CARDIAC TRANSPLANTATION

The main issue with cardiac transplantation revolves around donor availability (Table 95.1). The numbers of potential recipients who fulfil internationally accepted criteria² (Table 95.2) vastly outnumber the available donors, so the great majority of patients with severe end-stage heart failure inevitably die before a suitable donor heart becomes available.

Table 95.1 Illustration of the disparity between transplant operations and numbers of patients on the UK transplant registry

Source: www.uktransplant.org.uk.

Table 95.2 Criteria to select cardiac transplant recipients

NYHA, New York Heart Association; PAOP, pulmonary artery occlusion pressure (or ‘wedge’ pressure); PAP, pulmonary artery pressure; PVR, pulmonary vascular resistance.

The cardiac equivalent of dialysis, for the maintenance of the potential renal transplant recipient until an organ is available, is simply not feasible. However, there has been progress in the medical and surgical management of severe heart failure, some of which are highly specialised treatments with limited availability and some more routine and commonplace (Table 95.3). The use of inotropic drugs such as β-agonists (e.g. dobutamine), catecholamines (e.g. epinephrine) and phosphodiesterase inhibitors (e.g. milrinone) to support the failing heart and circulation is widely practised, as is the use of intra-aortic balloon pump (IABP) counterpulsation. These treatment options are, of course, highly invasive but may be used as rescue therapy in a patient with severe or end-stage cardiac failure who may be waiting for a transplant but in whom some event such as infection of worsening myocardial ischaemia has resulted in a catastrophic deterioration. The response of the failing heart to β-agonists may be disappointing because of the tendency to β-receptor downregulation from chronic overstimulation. In these cases the phosphodiesterase inhibitor drugs such as milrinone and enoximone may have greater and more sustained potency because of their intracellular site of action.

Table 95.3 Non-transplant or bridge to transplant treatment of severe cardiac failure

CCU, coronary care unit; ICU, intensive care unit.

Some patients who have been deemed inoperable in conventional terms may still benefit from cardiac surgical interventions, though in the setting of severe chronic cardiac failure the risk of death, serious morbidity and prolonged postoperative critical illness may be considered prohibitive. Sometimes a degree of reversible myocardial ischaemia may be demonstrated by thallium scanning and guide subsequent coronary artery bypass grafting. In some cases, the degree of secondary mitral valve regurgitation caused by dilatation of the left ventricle may become a haemodynamically significant lesion of itself and reconstruction of the mitral valve or remodelling of the left ventricle may prove beneficial. In extreme cases of cardiac decompensation and where other organ functions are maintained (an unusual combination) the use of mechanical assistance⁴ to support the heart and buy time for a donor heart to become available (‘bridge to transplant’) or to provide support while a severe but temporary process (such as some viral myocarditis episodes) subsides (‘bridge to recovery’) may be undertaken in highly specialised centres. The logical conclusion is to develop permanent mechanical support devices obviating the need for transplantation but this goal appears to be a long way in the future. The cost of such therapy in both financial and human terms has to be considered in the context of general health economics. These episodes are still at best pioneering, extremely invasive, draining on the resources of critical care, blood transfusion and pharmacy, and of limited outcome benefits. On the other hand, it can be argued that earlier use of potent mechanical assistance at a stage that other organs have yet to be irretrievably damaged should be more widely attempted and, by inference, outside the major cardiac specialist centres.