BJSM Other abnormal ECG findings Profound sinus bradycardia Diagnostic criteria Sinus bradycardia is one of the hallmark features of a wellconditioned athlete’s heart. It is the result of increased vagal tone and possible structural atrial remodelling.61 The sinus rate only rarely falls below 30 bpm or shows pauses of ≥3 s during an ECG recording at rest. Figure 13: The top row demonstrates atrioventricular nodal re-entrant tachycardia (AVNRT) and the bottom row is in normal sinus rhythm in the same patient. In lead II, retrograde P waves are present at the end of the QRS complex. In lead V1, a pseudo-R0 with right bundle branch block pattern is present due to the retrograde P waves. These deflections are not seen on the ECG when in sinus rhythm. This figure is only reproduced in colour in the online version. Evaluation Profound sinus bradycardia (<30 bpm) at rest in an athlete should be evaluated further but is not necessarily pathological (figure 16). If asymptomatic and the sinus rate quickly accelerates with an increase in sympathetic tone (ie, small exercise load), then additional testing is not usually necessary. The presence of symptoms, such as decreased exercise capacity or a predisposition for vasovagal syncope, may prompt additional testing to exclude primary sinus node disease. One might also consider temporary cessation of sports activity to evaluate reversibility, although even adaptive athlete’s heart sinus bradycardia may not be fully reversible.62 63 Figure 14: ECG demonstrating atrial fibrillation with no clear P waves and an ‘irregularly’ irregular QRS response. Fibrillatory activity is best seen in V1, as the fibrillation waves are irregular and of changing morphology. This figure is only reproduced in colour in the online version. Profound first-degree AV block Diagnostic criteria The high vagal tone in athletes also leads to a slowing of AV nodal conduction, and hence a lengthening of the PR interval. It is not uncommon to see PR intervals longer than 200 ms in athletes at rest. Even significant PR prolongation ≥300 ms may occur, although this by itself is not necessarily pathological and is usually asymptomatic. Figure 15: ECG demonstrating atrial flutter, as evidenced by regular, sawtooth flutter waves in the inferior leads and a positive deflection in V1. No isoelectric segment is present between the flutter waves. The QRS response is regular, in this case a 4 : 1 pattern. This figure is only reproduced in colour in the online version. Evaluation In asymptomatic athletes with a profound first-degree AV block (≥300 ms), the athlete should undergo a minimal exercise load (ie, like climbing a flight of stairs) to increase sympathetic tone. If this results in shortening and normalisation of the PR interval, the PR prolongation is due to functional (vagal) mechanisms and hence benign. If the PR interval does not normalise to ≤200 ms with exercise, a structural cause of AV conduction disturbance (such as Lyme disease or sarcoidosis) should be investigated. Athletes with a profound first-degree AV block (≥300 ms) who have symptoms (ie, syncope, palpitations) or a positive family history of cardiac disease or sudden death require additional evaluation to rule out pathological causes of heart block. 30 Sport & Geneeskunde | november 2013 | nummer 5 Pagina 29
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