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Published on : Jul 01, 2021 | Views : 1985 | Downloads : 12

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PATHOPHYSIOLOGY OF HEART FAILURE Prof. J. Hanacek
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Notes to heart physiology Essential functions of the heart to cover metabolic needs of body tissue (oxygen, substrates) by adequate blood supply to receive all blood comming back from the tissue Essential conditions for fulfilling these functions normal structure and functions of the heart adequate filling of the heart by blood normal structure and function of tissue surrounding heart
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Essential functions of the heart are secured by integration of its electrical and mechanical functions Cardiac output (CO) = heart rate (HR) x stroke vol.(SV) - changes of the heart rate - changes of stroke volume Control of HR: - autonomic nervous system - hormonal (humoral) control Control of SV: - preload, contractility, afterload, number and size of myocytes, heart architecture, synchronisation of function of the atrias and ventricles
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Adaptive mechanisms of the heart to increased load • Frank - Starling mechanism • Ventricular hypertrophy – increased mass of contractile elements  strength of contraction • Increased sympathetic adrenergic activity – increased HR, increased contractility • Incresed activity of R–A–A system
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Causes leading to changes of number and size of cardiomyocytes
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Preload Stretching the myocardial fibers during diastole by increasing end-diastolic volume  force of contraction during systole = Starling´s law preload = diastolic muscle sarcomere length leading to increased tension in muscle before its contraction (Fig.2,3) venous return to the heart is important  end-diastolic volume is influenced stretching of the sarcomere maximises the number of actin-myosin bridges responsible for development of force - optimal sarcomere length  2.2 m
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Myocardial contractility Contractility of myocardium Changes in ability of myocardium to develop force by contraction that occurs independently on changes in myocardial fibre length Mechanisms involved in changes of contractility  amount of created cross-bridges in the sarcomere by  of Ca ++i - catecholamines  Ca++i  contractility - inotropic drugs  Ca++i  contractility  contractility  shifting the entire ventricular function curve upward and to the left  contractility  shifting the entire ventricular function curve (hypoxia, acidosis) downward and to the right
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The pressure – volume loop • It is the relation between ventricular volume and pressure • This loop provides a convenient framework for understanding the response of individual left ventricular contractions to alterations in preload, afterload, and contractility • It is composed of 4 phases: - filling of the ventricle - isovolumic contraction of ventricle - isotonic contraction of ventricle (ejection of blood) - isovolumic relaxation of ventricle
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Pressure – volume loops recorded under different conditions
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It is expressed as tension which must be developed in the wall of ventricles during systole to open the semilunar valves and eject blood to aorta/pulmunary artery Laplace law: intraventricular pressure x radius of ventricle wall tension = -------------------------------------------------------- 2 x ventricular wall thickness  afterload: due to - elevation of arterial resistance -  ventricular size -  intrathoracic pressure (loss of myocard)  afterload: due to -  arterial resistance - myocardial hypertrophy -  ventricular size Afterload
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Heart failure Definition It is the pathophysiological process in which the heart as a pump is unable to meet the metabolic requirements of the tissue for oxygen and substrates despite the venous return to heart is either normal or increased
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Definition of the terms Myocardial failure = abnormalities reside in the myocardium and lead to inability of myocardium to fulfill its function Circulatory failure = any abnormality of the circulation responsible for the inadequacy in body tissue perfusion, e.g. decreased blood volume, changes of vascular tone, heart function disorders Congestive heart failure = clinical syndrome which is developed due to accumulation of the blood in front of the left or right parts of the heart
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General pathomechanisms involved in heart failure development Cardiac mechanical dysfunction can develop as a consequence in preload, contractility and afterload disorders Disorders of preload  preload  length of sarcomere is more than optimal    strength of contraction  preload  length of sarcomere is well below the optimal    strength of contraction
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Important: failing ventricle requires higher end-diastolic volume to achieve the same CO that normal ventricle achieves with lower ventricular volumes Disorders of contractility In the most forms of heart failure the contractility of myocardium is decreased (ischemia, hypoxia, acidosis, inflammation, toxins, metabolic disorders... ) Disorders of afterload due to: fluid retention in the body  increased blood volume  arterial resistance valvular heart diseases ( stenosis )
