Design of a Muscle-Powered Extra-Aortic Counterpulsation Device for Long-Term Circulatory Support

While great strides continue to be made in the treatment of congestive heart failure using mechanical ventricular assist devices (VADs), several longstanding difficulties associated with pumping blood continue to limit their long-term use. Among the most troublesome has been the persistent risk of clot formation at the blood-device interface, which generally requires VAD recipients to undergo costly — and potentially dangerous — anticoagulation therapy for the duration of the implant. Another serious and persistent problem with long-term use of these pumps is the increased risk of infection associated with the use of percutaneous drivelines. To address these issues we are currently exploring a new approach to blood pump design that aims to solve both these problems by avoiding them altogether. Toward that end, we propose to harness the body’s own endogenous energy stores in order to eliminate the need to transmit energy across the skin. Further, we intend to transfer the energy from this internal power source to the circulation without contacting the blood to obviate the thrombogenic risks imposed by devices placed directly into the bloodstream. To power the implant we will employ a device developed previously by our group called a muscle energy converter (MEC), shown in Figure 1. The MEC is, in essence, an implantable hydraulic actuator powered by the latissimus dorsi (LD) muscle with the capacity to transmit up to 1.37 joules of contractile work per stroke [1]. By training the muscle to express fatigue-resistant oxidative fibers and stimulating the LD to contract in coordination with the cardiac cycle, the MEC captures and transmits this contractile energy as a high-pressure low-volume (5 cc) hydraulic pulse that can be used, in principle, to actuate an implanted pulsatile blood pump. The goal of this research is to use the low-volume output of the MEC to drive a polymer-based aortic compression device for long-term circulatory support. In this context it is important to note that the idea of applying a counterpulsation device around the ascending aorta is not new. Indeed, this approach has been validated by clinical trials recently completed by Sunshine Heart Inc. showing that displacing 20 cc of blood at the aortic root has significant therapeutic benefits [2]. Unfortunately, while the pneumatic ‘C-Pulse’ device solves the blood-contacting problem, it suffers from the same limitations as traditional VADs — i.e., driveline infections. The device described here achieves the same volumetric displacement as the SSH device via geometric amplification of MEC outputs. Thus, through this mechanism we believe the low-volume power output of the MEC can be used to support heart failure patients while addressing the major limitations associated with long-term VAD use.