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Peak Oxygen Consumption (VO2)

Peak VO2 consumption has become an important tool in the decision regarding the timing of transplantation. It helps quantify the degree of cardiac dysfunction and offers an objective prognosis of the patient. Serial determinations of peak VO2 may be used to assess response to therapy and to track progression of disease. A peak VO2 greater than 14 ml/kg/min is associated with one-year survival greater than 90% and suggests that transplantation may be deferred. A peak VO2 less than 10-12 ml/kg/min is associated with a poor prognosis and patients should be considered for transplantation.

Systemic Diseases

Cardiac dysfunction may be a manifestation of some systemic diseases. Unfortunately, some systemic disease may preclude transplantation. Patients with diabetes mellitus often have renal dysfunction, peripheral vascular disease and retinal vascular disease, which may be exacerbated by the steroid therapy needed following transplantation. Such patients are typically unsuitable candidates. Systemic amyloidosis typically has multiorgan involvement and may recur in the transplanted heart. Therefore most programs recommend against heart transplantation for amyloidosis.

Pulmonary Vascular Resistance (PVR)

Determination of PVR is extremely important. Patients with left ventricular failure typically have elevated pulmonary artery pressures derived from hydrostatic pressure transmitted retrograde from elevated left-heart pressures. Once left-heart pressures are normalized following transplantation, the pulmonary artery pressures typically normalize. But long-standing left ventricular failure may also produce pulmonary vascular remodeling and a "fixed" increase in PVR; such "fixed" PVR is unresponsive to pulmonary vasodilator therapy.

Because cardiac donors almost invariably have normal pulmonary arterial pressure, the right ventricle of the donor heart is not conditioned to pump against a high resistance: the PVR of the recipient must be low enough to allow the transplanted heart to support the recipient's circulation. Heart transplantation into a recipient with increased PVR unresponsive to vasodilator therapy predictably leads to right ventricular failure of the transplanted heart, and death.

A potential heart transplant recipient must have a right-heart catheterization in order to accurately measure pulmonary arterial pressures, determine the transpulmonary gradient and calculate the PVR. If the patient is found to have increased PVR, provocative testing with vasodilator therapy is indicated in the cardiac catheterization suite. Using an infusion of sodium nitroprusside, an attempt should be made gently to vasodilate the systemic circulation without lowering systolic arterial blood pressure below 90 mm Hg. Such reduction in left ventricular afterload increases forward cardiac output. In turn, left atrial pressure (and pulmonary capillary wedge pressure) decrease, thereby lowering the hydrostatic component of the patient's pulmonary arterial pressure. During such provocative testing, the patient's hemodynamic variables typically mimic the situation

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