Thyroid hormone's effect on arrhyhtmogenesis

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THE ATHLETE’S ELECTROCARDIOGRAM

Bradyarrhythmias, such as sinus bradycardia greater than 30 beats/min (bpm), sinus arrhythmia, first-degree and second-degree (Mobitz type 1) atrioventricular block, wandering atrial pacemaker, and ectopic atrial rhythm, have been attributed to increased vagal tone following regular physical activity and are common in athletes (Figs. 1 and 2).Increased vagal tone also manifests as ethnic-specific early repolarization changes. White athletes typically show concave ST segment elevation, whereas Afro Caribbean/black athletes show convex ST segment elevation often associated with either biphasic or deep T-wave inversions (TWIs) in V1 to V4.3 Isolated Sokolow-Lyon voltage criteria (combined amplitude of S wave in V1 [SV1] 1 largest R wave in V5 or 6 [RV5/6] ≥3.5 mV, or R wave in aVL  ≥1.1 mV) for LVH and incomplete right bundle branch block (RBBB) are recognized manifestations of increased cardiac chamber size and wall thickness and regarded as normal physiologic adaptations in athletes.