Predictable reduction in left ventricular stroke work and oxygen utilization with an implantable centrifugal pump

Abstract

Previous investigations with roller pumps and pneumatic pulsatile assist devices have demonstrated that nearly complete capture of normal left ventricular end-diastolic volume was necessary for appreciable reductions in oxygen consumption and stroke work. We tested the hypothesis that a centrifugal pump would decrease left ventricular stroke work and oxygen consumption as a function of pump flow. Ten sheep (35 to 50 kg) were instrumented and placed on left atrium-to-descending aorta bypass with a small, lightweight (112 g), implantable centrifugal pump. The relations between pump flow as a percent of cardiac output (% bypass), left ventricular stroke work, and oxygen consumption were studied. Left ventricular stroke work was calculated from the pressure-volume loops obtained with micromanometer and conductance catheters and was indexed per 100 g of left ventricular wet weight. Oxygen consumption was calculated from left main coronary artery blood flow and the arterial-coronary sinus oxygen content difference, normalized to 100 g of left ventricular wet weight and a heart rate of 100 beats/min. Measurements were made in stepwise increments of pump flow from zero to the maximum obtainable and then reversed in similar decrements. Analyses were made for 27 complete runs. Our data demonstrate that reductions in left ventricular stroke work and oxygen consumption were achieved from zero to maximal bypass. There was an approximate 66% and 50% reduction in left ventricular stroke work and oxygen consumption, respectively, at 60% bypass. Thus, in contrast to other types of assist devices, our centrifugal pump in a left atrium-to-aorta circuit provides predictable and significant reductions in left ventricular stroke work and oxygen consumption at moderate levels of bypass. These data establish the physiogic bases for use of this device as temporary assist in patients with postcardiotomy low flow states.