Dual-chamber pacing in hypertrophic obstructive cardiomyopathy - A comparison of acute and chronic effects

This study describes the acute and chronic effects of dual-chamber (DDD) pa cing in 14 consecutive patients with hypertrophic obstructive cardiomyopath y (HOCM), whose symptoms were refractory to drug therapy. Although left ven tricular (LV) outflow tract pressure gradients diminished from 106+/-47 to 62+/-33 mmHg (p<0.001) by temporary pacing, the residual pressure gradients were >30 mmHg in the majority of those with concomitant reductions in card iac output. The DDD pacing was judged as insufficient by the acute study in the majority of patients. A dual-chamber pacemaker was, however, implanted in II patients, and the chronic pacing effects were evaluated. All symptom s (syncope, fainting, palpitation and dyspnea) subsided within 1 month. Lef t ventricular outflow tract pressure gradients diminished from 99+/-56 to 2 1+/-13 mmHg (p<0.004) at 1 week after, and to 17+/-12 mmHg (p<0.002) at 1 y ear after the implantation, as measured by Doppler echocardiography. Echoca rdiogram showed disappearance of the systolic anterior motion of the mitral valve, and significant regression of the septal hypertrophy (from 18.5+/-3 .3 to 15.7+/-4.1 mm, p<0.04). There was no significant correlation between the acute and chronic pacing effects in the reduction of the pressure gradi ents or symptomatic improvement. These results suggest that DDD pacemaker i mplantation is an effective treatment without any serious risks for patient s with drug-refractory HOCM. The chronic-pacing effect in the reduction of the pressure gradient, the regression of hypertrophy and symptomatic improv ement cannot be predicted by the assessment of temporary DDD pacing.