Relation between training-induced left ventricular hypertrophy and risk for ventricular tachyarrhythmias in elite athletes

Investigation of left atrial mechanical function and left ventricular systolic and diastolic parameters in athletes performing resistance exercise and combined exercise

Some individuals who go to fitness centers for various purposes perform resistance exercise (RE) alone, while others engage in combined exercise (CE) by including cardio exercises along with RE. Studying the effects of these two different training methods on left ventricular (LV) systolic and diastolic parameters and left atrial mechanical function is an important step toward understanding the effects of different types of exercise on cardiac function. This knowledge has significant implications for public health, as it can inform the development of targeted and effective exercise programs that prioritize cardiovascular health and reduce the risk of adverse outcomes. Therefore, the primary aim of this study is to comprehensively investigate the LV systolic and diastolic parameters of athletes who engage in RE and CE using ECHO, to contribute to the growing body of literature on the cardiovascular effects of different types of exercise. Forty-two amateur athletes aged between 17 and 52 were included in our study. The participants consisted of the RE (n = 26) group who did only resistance exercise during the weekly exercise period, and the CE group (n = 16) who also did cardio exercise with resistance exercises. After determining sports age (year), weekly exercise frequency (day), and training volume (min) in addition to demographic information of RE and CE groups, left ventricular systolic and diastolic parameters and left atrial functions were determined by ECHO. Findings from our study revealed that parameters including the left ventricular end-diastolic diameter (LVEDD) (p = .008), left ventricular end-diastolic volume (LVEDV) (p = .020), stroke volume index (SV-I) (p = .048), conduit volume (CV-I) (p = .001), and aortic strain (AS) (p = .017) were notably higher in the RE group compared to the CE group. Also left atrial active emptying volüme (LAAEV) of CE was higher than the RE group (p = .031). In conclusion, the cardiac parameters of the RE group showed more athlete's heart characteristics than the CE group. These results may help to optimize the cardiovascular benefits of exercise routines while minimizing the potential risks associated with improper training.

Interpretation and management of premature ventricular beats in athletes: An expert opinion document of the Italian Society of Sports Cardiology (SICSPORT)

Premature ventricular beats (PVBs) are recorded in a sizeable proportion of athletes during pre-participation screening, especially if the evaluation includes both resting and exercise ECG. While in the majority of cases no underlying heart disease is present, in others PVBs may be the sign of a condition at risk of sudden cardiac death, including cardiomyopathies, congenital, coronary artery, heart valves and ion channels diseases. In this expert opinion document of the Italian Society of Sports Cardiology, we propose a multiparametric interpretation approach to PVBs in athletes and a stepwise diagnostic algorithm. The clinical work-up should include the assessment of the probable site of origin based on the ECG pattern of the ectopic QRS and of the arrhythmia behavior (including the number of different PVB morphologies, complexity, response to exercise and reproducibility), as well as first-line tests such as echocardiography. Based on this initial evaluation, most athletes can be reassured of the benign nature of PVBs and cleared for competition under periodical follow-up. However, when the clinical suspicion is high, further investigations with non-invasive (e.g. cardiac magnetic resonance, cardiac computed tomography, genetic testing) and, in very selected cases, invasive (e.g. endocardial voltage mapping and endomyocardial biopsy) tests should be carried out to rule out a high-risk condition. Importantly, such advanced tests should be performed in centers with a consolidated experience not only in the technique, but also in evaluation of athletes.

Is Continuous ECG Recording on Heart Rate Monitors the Most Expected Function by Endurance Athletes, Coaches, and Doctors?

Heart rate monitors (HRMs) are important for measuring heart rate, which can be used as a training parameter for healthy athletes. They indicate stress-related heart rhythm disturbances—recognized as an unexpected increase in heart rate (HR)—which can be life-threatening. Most HRMs confuse arrhythmias with artifacts. This study aimed to assess the usefulness of electrocardiogram (ECG) recordings from sport HRMs for endurance athletes, coaches, and physicians, compared with other basic and hypothetical functions. We conducted three surveys among endurance athletes (76 runners, 14 cyclists, and 10 triathletes), 10 coaches, and 10 sports doctors to obtain information on how important ECG recordings are and what HRM functions should be improved to meet their expectations in the future. The respondents were asked questions regarding use and hypothetical functions, as well as their preference for HRM type (optical/strap). Athletes reported distance, pace, instant HR, and oxygen threshold as being the four most important functions. ECG recording ranked eighth and ninth for momentary and continuous recording, respectively. Coaches placed more importance on ECG recording. Doctors ranked ECG recording the highest. All participants preferred optical HRMs to strap HRMs. Research on the improvement and implementation of HRM functions showed slightly different preferences for athletes compared with coaches and doctors. In cases where arrhythmia was suspected, the value of the HRM’s ability to record ECGs during training by athletes and coaches increased. For doctors, this is the most desirable feature in any situation. Considering the expectations of all groups, continuous ECG recording during training will significantly improve the safety of athletes.

