An Unusual Presentation of Third-Degree Atrioventricular Block in a Patient With Hypertrophic Cardiomyopathy.

Patients with hypertrophic cardiomyopathy (HCM) are commonly affected by ventricular tachyarrhythmias such as ventricular tachycardia, leading to syncope and sudden cardiac death (SCD). Complete atrioventricular (AV) block in patients with HCM is very unusual but may also lead to syncope and SCD. We report a 52-year-old male who presented with recurrent episodes of pre-syncope and effort intolerance. A 12-lead ECG demonstrated deep T-wave inversion in the precordial leads with complete AV dissociation, and a two-dimensional echocardiogram revealed HCM without resting or provoked left ventricular outflow tract obstruction. The patient initially got a temporary transvenous pacemaker, followed by a dual-chamber rate-responsive pacemaker, which was subsequently upgraded to a dual-chamber implantable cardioverter-defibrillator after further risk stratification. Although rare, there have been a few reported cases of HCM complicated by atrioventricular block. This case should alert physicians to the possibility of atrioventricular block in patients with HCM, which could influence the management outcomes.