Mobitz type II second-degree AV block Diagnostic criteria An abrupt loss of P wave conduction (P wave with no ensuing QRS complex), without prior PR prolongation, represents Mobitz type II second-degree AV block (figure 17). If Mobitz type II or more advanced types of AV block including 2:1 or 3:1 occur during sinus rhythm, it may be indicative of underlying structural heart disease. Evaluation Suspected Mobitz type II second-degree AV block or other more advanced types of AV block (2:1 or 3:1 block) should first be differentiated from Wenckebach (Mobitz type I) second-degree AV block. Wenckebach (Mobitz type I) block is present when there is PR prolongation before a blocked P wave and a shorter PR in the first conducted beat after the block. Mobitz type I second-degree AV block is usually a functional block from increased vagal tone and does not constitute pathology in an athlete. Further diagnostic evaluation can be done with an ECG after minor exercise, as a slight increase in sympathetic tone will resolve the conduction disturbance in physiological cases. A Holter monitor (or other form of long-term ECG recording) also can assist in clarifying the type of AV block. Mobitz type II or higher degree (2:1 or 3:1) AV block requires further evaluation for underlying pathological cardiac disease. Third-degree AV block/complete heart block Diagnostic criteria Complete heart block is not an expression of athlete’s heart and should be considered an abnormal finding requiring additional evaluation. Evaluation With true third-degree AV block, there are more P waves than QRS complexes and the ventricular rhythm is perfectly regular due to an undisturbed junctional or ventricular pacemaker (figure 18). Complete heart block can easily be confused with AV dissociation without block—a situation where the junctional pacemaker is faster than the sinus node, leading to more QRS complexes than P waves. Intermittent ventricular capture by sinus P waves (resulting in an irregular ventricular response) excludes complete AV block. AV dissociation without block is the expression of autonomic mismatch between AV and sinus nodal modulation, but is not pathological. Like all other functional disturbances, a small exercise load with repeat ECG recording will show resolution of the ECG findings in AV dissociation. Figure 17: ECG showing Mobitz type II second-degree AV block. Note the presence of P waves with loss of conduction and no QRS complex (arrows) and without PR prolongation in the beats prior, nor PR shortening in the beats after (which would suggest Mobitz type I). Mobitz type II second-degree AV block in an athlete is not due to increased vagal tone and should prompt evaluation for underlying conduction disease. This figure is only reproduced in colour in the online version. Complete heart block requires further evaluation for underlying cardiac disease. ≥2 premature ventricular contractions Diagnostic criteria When two PVCs are recorded on a baseline (10 s) ECG, the likelihood is very high that the athlete has >2000 PVCs per 24 h. In athletes with >2000 PVCs per 24 h, underlying structural heart disease which may predispose to more nummer 5 | november 2013 | Sport & Geneeskunde 31 Figure 16: ECG in an asymptomatic long-distance runner showing profound sinus bradycardia (30 bpm) compatible with high vagal tone. The athlete showed a normal chronotropic response during exercise testing. Pagina 30
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Sport & Geneeskunde nummer 5 | November 2013 Lees publicatie 26Home