Assessment For Heart Transplantation
While heart transplantation remains an excellent treatment for advanced heart failure, the number of transplants performed in Europe is falling due to the lack of suitable donors. The assessment of potential recipients has therefore become more stringent in order to make optimal use of available organs. Many patients referred for transplantation can be improved with conventional cardiac surgery and/or improved medical management, including resynchronisation therapy with biventricular pacing. A classification of underlying diseases is given in Figure 39.
Assessment for transplantation
The assessment of potential recipients involves three components:
• functional capacity
• right heart catheterisation to assess pulmonary circulation
Evaluating functional capacity
Functional capacity can be partly assessed by the history (NYHA classification grade IV), but accurate quantification usually relies on cardiopulmonary exercise testing (CPET).
CPET involves accurate measurements of inspired and expired O2, expired CO2, minute ventilation and work done, typically while using a bicycle ergometer. The maximal oxygen uptake (VO2 peak) is usually that measured at the termination of exercise.
The CPET allows patients to be divided into three prognostic categories, providing full medical therapy, including beta-blockade, has been prescribed.
1. Peak VO2 <12 ml/kg/min with no contraindications to heart transplantation: 94% 1-year survival.
2. Peak VO2 <12 ml/kg/min with some contraindications to heart transplantation: 74% 1-year survival.
3. Peak VO2 >12 ml/kg/min: 47% 1-year survival.
Evaluating the pulmonary circulation
Chronic left ventricular failure is characterised by a loss of myo- cardial contractility and higher left ventricular diastolic pressures (LVEDP) in an effort to maintain cardiac output. Raised LVEDP leads to an increase in pulmonary venous pressure and pulmonary artery (PA) pressure. The rise in PA pressure is accompanied by a rise in pulmonary vascular resistance (PVR).
Raised PVR is usually reversible following transplantation, but can cause acute right ventricular failure in the newly transplanted heart, and accounts for 20% of early deaths post-transplant.
Therefore a high pulmonary artery pressure (>60 mmHg), high transpulmonary pressure gradient (TPG >15 mmHg), and high PVR (>5 Wood units) are contraindications to heart transplantation. To assess these values patients undergo right heart catheterisation using a Swan–Ganz catheter. The PVR can be improved by increasing diuretics and other anti-failure treatments. It should be regularly re-assessed while awaiting transplant.
Patients with previous cardiac surgery (congenital heart disease, previous coronary artery bypass graft [CABG] or valve surgery, previous heart transplant) have a higher morbidity and mortality related to adhesions and disruption of tissue planes.
Age – older patients have a poorer outcome, although chrono- logical age per se is not a contraindication if the patient is otherwise fit. Transplantation is rarely offered to patients ≥70 years.
Smoking – smokers have a reduced survival, with a higher incidence of cardiac allograft vasculopathy.
Cerebrovascular or peripheral vascular disease if symptomatic.
Lung disease – severe lung disease, with FEV1 and FVC <50% predicted.
Thromboembolic disease – recent pulmonary embolism is a contraindication (raises PA pressure and may proceed to lung abscess post-operatively).
Diabetes mellitus with severe end organ damage, e.g. nephropathy.
Kidney function – renal function is often affected by heart failure, and will be affected by the immunosuppression following surgery. In general, a glomerular filtration rate (GFR) above 40 ml/ min/1.73m2 is considered adequate. Patients with poor renal func- tion might be considered for later kidney transplant. Combined heart and kidney transplantation is now not normally done because of the excessive morbidity of two procedures.
Infection – active infection, or chronic viral infections (e.g. HIV, hepatitis C virus).
Malignancy – a recent history of cancer (except non-melanoma skin cancer) is a contraindication. A recurrence-free interval of 5 years is appropriate before transplantation might be considered.
Obesity – obese patients have increased morbidity and mortality, so patients with a BMI >30 kg/m2 are usually excluded.
Poor compliance – substance abuse, inability to stop smoking or a history of poor adherence to drug treatment are all predictors of a bad outcome due to inability to follow immunosuppressive drug regimens.
Bridge to transplantation
Many patients who have been deemed suitable for heart transplan- tation have such poor hearts that they are unlikely to survive the wait for a suitable heart, in spite of inotrope support on an intensive care unit. To support such hearts during this time increasing use is being made of mechanical circulatory support in the form of ventricular assist devices (VADs). These devices provide an additional pump to aid the circulation. The standard configuration is a pump draining blood from the apex of the left ventricle and returning it via a tube graft to the ascending aorta. This left-sided – LVAD –support is generally sufficient; the requirement for support of both ventricles predicts a much worse outcome.
In the short term, the very sick patient can be stabilised with externally placed (paracorporeal) pumps which give pulsatile flow. Longer-term support is best given by fully implanted miniature centrifugal, continuous-flow pumps. The current generation lies entirely within the pericardial cavity. Although there remain some unsolved problems of biocompatibility, particularly thrombosis, the need for rigorous anticoagulant control and infection, the 1-year survival, at 80–85%, is similar to heart transplantation. The future treatment for the very large number of patients with end-stage heart failure will be with these mechanical devices and their successors.