Development and testing of a muscle-powered cardiac assist device.

摘要

The use of skeletal muscle as an endogenous power source affords a unique opportunity to bring a completely implantable, tether-free cardiac assist system to fruition. Muscle-powered devices offer an attractive alternative to current long-term support schemes by eliminating the need to transmit energy across the skin, thereby reducing hardware requirements significantly. This would enhance patient quality-of-life by improving reliability and eliminating all external hardware components.;Toward that end an implantable muscle energy converter (MEC) has been designed to transmit the contractile energy of the latissimus dorsi muscle in hydraulic form. The MEC features a metallic bellows actuated by a rotary cam attached to a titanium rocker arm. The rocker arm is fixed to the humeral insertion of the muscle via a looped artificial tendon developed specifically for this purpose. The device housing is anchored to the ribcage using a perforated mounting ring and wire suture, a design feature also unique to this application. Lessons learned through seven previous design iterations have produced an eighth-generation pump with excellent durability, energy transfer efficiency, anatomic fit, and tissue interface characteristics.;In order to use the MEC to pump blood however, a practical means to deliver this energy to the bloodstream must be devised. Presented here are six prospective mechanisms whereby this might be accomplished, five of which eliminate blood contacting surfaces that often lead to thromboembolic complications in chronic VAD patients. One of these approaches, apical torsion, is examined in detail in order to determine whether this method is viable and warrants further research.;Results from computer simulations suggest that quarter-turn apical torsion can increase LV stroke work by nearly one third in non-dilated hearts with moderate contractile dysfunction (27% ejection fraction) while lowering epicardial fiber stress substantially. The predicted reduction in epicardial wall stress during torsion was consistent with the direction of rotation and the orientation of myofibers in this region. Moreover, in vivo testing of the apical torsion approach in pigs showed experimental results to be in substantial agreement with computer simulations. These data confine the feasibility of this approach and suggest that further research is warranted.