Ventricular arrhythmias and risk stratification of cardiac sudden death in athletes

Sudden cardiac death (SCD) of young athletes is an unexpected and tragic event that could occur during sport activities and is frequently related to ventricular arrhythmias. Identifying athletes at risk of SCD remains a major challenge. While specific characteristics of premature ventricular contractions are considered common and benign, other "uncommon" features should require more accurate investigations, in order to determine eligibility for competitive sports. The most common type of idiopathic premature ventricular contractions originates from ventricular outflow tract and is characterized by an ECG pattern with left bundle branch block and inferior QRS axis (infundibular pattern). Another pattern associated with a good prognosis is the "fascicular" morphology, characterized by a typical right bundle branch block, superior QRS axis morphology and QRS duration <130 ms. Conversely, other morphological features (such as left bundle branch block /intermediate or superior axis or right bundle branch block/intermediate or superior axis and wide QRS) correlate to an underlying substrate. In risk stratification setting, cardiac magnetic resonance plays a key role allowing an accurate identification of myocardial tissue abnormalities, which could affect athletes' prognosis. This review focuses on characteristics of premature ventricular contractions characteristics in terms of morphology, distribution, complexity and response to exercise and describes the possible underlying myocardial substrates. This review also critically analyzes the evaluation process of athletes with premature ventricular contractions necessary for an accurate risk stratification.

How to interpret right ventricular remodeling in athletes

Long-lasting athletic training induces an overload on the heart that leads to structural, functional, and electrical adaptive changes known as the "athlete's heart." The amount of this heart remodeling has been traditionally considered balanced between the left and the right heart chambers. However, during intense exercise, the right heart is exposed to a disproportional afterload and wall stress which over a long period of time could lead to more pronounced exercise-induced changes. Highly trained athletes, especially those involved in endurance sport disciplines, can develop marked right ventricular (RV) remodeling that could raise the suspicion of an underlying RV pathology including arrhythmogenic cardiomyopathy (ACM). The distinction between physiological and pathological RV remodeling is essential as ACM is a common cause of sudden cardiac death in athletes, and high-intensity exercise training has demonstrated to accelerate its phenotypic expression and worsen its prognosis. The distinction between physiological and pathological RV remodeling is essential since ACM is a common cause of sudden cardiac death in athletes, and high-intensity exercise training has demonstrated to accelerate the phenotypic expression and worsen the prognosis. This article outlines the physiological adaptation of the RV to acute exercise, the subsequent physiological structural and functional changes induced by athletic training and provides useful tips of how to differentiate between physiological RV remodeling and a cardiomyopathy phenotype.

Heart of the World's Top Ultramarathon Runner-Not Necessarily Much Different from Normal

The impact of ultramarathon (UM) runs on the organs of competitors, especially elite individuals, is poorly understood. We tested a 36-year-old UM runner before, 1–2 days after, and 10–11 days after winning a 24-h UM as a part of the Polish Championships (258.228 km). During each testing session, we performed an electrocardiogram (ECG), transthoracic echocardiography (TTE), cardiac magnetic resonance imaging (MRI), cardiac ³¹P magnetic resonance spectroscopy (³¹P MRS), and blood tests. Initially, increased cholesterol and low-density lipoprotein cholesterol (LDL-C) levels were identified. The day after the UM, increased levels of white blood cells, neutrophils, fibrinogen, alanine aminotransferase, aspartate aminotransferase, creatine kinase, C-reactive protein, and N-terminal type B natriuretic propeptide were observed. Additionally, decreases in hemoglobin, hematocrit, cholesterol, LDL-C, and hyponatremia were observed. On day 10, all measurements returned to normal levels, and cholesterol and LDL-C returned to their baseline abnormal values. ECG, TTE, MRI, and ³¹P MRS remained within the normal ranges, demonstrating physiological adaptation to exercise. The transient changes in laboratory test results were typical for the extreme efforts of the athlete and most likely reflected transient but massive striated muscle damage, liver cell damage, activation of inflammatory processes, effects on the coagulation system, exercise-associated hyponatremia, and cytoprotective or growth-regulatory effects. These results indicated that many years of intensive endurance training and numerous UMs (including the last 24-h UM) did not have a permanent adverse effect on this world-class UM runner’s body and heart. Transient post-competition anomalies in laboratory test results were typical of those commonly observed after UM efforts.

