Hemodynamic and Energetic Assessment of Calves Implanted with a Left Ventricular Assist Device (LVAD)

Abstract

Hemodynamic and ventricular energetic parameters were measured in calves implanted with the air driven Utah Ventricular Assist Device (UVAD). Uptake site was varied to determine the effect of control mode and vacuum augmentation of filling. Uptake was drawn solely from the left atrium or combined with a left ventricular apical vent. LVAD outflow returned to the descending, thoracic aorta. Control modes examined included asynchronous pumping as well as 1:1 and 1:2 synchronous diastolic counterpulsation. The 85cc LVAD, vacuum formed from PELLETHANE^®, was implanted acutely in four animals and chronically in six (7, 49 and 116 days paracorporeally, 1, 28 and 32 days intrathoracically). Instantaneous blood pressures, intramyocardial pressure, aortic outflow, oxygen consumption, LVAD output and drive parameters were recorded.

LVAD output was independent of control mode when the natural heart rate was ≥ 80 beats per minute. Intrathoracically positioned LVADs pumped a mean flow of ≈5 liters/min without vacuum augmentation of filling. Paracorporeally positioned LVADs pumped ≈3 liters/min mean flow without vacuum augmentation and up to ≈6 liters/min with 38 mm Hg of vacuum augmentation of filling. Instantaneous ascending aortic pressure and flow showed distinct beat-to-beat variation depending on LVAD control mode. Lower average ventricular afterload was observed when pumping the LVAD asynchronously or 1:2 synchronously. In one acute preparation, left ventricular myocardial oxygen consumption was reduced from the unassisted average control level by 37% for the asynchronous and 1:1 synchronous control modes with left atrial uptake. With combined uptake, oxygen consumption was reduced an additional 30% during asynchronous control or 11% during 1:1 synchronous control without any change in LVAD output. Endocardial/epicardial blood flow ratio was similar and ≥1.12 for all test conditions. Renal and brain blood flow was maintained, or slightly elevated during ventricular assistance. Intramyocardial pressures were monitored using Millar catheter tip transducers. In an acute preparation, left ventricular assistance reduced peak intramyocardial pressure. Changing from atrial to combined uptake cannulation further reduced peak intramyocardial pressure for asynchronous and 1:1 synchronous LVAD control. Reduced end-diastolic intramyocardial pressures were seen with all modes of LVAD control.

These data demonstrate excellent UVAD pumping function and suggest that left ventricular assistance does not compromise endocardial blood flow while sustaining blood flow to other major organs. Regardless of the uptake site, asynchronous or 1:2 synchronous LVAD control may be clinically preferable for effective reduction of left ventricular myocardial oxygen consumption.