Organ Matching and Allocation—Recipient Considerations

Heart transplantation may be considered for any otherwise healthy patient with cardiac disease that significantly threatens survival or quality of life despite optimal medical or surgical intervention. About 90% of patients who undergo transplantation have end-stage cardiac failure as a result of ischemic or idiopathic dilated cardiomyopathy.^{[284] [285]} Most of the remainder suffer from congenital defects, valvular heart disease, or increasingly, dysfunction of a previously placed cardiac graft (retransplantation). At the time of placement on a waiting list, most patients have New York Heart Association (NYHA) functional class III or IV symptoms^[297] with a poor LV ejection fraction (<20%). These criteria alone are neither necessary nor sufficient.^[289] In a small minority of patients without heart failure per se, a heart transplant is indicated to treat uncontrolled ventricular arrhythmias, idiopathic hypertrophic cardiomyopathy, intracardiac tumors, and life-threatening ischemia that is not amenable to revascularization.

As with donor inclusion criteria, the issue of whom to consider for transplantation is complicated by the significant disparity between organ availability and the length of the waiting list. For this reason, the accepted guidelines serve to channel available organs to those for whom early and longer-term success is likely. Traditional guidelines have excluded patients older than 55 years, yet observation of the comparable benefit to older patients has led to the inclusion of patients older than 65 years in later eras^[285] and, in some centers, even patients older than 70.^[294] Likewise, patients with insulin-dependent diabetes who have minimal target organ damage may receive transplants with good results.^[298] Renal and hepatic dysfunction are common sequelae of severe cardiac disease, and transplantation is generally considered appropriate in patients with mild dysfunction that is deemed likely to normalize with improved cardiac output after transplantation.^[298] Table 56-2 outlines suggested criteria for recipient selection, but exceptions are frequently based on institution-specific opinion and expertise. Evolving experience continues to expand our knowledge of how to best manage the scarce donor organ supply.

Less controversy surrounds the issue of pulmonary vascular resistance (PVR). Preoperative measurement of PVR

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When conventional medical therapy fails to maintain hemodynamic or respiratory stability in patients awaiting transplantation, they may require intravenous inotropic support, either in the hospital or at home. Recent success has also been reported in selected cases with the use of biventricular pacing devices as a temporizing measure in transplant candidates in the ambulatory setting.^[306] Mechanical ventilation or one of several forms of mechanical circulatory support may be used as an interim measure ("bridge to transplantation"). It is known that such patients experience higher operative mortality rates with transplantation (approximately 14% versus 6% in healthier recipients).^{[285] [289] [298]} The high mortality rate of this subgroup without transplantation so severely jeopardizes the overall survival benefit (i.e., for the waiting list population taken as a whole) that donor organs are preferentially allocated to these patients. Indeed, fully three quarters of those who received transplants in the United States in 2001 belonged to this high-priority (status 1) category. ^[284]

To select a recipient, consideration is given to the geographic proximity to the donor, as well as the time accrued on the waiting list (in the United States, this list is a registry of recipient candidates and is maintained by UNOS). In this way, fairness to those on the waiting list is balanced with the recognition that transit time is of importance to subsequent organ function.^[285] ABO blood typing is the only laboratory basis used for initial allocation. ABO compatibility is essential, although rare intentional exceptions have been reported. ^[307] Grouping need not be identical (e.g., a group A donor organ may be matched to a group AB patient). Variably practiced, a confirmatory crossmatch may be performed to ensure compatibility between the recipient's serum and donor antigen, particularly in cases in which the recipient is known to harbor antibodies to a high percentage of nonself antigen (a highly positive panel-reactive antibody test).^[308] Although CMV mismatch is not known to affect survival in selected cases, the CMV status of the donor may be taken into account by those caring for certain high-risk recipients.^[285] Patients waiting for heart transplantation are stratified according to the urgency of need. Higher priority is awarded those who require intravenous inotropes, mechanical circulatory assistance, or positive-pressure ventilation, regardless of whether such therapy is administered in the hospital or the ambulatory setting.^[309]

Acceptance of a donor organ may be based on the match between the donor and recipient in terms of height, weight, and perhaps age. A significant size mismatch can compromise the outcome. The use of a relatively elderly heart in a young patient may also be undesirable. Doctors caring for the recipient ultimately determine the importance of these factors in individual cases.