How to evaluate premature ventricular beats in the athlete: critical review and proposal of a diagnostic algorithm

Although premature ventricular beats (PVBs) in young people and athletes are usually benign, they may rarely mark underlying heart disease and risk of sudden cardiac death during sport. This review addresses the prevalence, clinical meaning and diagnostic/prognostic assessment of PVBs in the athlete. The article focuses on the characteristics of PVBs, such as the morphological pattern of the ectopic QRS and the response to exercise, which accurately stratify risk. We propose an algorithm to help the sport and exercise physician manage the athlete with PVBs. We also address (1) which athletes need more indepth investigation, including cardiac MRI to exclude an underlying pathological myocardial substrate, and (2) which athletes can remain eligible to competitive sports and who needs to be excluded.

Assessment of premature ventricular beats in athletes

INTRODUCTION

Premature ventricular complexes (PVC) are generally considered as a benign electrocardiographic abnormality in the athletic population. However it may be indicative of underlying heart disease which may increase the risk of sudden death. This implies the need for cardiological evaluation before indicating the ability to practice competitive sports.

AIM

The aim of this study was to evaluate an athlete population with PVC and establish underlying etiologies in order to take a decision regarding practicing sports.

METHODS

This is a prospective study which included athletes examined in the Tunisian National Centre of Sports Medicine and Sports Science (TNCSM) from January 2013 to June 2015 who presented PVC on an electrocardiogram.

RESULTS

Five thousand seven hundred and ninety eight athletes were referred to the TNCSM. We identified 42 athletes having PVC with a prevalence of 1.8%. The average age of the study population was 21.6±5.99 years. 83% were men. 88% were asymptomatic. The electrocardiogram was considered normal in 62% of the athletes according to the Seattle criteria. At the Holter monitoring, the average number of PVC was 920 PVC/24hours. Thirteen athletes had doublets and 11 had triplets. One patient had polymorphic PVC and an R/T phenomenon. The transthoracic echocardiography (TTE) was normal in 71% of cases. Three athletes had hypertrophic cardiomyopathy (HCM). All patients underwent a stress test. The PVC disappeared in 12% of athletes MRI was performed in 10 athletes confirming the three cases of HCM and revealing a case of arrhythmogenic right ventricular dysplasia and a case of compression of the right ventricle by pectus exacavatum.

CONCLUSION

After this assessment, five athletes were not allowed to practice sport. This study shows the necessity of a thorough cardiological assessment of athletes with ventricular arrhythmia in order to detect underlying heart disease and prevent sudden death in this young apparently healthy population.

Cardiovascular Effects and Benefits of Exercise

It is widely accepted that regular physical activity is beneficial for cardiovascular health. Frequent exercise is robustly associated with a decrease in cardiovascular mortality as well as the risk of developing cardiovascular disease. Physically active individuals have lower blood pressure, higher insulin sensitivity, and a more favorable plasma lipoprotein profile. Animal models of exercise show that repeated physical activity suppresses atherogenesis and increases the availability of vasodilatory mediators such as nitric oxide. Exercise has also been found to have beneficial effects on the heart. Acutely, exercise increases cardiac output and blood pressure, but individuals adapted to exercise show lower resting heart rate and cardiac hypertrophy. Both cardiac and vascular changes have been linked to a variety of changes in tissue metabolism and signaling, although our understanding of the contribution of the underlying mechanisms remains incomplete. Even though moderate levels of exercise have been found to be consistently associated with a reduction in cardiovascular disease risk, there is evidence to suggest that continuously high levels of exercise (e.g., marathon running) could have detrimental effects on cardiovascular health. Nevertheless, a specific dose response relationship between the extent and duration of exercise and the reduction in cardiovascular disease risk and mortality remains unclear. Further studies are needed to identify the mechanisms that impart cardiovascular benefits of exercise in order to develop more effective exercise regimens, test the interaction of exercise with diet, and develop pharmacological interventions for those unwilling or unable to exercise.

