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

Abstract

It has been reported that older patients with hypertrophic obstructive cardiomyopathy (HOCM) benefited the most from dual chamber (DDD) pacing. Since in older patients the distribution of septal hypertrophy and left ventricular (LV) cavity shape differs from that in younger patients, we decided to study the efficacy of DDD pacing on the reduction of LV outflow tract (LVOT) gradient in different patterns of septal hypertrophy. We compared HOCM patients with nonreversed septal curvature, thus preserving the elliptical LV cavity contour (common in the elderly), (group I) versus patients with reversed 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 pacemaker, the LVOT gradient was measured using Doppler echocardiography at various programmed AV delay intervals to determine the maximal percentage decrease of LVOT gradient from baseline. The measurement was repeated after at least a 6-month follow-up (chronic DDD pacing). The baseline LVOT gradient was comparable between groups (79 +/- 28 vs 81 +/- 25 mmHg, P = 0.92). The LVOT gradient reduction at acute DDD pacing was significantly greater in group I than group II (61 +/- 18% vs 23 +/- 10%, P = 0.0001). This difference in favor of the patients from group I was maintained at midterm follow-up (69 +/- 17% vs 40 +/- 17% P = 0.0076). In conclusion, patients with normal septal curvature and preserved elliptical LV cavity shape had a greater reduction of LVOT gradient after DDD pacing than patients with reversed septal curvature deforming LV cavity. The proposed criterion assessing the septal curvature may be useful to predict the efficacy of DDD pacing in the reduction of LVOT gradient.