The importance of ventricular septal morphology in the effectiveness of dual chamber pacing in hypertrophic obstructive cardiomyopathy

It has been reported that elder patients with hypertrophic obstructive card iomyopathy (HOCM) benefited the most from dual chamber (DDD) pacing. Since in older patients the distribution of septal hypertrophy and left ventricul ar (LV) cavity shape differs from that in younger patients, we decided to s tudy the efficacy of DDD pacing on the reduction of LV outflow tract (LVOT) gradient in different patterns of septal hypertrophy. We compared HOCM pat ients with nonreversed septal curvature, thus preserving the elliptical LV cavity contour (common in the elderly), (group I) versus patients with reve rsed septal curvature, deforming the LV cavity to a crescent shape (common in the young), (group II). Eighteen HOCM patients were studied (11 patients in group I and 7 patients in group II). After implantation of a DDD pacema ker, the LVOT gradient was measured using Doppler echocardiography at vario us programmed AV delay intervals to determine the maximal percentage decrea se of LVOT gradient from baseline. The measurement was repeated after at le ast a 6-month follow-up (chronic DDD pacing). The baseline LVOT gradient wa s comparable between groups (79 +/- 28 vs 81 +/- 25 mmHg, P = 0.92). The LV OT gradient reduction at acute DDD pacing was significantly greater in grou p I than group II (61 +/- 18% vs 23 +/- 10%, P = 0.0001). This difference i n favor of the patients from group I was maintained at midterm follow-up (6 9 +/- 17% vs 40 +/- 17% P = 0.0076). In conclusion, patients with normal se ptal curvature and preserved elliptical LV cavity shape had a greater reduc tion of LVOT gradient after DDD pacing than patients with reversed septal c urvature deforming LV cavity. The proposed criterion assessing the septal c urvature may be useful to predict the efficacy of DDD pacing in the reducti on of LVOT gradient.