Critical Analysis of Intra-aortic Balloon Counterpulsation and Transapical Left Ventricular Bypass in the Sufficient and Insufficient Circulation

Abstract

Reduction of cardiac work/ oxygen consumption (LVQO2) may be beneficial in diminishing ischemic damage after myocardial infarction (MI). This study compares intra-aortic balloon pumping (IABP) and transapical left ventricular bypass (TALVB) to a specially developed method of LV assistance, i.e. transapical left ventricular bypass with complete LVdecompression (TALVB/ TD), a) in the sufficient circulation of swine for effectiveness in actively reducing myocardial oxygen requirements and b) in the insufficient circulation for effectiveness in improving circulatory dynamies, to reduce gross size and to prevent morphological damage in myocardial infarction in swine. Thirty-four pigs (17-29 kg) had standardized general anesthesia. a) In 10 of these animals LVQO2 was determined by measuring left coronary artery blood flow (LCBF) electromagnetically, blood samples for 02-content were taken from the aorta and the coronary vein draining the LV. Cardiac work/ oxygen consumption was related , during variable degrees of IABP assist and during total bypass , with graded reduction of LV pressure work , culminating in complete LV decompression (LV press. max. permanently below 8 mmHg). b) Twenty-four pigs underwent ligation of the LAD distal to the first diagonal branch and were divided into 4 groups. Six pigs served as controls. Starting 45 minutes after ligation 6 had 24-hour treatment with IABP, 6 had 24-hour TALVB and 6 animals were treated with TALVB/TD. Heart rate , central venous , pulmonary artery , aortic and left ventricular pressures and cardiac output were recorded prior to ligation and at 1/2, 1, 2 , 3, änd 24 hours. At 24 hours myocardial infarct size (MIS) was quantitated in g infaret per 100 g left ventricular and septal mass, and infarcted areas were examined histologically. a) In the sufficient circulation , heart rate , cardiac output, mean aortic , pulmonary artery , and central venous pressures were not significantly changed by IABP, TALVB, and TALVB/TD assist. During IABP (1:1), LVQO2 was decreased only 2.8%, LCBF was increased 4.4%, which is not significantly different from controls. Total LV bypass decreased LCBF 8.3% and LVQO2 18.1 %, total LV bypass with complete LV decompression reduced LCBF 31 % and LV(2O2 60.4% from control values. b) MI reduced mean aortic pressure (24.5%) and cardiac Output (47. 5%) significantly (p < .05). Confirmed in switchon/switch-off studies, IABP increased mean aortic pressure and cardiac output 4% to 9%. TALVB displaced 70% to 100% of the LV volume work, LV decompression was seen in 5 of the 6 TALVB animals (LVP syst. = AOP-11 mmHg). Transapical left ventricular bypass with a complete LV decompression immediately took over 100% LV volume work