EFFECT OF DUAL-CHAMBER PACING ON SYSTOLIC AND DIASTOLIC FUNCTION IN PATIENTS WITH HYPERTROPHIC CARDIOMYOPATHY - ACUTE DOPPLER-ECHOCARDIOGRAPHIC AND CATHETERIZATION HEMODYNAMIC-STUDY

Objectives. This study sought to evaluate prospectively the acute hemo dynamic effect of dual-chamber pacing by using a combined hemodynamic approach of high fidelity pressure and Doppler velocity measurements. Background. Dual-chamber pacing has been proposed recently as an alter native in the symptomatic treatment of patients with hypertrophic obst ructive cardiomyopathy. Although early reports documented a decrease i n left ventricular outflow tract gradient and symptomatic improvement, questions remain about the he modynamic effects of dual chamber pacin g on systolic and diastolic function. Methods. Twenty-nine patients wi th hypertrophic cardiomyopathy underwent a combined cardiac catheteriz ation and Doppler echocardiographic study during normal sinus rhythm a nd P- synchronous pacing at various atrioventricular (AV) intervals. H igh fidelity pressure measurements of left ventricular inflow and left atrial pressures, ascending aortic pressure, thermodilution cardiac o utput and Doppler mitral flow velocity curves were obtained to evaluat e both systolic and diastolic left ventricular function. Results. Duri ng AV pacing at the shortest delay of 60 ms, there was a significant d ecrease in cardiac output (p < 0.05) and peak positive dP/dt (p < 0.05 ), an increase in mean left atrial pressure (p < 0.05) and a prolongat ion of tau, the time constant of relaxation (p < 0.05), compared with that during normal sinus rhythm. During pacing at the optimal AV delay (longest AV interval with pre excitation), there was a similar trend, with deterioration in both systolic and diastolic function variables but of lesser magnitude than that during pacing at the shortest AV int ervals. The deterioration in both systolic and diastolic function was present in 21 patients with and 8 without left ventricular outflow obs truction. There was a modest decrease in left ventricular outflow trac t gradient from 73.3 +/- 45.0 (mean +/- SD) to 61.3 +/- 40.5 mm Hg (p = 0.03) during dual chamber pacing at the optimal AV delay compared wi th that during normal sinus rhythm. Conclusions. The acute effect of p acing the right atrium and ventricle may be detrimental to both systol ic and diastolic function of the left ventricle, particularly at the s hort AV intervals. Further studies of the long-term effects of dual ch amber pacing in carefully performed randomized studies are needed.