Atrial Synchronous Versus AV Sequential Pacing for Hypertrophic Cardiomyopathy (HOCM)

Dual chamber (DC) pacing has proven effective in reducing the left ventricular outflow tract gradient (LVOTG) in most patients (pts) with HOCM refractory to drug therapy. However, optimal pacemaker (PM) programming including pacing mode and atrioventricular delay (AVD) has not been established. Accordingly, we performed continuous-wave transthoracic Doppler echocardiography on 7 pts with DC PMs (5 male, 2 female, mean age 64.7 ± 12.7 years) with HOCM and resting peak LVOTG exceeding 25 mmHg to evaluate the effects on peak LVOTG of atrial synchronous pacing (VDD) and AV sequential pacing (DDD) at 10 bpm above sinus rhythm while varying the AVD in steps of 20 msec to minimum of 40 msec. Conclusions: 1) At AVD of 100 to 140 msec, DDD pacing significantly reduced the peak LVOTG while VDD pacing did not. 2) At AVD less than 100 msec, VDD pacing significantly reduced peak LVOTG only at AVD of 40 msec, while DDD pacing at 10 bpm above sinus rhythm reduced peak LVOTG at all AVD used. Therefore PMs which have the capability to program different AVD for VDD and DDD modes and that provide programmable AVDs less than 60 msec are optimal for HOCM pts.