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Characteristic features of systolic dysfunction (systolic failure) • ventricular dilatation • reducing ventricular contractility (either generalized or localized) • diminished ejection fraction (i.e. that fraction of end-diastolic blood volume ejected from the ventricle during each systolic contraction – less then 45%) • in failing hearts, the LV end-diastolic volume (or pressure) may increse as the stroke volume (or CO) decreases
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Characteristic features of diastolic dysfunctions (diastolic failure) • ventricular cavity size is normal or smaller than normal • myocardial contractility is normal or hyperdynamic • ejection fraction is normal (>50%) or supranormal • ventricle is usually hypertrophied • ventricle is filling slowly in early diastole (during the period of passive filling)  end-diastolic ventricular pressure is increased
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Causes of heart pump failure A. MECHANICAL ABNORMALITIES 1. Increased pressure load – central (aortic stenosis, aortic coarctation...) – peripheral (systemic hypertension) 2. Increased volume load – valvular regurgitation – hypervolemia 3. Obstruction to ventricular filling – valvular stenosis – pericardial restriction
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B. MYOCARDIAL DAMAGE 1. Primary a) cardiomyopathy b) myocarditis c) toxicity (e.g. alcohol) d) metabolic abnormalities (e.g. hyperthyreoidism) 2. Secondary a) oxygen deprivation (e.g. coronary heart disease) b) inflammation (e.g. due to increased metabolic demands) c) chronic obstructive lung disease
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C. ALTERED CARDIAC RHYTHM 1. ventricular flutter and fibrilation 2. extreme tachycardias 3. extreme bradycardias
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Pathomechanisms involved in heart failure A. Pathomechanisms involved in myocardial failure Damage of cardiomyocytes   contractility,  compliance Consequences:  defect in ATP production and utilisation  changes in contractile proteins  uncoupling of excitation – contraction process   number of cardiomyocytes impairment relaxation of cardiomyocytes with decrease compliance of myocardium impaired of sympato-adrenal system (SAS)   number of 1-adrenergic receptors on the surface of cardiomycytes
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In normal conditions, the ryanoid channel in SR is stabilized, but in heart failure abnormal calcium leak is induced. In heart failure, channel gating is hypersensitized to calcium: at a lower concentration of calcium, the channel is more activated.
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2. Changes of neurohumoral control of the heart function Physiology: • SNS   contractility  HR  activity of physiologic pacemakers Mechanism:   sympathetic activity  cAMP  Ca ++i  contractility   sympathetic activity  influence of parasympathetic system on the heart • Pathophysiology: normal neurohumoral control is changed and creation of pathologic neurohumoral mechanisms are present
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Endothelin Nitric oxyde Bradykinin Pro-proliferative effects Anti-proliferative effects
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Chronic heart failure (CHF) is characterized by an imbalance of neurohumoral adaptive mechanisms with a net results of excessive vasoconstriction and salt and water retention Catecholamines : - concentration in blood : norepinephrin – 2-3x higher at the rest than in healthy subjects - circulating norepinephrin is increased much more during equal load in patients suffering from CHF than in healthy subject  number of beta 1 – adrenergic receptors   sensitivity of cardiomyocytes to catecholamines    contractility System rennin – angiotensin – aldosteron heart failure  CO  kidney perfusion  stim. of RAA system
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Important: Catecholamines and system RAA = compensatory mechanisms  heart function and arterial BP The role of angiotensin II in development of heart failure  vasoconstriction (mainly in resistant vesels)  retention of Na  blood volume  releasing of arginin – vasopresin peptide (AVP –antidiuretic hormon) from neurohypophysis
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  sensitivity of vessel wall to norepinephrine mitogenic effect on smooth muscles in vessels and on cardiomyocytes in the heart  hypertrophy  constriction of vas efferens (in glomerulus)   sensation of thirst   secretion of aldosteron from adrenal gland  mesangial conctraction  glomerular filtration rate facilitation of norepinephrine release from sympathetic nerve endings mitogenic effect on fibrocytes in vessel wall and in myocardium
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Pathogenesis of heart failure Douglas L. Mann, 2004 Index event – primary cause of heart damage Secondary damage – remodeling Adrenergic, RAA, cytokine systems are involved in the remodeling
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Pathophysiology of diastolic heart failure systolic heart failure = failure of ejecting function of the heart diastolic heart failure = failure of filling the ventricles,  resistance to filling of ventricles But, which of the cardiac cycle is real diastole ? Diastolic failure is a widely recognized clinical entity
