BackgroundSudden cardiac death in competitive athletes is rare but it is significantly more frequent than in the normal population. The exact cause is seldom established and is mostly attributed to ventricular fibrillation. Myocardial hypertrophy and slow heart rate, both characteristic changes in top athletes in response to physical conditioning, could be associated with increased propensity for ventricular arrhythmias. We investigated conventional ECG parameters and temporal short-term beat-to-beat variability of repolarization (STVQT), a presumptive novel parameter for arrhythmia prediction, in professional soccer players.MethodsFive-minute 12-lead electrocardiograms were recorded from professional soccer players (n = 76, all males, age 22.0±0.61 years) and age-matched healthy volunteers who do not participate in competitive sports (n = 76, all males, age 22.0±0.54 years). The ECGs were digitized and evaluated off-line. The temporal instability of beat-to-beat heart rate and repolarization were characterized by the calculation of short-term variability of the RR and QT intervals.ResultsHeart rate was significantly lower in professional soccer players at rest (61±1.2 vs. 72±1.5/min in controls). The QT interval was prolonged in players at rest (419±3.1 vs. 390±3.6 in controls, p<0.001). QTc was significantly longer in players compared to controls calculated with Fridericia and Hodges correction formulas. Importantly, STVQT was significantly higher in players both at rest and immediately after the game compared to controls (4.8±0.14 and 4.3±0.14 vs. 3.5±0.10 ms, both p<0.001, respectively).ConclusionsSTVQT is significantly higher in professional soccer players compared to age-matched controls, however, further studies are needed to relate this finding to increased arrhythmia propensity in this population.

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IntroductionRegular sport activity is very healthy but sometimes it is overshadowed by tragedies of athletes. It is appalling when a young person dies on the field, especially when they are elite competitors who are exemplars of good health and stamina. Because these tragedies manifest in seemingly healthy organism without previous symptoms or complaint, they became the focus of attention for both physicians and the media. The incidence of sudden death of athletes is very low (1:50 000-100 000) [1][2][3], but it is still 2 to 4 times more frequent than that of the agematched non-trained population [3,4].Sudden cardiac death (SCD) or syncope in athletes usually does not occur during or immediately after peak performance, but during warm-up or shortly after training. At this point symphathetic tone is still elevated but oxygen demand does not differ from resting levels. These circumstances do not support the ischemic origin of SCD but highlight the importance of intracellular cAMP level caused by increased sympathetic tone. The mediators of symphathetic nervous system are the catecholamines (epinephrin, norepinephrin) which can be measured in human blood. The increased sympathetic tone causes elevated cathecolamine levels. This effect in athletes can enhance susceptibility to arrhythmia by increasing both trigger activity (extrasystoles) [5][6][7] and arrhythmia substrate (repolarization inhomogeneity) [8][9][10].As the ECG leads show the regional electrical activity of myocardium, the difference between QT intervals and the QT-dispersion gives information about spatial inhomogeneity of repolarisation [11,12].Our aim in this study was to investigate the correlation between the sympathetic tone and the repolarization instability in different sports and in non-trained healthy controls. Phone: +3620/825-0263; E-mail: komkazsolt@gmail.com Abstract: Sudden cardiac death (SCD) of athletes usually occurs during warm-up or shortly after training. At this point sympathetic tone is still elevated but oxygen demand does not differ from resting levels. It is supposed not to have a primarily ischemic origin but most likely relates to repolarization abnormalities which can be associated with intracellular cAMP level caused by increased sympathetic tone. The mediators of sympathetic nervous system are the catecholamines (epinephrin, norepinephrin). Measuring QT-dispersion can show the repolarization's inhomogeneity. 27 elite soccer players, 28 triathletes and 29 non-trained control person took part in our study. It was recorded cardiac ultrasound, an ECG and taken blood before and after exercise. We found significantly higher QT-dispersion and catecholamines in soccer players compared to the triathletes and the controls. However the soccer players did not show larger athlete's heart than the triathletes. After exercise the increased repolarization inhomogeneity persisted in soccer players, but in triathletes it decreased. Increased sympathetic tone in athletes can enhance arrhythmia propensity. Our data may explain why the socce...

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