The availability of heart transplants is limited by the number of donor organs. The donors are victims of brain death often occurred because of traumatic brain injury in car accidents. Furthermore, the usage of a heart for transplantation is often limited by comorbidities and constitutional peculiarities of a donor. Also, there is such limitation as long distances between an organ recovery center and a center of transplantation, owing to a short period of ischemia of a donor organ (4-6 hours).
Potential donors must meet the criteria of brain death; they cannot have evident pathology of a heart. For the initial screening of potential donors, echocardiography is used. The indicators of possible heart transplantation are a good ejection fraction (> 50%), normal condition of valve structures, and absence of left ventricular hypertrophy. There are minimal violations: initial degree of inefficiency of mitral, tricuspid valves, marginal left ventricular hypertrophy, and some reduced ejection fraction. Additionally, condition of a potential recipient has to be taken into account: in case of critical conditions, a "non-ideal" heart may be acceptable for transplantation. Donors with known risk factors for coronary heart disease (45-50 years old, with a history of smoking, and others) have to undergo coronary angiography.
The universal donor eligibility criteria are age under 65 years, normal heart function, an absence of CHD. When these criteria are met, selection of donor-recipient pairs for blood group (ABO) and anatomical dimensions is made.
The final decision about the suitability of a heart transplant is made only after direct examination of a heart when sternotomy has been made by an experienced surgeon. Consideration should be given to the signs of a concussion of a heart for evaluating its overall function. A heart is perfused with cold cardioplegic solution, and then it is removed and placed in cold crystalloid solution. Transportation is carried out in a special thermoinsulating container.
Anatomy and principle of the operation
The operation is performed under artificial circulation.
Preparing a heart for transplantation, attention is paid to an oval window. If an oval window is functioning, it may be needed to perform its closure. In recent years, many centers have performed the plasty of a tricuspid valve ring for preventing failure of a valve in postoperative period (due to acute pulmonary hypertension). So, according to some studies, the frequency of tricuspid valve inefficiency after cardiac transplantation without tricuspid valve plasty in 5 years was 50%.
Transplanting a heart, the first stage is removal of the ventricles of a heart. Large vessels, left and right atria of a recipient are not removed.
Figure 1. Schematic representation of thoracic organs after removing a heart of a recipient (kardioektomy) under artificial circulation
Then, a donor heart is implanted and grafted.
Various ways of arranging a donor heart in a chest are possible: orthotopic and heterotopic. The last option is accompanied by lungs compression, difficulties of subsequent heart biopsies, need of anticoagulation therapy; nevertheless, this method is a version of a choice for severe pulmonary hypertension.
Figure 2. Heterotopic heart transplantation
Orthotopic heart transplant is performed based on the method of Shumway-Lower (with anastomosis of both atria) or the procedure with bicaval anastomosis. The first method is technically easier and allows reducing time for 10-15 minutes of ischemia. The second method has several advantages; it allows reducing the size of right atrium and reducing the incidence of tricuspid regurgitation.
With prolonged period of ischemia (for example, when transportation is long or sustained release in the presence of heart surgery in the recipient in history, as it happens with implanted ventricular bypass system) can improve the conditions of a donor heart by perfusion of cold blood cardioplegic solution through the coronary sinus donor heart. The principal means of preserving a donor organ is a local cooling.
Figure 3. the method of Shumway-Lower
Figure 4. Bicaval method
Performing heart transplantation, sinus nodes of a donor and a recipient are saved. Approximately in 3 weeks after an operation, having two prongs P can be seen on ECG. In any case, the electrical activity of a heart depends on an autonomous operation of the electrical system of a donor heart and it is not regulated by nerves of a recipient.