Ventricular Arrhythmias in Young Competitive Athletes: Prevalence, Determinants, and Underlying Substrate

BACKGROUND

Whether ventricular arrhythmias (VAs) represent a feature of the adaptive changes of the athlete's heart remains elusive. We aimed to assess the prevalence, determinants, and underlying substrates of VAs in young competitive athletes.

METHOD AND RESULTS

We studied 288 competitive athletes (age range, 16-35 years; median age, 21 years) and 144 sedentary individuals matched for age and sex who underwent 12-lead 24-hour ambulatory electrocardiographic monitoring. VAs were evaluated in terms of number, complexity (ie, couplet, triplet, or nonsustained ventricular tachycardia), exercise inducibility, and morphologic features. Twenty-eight athletes (10%) and 13 sedentary individuals (11%) showed >10 isolated premature ventricular beats (PVBs) or ≥1 complex VA (P=0.81). Athletes with >10 isolated PVBs or ≥1 complex VA were older (median age, 26 versus 20 years; P=0.008) but did not differ with regard to type of sport, hours of training, and years of activity compared with the remaining athletes. All athletes with >10 isolated PVBs or ≥1 complex VA had a normal echocardiographic examination; 17 of them showing >500 isolated PVBs, exercise-induced PVBs, and/or complex VA underwent additional cardiac magnetic resonance, which demonstrated nonischemic left ventricular late gadolinium enhancement in 3 athletes with right bundle branch block PVBs morphologic features.

CONCLUSIONS

The prevalence of >10 isolated PVBs or ≥1 complex VA at 24-hour ambulatory electrocardiographic monitoring did not differ between young competitive athletes and sedentary individuals and was unrelated to type, intensity, and years of sports practice. An underlying myocardial substrate was uncommon and distinctively associated with right bundle branch block VA morphologic features.

Mechanisms contributing to myocardial potassium channel diversity, regulation and remodeling

In the mammalian heart, multiple types of K(+) channels contribute to the control of cardiac electrical and mechanical functioning through the regulation of resting membrane potentials, action potential waveforms and refractoriness. There are similarly vast arrays of K(+) channel pore-forming and accessory subunits that contribute to the generation of functional myocardial K(+) channel diversity. Maladaptive remodeling of K(+) channels associated with cardiac and systemic diseases results in impaired repolarization and increased propensity for arrhythmias. Here, we review the diverse transcriptional, post-transcriptional, post-translational, and epigenetic mechanisms contributing to regulating the expression, distribution, and remodeling of cardiac K(+) channels under physiological and pathological conditions.

Reduced Ventricular Arrhythmogeneity and Increased Electrical Complexity in Normal Exercised Rats

BACKGROUND

The mechanisms whereby aerobic training reduces the occurrence of sudden cardiac death in humans are not clear. We test the hypothesis that exercise-induced increased resistance to ventricular tachycardia and fibrillation (VT/VF) involve an intrinsic remodeling in healthy hearts.

METHODS AND RESULTS

Thirty rats were divided into a sedentary (CTRL, n = 16) and two exercise groups: short- (4 weeks, ST, n = 7) and long-term (8 weeks, LT, n = 7) trained groups. Following the exercise program hearts were isolated and studied in a Langendorff perfusion system. An S1-S2 pacing protocol was applied at the right ventricle to determine inducibility of VT/VF. Fast Fourier transforms were applied on ECG time-series. In-vivo measurements showed training-induced increase in aerobic capacity, heart-to-body weight ratio and a 50% low-to-high frequency ratio reduction in the heart rate variability (p<0.05). In isolated hearts the probability for VF decreased from 26.1±14.4 in CTRL to 13.9±14.1 and 6.7±8.5% in the ST and LT, respectively (p<0.05). Duration of VF also decreased from 19.0±5.7 in CTRL to 8.8±7.1 and 6.0±5.8 sec in ST and LT respectively (p<0.05). Moreover, the pacing current required for VF induction increased following exercise (2.9±1.7 vs. 5.4±2.1 and 8.5±0.9 mA, respectively; p<0.05). Frequency analysis of ECG revealed an exercise-induced VF transition from a narrow single peak spectrum at 17 Hz in CTRL to a broader range of peaks ranging between 8.8 and 22.5 Hz in the LT group (p<0.05).

