ABC | Volume 115, Nº1, July 2020

Short Editorial Atrioventricular Conduction System Disorders and Potential Risks of Arrhythmic Events in Endurance Athletes Carlos Alberto Cordeiro Hossri 1,2, 3 Instituto Dante Pazzanese de Cardiologia, 1 São Paulo, SP – Brazil Hospital do Coração, 2 São Paulo, SP – Brazil HCor - Associação Beneficiente Síria, 3 São Paulo, SP – Brazil Short Editorial related to the article: Assessing Dynamic Atrioventricular Conduction Time to RR-interval Coupling in Athletes and Sedentary Subjects Mailing Address: Carlos Alberto Cordeiro Hossri • Instituto Dante Pazzanese de Cardiologia – Av. Dr. Dante Pazzanese, 500. Postal Code 04012-909, São Paulo, SP – Brazil E-mail: cahossri@gmail.com Keywords Keywords: Athletes; Resistance Training; Physical Fitness; Ventricular Remodeling; Sedentarism; Arrhythmias, Cardiac; Eletrocardiography/methods; Ventricular Function. Some disorders found on electrocardiograms are commonly seen in endurance or high-performance athletes and often have characteristics that are similar to those observed in elderly individuals or in those with cardiovascular disease. 1-4 High-intensity training done by high-performance athletes can induce intrinsic physiological adaptations to the cardiac stimulus conduction system and, consequently, a higher prevalence of abnormalities in atrioventricular (AV) conduction. 3,5 The physiological or even pathophysiological mechanisms by which athletic training induces such intrinsic changes in the cardiac conduction system still have limited understanding, and are likely to be multifactorial. However, the anatomical changes observed, such as atrial and ventricular dilation, demonstrated the creation of a mechanical-electrical remodeling necessary to cause intrinsic AV electrophysiological adaptations. 4-6 Among the most common electrocardiographic expressions, resulting from cardiac changes induced by high-performance sports and high levels of training, include sinus bradycardia and AV block. They do not usually require special care or attention as long as they are asymptomatic or do not produce pauses longer than 4 seconds. First-degree AV block is more common, followed by 2 nd degree Mobitz I AV block. Mobitz II and 3 rd degree atrioventricular blocks are more unusual findings, even in athletes, and should be considered a sign of potential organic injuries. The occurrence of complex ventricular forms of arrhythmia should always lead to cardiological examination in search of cardiogenic substrate, especially hypertrophic or dilated cardiomyopathy. The presence of ventricular arrhythmias with no evidence of underlying heart disease does not appear to indicate any special or increased risk of sudden cardiac death. Higher incidence of right and/or left ventricular hypertrophy, reversible ST-segment elevation on exercise and reversible abnormalities on exercise on T waves (T negativity, sudden and/or excessive T waves) can be considered physiological abnormalities in the athletes’ ECG scans. Endurance or major physical training exposes the heart to intense overloads over time. These constant exposures to intense training can generate cardiac automatism disorders as described, in addition to atrioventricular conduction disorders, depolarization and ventricular repolarization. 1,2,6 Besides, these cardiac structural adjustments can be remarkable and lead to increases of up to 85% in left ventricular mass. Although these functional and structural abnormalities are documented, their actual limits within standards considered normal, as well as their long-term consequences, are still unknown. Stein et al. 5 described high-performance training actions as a corollary of their effects on sinus node, where increased parasympathetic tone, reduced sympathetic tone and non- autonomic components can contribute to sinus bradycardia and adaptations to the special system of cardiac conduction. Such mechanisms lead to a higher prevalence of abnormalities in intrinsic atrioventricular conduction observed in athletes. In elite athletes, in addition to the predominance of vagal tone and, consequently, bradycardia at rest, which increase absolute QT interval duration, 7,8 an increase in left ventricular mass is considered a benign physiological phenomenon, also known as “athlete’s heart”. Observations made, such as a slightly prolonged isolated QT interval in athletes, may reflect the late repolarization resulting from increased ventricular wall thickness 8,9 and/or bradycardia, both as a reflex of training and ultimately as a form of impairment to the special conduction system of the cardiac stimulus. 10,11 These endurance athletes often present AV node remodeling, characterized by varying degrees of AV conduction block, low non-sinus atrial or junctional rhythm and, more rarely, complete AV block. 1,2,6,9 These AV conduction disorders depend on the fitness status and are related not only to increased parasympathetic activity on the AV node, but also to the secondary remodeling of the AV node fibers and to cell-to-cell coupling. 8,9 Thus, the analysis of autonomic contributions to the dependence of the variability in the dynamic duration of ventricular repolarization (DVR) can be a valuable tool to assess the adaptation of DVR to the cardiac cycle duration in this population. 12 In a previous study, Nazario and Benchimol-Barbosa 13 described the variability in the duration of beat-by-beat ventricular repolarization assessed by phases of cardiac DOI: https://doi.org/10.36660/abc.20200668 78