VDD PACING AT SHORT ATRIOVENTRICULAR INTERVALS DOES NOT IMPROVE CARDIAC-OUTPUT IN PATIENTS WITH DILATED HEART-FAILURE

Atrial synchronous pacing with short, nonphysiological atrioventricula r (AV) intervals has been reported to increase cardiac output in selec ted patients with severe dilated heart failure. The aim of this study was to determine the acute effect of atrial synchronous pacing with sh ort AV intervals in a consecutive series of patients with dilated hear t failure. Twelve patients with a mean ejection fraction of 21% +/- st andard error 2.5% were studied. Pacing catheters were placed in the hi gh right atrium and right ventricular apex and a balloon flotation cat heter in the pulmonary artery for measurement of cardiac output. Simul taneous transthoracic echocardiography was performed for measurement o f left ventricular filling time and mitral regurgitation. In a randomi zed crossover design, measurements were made during VDD pacing at prog rammed AV intervals of 100 and 60 msec and during a control period in sinus rhythm. Left ventricular filling time increased at AV intervals of 100 and 60 msec (mean difference 37 +/- 9 and 34 +/- 11 msec, respe ctively, both P < 0.01 compared to control). Despite increases in vent ricular filling time, stroke, and cardiac index declined with short at rioventricular intervals (at an AV interval of 60 msec, stroke index f ell by 2.1 +/- 0.5 mL/m(2), P < 0.05 and cardiac index by 125 +/- 45 m L/m(2); P = NS). Heart rate was unchanged at both AV intervals (78 +/- 4.9 at control, 78 +/- 5.2 at 100 msec and 79 +/- 4.9 beats/min at 60 msec; P = NS). The decrease in stroke index at an AV interval of so m sec was inversely related to control left ventricular filling time (r = 0.74; P = 0.01) and ejection fraction (r = 0.69; P = 0.02) and direc tly related to heart rate (r = 0.77; P ( 0.02). The change in stroke i ndex at an A V delay of 60 msec wets also inversely related to the cha nge in mitral regurgitation induced by pacing (r = 0.84; P = 0.01). Th us, in a group of patients with stable dilated heart failure, atrial s ynchronous pacing with short AV intervals did not improve cardiac outp ut. The change in cardiac output with pacing was inversely related to baseline left ventricular function and to the change in mitral regurgi tation induced by pacing.