The Effect of Intra-Aortic Balloon Counterpulsation on Coronary Blood Flow Velocity Distal to Coronary Artery Stenoses

Abstract

Despite the accepted clinical benefit of intra-aortic balloon counterpulsation (IABC), the physiologic explanation for its benefit remains controversial. Indirect methods of measuring coronary blood flow during IABC in obstructive coronary disease have yielded conflicting results. The direct measurement of coronary blood flow velocity distal to sites of stenoses by methods that do not potentially impede flow has not been previously reported. The aim of our study was to determine the effect of IABC on coronary blood flow velocity distal to a coronary stenosis by employing a method that would not impede flow through the stenosis. In an open-chest canine model, phasic and mean left anterior descending coronary artery flow velocities distal to varying degrees of stenosis were continuously measured by an epicardial Doppler probe with and without counterpulsation. All hemodynamic parameters were recorded in the absence of stenosis (n = 5) and the presence of subcritical (n = 5) and critical stenoses (n = 5). Heart rate was not affected by counterpulsation. Systolic blood pressure and rate-pressure product declined at all times with IABC. Compared to baseline, peak aortic diastolic pressure was augmented by an average of 24 mm Hg during IABC (p < 0.05). However, mean coronary artery flow velocities remained unchanged (101, 103 and 98% of baseline for no stenosis, subcritical stenosis and critical stenosis, respectively; p > 0.05 compared to baseline). Peak diastolic flow velocities were 106,102 and 96% of baseline for no stenosis, subcritical and critical stenoses, respectively (p > 0.05). Despite the augmentation of peak diastolic pressure, distal coronary blood flow velocity was not increased by IABC in this canine model, irrespective of the severity of proximal coronary stenosis. These data suggest that augmentation of coronary artery flow distal to sites of stenoses is not primarily responsible for the clinical benefit observed when IABC is used in the setting of obstructive coronary artery disease. The reduction in afterload and myocardial oxygen demand observed in this model agrees with previous studies and likely accounts, at least in part, for the positive clinical results with IABC.