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Prolonged QT Interval in Athletes: Distinguishing between Pathology and Physiology 1
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Abstract Background: The physiological QT prolongation in athletes is expected to widen the gray zone between physiology and pathology of QT, increasing the diagnostic challenges encountered in athletes with QT prolongation. Summary: According to international recommendations for electrocardiogram in athletes, further evaluation for long QT syndrome (LQTS) is indicated in male athletes with corrected QT (QTc) ≥470 ms and in female athletes with QTc ≥480 ms. Apart from QTc ≥500 ms, diagnostic challenges arise in borderline cases of QTc prolongation, where further clinical investigations are needed to be performed to clarify whether LQTS exists. Clinical diagnostic investigations, including exercise testing, are more readily available, convenient, and easily interpretable, as well as less costly than genetic testing for LQTS. The main findings on exercise testing that are suggestive of LQTS can be the paradoxical prolongation of QTc during exercise and QTc ≥480 ms at fourth min of recovery. Key Messages: Exercise testing appears to have an important role in the diagnostic evaluation of athletes with prolonged QT interval, when genetic testing is not available. 2
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Diagnostic Evaluation of Athletes with Prolonged QT Interval Diagnostic Algorithm According to international recommendations for ECG in athletes, further evaluation for LQTS is indicated in male athletes with QTc ≥470 ms and female athletes with QTc ≥480 ms [6]. Figure 1 shows an algorithm for the diagnostic evaluation of athletes with suspected LQTS. When QTc ≥500 ms, there is unequivocal diagnosis of LQTS, whereas for borderline cases of QTc prolongation (i.e., 470 ms ≤ QTc <500 ms for males, 480 ms ≤ QTc <500 ms for females) further clinical investigations are needed to be performed to clarify whether LQTS exists [6, 7] 3
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4 In cases of athletes with borderline QTc prolongation, personal and family history should be evaluated and, if they are not suggestive of LQTS, a second ECG should be performed on a different day to confirm QTc prolongation. When the personal or family history is positive, further evaluation of the athlete is needed, including calculation of Schwartz score for LQTS, exercise testing, and ambulatory ECG monitoring, along with screening of the athlete’s relatives using resting ECG [6, 8]. Specifically, in case of Schwartz score ≥3.5, there is high probability for LQTS [8]. With regard to exercise testing, paradoxical prolongation of QT with increasing HR during exercise and QTc ≥480 ms at the fourth min of recovery suggest the presence of LQTS [
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5 Detection of excessive prolongation of QTc (i.e., ≥500 ms), T wave abnormalities, or polymorphic ventricular tachycardia (VT) on 12-lead ECG monitoring is indicative of LQTS [11]. Identification of prolonged QTc in a relative is suggestive of the presence of LQTS in this family. If a least one of these investigations is positive in an athlete, the diagnosis of LQTS can be reasonably confirmed. When all these investigations are negative, genetic testing for the three major LQTS-associated genes of KCNQ1, KCNH2, and SCN5A can be performed [12]. A pathogenic or likely pathogenic mutation for these genes confirms diagnosis of LQTS type 1, 2, and 3, respectively, that collectively comprise 75% of LQTS etiology [4, 5, 12]
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6 Diagnostic Investigations in Athletes with Prolonged QT Interval History With regard to personal history, an athlete with prolonged QTc should be asked whether there is history of syncope, pre-syncope, palpitations, or epileptic seizures [6]. Syncopal episodes in an individual with LQTS may give rise to epileptic seizures, due to cerebral ischemia, making the false diagnosis of epilepsy. Questions about family history should include any occurrence of the following in a relative: unexplained SCD at young age, onesided motor
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7 Considering the diurnal and day-to-day variation of QTc, international recommendations for ECG in athletes state that for an athlete with negative personal and family history and borderline QTc prolongation, a repeat ECG should be performed to confirm QTc prolongation [6, 15, 16]. Before evaluation of an athlete with prolonged QTc, reversible extrinsic factors should be excluded, such as electrolyte abnormalities (i.e., hypocalcaemia, hypokalemia, hypomagnesaemia) and QT-prolonging medications [1
