IMPACT OF DUAL-CHAMBER PERMANENT PACING IN PATIENTS WITH OBSTRUCTIVE HYPERTROPHIC CARDIOMYOPATHY WITH SYMPTOMS REFRACTORY TO VERAPAMIL AND BETA-ADRENERGIC BLOCKER THERAPY

Background. Patients with obstructive hypertrophic cardiomyopathy (HCM) with symptoms refractory to drugs (beta-blockers or verapamil) are candidates for cardiac surgery (left ventricular septal myectomy or mitral valve replacement). The present study examines prospectively the ability of dual-chamber (DDD) pacing to improve symptoms and relieve left ventricular outflow obstruction in such patients. Methods and Results. Forty-four consecutive patients with obstructive HCM who had failed to benefit from pharmacotherapy underwent treadmill exercise tests, echocardiography, and cardiac catheterization before and 1.5-3 months after implantation of a DDD pacemaker. Symptoms (angina, dyspnea, palpitations, presyncope, and syncope), New York Heart Association functional class status (1.7+/-0.7 versus 3.4+/-0.5, p<0.00001), and exercise durations were improved at follow-up evaluation. This was associated with significant reduction in left ventricular outflow tract gradient (38+/-38 versus 87+/-43 mm Hg, p<0.0001) and significant increases in cardiac output and systemic arterial pressures. Notably, when pacing was discontinued and comparisons were made in sinus rhythm, treadmill exercise durations were greater and left ventricular outflow tract gradients were less at the follow-up evaluation compared with the baseline study. Conclusions. DDD pacing is an effective alternative to surgery in most patients with obstructive HCM with drug-refractory symptoms. The beneficial effects of pacing continue to be evident when pacing is acutely discontinued.