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Definition of diastolic heart failure It is pathophysiological process characterized by symptoms and signs of congestive heart failure, which is caused by increased filling resistance of ventricles and increased intraventricular diastolic pressure Primary diastolic heart failure no signs and symptoms of systolic dysfunction is present - ! up to 40% of patients suffering from heart failure! Secondary diastolic heart failure - diastolic dysfunction is the consequence of primary systolic dysfunction
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Main causes and pathomechanisms of diastolic heart failure 1. structural disorders passive chamber stiffness intramyocardial – e.g. myocardial fibrosis, amyloidosis, hypertrophy, myocardial ischemia... b) extramyocardial – e.g. constrictive pericarditis 2. functional disorders   relaxation of chambers e. g. myocardial ischemia, advanced hypertrophy of ventricles, failing myocardium, asynchrony in heart ventricle functions
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Causes and mechanism participating on impaired ventricular relaxation a) physiological changes in chamber relaxation due to: – prolonged ventricular contraction Relaxation of ventricles is not impaired ! b) pathological changes in chamber relaxation due to: Impaired relaxation process  delayed relaxation (retarded)  incomplete (slowed) relaxation
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 Consequences of impaired ventricular relaxation filling of ventricles is more dependent on diastasis and on the systole of atrias than in healthy subjects Symptoms and signs:  exercise intolerance = early sign of diastolic failure   coronary blood flow during diastole  Causes and mechanisms involved in development of ventricular stiffness  ventricular compliance = passive property of ventricle Source of compliance: cardiomyocytes and other types of cells in the heart tissue to stretching
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 Ventricular compliance is caused by structural abnormalities localized in myocardium and in extramyocardial tissue a) Intramyocardial causes : myocardial fibrosis, hypertrophy of ventricular wall, restrictive cardiomyopathy b. Extramyocardial causes : constrictive pericarditis The role of myocardial remodelling in genesis of heart failure  adaptive remodelling of the heart  pathologic remodelling of the heart
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Main causes and mechanisms involved in pathological remodelation of the heart 1.Increased amount and size of myocytes = hypertrophy Due to: -  volume and/or pressure load (excentric, concentric hypertrophy) - hormonal stimulation of cardiomyocytes by norepinephrine, angiotenzine II, endothelin... 2. Increased % of non-myocytic cells in myocardium and their influence on structure and function of heart a. endothelial cells – endothelins : mitogenic ability   stimulation growth of smooth muscle cells of vessels, fibroblasts b. fibroblasts -  production of kolagens
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Symptoms and signs of heart failure forward failure: symptoms result from inability of the heart to pump enough blood to the periphery (from left heart), or to the lungs (from the right heart) a) forward failure of left heart:- muscle weakness, fatigue, dyspepsia, oliguria....  general mechanism: tissue hypoperfusion b) forward failure of right heart: - hypoperfusion of the lungs  disorders of gas exchange decreased blood supply to the left heart
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2. backward failure: – symptoms result from inability of the heart to accept the blood comming from periphery and from lungs backward failure of left heart: – increased pulmonary capillary pressure  dyspnoea and tachypnoea, pulmonary edema (cardiac asthma)   arterial hypoxemia and hypercapnia.... b. backward failure of right heart: – increased pressure in systemic venous system   peripheral edemas, hepatomegaly, ascites nocturnal diuresis....
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Processes involved in the picture of left ventricular remodeling Alterations in myocyte biology Excitation contraction coupling Myosin heavy chain (fetal) gene expression Adrenergic desensitization Hypertrophy with loss of myofilaments Cytoskeletal proteins Myocardial changes Myocyte loss Necrosis Apoptosis Alterations in extracellular matrix Matrix degradation Replacement Fibrosis Alterations in left ventricular chamber geometry Spherical shape Wall thinning Mitral valve incompetence
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Mechanical disadvantages created by LV remodeling Increased wall stress (afterload) Afterload mismatch Episodic subendocardial hypoperfusion Increased oxygen utilization Functional mitral regurgitation Worsening hemodynamic overloading Worsening activation of compensatory mechanisms Activation of maladaptive gene expression Activation of maladaptive signal transduction pathways
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Characteristics of pathological and physiological cardiac hypertrophy Pathologic cardiac hypertrophy Physiologic cardiac hypertrophy Stimuli Pressure load in a disease setting Regular physical activity or chronic exercise training (e.g. hypertension, aortic coarction) Volume load (e.g. running, walking, swimming) or volume load (e.g. valvular disease) Pressure load (e.g. strength training: weight lifting Cardiomyopathy (familial, viral, toxic, metabolic) Cardiac morphology Increased myocyte volume Increased myocyte volume Formation of new sarcomeres Formation of new sarcomeres Interstitial fibrosis Myocyte necrosis and apoptosis Fetal gene expression Usually upregulated* Relatively normal* Cardiac function Depressed over time Normal or enhanced Completely reversible Not usually Usually Association with heart failure and increased Yes No mortality McMullen and Jennings, 2007