5000 resistance.
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Wilson central terminal For recording chest leads Wilson lead for the chest leads In chest leads positive electrodes , V1 to V 6 are placed on the precordium. Wilson's central terminal serves as the negative pole. From Goldberger Al: clinical electrocardiography , A simplified approach . 7th ed. St. Louis ,CVMosby.2006 CHAPTER 13Electrocardiography David M. Mirvis and Ary L. Goldberger. http://www.doctor33.it/cont/download-center-files/17519/cap-electrocardiography-x20968allp1.pdf
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Augmented Unipolar Limb Leads. In this type of recording, two of the limbs are connected to the negative terminal of the ECG (Has zero potential). Third limb is connected to the positive terminal. When the positive terminal is on the right arm,it is named as as the aVR lead. When on the positive electrode is on the left arm, it is named as aVL lead. When on the positive electrode is on the left leg, it is named as the aVF lead. Electrical connection for recording augmented limb leads From Goldberger Al: clinical electrocardiography , A simplified approach 7th ed. St. Louis ,CVMosby.2006 CHAPTER 13ElectrocardiographyDavid M. Mirvis and Ary L.Goldberger. http://www.doctor33.it/cont/download-center-files/17519/cap-electrocardiography-x20968allp1.pdf Figure modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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Augmented unipolar leads. Orientation of the lead placement and direction of lead aVL the positive electrode is on the left shoulder. At – 30* aVR the positive electrode is on the right shoulder. At -150 * aVF the positive electrode is on the left foot. At +90* Note that the positive electrodes of aVR and aVL are located in the negative electric zone. Chapter V The 12-Lead EKG Modifed From https://www.nurseslearning.com/courses/nrp/nrp1619/Section%205/index.htm
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Six limb leads measure the electrical activity of the heart along the frontal plan. In frontal plane patient is in anatomical position & facing you. Therefore patient’s left side is on your right side. The six limb leads measure a circle or 360 degrees around the heart. This six fontal plane leads placed across the heart form the hex axial reference system. Note that aVR and aVL has positive terminal in the superior (Negative zone) . Inferior Superior Right Left inferior half (Positive electric zone +0* to +180* Superior half (Negative electric zone - 0* to -180* Modified from https://www.nurseslearning.com/courses/nrp/nrp1619/Section%205/index.htm
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Chest or precordial leads
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The Chest Leads (or Precordial Leads). The precordial (chest leads) leads each consist of a positive electrode strategically placed on the chest of the patient. The unipolar chest leads detect electrical impulses from the heart along the horizontal (transvers ) plane of the heart. This tracing gives a different view of the heart and allows detection of arrhythmias that may not be detectable in the frontal plane angles.
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chest leads They record the electrical activity of the heart in transverse ( Horizontal )plan different positions on the chest . six positive electrodes, named V1 to V6, are placed on front of the chest (precordium.) ECG tracing of chest leads Right Figur from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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From https://thoracickey.com/wp-content/uploads/2016/12/image00966-1.gif *Polarity of horizontal (Cross sectional ) plan ECG leads Posterior Horizontal body plan consists of two axis . 1. Z (Anterior-posterior ) & 2. Y axis (Superior-inferior) Six precordial leads (V1 to V6) measure electrical activity along the horizontal plan. Front-back direction (Z axis). Right-left direction. (X axis). P R L A *Polarity of ECG leads means orientation of positive and negative ends of the ECG leads.
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Modified From http://www.nataliescasebook.com/img/ECG-basics/Cardiac_Dipole.gif Mr Clarkson Abigail Spatial orientation of the QRS Vectors with the six limb leads. Records electrical activity in frontal plan. X axis (Right –left) & Y axis ( Superior – inferior).
