The pumping and left ventricular unloading capabilities of the ventricular synchronous skeletal-muscle ventricle

The pumping and left ventricular unloading capabilities of the left ventricular, ventricular synchronous skeletal-muscle ventricle were determined in nine anesthetized dogs ranging in weight from 20.7 to 31.8 kg. The ventricular synchronous skeletal-muscle ventricle consists of the left rectus abdominis muscle wrapped around a 4-mil-thick polyethylene pouch (wrapped volume 80 to 100 ml) connected to the left ventricular apex with no valve and to the aorta via a prosthetic heart valve. The rectus muscle is timed to contract tetanically and relax during left ventricular ejection. This arrangement provides a high precontraction pressure for the rectus muscle and a high muscle capillary blood flow during skeletal muscle relaxation. The timing signal for initiation of the train of stimulating pulses (40/sec) was derived from the ventricular electrogram. The delay for the stimulus train determines the preload for the rectus muscle and along with the stimulus train duration determines ventricular synchronous skeletal-muscle ventricle stroke volume, which was measured by electric impedance. With unconditioned rectus muscles (70 to 120 gm) and with a pumping ratio of 1:3, ventricular synchronous skeletal-muscle ventricle stroke volume average 26.1 ml, which provided an average output of 876 ml/min. The normalized ventricular synchronous skeletal-muscle ventricle output was 35.6 ml/min per kilogram of body weight. In a typical resting dog (and man), the normalized cardiac output is 70 ml/min per kilogram. Therefore the ventricular synchronous skeletal-muscle ventricle is capable of pumping 52% of the cardiac output (with a pumping ratio of 1:3). The optimum train delay from the apex of the ventricular electrogram ranged from 10 to 100 msec. The left ventricular ejection period averaged 309 msec, and this determines the time available for the rectus muscle to contract and relax. Evidence for unloading the left ventricle is shown by the reduced left ventricular diastolic pressure and stroke volume for the postassisted beats.