Effect of Heart Rate, Exercise, and Nitroglycerin on the Cardiac Dynamics in Complete Heart Block

Abstract

A patient with complete heart block with a rate of 30/minute is presented with congestive heart failure refractory to medical management. Prior to implantation of a permanent cardiac pacemaker, optimum rate of pacing was established using a bipolar electrode catheter placed in the right ventricle, controlled from an external source. Optimum rate of pacing is defined as that rate which provides maximal increase in cardiac output, a stable stroke volume, and only a modest increase in systemic pressure and left ventricular work. Studies of cardiac dynamics were done using the indicator-dilution technique. Post-operatively, studies at a paced rate of 72/minute showed an increased cardiac output and stable stroke volume, and neither were increased by moderate exercise or nitroglycerin. Thus, heart rate is an important determinant of cardiac output within well defined limits. This case illustrates the use of artificial pacemaking in the treatment of refractory cardiac decompensation secondary to complete heart block, even in the absence of Stokes-Adams attacks.