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Spatial orientation of the QRS Vectors with the six chest leads. Records electrical activity in horizontal plan. X axis (Right –left) & Z axis (Anterior –Posterior). Anterior Posterior Modified From http://www.nataliescasebook.com/img/ECG-basics/Cardiac_Dipole.gif Mr Clarkson Abigail
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*Summary of the electrical connection of leads used during ECG recording. The standard ECG leads consists of 3 different sets of electrical connection. “The bipolar leads I, II, and I11 are recorded via the stable Wilson central terminal (WCT).” “The unipolar chest leads V1-V6 leads are recorded via the stable Wilson central terminal (WCT).” “The unipolar limb leads aVR, aVL, and aVF leads recorded via the Goldberger central terminal ( GCT)” . *Reference Madias JE. On recording the unipolar ECG limb leads via the Wilson's vs the Goldberger's terminals: aVR, aVL, and aVF revisited. Indian Pacing Electrophysiol J. 2008;8(4):292-297.
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Location of ECG electrodes for recording 12 leads ECG. Ten electrodes are required to produce 12-lead ECG. 1.Four limbs electrodes . (Right arm , left arm , Right leg , left leg) 2. Six chest electrodes. V1, 4th intercostal space right sternal border. V2, 4th intercostal space left sternal border. V3, 4th intercostal space between V2 & V4 . V4, 5TH intercostal space mid clavicular line. V5, 5TH intercostal space anterior axillary line. V6, 5TH intercostal space mid axillary line. Electrode locations of left sided chest ECG leads V1 to V6. Figure modified from https://www.emergencymedicinekenya.org/quick-tip-how-to-take-the-perfect-12-lead-ecg/
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Standard 12-lead ECG electrodes location. As discussed 10 electrodes are required for recording 12 leads ECG. Four in four limbs and six on the chest. Location of limb leads are straight foreword, however chest lead electrode attachment site needs brief description. To locate the exact site of electrode placement we need to identify few land marks (surface anatomy) on the front of thorax. Sternal angle & arbitrary lines are important land marks for locating the intercostal space & location of the electrode placement site.
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Arbitrary lines on the anterior aspect of thorax Arbitrary lines on the lateral aspect of the body. Modified from Chapter 10 The Chest https://clinicalgate.com/the-chest/ B, Landmarks on the lateral view. A, Topographic landmarks of the anterior thorax. Thoracic cage landmarks.
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From https://litfl.com/wp-content/upload by Dr Mike Cadogan, Land marks ,intercostal space & arbitrary lines for location of six chest electrode placement.
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It can be simpler to leave V1 and V2 in their usual positions. Transfer leads V3-6 to the right side of the chest (i.e. V3R to V6R) in the same positions as is in left sided chest leads. From https://www.aclsmedicaltraining.com/wp-content/uploads/2016/01/V1R-V6R-1024x768.jpg V1R Left 4th intercostal space left sternal border. V2R Right 4th intercostal space right sternal border. V3R Right 4th intercostal space between V2 & V4 . V4R Right 5TH intercostal space mid clavicular line. V5R Right 5TH intercostal space anterior axillary line. V6R Right 5TH intercostal space mid axillary line.. Electrode locations of right sided chest leads
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Posterior chest leads. Anterior chest leads V4 to V6 , In 12 lead ECG are replaced by posterior leads. Lead V4 cable is connected to V7. Lead V5 cable to V8. lead V6 cable is connected to V9. Leads V7-9 are placed on the posterior chest wall in the following positions: V7 – Left posterior axillary line, in the same horizontal plane as V6. V8 – Tip of the left scapula, in the same horizontal plane as V6. V9 – Left paraspinal region, in the same horizontal plane as V6. From http://nps.freeservers.com/Image16.gif
