Physiology of the Transplanted Heart

Compared to the normal heart, differences in the physiology of the transplanted heart derive largely from the fact that the transplanted heart is denervated. Data suggesting that some degree of reinnervation occurs include case reports of angina and the presence of cardiotonic reflexes among some transplant recipients. But functionally the heart remains denervated. Loss of vagal tone results in a somewhat higher resting heart rate. Carotid baroceptor reflexes are typically absent. Increases in heart rate and contractility must rely upon circulating catecholamines. Therefore heart rate increases slowly with the onset of exercise and remains elevated longer after cessation of exercise, which parallels the changes in circulating catecholamine levels. In addition to an increase in p-adrenergic receptor density, the myocardial p-andrenergic receptors of the denervated heart are more sensitive to catecholamines to provide normal cardiac output over a broad range of total body oxygen requirements (Fig. 11.4).

Survival Following Transplantation

The operative mortality rate associated with cardiac transplantation in most centers is typically between 3% and 5%. The principal cause of death within the first 30 days is primary allograft failure (25%). Primary allograft failure typically results from inadequate myocardial preservation of the donor heart or prolonged ischemic time. Other leading causes of early mortality include infection (15-20%), acute right ventricular failure usually resultant to increased PVR in the recipient (15%) and rejection (15%).

Risk factors for death within the first year are shown in Table 11.7. As with other surgical procedures, patient-specific risk factors reflecting greater illness of the patient or increased patient age increase the operative risk of the transplant procedure. Transplant centers performing fewer than nine transplants per year have lower survival rates. Donor-specific risk factors include female gender of the donor and increased donor age. Ischemic time of the donor heart is a well recognized risk factor and adds approximately 10% risk of death for each one hour ischemia.

Data from the ISHLT Registry indicate that the one-year survival following the cardiac transplantation is 82% worldwide. Individual programs, however, have

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