PARTIAL UNLOADING WITH A ROTARY LEFT VENTRICULAR ASSIST DEVICE REDUCES MYOCARDIAL OXYGEN CONSUMPTION AND STROKE WORK IN CHRONIC HEART FAILURE

Abstract

Background:Complete unloading with a left ventricular assist device may aggravate cardiac dysfunction through geometric and hemodynamic alterations associated with LV decompression. We investigated whether partial unloading with an LVAD, where only a portion of the cardiac output is contributed by mechanical assistance, significantly reduces LV oxygen consumption (LVVO2) and stroke work (SW) in chronic heart failure. Methods:Five sheep underwent coronary microembolization to induce heart failure (ejection fraction <35% for 2 consecutive weeks). Four months later, a centrifugal LVAD was implanted. LV bypass was incrementally increased from 0% to 25% 50%, 75%, and finally 100% support. LV stroke work was determined as the area enclosed by pressure-volume loops. Pulmonary artery (PA) and left main coronary artery flows were obtained, and LV decompression was visualized using transepicardial echocardiography. Results:LVVO2 (μ L/100gmLV/beat) at 0% unloading measured 41.1 ± 5.8 in the ischemic heart. LVVO2 was 27.0 ± 6.7, 23.6 ± 7.6, 17.6 ± 7.7, and 10.8 ± 8.7 at 25%, 50%, 75%, and 100% unloading (p < 0.05 at all increments as compared to baseline). SW (mmHg*mL measured 1677.6 ± 141.5 at O%, and 1480.8 ± 100.5, 1165.7 ± 71.3, 727.7 ± 73.1, and 370.1 ± 172.1 at 25%, 50%, 75%, and 100% unloading. PA and left main coronary artery flows were unaffected or even improved with partial unloading. Geometric alterations, including leftward septal shift, occurred at 75% and 100% unloading. These changes were minimized with partial unloading. Conclusion:Partial unloading of as little as 25% with a centrifugal LVAD significantly reduces LVVO2 by 34% while only reducing LV stroke work by 12%. Coronary and systemic blood flow is maintained, and geometric alterations associated with complete LV decompression are minimized.