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From https://litfl.com/wp-content/upload by Dr Mike Cadogan, Five -electrode system (Monitoring leads). Uses 5 electrodes (RA, RL, LA, LL and Chest). Monitor displays the bipolar leads (I, II and III) and single chest lead. Chest lead (depending on position of the brown chest lead V. (Any positions V1–6). 5-lead electrode placement
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3-electrode system( Monitoring ). Uses 3 electrodes (RA, LA and LL). Monitor displays the bipolar leads only (I, II and III). To get best results – Place electrodes on the chest wall equidistant from the heart (rather than the specific limbs). 3-lead electrode placement From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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Lewis lead The Lewis lead configuration can help to detect atrial activity and its relationship to ventricular activity. Named after Welsh cardiologist Sir Thomas Lewis (1881-1945) who first described it in 1913. Lewis lead placement Right Arm (RA) electrode on manubrium Left Arm (LA) electrode over 5th ICS, right sternal border. Left Leg (LL) electrode over right lower costal margin. Monitor Lead I Useful in: Observing flutter waves in atrial flutter Detecting P waves in wide complex tachyarrhythmia to identify atrioventricular dissociation From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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ECG paper
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ECG PAPER. ECG paper is marked with a grid of small and large squares.(Similar to graph paper) The EKG paper records time sequences on the X axis (horizontal deflections). It records voltage or amplitude of the electrical activity of the heart on Y axis (vertical axis ). From https://physicaltherapyreviewer.files.wordpress.com/2018/09/ecg-paper.png X axis (horizontal axis) . Y axis (vertical axis )
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Horizontal lines (X axis) The horizontal lines measure time intervals and heart rate. The ECG paper speed is normally set at 25 mm/sec but can be increased to ≥50 mm /sec. ECG paper Key Horizontal (X ) axis.( If paper speed is 25mm/sec). Thin Lines= 1 mm intervals or 0.04 sec (40 m sec.) Thick lines= 5 mm intervals or 0 .2sec (200 m sec.) From https://physicaltherapyreviewer.files.wordpress.com/2018/09/ecg-paper.png
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Vertical lines (Y axis). Vertical lines measure the amplitude (height or depth ) of the ECG waves. The amplitude of ECG waves is measured from the baseline ( isoelectric line) to the peak (of upward deflection (positive wave ) or nadir of the downward deflection (Negative wave). In Standard setting one mV deflection corresponds to 10mm thus one mm is equal to 0.1mV. This voltage setting can be increased to one mV =20mm or reduced to one mV= 5mm if the ECG complexes recorded are very low or high respectively. ECG paper Key Vertical (Y) axis.( Normal standardization ). 10 mm = 1 mV (I mm = 0.1 mV). From https://physicaltherapyreviewer.files.wordpress.com/2018/09/ecg-paper.png
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ECG paper Key Horizontal (X ) axis.( If paper speed is 25mm/sec). Thin Lines: 1 mm intervals or 0.04 sec (40 m sec.) Thick lines: 5 mm intervals or 0 .2sec (200 m sec.) Vertical (Y) axis.( Normal standardization ). 10 mm = 1 mV (I mm = 0.1 mV). From https://physicaltherapyreviewer.files.wordpress.com/2018/09/ecg-paper.png
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by Dr Mike Cadogan, From https://litfl.com/wp-content/upload 1mm (small square) = 0.04 sec (40ms) . Why ? 5mm (large square) = 0.2 sec (200ms) ECG is recorded on a graphic paper at different speed . Following recording illustrates important measurements of ECG tracing. Time (Running velocity) is displayed on x axis , and amplitude (Voltage) is displayed on Y axis. Guess what is the paper running speed ? Paper(running) speed is 25mm/ sec.
