Optimal ventricular pacing rate in fetal lambs with complete atrioventricular block

Objective: This study was undertaken to determine the optimum ventricular pacing rate at which the optimal cardiac function can be attained in fetal lambs with complete atrioventricular block. Study Design: Complete atrioventricular block was created by cryosurgery in 12 fetal lambs, and the ventricle was paced randomly at rates of 60, 90, 120, 150, 180, 210, 240, and 270 beats/min. The aortic pressure, central venous pressure, and right ventricular cardiac output were measured before cryosurgery and during ventricular pacing. Results: Complete atrioventricular block was created in 9 of 12 fetal lambs. Systolic aortic pressure significantly decreased at pacing rates of 60, 90 and 240 beats/min (P< .01), and central venous pressure was increased significantly at a pacing rate of 60 beats/min (P< .01) compared with the control. Right ventricular cardiac output significantly decreased at pacing rates of 60, 90, 120, 180, 210, 240, and 270 beats/min (P< .01), although no significant difference was found at the pacing rate of 150 beats/min compared with control. Conclusion: Ventricular pacing at a rate of 150 beats/min gave the highest aortic pressure, the lowest central venous pressure, and the highest right ventricular cardiac output in fetal lambs with complete atrioventricular block. (Am J Obstet Gynecol 2002;186:1052-5.)