Exercise-induced intranodal atrioventricular block.

Exercise-induced atrioventricular (AV) block in patients with normal AV conduction at rest is rare. Herein, we describe the case of a 67-year-old woman with normal 1 : 1 AV conduction at rest, who developed complete AV block during a treadmill test. Our patient complained of effort-related dizziness and dyspnea, which had been ongoing for 3 months. The patient's physical examination was normal. The resting electrocardiogram showed left anterior fascicular block with a PR interval of 0.19 seconds. The echocardiogram was normal except for mild aortic valve regurgitation. During the treadmill test, the patient developed complete AV block at a sinus rate of 90 beats/min, which was followed by 2 : 1 AV block associated with dyspnea and dizziness. The patient's coronary angiogram was normal, and the ergonovine provocation test was negative. Electrophysiological studies demonstrated rate-dependent intranodal AV block. The patient received implantation of a permanent dual chamber (DDD) pacemaker and had no further symptoms during the follow-up period.