Heart Transplantation

Heart transplantation is a surgical procedure to implant a healthy heart into a patient with heart failure. Heart transplantation is usually the last option on a list of treatments for heart diseases. The primary diagnoses of patients receiving heart transplants are coronary artery disease, cardiomyopathy, and congenital diseases. The first heart transplant was performed by Professor Christiaan Barnard at Groote Schuur Hospital in South Africa in December 1967. A major barrier to transplantation is the process of rejection in which the recipient's immune system recognizes the graft being foreign and attacks it. The antigens responsible for this reaction are the HLA system. The HLA genes are highly polymorphic and any two individuals (except identical twins) will express different HLA proteins.

The three organ rejection reactions are hyperacute, acute, and chronic. Hyperacute rejection occurs within minutes or hours of transplantation and can be recognized by the surgeon just after the graft vasculature is anastomosed to the recipient's. This process occurs when preformed antidonor antibodies are present in the circulation of the recipient. An acute rejection occurs within days of transplantation in an untreated recipient or may occur months or years later when the immunosuppression has ended. Acute rejection is a combined process in which cellular and humoral parts of the immune system contribute. Chronic rejection presents in patients over a period of four to six months. It is usually irreversible and is the single largest cause of organ transplant rejection.

Mechanisms for increasing graft survival are to match more of the HLA genes between the recipient and the donor. Also, patients are given immunosuppressive drugs to prevent attack of the transplanted organ by the transplant recipient's immune system. Common drugs are cyclosporine, azathioprine, steroids, rapamycin, and mycophenolate mofetil. A common side effect of immunosuppressive treatment is for the recipient to be more susceptible to opportunistic infections most likely by fungal or viral organisms. Also, these patients are at a higher risk for cancers that are caused by viruses. Current research to overcome this obstacle of immunosuppression is looking at inducing donor-specific tolerance in host T lymphocyte cells.

The United Network for Organ Sharing (UNOS) is a private, nonprofit organization that matches available organ donors with waiting transplant recipients through the national Organ Procurement and Transplantation Network (OPTN). Organ procurement is dependent on recipient time on waiting list, severity of disease, ABO blood type, and body size. Contraindications specific to heart transplants are if the patient has an active infection, pulmonary hypertension, untreatable liver or kidney disease, chronic lung disease, mental illnesses, disease of the blood vessels in the brain, and continued alcohol or drug abuse.

In general, the two forms of heart procedures are orthotopic or heterotopic. In an orthotopic procedure, the patient's heart is removed leaving portions of the left and right atrium, pulmonary vein, and aorta. The new heart is then modeled to fit the recipient's chest and the different chambers and vessels are anastomosed together. In a heterotopic procedure, the pa-tient's own heart is not removed before implanting the donor heart. The two hearts are connected together to form a “double heart.” This way, the patient's own heart may recover from the decreased workload and be able to function normally in the future. This procedure is also done if the donor heart is large enough to sustain the patient's body or if the donor heart is too weak. In both procedures, the donor heart is stimulated to maintain a regular beat through medications or a pacemaker. After the surgery, the patient usually [Page 819]remains in the intensive care unit for 24 to 72 hours. Also for the next few months following the surgery, the patient revisits the transplant center for weekly physical examinations.

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