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Why is 1 mm(on horizontal axis ) = 40 m sec if ECG is recorded at speed of 25 mm/sec. ? Explanation of why is 1 mm = 40 msec. at paper speed of 25 mm /sec. Speed of 25mm/sec means 25 mm is = (one second ) or 1000 msec. So 25 mm = 1000 msec. Thus 1mm = 1000 ÷ 25 = 40m sec. by Dr Mike Cadogan, From https://litfl.com/wp-content/upload
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Explanation of why is 1 mm = 20 msec. at paper speed of 50 mm /sec. Speed of 50mm/sec means 50 mm is = (one second ) or 1000 msec. So 50 mm = 1000 msec. Thus 1mm = 1000 ÷ 50 = 20m sec. Why is 1 mm(on horizontal axis ) = 20 m sec if ECG is recorded at speed of 50 mm/sec. ? Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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Explanation of why the interval, segments and width of waves doubles at speed of 50mm/sec.? P wave width in 25mm strip is 2.5 mm (2.5X 40)= 100 m sec In same ECG at 50mm strip P wave width 5 mm = 200 msec (Doubles). This is because in 25mm speed 1mm =40 m secs but at 50 mm speed 1mm= 20 m sec. Therefore at speed of 25mm/sec, 1mm (40 m sec ) = 2mm (20 x 2= 40 m sec.)at speed of 50 mm Impact of recording ECG at different speeds . What will be effect of 50mm speed on width of P and QRS width ECG intervals and & why ? Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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Why use 50 mm/second recording ? Reveal flutter waves in 2:1 block. Red arrows (P or F waves) by Dr Mike Cadogan, Modified From https://litfl.com/wp-content/upload
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Estimation of heart rate ( P or QRS ) rate ? At paper speed of 25 mm/sec, one second of strip = 25 mm. One minute of strip = 25x 60 = 1500 mm(small square). Estimation of QRS rate in a subject with regular heart rate. Count the number of small square between to two QRS . In this example it is 10 (small squares) mm as shown in the fig. In this ECG ten mm =one beat (QRS). So one mm QRS rate = So 1500 mm QRS rate = In 1500 mm or one minute we will have = In this complex there are 15 mm between QRS therefore QRS rate will be 1500 ÷ 100 = 100 beats /min. -------10 mm ------ -------10 mm ------ 10 1 10 1 10 1 X (QRS),beats X 1500 (QRS) x1500=150 beats/min Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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Alternate less preferable method of estimating QRS rate in a subject with regular heart rate. At a paper speed of 25 mm/second one second of strip = 25 mm (small squares) or five large squares. One minute of strip = 25x 60 = 1500 mm(small square) = 300 large squares The number of large square in one beat I e between to two QRS in this ECG =4 In this ECG 4 large square =one beat (QRS). One large square = 1÷4 beats (QRS). So in 300 large square( one minute) we have = 300 ÷ 4 = 75 beats/min. *This is less preferable method by Dr Mike Cadogan, Modifed From https://litfl.com/wp-content/upload
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Example of 1500 (small squares) versus 300 (large square) method. Which one is preferable , justify ? Two methods of calculating heart rate Using 1500 divided by number of small squares between R-R. Using 300 divided by number of large squares between R-R. Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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If rhythms is irregular we can estimate average heart ( QRS) rate from 10 second strip. At a paper speed of 25 mm/second one second of strip = 25 mm (small squares). Ten seconds strip = 250 mm (small squares) . As one large square consists of 5 small squares therefore 250 small squares = 50 large squares. Therefore Ten seconds strip = 50 large squares. The number of QRS complexes (count R waves) on the rhythm strip gives the average rate over a ten-second period. This is multiplied by 6 (10 seconds x 6 = 1 minute) to give the average beats per minute. The above 10 second rhythm strip has 9 QRS beats 3rd Method of estimation of heart rate . Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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Calculate atrial( P ) &ventricular(QRS) rates separately if their rates are not same e.g. complete heart block) ECG derived estimation of heart rate using three techniques at paper speed 25 mm /sec Above 10 second strip has 9 beats Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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From https://www.nurseslearning.com/courses/nrp/nrp1619/Section%202/index.htm Estimation of heart beat , dividing 1500 by number of small squares .
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ECG Axis
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What is mean axis of a vectors ? A.. The directions of each of kick in different directions during the foot ball game , represents small vectors of directions of motion of the ball .(Figure A) B. Single vector represents the average direction of and magnitude ( distance) of these kicks. This is mean axis of direction of the movement (vector ) of the ball.(Figure B). B Foot ball match. From The Only EKG Book You'll Ever Need, 5th Edition Malcolm s. Thaler
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What is axis of ECG waves (Vector) ? This refers to directions of the vectors of depolarization or repolarization. During depolarization of atria or ventricles electrical waves (vectors ) are generated . It spreads across the muscle mass generating multiple small vectors , having different directions and magnitude(force). What is mean electrical axis ? Mean electrical axis is the over all (average) direction of vectors of electrical conduction. By convention the electrical axis is referred to QRS axis ( ventricular depolarization ). However mean electrical axis of P wave ( atrial depolarization ) and T wave (ventricular repolarization ) can be also be determined with same method.
