The muscle-powered dual-chamber counterpulsator: Rheologically superior implantable cardiac assist device

To enable long-term studies of a totally implantable cardiac assist device powered by transformed fatigue-resistant skeletal muscle, we developed a dual-chamber extraaortic counterpulsation system that uses hydraulic fluid for power transfer. Six dogs had our dual-chamber extraaortic counterpulsator implanted, 2 of which had undergone prior transformation of their latissimus dorsi muscle. The blood pump, with a Dacron graft at each end, was anastomosed end-to-side and parallel to the thoracic aorta, allowing continuous blood flow to minimize thrombus formation caused by stasis and turbulence. The blood pump was powered by a hydraulic bulb placed beneath the latissimus dorsi muscle. The latissimus dorsi muscle was stimulated to contract during diastole using a synchronized burst electrical stimulator. The ratio of diastolic pressure time product over systolic time tension index, which reflects the myocardial oxygen supply and demand ratio, was calculated from ascending aortic pressure tracings. A consistent increase in this ratio of 44% in 4 dogs with nontransformed latissimus dorsi muscle and of 70% in 2 dogs with transformed latissimus dorsi muscle was obtained when the device was activated. Preliminary chronic implantation studies using a Medtronic cardiomyo-stimulator (Model SP1005) as the burst stimulator for our dual-chamber extraaortic counterpulsator produced an average augmentation in aortic diastolic pressure of 34 mm Hg for up to six days. Our results indicate that, with further refinement of this device, a long-term totally implantable cardiac assist device powered by endogenous skeletal muscle will be feasible.