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8 Epinephrine QT Stress Testing Epinephrine stress testing can be used as a diagnostic tool for LQTS, primarily type 1 [37]. Specifically, paradoxical prolongation of QT during intravenous infusion of epinephrine is indicative of LQTS type 1, whereas appearance of notched T waves suggests LQTS type 2 [37]. This test does not aid to diagnosis of LQTS type 3 [37]. Epinephrine testing is prone to false positives and is associated with suboptimal positive predictive value [37]. This test is not usually preferred for the evaluation of athletes with suspected LQTS, as it is classically reserved for individuals unable to perform exercise testing, which is not the case for healthy athletes
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9 Supine-Standing Test The transition from supine to standing position can normally induce a mild QTc prolongation during HR acceleration, since the RR interval shortens more than the QT interval [38]. Although the exaggerated QTc prolongation upon standing of individuals with LQTS has been demonstrated to confer incremental diagnostic value over supine ECG, specific cut-offs of the QTc increase on supine-standing test have not been proposed yet [38]
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10 Ambulatory ECG Monitoring Ambulatory 12-lead ECG monitoring in athletes with borderline QTc prolongation on resting ECG can potentially detect excessive prolongation of QTc (i.e., ≥500 ms) or T wave abnormalities indicative of LQTS, including occasional biphasic T waves and episodes of T wave alternans [39]. Considering that the normal QTc values relevant for the baseline resting ECG may not be pertinent to the ambulatory ECG monitoring, only detection of excessive QTc prolongation on ambulatory ECG monitoring could be considered diagnostic. According to European Society of Cardiology (ESC) guidelines, athletes with borderline QTc prolongation should be subjected to ECG monitoring for detection of subclinical arrhythmias [11]. Documentation of episodes of polymorphic VT renders diagnosis of LQTS very likely.
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11 Genetic Testing Both ESC and Heart Rhythm Society (HRS)/European Heart Rhythm Association (EHRA)/Asia Pacific HRS (APHRS) guidelines state that documentation of a pathogenic mutation in a LQTS gene is sufficient for diagnosis of LQTS irrespective of QT duration [4, 5]. Genetic testing for LQTS is highly indicated, since the signal/noise ratio is high (19:1), attributed to a high yield of genetic testing (80%) and low percentage of controls with rare variants of uncertain significance [12]. Genetic testing should be reserved for cases with a high probability diagnosis of LQTS and not as an attempt to clarify an uncertain diagnosis
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12 Variant-specific genetic testing can be performed in relatives after the identification of the disease-causing variant [40]. Approximately 75% of individuals with a clinically definite LQTS diagnosis have mutations in one of the following three genes: KCNQ1 (LQTS type 1), KCNH2 (LQTS type 2), and SCN5A (LQTS type 3) [12]. Thus, genetic testing for LQTS classically involves these three genes. However, 15–20% of LQTS may remain genetically elusive after genetic testing of all the known genes [12].
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13 Reaching a Diagnosis in Athletes with Prolonged QT Interval Diagnosis of LQTS can be based on either HRS/EHRA/ APHRS or ESC guidelines [4, 5]. Diagnostic criteria of both guidelines include Schwartz score ≥3.5 or pathogenic mutation in a LQTS gene. Diagnostic criteria of HRS/ EHRA/APHRS guidelines also include QTc ≥500 ms or QTc = 480–499 ms with unexplained syncope, whereas the respective QTc values of ESC guidelines are 20 ms lower. Taking into account the normal prolongation of QTc in athletes, the higher cut-offs of HRS/EHRA/ APHRS recommendations may be more relevant for athletes and more consistent with international recommendations for ECG in athletes. Both guidelines mention that diagnosis of LQTS can be based on identification of pathogenic mutations for LQTS genes. The more recent American College of Medical Genetics and Genomics (ACMG) guidelines report that both pathogenic and likely pathogenic mutations can be used in clinical decision-making [42]. In current clinical practice, both pathogenic and likely pathogenic variants are classically used to set the diagnosis of LQTS, in accordance with ACMG guidelines.