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Mean electrical axis vectors of P and QRS vectors. In normal heart the mean axis of P waves(atrial depolarization) & QRS (ventricular depolarization ) vectors is directed inferiorly to the left at an angle of +0 - * + 90*. Most often around an angle 40 * to 60 * ,Why ? Atrial depolarization starts from Right atrium (SA nodes) located superiorly and right corner therefore normal mean axis of the P wave vector is directed inferiorly and towards left. Atria are located superior to ventricles therefore direction of ventricular depolarization (QRS) is directed inferiorly. Long axis of heart is placed at an angle of 45* to the long axis of body plan (sagittal plan) , moreover thicker LV generates a stronger depolarizing current than that generated by the less bulky RV. Thus normal mean axis of QRS points downward and to the left. This is termed mean electrical axis of P wave and QRS.
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Keep in mind the rules of electrical conduction across myocardial cell. A wave of depolarization travelling toward a positive electrode results in a positive (upward ) deflection in the ECG tracing. A wave of depolarization travelling away from a positive electrode results in a negative (downward ) deflection. A wave of repolarization travelling toward a positive electrode results in a negative deflection. A wave of repolarization travelling away from a positive electrode results in a positive deflection. A wave of depolarization or repolarization travelling perpendicular (At 90* ) to an electrode axis results no net (Isoelectric ) deflection. From https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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Methods of estimating mean QRS axis . There are many methods of estimating mean QRS axis. One simple method is described. First step is to look at limb Lead I and aVF. Examine the QRS complex in each lead & determine if the main QRS is Positive , Negative or Isoelectric (Eqviphasic). Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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look at LEAD I and LEAD aVF. A positive QRS in Lead I puts the axis in roughly directed toward the positive end of lead I. A positive QRS in Lead aVF similarly directed toward the positive end of lead aVF. Combining both coloured areas – the quadrant of overlap determines the axis. Thus If Lead I and aVF are both positive, the axis is between 0° and +90° (i.e. normal axis) Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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Normal Axis = QRS axis between -30° and +90°. Left Axis Deviation ( LAD)= QRS axis less than -30°(-31 to -90). Right Axis Deviation (RAD) = QRS axis greater than +90°. Extreme Axis Deviation = QRS axis between -90° and 180° ( “Northwest Axis”). Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan, LAD= Left axis deviation. RAD = Right axis deviation
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Summary of mean QRS direction and mean QRS axis. Modifed From https://litfl.com/wp-content/upload by Dr Mike Cadogan,
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Morphology (Shape ) of P, QRS and T waves in different ECG leads of normal subject. Remember the rules of electrical conduction across cardiac cell already discussed.
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Vector of P, QRS and T waves and their shape. Vector is a symbolic representation of a physical force. It has direction and magnitude, conventionally represented by an arrow. Movement of electrically charged particles during action potential generate an electrical vector. Shape of the different ECG waves depends on the direction and magnitude of these vectors. As the wave of action potential moves across the cardiac chambers multiple vectors are generated. Direction of the wave of conduction changes during its course from atria through ventricle. Additionally the recording electrodes are placed at different positions of the body. Each of these "see and record the sequence of action potential vectors from a different angles. Therefore the generated waves in the ECG have different shapes . We will discuss spatial orientation of the ECG electrode in relation to the cardiac chambers . Also orientation of the vectors generated and understand the variation in shape and magnitude of PQRST in different ECG leads. From https://teachpe.com/images/anatomy-physiology/heart-conduction500.jpg
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This a 12 lead ECG .These are named as 1, 11, 111, aVR, a VL, aVR and V1 to V6. Note that some of the leads have totally different shapes of the wave forms. Compare lead 1 with aVR, and Lead V1 with leads V5 &V6. In next few slides we will discuss the reasons for these difference in the shapes (morphology).
