Evaluation of mechanical left ventricular assistance with left atrium to aorta bypass in dogs.

Abstract

Effects of the left heart bypass (LHB) by the left atrium (LA) to the aorta (AO) shunt on the heart were evaluated by measuring such parameters as tension time index (TTI), diastolic pressure time index (DPTI), DPTI/TTI ratio, coronary blood flow and myocardial oxygen consumption (MVO2) in open-chest dogs. A pneumatically driven bypass pump made of polyurethane was utilized in this study. No significant change of MV02 was observed with surgical maneuver to connect the LA-AO LHB pump to experimental animals. During synchronous pumping of LHB, TTI decreased by 35%, MVO2 decreased by 56% of the control and DPTI/TTI ratio increased by 79%. However, coronary flow decreased by 35%, presumably due to autoregulation mechanism of the coronary circulatory system. Both synchronous and asynchronous LHB demonstrated the same level of effect in volume unloading. However, significant diastolic augmentation was noted only in the former. LA-AO LHB, which has a sufficient supporting effect and does not damage the ventricular wall, was considered to be very useful for temporary support for the failing heart, especially for postoperative low output state.left ventricular assistance; TTI; DPTI; MVO2; coronary blood flow Left heart bypass, a method of mechanical assistance for severe left heart failure, has been utilized clinically (DeBakey 1971;Litwak et al. 1976;Norman 1977; Pierce et al. 1978) and some have reported satisfactory results (DeBakey 1971;Litwak et al. 1976). Several methods of left heart bypass have been developed and they are divided into two main groups by the sites of blood drainage, that is, the left atrium to aorta bypass group (LA-AO LHB) and the left ventricle to aorta bypass group (LV-AO LHB). LA-AO LHB appears not to suppress left ventricular function and synchronous pumping to the natural heart rhythm is not mandatory with this method. In experimental set up with a normal heart, however, LA-AO LHB occasionary fails to drive a sufficient blood volume for the bypass. Thus, skeptism was raised for the use of LA-AO LHB, and many investigators have experimented LV-AO LHB (Hughes et al. 1975;Watanabe et al. 1975; Pierce et al. 1978). It is obvious that the LV-AO LHB is able to replace most of the cardiac