CONCLUSION

Exercise in rats leads to reduced VF propensity associated with an intrinsic cardiac remodeling related to a broader spectral range and faster frequency components in the ECG.

Nonsustained ventricular tachycardia

Nonsustained ventricular tachycardia (NSVT) has been recorded in a wide range of conditions, from apparently healthy individuals to patients with significant heart disease. In the absence of heart disease, the prognostic significance of NSVT is debatable. When detected during exercise, and especially at recovery, NSVT indicates increased cardiovascular mortality within the next decades. In trained athletes, NSVT is considered benign when suppressed by exercise. In patients with non-ST-segment elevation acute coronary syndrome, NSVT occurring beyond 48 h after admission indicates an increased risk of cardiac and sudden death, especially when associated with myocardial ischemia. In acute myocardial infarction, in-hospital NSVT has an adverse prognostic significance when detected beyond the first 13 to 24 h. In patients with prior myocardial infarction treated with reperfusion and beta-blockers, NSVT is not an independent predictor of long-term mortality when other covariates such as left ventricular ejection fraction are taken into account. In patients with hypertrophic cardiomyopathy, and most probably genetic channelopathies, NSVT carries prognostic significance, whereas its independent prognostic ability in ischemic heart failure and dilated cardiomyopathy has not been established. The management of patients with NSVT is aimed at treating the underlying heart disease.

Exercise training and PI3Kα-induced electrical remodeling is independent of cellular hypertrophy and Akt signaling

In contrast with pathological hypertrophy, exercise-induced physiological hypertrophy is not associated with electrical abnormalities or increased arrhythmia risk. Recent studies have shown that increased cardiac-specific expression of phosphoinositide-3-kinase-α (PI3Kα), the key mediator of physiological hypertrophy, results in transcriptional upregulation of ion channel subunits in parallel with the increase in myocyte size (cellular hypertrophy) and the maintenance of myocardial excitability. The experiments here were undertaken to test the hypothesis that Akt1, which underlies PI3Kα-induced cellular hypertrophy, mediates the effects of augmented PI3Kα signaling on the transcriptional regulation of cardiac ion channels. In contrast to wild-type animals, chronic exercise (swim) training of mice (Akt1(-/-)) lacking Akt1 did not result in ventricular myocyte hypertrophy. Ventricular K(+) current amplitudes and the expression of K(+) channel subunits, however, were increased markedly in Akt1(-/-) animals with exercise training. Expression of the transcripts encoding inward (Na(+) and Ca(2+)) channel subunits were also increased in Akt1(-/-) ventricles following swim training. Additional experiments in a transgenic mouse model of inducible cardiac-specific expression of constitutively active PI3Kα (icaPI3Kα) revealed that short-term activation of PI3Kα signaling in the myocardium also led to the transcriptional upregulation of ion channel subunits. Inhibition of cardiac Akt activation with triciribine in this (inducible caPI3Kα expression) model did not prevent the upregulation of myocardial ion channel subunits. These combined observations demonstrate that chronic exercise training and enhanced PI3Kα expression/activity result in transcriptional upregulation of myocardial ion channel subunits independent of cellular hypertrophy and Akt signaling.

Is the 'athlete's heart' arrhythmogenic? Implications for sudden cardiac death

Whether the ventricular hypertrophic response to athletic training can predispose to fatal ventricular dysrhythmias via mechanisms similar to that of pathological hypertrophy is controversial. This review examines current information regarding the metabolic and electrophysiological differences between the myocardial hypertrophy of heart disease and that associated with athletic training. In animal studies, the biochemical and metabolic profile of physiological hypertrophy from exercise training can largely be differentiated from that of pathological hypertrophy, but it is not clear if the former might represent an early stage in the spectrum of the latter. Information as to whether the electrical remodelling of the athlete's heart mimics that of patients with heart disease, and therefore serves as a substrate for ventricular dysrhythmias, is conflicting. If ventricular remodelling associated with athletic training can trigger fatal dysrhythmias, such cases are extraordinarily rare and thereby impossible to investigate by any standard experimental approach. Greater insight into this issue may come from a better understanding of the electrical responses to both acute bouts of exercise and chronic training in young athletes.