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Vectors of Ventricular depolarization generating of QRS waves . Wave of Depolarization spreading across the ventricle has four vectors with different directions and magnitude. Vector 1 depolarization of interventricular septum. Vector 2 depolarization of the Left ventricular apex. Vector 3 depolarization of the Left ventricular free wall . Vector depolarization of the ventricular basal segments. Note that the LV free wall is massive therefore activation of RV is masked by LV forces. Thus in normal, RV depolarization force does not contribute much in the genesis of QRS. This is why normal QRS axis points mostly downward and to the left.( +0 - + 90) CV physiology Richard E. Klabunde (modified) Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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Vectors of Ventricular depolarization & concepts of generation of QRS. Depending on the location direction and magnitude ventricular depolarization has four vectors. Vector 1 (Panel A) First part of ventricle to depolarize is left side of the mid basal IV septum. Therefore vector 1 is directed from left towards the right. Magnitude of the Vector is small due to less septal muscle mass. Vector 2 (Panel B). About 20 milliseconds later, the mean electrical vector 2 depolarize LV apex . It points inferiorly & left toward ,has larger magnitude due to larger LV muscle mass. Vector 3 (Panel C). After another 20 milliseconds, the mean vector 3 is pointing toward the left & anterior chest . It depolarizes free wall of LV. from the endocardial to the epicardial surface. Vector 3 has high magnitude due to larger muscle mass LV free wall. Vector 4 (Panel D). Vector 4 depolarize inferior basal parts of ventricle This vector is directed posteriorly and superiorly. Vector size is not large Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 111-

Reminder ECG rules of conduction. Wave of depolarization travelling toward a positive electrode ( < 90*)results in a positive deflection . Wave of depolarization travelling away from a +VE electrode (>90*) results in a negative deflection. Wave of depolarization travelling perpendicular(90*) to +VE electrode axis results no net deflection. The voltage amplitude is directly related to the mass of tissue undergoing depolarization. Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 112-

Morphology (shape ) of QRS waves generated by four vectors in different ECG leads . QRS morphology in lead 11, generated by vector 1 , locate in mid basal IV septum. A1 A2 Fig A1 is showing first vector of ventricular depolarization which is small in magnitude and is directed from left to right (at an angle of +150* ( away from the positive electrode of lead 11). + sign in the figure refers to positive electrode of lead 11. Vector 1 will generate which type of wave in the lead 11 & what will be its magnitude( Voltage)? Vector 1 is heading slightly away from the positive electrode (to the right of a line perpendicular to the lead axis) therefore will record a small negative deflection (Q wave of the QRS).(Fig. A2) Vector 1 Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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B1 B2 Figure B1 is showing large magnitude Vector 2 (Red arrow ) directed inferiorly & slight towards left (60*). + sign in the figure refers to positive lead 11 electrode. Vector 11 will generate which type of wave in the lead 11 and what will be its magnitude (Voltage)? Vector 2 is directed inferiorly towards LV apex, heading toward the positive electrode of lead 11. This will generate a very tall positive deflection (R wave of the QRS) (Panel B 2). QRS morphology in lead 11, generated by vector 2 directed towards LV apex) Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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C 1 C 2 Figure C 1 above is showing large magnitude Vector 3 (Red arrow ) spreads from the endocardial to the epicardial surface directed anteriorly and left wards ( -10* to + 0* ). + sign in the figure refers to positive lead 11 electrode. Vector 3 will generate which type of wave in ECG lead 11 & what will be its Voltage)? Vector 3 points LV free wall (anterolateral) towards left & *anteriorly ( - 10* to + 0 *) & has large magnitude . Though the magnitude is large but as it is not parallel to the positive pole of lead 11 it generate small r wave (contributes small portion of R wave generated mainly by vector 2 ( C2). QRS morphology in lead 11, generated by vector 3, directed from endocardial to the epicardial surface, LV free wall. Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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D 1 D2 Figure D 1 above is showing small magnitude Vector 4 ( Red arrow ) directed at -70 * to -80* . Vector 4 will generate which type of wave in the lead 11 & what will be its magnitude(Voltage)? This vector is directed posteriorly and superiorly. Vector size is not large directed away from the positive electrode of lead 11 small s wave in lead 11.(Panel D 2). QRS morphology in lead 11, generated by vector 4 , located inferior basal parts of ventricle & directed posteriorly and superiorly . Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 116-

