Intrinsic Versus Extrinsic Sinus and Atrioventricular Nodes Dysfunction in Athletes: Insights From Transesophageal Electrophysiological Testing With Autonomic Blockade

Background: While sinus bradycardia and atrioventricular (AV) block in athletes have traditionally been viewed as benign consequences of enhanced vagal tone, recent evidence suggests that, in some individuals, nodal dysfunction may be intrinsic and potentially mediated by epigenetic mechanisms. Therefore, differentiating between these mechanisms is crucial for guiding appropriate clinical management. Methods: Among 550 elite athletes undergoing routine cardiovascular evaluation, 72 were referred for a transesophageal electrophysiological study (EPS): 58 with significant sinus bradycardia or suspected AV node dysfunction (cases) and 14 athletes with symptoms consistent with supraventricular tachyarrhythmias but no bradyarrhythmia (controls). All participants underwent an EPS to assess corrected sinus node recovery time (CSNRT) and AV nodal Wenckebach point. In the case group, 24 athletes exhibited abnormal parameters at baseline and underwent a repeat EPS following complete autonomic blockade with intravenous propranolol and atropine, aimed at suppressing extrinsic autonomic influences. Results: The corrected sinus node recovery time exceeded 550 ms in 18 (31%) cases, and the Wenckebach point was greater than 500 ms in 8 (14%) cases. In all eight athletes with baseline AV conduction abnormalities, they normalized after autonomic blockade, consistent with a functional vagal mechanism. In contrast, the mean sinus rate remained unchanged after autonomic blockade, and in 12/18 (67%) of the athletes with prolonged CSNRT, continued to exhibit abnormal values despite autonomic suppression, indicating a probable intrinsic origin. Control subjects showed normal EPS parameters. Conclusions: The EPS with a pharmacological autonomic blockade represents a useful approach for distinguishing extrinsic, functional bradycardia from intrinsic nodal disease in athletes. While AV node dysfunction appears exclusively vagally mediated and reversible, a subset of sinus node dysfunction cases may reflect early, possibly epigenetically driven, intrinsic alterations.