Three-dimensional echocardiographic characterization of left ventricular remodeling in Olympic athletes

The aim of the present study was to assess, using 3-dimensioanl echocardiography, the morphologic characteristics, determinants, and physiologic limits of left ventricular (LV) remodeling in 511 Olympic athletes (categorized in skill, power, mixed, and endurance sport disciplines) and 159 sedentary controls matched for age and gender. All subjects underwent 3-dimensional echocardiography for the assessment of LV volumes, ejection fraction, mass, remodeling index (LV mass/LV end-diastolic volume), and systolic dyssynchrony index (obtained by the dispersion of the time to minimum systolic volume in 16 segments). Athletes had higher LV end-diastolic volumes (157 ± 35 vs 111 ± 26 ml, p <0.001) and mass (156 ± 38 vs 111 ± 25 g, p <0.001) compared to controls. Body surface area and age had significant associations with LV end-diastolic volume (R(2) = 0.49, p <0.001) and mass (R(2) = 0.51, p <0.001). Covariance analysis showed that also gender and type of sport were significant determinants of LV remodeling; in particular, the highest impact on LV end-diastolic volume and mass was associated with male gender and endurance disciplines (p <0.001). Regardless of the type of sport, athletes had similar LV remodeling indexes to controls (1.00 ± 0.06 vs 1.01 ± 0.07 g/mL, p = 0.410). No differences were found between athletes and controls for the ejection fraction (62 ± 5% and 62 ± 5%, p = 0.746) and systolic dyssynchrony index (1.06 ± 0.40% and 1.37 ± 0.41%, p = 0.058). In conclusion, 3-dimensional echocardiographic morphologic and functional assessment of the left ventricle in Olympic athletes demonstrated a balanced adaptation of LV volume and mass, with preserved systolic function, regardless of specific disciplines participated.

Patterns of ventricular tachyarrhythmias associated with training, deconditioning and retraining in elite athletes without cardiovascular abnormalities

Ventricular tachyarrhythmias commonly occur in trained athletes during ambulatory Holter electrocardiography and are usually associated with a benign course. Such arrhythmias have been demonstrated to be sensitive to short periods of athletic deconditioning; however, their response to retraining is not known. Twenty-four hour Holter electrocardiographic monitoring was performed at peak training and after 3 to 6 months of deconditioning and was repeated in the present study after 2, 6, and 12 months of retraining in 37 athletes with frequent and complex ventricular tachyarrhythmias and without cardiovascular abnormalities. These subjects showed partial (101 to 500 ventricular premature complexes [VPCs]/24 hours) or marked (<100 VPCs) reversibility of arrhythmias after deconditioning. Retraining initially resulted in a significant increase in arrhythmia frequency compared with deconditioning (from 280 ± 475 to 1,542 ± 2,186 VPCs; p = 0.005), couplets (0.14 ± 0.42 to 4.4 ± 8.2; p = 0.005), and nonsustained ventricular tachycardia (from 0 to 0.8 ± 1.8; p = 0.02). Subsequently, a progressive reduction was seen in the frequency of all ventricular arrhythmias during the 1 year of training to well below that at the peak training levels (VPCs 917 ± 1,630, couplets 1.8 ± 4.2, and nonsustained ventricular tachycardia 0.4 ± 1.2). Such annual arrhythmia reduction was significantly greater statistically in those athletes with marked reversibility after deconditioning than in the athletes with partial reversibility (69 ± 139 vs 1,496 ± 1,917 VPCs/24 hours, respectively; p = 0.007). No cardiac events or symptoms occurred during 1 year of follow-up. In conclusion, in elite athletes without cardiovascular disease, a resumption in intense training after deconditioning was associated with variable, but prolonged, suppression of ventricular ectopy. The absence of adverse clinical events or symptoms associated with the resumption of training supports the continued eligibility in competitive sports for such athletes and is also consistent with the benign nature of physiologic athlete's heart syndrome.

Sports and arrhythmias: a report of the International Workshop Venice Arrhythmias 2009

This article is a report of an international symposium, endorsed by the Section on Sports Cardiology of the European Association for Cardiovascular Prevention and Rehabilitation, the Italian Society of Sports Cardiology, and the Italian Federation of Sports Medicine, which was held within the 11th International Workshop on Cardiac Arrhythmias (Venice Arrhythmias 2009, Venice, Italy, October 2009). The following main topics were discussed during the symposium: the role of novel diagnostic examinations to assess the risk of sudden death in athletes, controversies on arrhythmic risk evaluation in athletes, controversies on the relationship between sports and arrhythmias, and controversies on antiarrhythmic treatment in athletes.