Summary of the vectors of Ventricular depolarization generating QRS in lead 11. 1 Mid basal septum From left to right (+150*). Small Q 2 L V apex Left and inferiorly (+60*) Tall R 3 LV free wall (anterolateral) Left & *anteriorly ( - 10* -0 *) Small R *Vector 3 spreads from the endocardial to the epicardial surface anteriorly and left wards. 4 Inferior basal part of LV. Posterior and superior ( -80*) Small Q Vector 1 Vector 2 *Vector 3 Vector 4 Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
Slide 117-

Remember the rules of electrical conduction across cardiac cell. Depolarization wave traveling toward a positive electrode ( At< 90*)results in a positive deflection . Depolarization wave traveling away from a +VE electrode (At>90*) results in a negative deflection. Depolarization wave traveling perpendicular(At 90*) to the +VE electrode results no net deflection. Appreciate the changes in QRS shape in lead 1 & aVF with the change in the direction of the of four LV Vectors . From C:\Users\DELL\Pictures\QRS vectors animation.gif
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TASK 1 You will be given task to draw QRS waves in 6 limb leads with help of the vectors discussed . Don’t get embarrassed if your ECG findings doesn't’ exactly tally with that shown in the diagram or some other ECG books . This is because the anatomical position of the heart in normal person, has acceptable variation. Therefore there may be minor variations in the QRS complex of normal ECG mentioned in different books . In normal persons , small r or small q waves may be present in some and absent in others due to variation of heart position and direction of vectors.
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From http://www.ems12lead.com/wp-content/uploads/sites/42/2014/12/04-Negatives-+-Heart-+-Vector.png TASK 1 Fig. showing four vectors of ventricular depolarization ( red arrows). Is also showing the directions & polarity of 6 limbs leads. Draw expected ECG wave forms, QRS in these limb leads. Don’t click the next slide till you have completed the task. If you need clues (help ) you can see the rules of electrical conduction across cardiac cell in previous slide. Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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From http://www.ems12lead.com/wp-content/uploads/sites/42/2014/12/04-Negatives-+-Heart-+-Vector.png Compare your ECG tracing with the one shown below.
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TASK 2 You will be given task to draw QRS waves in 6 chest leads with help of the vectors discussed . Don’t get embarrassed if your ECG findings doesn't’ exactly tally with that shown in the diagram or some other ECG books . This is because the anatomical position of the heart in normal person, has acceptable variation. Therefore there may be minor variations in the QRS complex of normal ECG mentioned in different books . In normal persons small r or small q waves may be present in some and absent in others due to variation of heart position and direction of vectors.
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TASK 2 Fig. A is showing four vectors of ventricular depolarization ( red arrows). Fig B showing the 6 chest leads (V1 to V6) Draw expected waves form of ECG( QRS) in leads V1 to V6. Don’t click the next slide till you have completed the task. If you need clues (help ) you see the rules of electrical conduction across cardiac cell in previous slide. A B https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16 Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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Compare your ECGs tracings with the one shown below. A B Modified from https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16 From http://www.ems12lead.com/wp-content/uploads/sites/42/2014/12/04-Negatives-+-Heart-+-Vector.png
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Ventricular repolarization (Genesis of T wave)
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+ - + - Depolarization vector. Repolarization vector. From https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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Vector of ventricular depolarization (QRS) & repolarization (T wave ). Vectors of depolarization and repolarization has opposite charges . Thus theoretically T wave (generated by repolarization ) should be in opposite direction to that of QRS ( depolarization). However in normal subjects ,leads with upright QRS has upright T waves , Why ? + - Depolarization vector. Repolarization vector. + - + Select correct wave From http://www.ems12lead.com/wp-content/uploads/sites/42/2014/12/04-Negatives-+-Heart-+-Vector.png correct wave
