Pacing-Induced Electrophysiological Remodeling in Hypertrophic Obstructive Cardiomyopathy-Observations on Cardiac Memory

Background: Hypertrophic cardiomyopathy carries an increased risk for sudden cardiac death. While pacing therapy reduces the left ventricular outflow tract gradient and improves symptoms in a subgroup of hypertrophic obstructive cardiomyopathy (HOCM) patients, its electrophysiological consequences are unknown and were therefore assessed in this prospective study. Methods and Results: Fifteen consecutive HOCM patients were studied and compared with 14 patients without HOCM paced because of sinus bradycardia. ECG intervals were measured before pacemaker implantation and after ≥3 months of DDD pacing in HOCM patients and ≥5 weeks in controls. Both groups showed similar ECG signs of cardiac memory development. In HOCM patients, with baseline QTc 447 ± 33 ms, cardiac memory development was not associated with any significant changes in ECG intervals. In contrast, baseline repolarization in control patients was significantly prolonged by 6% (QTc 429 ± 33 vs 454 ± 46 ms; P < 0.05). Furthermore, in HOCM patients repolarization was 7% shorter during DDD pacing compared to sinus rhythm (JTc 329 ± 25 vs 353 ± 21 ms; P < 0.05), despite a significantly prolonged ventricular activation time (QRS duration 155 ± 16 vs 91 ± 9 ms; P < 0.01). Conclusions: Importantly, the development of cardiac memory‐induced different repolarization responses depending on baseline structure and electrophysiology. In HOCM patients repolarization was shorter during right ventricular apical pacing than during normal activation despite prolonged activation time.