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.
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