V4) followed by T wave inversion. On the basis of current data, T wave inversions preceded by ST segment elevation are present in leads V1–V4 in up to 13% of black/African athletes and do not require further assessment in the absence of symptoms, positive family history or abnormal physical examination.12 13 A junctional (nodal) rhythm or wandering atrial pacemaker may be observed in up to 8% of all athletes under resting conditions.11 First-degree AV block (4.5–7.5%) and less commonly Mobitz type I second-degree AV block are also seen in athletes and a result of increased vagal tone.6 11 14 Increased cardiac chamber size Voltage criterion for LVH is present in approximately 45% of male athletes and 10% female athletes.6 11 15 Increased QRS voltage is more common in black/African athletes.13 Although there are several voltage criteria to define LVH, the Sokolow-Lyon criterion is used most commonly. The Sokolow-Lyon voltage criterion for LVH is defined as the sum of the S wave in V1 and the R wave in V5 or V6 (using the largest R wave) as >3.5 mV (35 small squares with a standard amplification of the ECG at 10 mm/1 mV). The isolated presence of high QRS voltages fulfilling the Sokolow-Lyon voltage criterion for LVH is regarded as a normal finding in athletes related to physiological increases in cardiac chamber size and/or wall thickness and does not in itself require additional evaluation (figure 1). However, the additional presence of nonvoltage criteria for LVH such as left atrial enlargement, left axis deviation, ST segment depression, T wave inversion or pathological Q waves should raise the possibility of pathological LVH and should prompt further evaluation. IRBBB (commonly characterised as an rSR0 pattern in V1 with QRS duration <120 ms) is commonly present in athletes (12–32%) and thought to reflect an increase in right ventricular (RV) size secondary to regular training.6 11–14 Normal ECG findings in athletes Sinus bradycardia The normal heartbeat is initiated by the sinus node which is located high in the right atrium near the junction of the superior vena cava and the right atrial appendage. To be classified as sinus rhythm, three criteria must be met: (1) there must be a P wave before every QRS complex, (2) there must be a QRS complex after every P wave and (3) the P wave must have a normal axis in the frontal plane (0– 90°s). Assuming an intact sinus node, the heart rate is set by the balance between the sympathetic and parasympaFigure 1 ECG of a 29-year-old asymptomatic soccer player demonstrating sinus bradycardia, early repolarisation with ST elevation (arrows) and peaked T waves, and voltage criteria for left ventricular hypertrophy. These are common findings related to regular training. This figure is only reproduced in colour in the online version. Figure 2 ECG demonstrates sinus bradycardia with a heart rate of 40 bpm. The three required features of sinus bradycardia include: (1) P wave before every QRS complex, (2) QRS after every P wave and (3) normal P wave axis (frontal plane 0–90°s). This figure is only reproduced in colour in the online version. Figure 3 ECG demonstrates sinus arrhythmia. Note the irregular heart rate that varies with respiration. The P waves are upright in leads I and aVF (frontal plane) suggesting a sinus origin. This figure is only reproduced in colour in the online version. nummer 2 | mei 2013 | Sport & Geneeskunde 27 Pagina 26
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