The Patient with a Transplanted Heart
The number of patients with cardiac transplants is increasing because of both the increasing frequency of transplantation and improved post-transplant survival rates. These patients may pres-ent to the operating room early in the postoperative period for mediastinal exploration or retransplan-tation, or they may appear later for incision and drainage of infections, orthopedic surgery, or unrelated procedures.The transplanted heart is totally denervated, so direct autonomic influences are absent.Cardiac impulse formation and conduction are nor-mal, but the absence of vagal influences causes a rel-atively high resting heart rate (100–120 beats/min). Although sympathetic fibers are similarly inter-rupted, the response to circulating catecholamines is normal or even enhanced because of denervation sensitivity (increased receptor density). Cardiac out-put tends to be low-normal and increases relatively slowly in response to exercise because the response is dependent on an increase in circulating catechol-amines. Because the Starling relationship between end-diastolic volume and cardiac output is normal, the transplanted heart is also often said to be preload dependent. Coronary autoregulation is preserved.
Preoperative evaluation should focus on evalu-ating the functional status of the transplanted organ and detecting complications of immunosuppression.Rejection may be heralded by arrhythmias (in the first 6 months) or decreased exercise tolerance from a progressive deterioration of myocardial perfor-mance. Periodic echocardiographic evaluations are commonly used to monitor for rejection, but the most reliable technique is endomyocardial biopsy. Accelerated atherosclerosis in the graft is a very common and serious problem that limits the life of the transplant. Moreover, myocardial ischemia and infarction are almost always silent because of the denervation. Because of this, patients must undergo periodic evaluations, including angiography, for assessment of coronary atherosclerosis.
Immunosuppressive therapy usually includes cyclosporine, azathioprine, and prednisone. Important side effects include nephrotoxicity, bone marrow suppression, hepatotoxicity, opportunistic infections, and osteoporosis. Hypertension and fluid retention are common and typically require treat-ment with a diuretic and an ACE inhibitor. Stress doses of corticosteroids are needed when patients undergo major procedures.
Almost all anesthetic techniques, including regional anesthesia, have been used successfully for trans-planted patients. The preload-dependent func-tion of the graft makes maintenance of a normal or high cardiac preload desirable. Moreover, the absence of reflex increases in heart rate can make patients particularly sensitive to rapid vasodilata-tion. Indirect vasopressors, such as ephedrine, are less effective than direct-acting agents because of the absence of catecholamine stores in myocardial neurons. Isoproterenol or epinephrine infusions should be readily available to increase the heart rate if necessary.
Careful electrocardiographic monitoring for ischemia is necessary. The ECG usually demon-strates two sets of P waves, one representing the recipient’s own sinoatrial node (SA) (which is left intact), and the other representing the donor’s SA node. The recipient’s SA node may still be affected by autonomic influences, but it does not affect car-diac function. Direct arterial pressure monitoring should be used for major operations; strict asepsis should be observed during placement.In a recently transplanted patient, the right ven-tricle of the transplanted heart may not be able to overcome the resistance of the pulmonary vascu-lature. Right ventricular failure can occur periop-eratively, requiring the use of inhaled nitric oxide, inotropes, and, at times, right ventricular assist devices.