CARDIAC TRANSPLANTATION (also
see Chapter 50
)
Over 2000 heart transplantation procedures are performed each
year,[284]
and to date, over 60,000 patients have
received heart transplants worldwide. Most of these transplants have been performed
as treatment of end-stage cardiac failure refractory to conventional medical therapy.
Lengthy waiting lists and limited organ supply continue to provide impetus for the
development of long-term
(destination) ventricular assist devices, implantable artificial heart technology,
and even xenotransplantation. Yet, the existing expertise in cardiac transplantation
can provide dramatic improvement in functional status and longevity for patients
with an otherwise poor prognosis. Indeed, 50% of modern-era heart recipients are
alive at 9.3 years, and among those who survive the first year, nearly half are living
after 12 years.[285]
Although the introduction
of cyclosporine in 1981 led to dramatic improvements in immunosuppressive therapy
and patient outcome, acute rejection continues to be a major contributor to mortality
in the first year after transplantation. As with other organ transplants, infection
and malignancy pose major obstacles to true long-term survival, with additional significant
mortality referable to the heart's unique expression of chronic rejection, coronary
artery vasculopathy.[286]
[287]
Retransplantation carries a poorer prognosis than first-time transplantation does
(49% 5-year graft survival rate versus 69% for first-time recipients),[284]
[288]
but it may provide hope for patients who survive
beyond the useful life of their graft.[289]
Organ Matching and Allocation—Donor Considerations
Currently, hearts become available for transplantation from human
donors who meet the accepted criteria for brain death but have otherwise maintained
organ function by virtue of supportive intervention. Most cardiac organ donors are
young (<45 years), without a history of hypertension, CAD, malignancy, or other
major systemic illness, and typically have suffered fatal intracranial hemorrhage
or head injury. The initial review of a potential donor's medical history includes
consideration of the events leading to brain death and course in the ICU. This process
excludes those with unstable hemodynamics or a significant requirement for inotropic
circulatory support. Other complications during the patient's management that may
render the heart unsuitable for transplantation include severe ventricular arrhythmias,
cardiac arrest, prolonged hypotensive episodes, sepsis, or hypoxemia despite optimal
ventilatory support.[290]
[291]
[292]
Donors still considered appropriate with
regard
to these criteria undergo a specialized cardiac evaluation (secondary screening),
including ECG, echocardiography, and in selected cases (e.g., male older than 40
years or female older than 45), angiography. Taken together, such investigations
are performed to detect and exclude those with significant myocardial or valvular
dysfunction, cardiac contusion, LV hypertrophy, or previously unrecognized significant
CAD.[290]
[291]
In addition to ABO blood assignment, serologic assessment of the potential donor's
HIV, cytomegalovirus (CMV), and hepatitis status is performed. Criteria for the
selection of donors have been liberalized in recent years because of widening of
the disparity between the length of transplant waiting lists and the number of available
organs.[292]
[293]
[294]
Although this change has expanded the number
of donor organs by 15% to 25%,[292]
[295]
outcomes have not been significantly compromised.[292]
[293]
[294]
[295]
A full understanding of which donor criteria may safely be relaxed
is still under development. Still, many centers accept organs from older donors
or those who have CAD, a decreased ejection fraction, or LV hypertrophy. Donor hearts
with limited angiographically demonstrable coronary stenosis may undergo revascularization
at the time of engraftment.[294]
The long-term
significance of so-called marginal donor organs is unknown in many cases because
of the relative novelty of their use, yet many institutions report good short- and
medium-term results.[296]
Regardless of the preoperative historical and investigative data,
the acceptability of the donor organ ultimately depends on direct inspection (tertiary
screening) by the surgical team at the time of procurement. Significant unrecognized
coronary plaque, cardiac contusions, or defects may necessitate cancellation of the
proposed transplant procedure.
