may be more than two different P wave morphologies known as a wandering atrial pacemaker. Ectopic atrial rhythms occur due to a slowed resting sinus rate from increased vagal tone in athletes, and sinus rhythm replaces the ectopic atrial rhythm when the heart rate is increased vagal activity or intrinsic AV node changes, and typicincreased during exercise. ally resolves with faster heart rates during exercise. First-degree AV block In first-degree AV block, the PR interval is prolonged (>200 ms) but is the same duration on every beat (figure 6). This represents a delay in AV nodal conduction in athletes, due to -increased vagal activity or intrinsic AV node changes, and typically resolves with faster heart rates during exercise. Mobitz type I (Wenckebach) second-degree AV block In Mobitz type I second-degree AV block, the PR interval progressively lengthens from beat to beat, until there is a non conducted P wave with no QRS complex (figure 7). The first PR interval after the dropped beat is shorter than the last conducted PR interval before the dropped beat. This represents a greater disturbance of AV nodal conduction than first-degree AV block, but with exercise there should be a return of 1:1 conduction. Incomplete right bundle branch block IRBBB is defined by a QRS duration <120 ms with an RBBB pattern: terminal R wave in lead V1 (rsR0) and wide terminal S wave in leads I and V6 (figure 8). IRBBB is seen in less than 10% of the general population but is observed in up to 40% of highly trained athletes, particularly those engaged in endurance training and mixed sport disciplines that include both aerobic and anaerobic components.14 18 19 It has been suggested that the mildly delayed RV conduction is caused by RV remodelling, with increased cavity size and resultant increased conduction time, rather than an intrinsic delay within the His-Purkinje system itself.20 The occurrence of IRBBB in an asymptomatic athlete with a negative family history and physical examination does not require further evaluation. During the physical examination, particular care should be devoted to the auscultation of a fixed low limb-lead voltages, prolonged S wave upstroke and/or presplitting of the second heart sound because IRBBB can be an mature ventricular beats with a left bundle branch block (LBBB) associated ECG finding in patients with an atrial septal defect. morphology (figure 9). IRBBB may be seen in patients with arrhythmogenic RV carFigure 7 ECG shows Mobitz type I (Wenckebach) second-degree AV block demonstrated by progressively longer PR intervals until there is a non-conducted P wave (arrows) and no QRS complex. Note the first PR interval after the dropped beat is shorter than the last conducted PR interval prior to the dropped beat. This figure is only reproduced in colour in the online version. Figure 8 ECG demonstrates incomplete right bundle branch block (IRBBB) with rSR0 pattern in V1 and QRS duration of <120 ms. IRBBB is a common and normal finding in athletes and does not require additional evaluation. This figure is only reproduced in colour in the online version. Figure 9 ECG from a patient with arrhythmogenic right ventricular cardiomyopathy showing delayed S wave upstroke in V1 (arrow), low voltages in limb leads <5 mm (circles) and inverted T waves in anterior precordial leads (V1–V4) and inferior leads (III and aVF). This figure is only reproduced in colour in the online version. nummer 2 | mei 2013 | Sport & Geneeskunde 29 Pagina 28
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