MECHANICAL DEVICES: A 'BRIDGE TO TRANSPLANTATION'

SUMMARY In many ways, the anesthetic management of patients receiving mechanical circulatory support as a bridge to cardiac transplantation is not drastically different than that of patients undergoing emergent cardiac repair who are in cardiogenic shock. The critical time period of anesthetic management in this patient population is after arrival in the operating room and prior to initiating CPB. It is during this interval that the patient is most vulnerable to hemodynamic deterioration and/or cardiac arrest. If right ventricular failure and bleeding do not occur, then implantation of these devices is relatively straightforward. The transition from CPB to assist device support may require some pharmacologic manipulation, but for the most part, the drugs and dosages used are identical to those used during routine cardiac surgery. In many cases, patients leave the operating room requiring significantly less inotropic support than preoperatively. Systemic perfusion is greatly enhanced as manifested by a cardiac index greater than 2.2 L/min/m2, increases in mixed venous oxygenation saturation, increased urine output, improved peripheral circulation, decreased cardiac chamber pressures, increased systemic pressure, and a reduction of the pulmonary arterial pressure. Results from the authors' institution are supported by data from other FDA-approved investigators using Thoratec, Novacor, and Thermo Cardiosystems VADs in which patients who were bridged and subsequently transplanted had outcomes at least as good as those in the routine cardiac transplant population.3, 31 The intense competition for the limited supply of donor organs will continue to increase, making it imperative that we optimize the results in all cardiac transplant patients, including those who require mechanical support prior to transplantation. The high hospital survival rate of greater than 96% in our series is primarily attributable to our insistence on transplanting patients who had reversed their organ dysfunction, were nutritionally improved, and, in most cases, ambulatory with markedly improved exercise tolerance when compared with their preimplant state. Thus, these “rehabilitated” patients were excellent candidates for transplantation by the time they received their donor hearts. Considering the severe shortage of donor hearts for transplantation, bridging to transplantation with mechanical devices is not likely to substantially lower the number of patients dying while on the waiting list; however, these bridging experiences have greatly increased our knowledge of patient-device interactions and will be of great value in planning protocols for permanent, totally implantable systems. The concept of patients supported with VADs leaving the hospital has already become a reality. Two patients supported with the Novacor LVAS and the standard large console were managed in a residence facility.7 At least one Thermo Cardiosystems patient has been supported out of the hospital with a wearable battery pack that allows much greater mobility and more normal activity. Both the Novacor and Thermo Cardiosystems wearable battery pack systems have received FDA approval and are in the beginning stages of clinical trials. Once this technology is perfected and becomes widely available, the implantation of permanent mechanical circulatory support systems may afford an additional therapeutic option for the estimated 15,000 potential transplant patients each year.