Thermedics' approach to ventricular support systems.
Temporary and permanent ventricular assist systems, developed by Thermedics, Inc., are described, including rationale, design, operation and surgical applications. Clinical data are presented for pneumatically driven temporary left ventricular assist devices (LVAD). Usefulness of this device rests on the assumption that tissue of a weakened heart can recover if relieved for a time by an LVAD. The surgical implantation of an LVAD is reported in a case where the patient later received a heart transplant. The concept and technology of the subsystems of a permanent ventricular assist system (VAS), now ready for preclinical trials, are discussed. Design of a low-speed, torque-motor driven blood pump is described. Details are presented on transcutaneous energy transmission by means of a transformer, one of whose coils is embedded under the skin. Though less efficient than percutaneous transmission, the method eliminates infection risk. Special types of polyurethanes are analyzed in respect to their biocompatibility. It is concluded that flocking of the polyurethane surface allows the growth of a biological lining which is highly antithrombogenic. Sintered metal powders are found to be most efficient for fabrication of rigid pump components. A lenticular pump design is proposed to solve the problem of pressure differentials in the sealed device. Cardiac endocrine functions are cited in support of using assist devices that leave the heart in place.