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Vector of ventricular depolarization (QRS) & repolarization (T wave ). Vectors of depolarization and repolarization has opposite charges . Thus theoretically T wave (generated by repolarization ) should be in opposite direction to that of QRS ( depolarization) However in normal subjects ,leads with upright QRS (lead 1 , 11 & chest leads V 4 to 6,) T wave exhibits a positive deflection ,as seen previous slides. Why is T wave upright in ECG leads with upright QRS ? The reason for this is that the last cells to depolarize ( Subepicardial cells )in the ventricles are first to repolarize. Why ? Will discuss this in next slide. + - Depolarization vector. Repolarization vector. + - + Subepicardial subendocardial From https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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- + - + + - Wave of depolarization. + - Direction of the ventricular repolarization vector and T wave morphology (Theoretically ) ? Figure A shows the direction of two vector from endocardium towards epicardium. A In this setting +ve end of the depolarization vector is directed towards the +ve end of electrode V6. QRS Is positive. If repolarization starts from the endocardium towards epicardium negative end of repolarization vector is directed towards the V6 electrode therefore T wave is inverted. Wave of repolarization Repolarization Depolarization + V6 QRS ? T wave ? Modified from https://ecgwaves.com/ecg-topic/cardiac-electrophysiology-ecg-action-potential-automaticity-vector/
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Wave of repolarization Wave of depolarization. + + - - Direction of the ventricular repolarization vector and T wave morphology.(Reality ) Note. Figure B shows the direction of repolarization from epicardium towards endocardium. Thus normally T wave is recorded upright in leads with upright QRS as in this example . B In this setting +ve end of the depolarization vector is directed towards the +ve end of electrode thus QRS Is upright. Normally repolarization starts from the epicardium toward endocardium . Thus normally ,+ve end of repolarization vector is directed towards the positive electrode therefore T wave is upright. - + Repolarization Depolarization + V6 - + T wave ? Modified from https://ecgwaves.com/ecg-topic/cardiac-electrophysiology-ecg-action-potential-automaticity-vector/
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Modified from https://ecgwaves.com/ecg-topic/cardiac-electrophysiology-ecg-action-potential-automaticity-vector/ In normal subjects epicardial cells (red) has short action potential. (Fig, A ). Therefore the epicardial cell repolarize earlier than the endocardial cells.( Fig A) Direction of repolarization is opposite to that of depolarization ie from epicardium towards endocardium. ( Fig B). Thus Vector of repolarization travel away from the overlying recording electrode with positive end of the repolarization facing the positive electrode (Fig B). This generates a positive Upright T waves in lead with upright QRS . Why is vector directed from epicardium to endocardium ? + + - - A C B
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Electrophysiological characters of T wave. T wave is longer in duration than the QRS complex ? The longer duration occurs because conduction of the repolarization wave is slower than the wave of depolarization. Why ? The reason for this is that the repolarization wave does not utilize the high-velocity bundle branch and purkinje system. Primarily it travels on muscle cell-to-cell conduction.(Which has slow conduction.) Sometimes a small positive U wave may be seen following the T wave . This wave represents the last remnants of ventricular repolarization. Inverted T waves ( in leads with upright QRS ) or prominent U waves indicates underlying pathology or conditions affecting repolarization. From https://www.cvphysiology.com/ Cardiovascular Physiology Concepts. Prof. Richard E. Klabunde, Revised 12/6/16
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Summary orientation of the Waves of the Normal ECG. P wave Due to small muscle mass P wave is small (low voltage ) and normally it is directed inferio lateral direction around +60*. Normal P wave is usually most positive in lead II and most negative in lead AVR. Why ? Reason is mean axis of P wave vector is around + 40 to + 60*directed towards positive electrode of lead 11 , but towards negative electrode of aVR. P wave ,not always but is often biphasic in leads III and aVL , why ? This is because P wave vector is at an angle of 70 to 80* to the positive leads of 111 and aVL. QRST Wave The QRS complex is large, and tall R waves (positive deflections) are usually seen in most left lateral and inferior leads. R-wave progression refers to the sequential increase in height of R waves as one proceeds across the precordial leads from V1 to V5. A small initial Q wave, representing septal depolarization, can often be seen in one or several of the left lateral leads, and sometimes in the inferior leads. T wave is variable, but in normal subject is concordant with QRS (In same direction as is QRS). It is Upright in inferior leads ,V4 to V6 and inverted in aVR. From The Only EKG Book You'll Ever Need, 5th Edition Malcolm s. Thaler