Exercise-induced second-degree atrioventricular block

In this report we describe the case of a 56-year-old woman with normal 1 : 1 AV conduction at rest who developed 2 : 1 AV block during treadmill exercise testing. Electrophysiological study documented 2 : 1 AV block proximal to the His bundle with reappearance of 1 : 1 AV conduction at a higher pacing atrial rate. A gap phenomenon involving a proximal and distal part of the AV node may be a likely explanation of paradoxical AV conduction in our case.