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14 Management of Athletes with LQTS If an athlete is diagnosed with LQTS, lifestyle changes are recommended by both HRS/EHRA/APHRS and ESC QT Prolongation in Athletes Cardiology 2022;147:578–586 583 DOI: 10.1159/000526385 guidelines, including avoidance of QT-prolonging drugs, as well as early identification and correction of electrolyte abnormalities leading to QT prolongation [4, 5]. Although beta blockers are recommended in essentially all individuals with LQTS, particularly for types 1 and 2, athletes are usually not eligible for this therapy, due to the commonly encountered low HR [4, 5, 12, 43]. This consideration is more relevant for endurance athletes, who are characterized by even lower HR. Thus, tolerability of b-blocker therapy in athletes is questionable. However, the decrease in volume of exercise training of an athlete following the recommended disqualification from competitive sports may result in such an increase in HR, rendering this athlete eligible for b-blocker therapy. Left cardiac sympathetic denervation can be applied as add-on therapy in athletes with LQTS. Finally, sodium channel blockers, such as mexiletine, can have a role in LQTS type 3 [4].
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15 Exercise Recommendations in Athletes with LQTS Genetic testing for LQTS in an athlete can aid to exercise recommendations. According to ESC guidelines, if diagnosis of LQTS is genetically confirmed in an athlete, restriction from competitive sports will be indicated, especially for LQTS type 1, that carries the highest risk of exercise-related SCD [11, 44]. Considering that swimming appears to convey the highest risk of exercise-related SCD in individuals with LQTS, restriction of an athlete with LQTS from not only competitive, but also recreational swimming is reasonable [44]. Swimming without diving or without head under water in any other way may be associated with relatively lower arrhythmic risk, since face immersion in cold water has been found to induce QT prolongation and T wave changes in children with LQTS [45]. Even more, early defibrillation can be impractical in water sports, mandating a stricter approach for swimming [11]. In this respect, recreational exercise, apart from swimming, is permitted for an athlete with LQTS.
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16 A more lenient approach is adopted by American Heart Association (AHA)/American College of Cardiology (ACC) guidelines, mentioning that athletes with LQTS can participate in competitive sports, provided they have been asymptomatic on treatment for at least 3 months and all the necessary precautionary measures are applied, including avoidance of electrolyte abnormalities and dehydration, availability of a personal automatic external defibrillator, and formation of an emergency action plan [46]. However, efficacy of automatic external defibrillator may not be high enough in athletes suffering cardiac arrest, even when applied early enough [47]
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17 In support of a more liberal management of athletes with LQTS, a recent study by Tobert et al. [48] demonstrated that optimally treated athletes with LQTS experienced a low event rate of breakthrough cardiac events (i.e., <2% risk per annum) with no deaths during an average followup of 4 years. Specifically, breakthrough cardiac events occurred in 5.9% of athletes with LQTS with only 1.0% experiencing sports-related cardiac events, while the cardiac event rate was similar between the period of the athletic career and outside of this period [48]. In this respect, AHA/ACC guidelines appear to be more evidence-based and may be more reasonable than ESC guidelines regarding the management of athletes with LQTS.
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18 QT during Recovery Abnormal QT prolongation during recovery of exercise testing has been found to characterize individuals with LQTS type 1 and 2, whereas QT changes during recovery appear not to differ between LQTS type 3 and controls [49, 50, 53]. Individuals with LQTS type 1 display a sustained QTc prolongation throughout the whole recovery with decreasing magnitude of QTc prolongation from early to late recovery, while for LQTS type 2 the magnitude of QTc prolongation increases from early to late recovery [52, 54]. The abovementioned data imply that the diagnostic performance of abnormal QTc prolongation during recovery may be enhanced at late rather than early recovery, at least for LQTS type 2. The inclusion of QTc at fourth min of recovery in the Schwartz diagnostic criteria for LQTS was actually based on the findings of awell-designed study performed by Sy et al. [8, 10]
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19 Conclusions In conclusion, exercise testing plays an important role in the diagnostic evaluation of individuals with borderline QTc prolongation. The most widely accepted criteria for diagnostic confirmation of LQTS on exercise testing include paradoxical prolongation of QTc during exercise and detection of QTc ≥480 ms at fourth min of recovery. Further well-designed studies are needed to explore the diagnostic performance of exercise testing in various subpopulations with QT prolongation, including ath