Rapid return of left ventricular outflow tract obstruction and symptoms following cessation of long-term atrioventricular synchronous pacing for obstructive hypertrophic cardiomyopathy

Atrioventricular (AV) synchronous pacing reduces left ventricular (LV) outf low tract obstruction and symptoms in patients with obstructive hypertrophi c cardiomyopathy (HC). The duration of gradient reduction, if pacing is dis continued for a prolonged period of time, is unknown. This question is addr essed in the present randomized double-blind crossover study comparing cont inued with inactivated pacing. Ten patients, successfully paced for greater than or equal to 6 months, were randomized to continue pacing or to have t heir pacemakers inactivated after examinations, including echo-Doppler imag ing, exercise testing, and a quality-of-life questionnaire. When entering t he study, the patients were in New York Heart Asssosciation functional clas ses I to II. After pacemaker programming, examinations were repeated at 1, 4, and 12 weeks. At the 12-week follow-up the alternate pacing mode was pro grammed, and the patient entered the second study arm. Premature pacemaker pacing occurred if severe clinical deterioration or a significant increase of the LV outflow tract obstruction were evident. Three patients started in the inactive mode and 7 patients in the active mode. All patients who star ted with the pacemaker inactivated required early reprogramming due to retu rn of symptoms after 7, 10, and 13 days, respectively. All 7 patients who s tarted in the active pacing mode completed the first period; however, after reprogramming to the inactive mode they required early activation after 1 to 20 days due to reappearance of intolerable subjective symptoms. The LV o utflow tract gradient increased significantly after inactivation of pacing in all patients (22 +/- 21 mm Hg to 47 +/- 21 mm Hg). Thus, AV synchronous pacing effectively relieves symptoms and reduces the LV outflow tract gradi ent in patients with obstructive HC. This improvement, which is rapidly est ablished with the initiation of cardiac pacing, is not persistent after ces sation of pacing. Reinitialization of pacing promptly reduces the LV outflo w tract obstruction and relieves symptoms to a preexisting extent. (C) 1999 by Excerpta Medica, Inc.