Homeostatic regulation of electrical excitability in physiological cardiac hypertrophy

Pathological biomechanical stresses cause cardiac hypertrophy, which is associated with QT prolongation and arrhythmias. Previous studies have demonstrated that repolarizing K(+) current densities are decreased in pressure overload-induced left ventricular hypertrophy, resulting in action potential and QT prolongation. Cardiac hypertrophy also occurs with exercise training, but this physiological hypertrophy is not associated with electrical abnormalities or increased arrhythmia risk, suggesting that repolarizing K(+) currents are upregulated, in parallel with the increase in myocyte size, to maintain normal cardiac function. To explore this hypothesis directly, electrophysiological recordings were obtained from ventricular myocytes isolated from two mouse models of physiological hypertrophy, one produced by swim-training of wild-type mice and the other by cardiac-specific expression of constitutively active phosphoinositide-3-kinase-p110α (caPI3Kα). Whole-cell voltage-clamp recordings revealed that repolarizing K(+) current amplitudes were higher in ventricular myocytes isolated from swim-trained and caPI3Kα, compared with wild-type, animals. The increases in K(+) current amplitudes paralleled the observed cellular hypertrophy, resulting in normalized or increased K(+) current densities. Electrocardiographic parameters, including QT intervals, as well as ventricular action potential waveforms in swim-trained animals/myocytes were indistinguishable from controls, demonstrating preserved electrical function. Additional experiments revealed that inward Ca(2+) current amplitudes/densities were also increased in caPI3Kα, compared with WT, left ventricular myocytes. The expression of transcripts encoding K(+), Ca(2+) and other ion channel subunits was increased in swim-trained and caPI3Kα ventricles, in parallel with the increase in myocyte size and with the global increases in total cellular RNA expression. In contrast to pathological hypertrophy, therefore, the functional expression of repolarizing K(+) (and depolarizing Ca(2+)) channels is increased with physiological hypertrophy, reflecting upregulation of the underlying ion channel subunit transcripts and resulting in increased current amplitudes and the normalization of current densities and action potential waveforms. Taken together, these results suggest that activation of PI3Kα signalling preserves normal myocardial electrical functioning and could be protective against the increased risk of arrhythmias and sudden death that are prevalent in pathological cardiac hypertrophy.

Athlete's heart: the potential for multimodality imaging to address the critical remaining questions

Moderate exercise is a powerful therapy in the treatment and prevention of cardiac disease, but intense habitual exercise leads to cardiac adaptations for which the prognostic benefits are less clear. The athlete's heart syndrome refers to the morphological and electrical remodeling which occurs to varying extents dependent upon the sporting discipline. Its accurate differentiation from pathological entities is critical. This review describes the role multi-modality imaging serves in determining the limitations and consequences of intense exercise. Tissue characterization and imaging studies during exercise are emphasized as important future directions of inquiry with the potential to address remaining controversies.

Sudden unexpected death in young athletes: reconsidering "hypertrophic cardiomyopathy"

Hypertrophic cardiomyopathy is considered a principal cause of sudden unexpected cardiac death in young athletes. However, a number of demographic features observed in these deaths are not consistent with the diagnosis. All of these characteristics instead share in common a propensity for ventricular hypertrophy, implying that these deaths may reflect electrical stability in the extremely rare athlete with exaggerated myocardial hypertrophy in response to sports training. This review provides an evidence-based line of reasoning that supports this concept.

Normal resting electrocardiographic variants in young athletes

With a growing awareness of the tragedy of sudden cardiac arrest (SCA) in young athletes, more extensive pre-participation examinations are being performed prior to competitive sport participation. In addition to a history and physical, young athletes often have a 12-lead resting electrocardiogram (ECG) to better identify heart disease associated with SCA. Complicating this process is that certain "abnormal" resting ECG findings are considered normal variants in healthy children and young adults. The ability to recognize these normal variants is often useful in preventing excessive referral of patients to cardiologists for evaluation of resting ECG's that are benign variations of normal and in making sound decisions regarding appropriate clearance to exercise. This review describes these normal variants.

KEYWORDS

normal variants; early repolarization; athlete's heart.