Heart Transplantation: The Operation - pediagenosis
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Wednesday, December 11, 2019

Heart Transplantation: The Operation

Heart Transplantation: The Operation
Donor selection
Waiting list mortalit
The appropriateness of using any organ for transplantation must be balanced against the risk of the recipient dying on the waiting list if the transplant does not proceed, and in the knowledge that many other patients who might potentially benefit from transplantation have been excluded from the list because of donor organ shortage. In the first year on the waiting list around 60% of patients will receive a heart, while 10–15% will die waiting.

Heart Transplantation: The Operation, Transplanting the heart

Suitable hearts
As with all organs, donor sepsis and current or recent malignancy are contraindications, apart from primary intracranial malignancy. The heart must be ABO-compatible and lacking HLA anti- gens to which the recipient has pre-existent antibodies; 30–40% of recipients are sensitised in this fashion.
Other considerations include the following.
·   Donor age: older donors have an increased burden of coronary artery disease, and donors over 55 years are seldom used.
·    Donor coronary artery disease is associated with early graft failure, unless corrective surgery is performed to bypass the donor coronary arteries.
·   Donor valvular disease or significant left ventricular hypertrophy. Echocardiography is a useful way to identify diseased valves (some of which can be repaired) and left ventricular hypertrophy. A septal thickness of >1.6 cm is a contraindication to donation.
·     Death from carbon monoxide poisoning with carboxyhaemoglobin level above 20%.
·    Donor size: aim is to use hearts from donors with similar weight to recipient; smaller donor hearts and hearts from females, particularly for recipients with pulmonary hypertension, tend to fare poorly.
·    Left ventricular dysfunction is a common complication of brain stem death, probably related to the catecholamine storm that occurs. With time and donor fluid management some of these hearts will recover and be suitable for transplantation; severe dysfunction (hypokinesia, arrhythmia) is a contraindication.
The donor heart must be macroscopically examined by the retrieving surgeon. In addition, measurement of cardiac output and left-side filling pressures, usually with a Swan Ganz catheter is an essential part of donor assessment.

Transplanting the heart
Removing the recipient heart
The heart is approached through a midline incision dividing the sternum along its length, a median sternotomy. The recipient is placed on cardiopulmonary bypass so the oxygenation and pump functions are provided. Cannulae are placed in the ascending aorta and separate cannulae in the superior and inferior vena cavae.
Blood is then pumped from the vena cavae to the bypass machine and back into the aortic cannula, and the patient is cooled to 30°C. When the donor heart is within 20 minutes of the recipient centre the recipient’s heart is removed. The aorta is cross-clamped and the cavae snared around the cannulae. The aorta and pulmonary arteries are divided just above the valves. Both cavae are divided to leave an adequate cuff for sewing to the donor right atrium. The left atrium is divided along the atrioventricular (AV) groove, leaving a cuff that contains all the pulmonary veins

Bi-caval implantation technique
The bi-caval implantation technique involves leaving the donor right atrium intact and instead performing separate anastomoses with the inferior vena cava (IVC) and superior vena cava (SVC). The benefits of having a normal size atrium include less atrial dysthyhmia, pacemaker requirement, tricuspid regurgitation and right ventricular dysfunction.

Additional considerations
Primary dysfunction of the donor heart is the cause of most early morbidity and mortality. Ischaemic time is very important. Mortality increases in a measurable fashion for every hour after the circulation stops. Good communication is essential between donor and recipient teams to minimise delays.

Previous cardiac surgery
Patients who have previously undergone a median sternotomy for cardiac surgery require much longer for cardiectomy, so it may be necessary to delay the explantation of the donor heart until the recipient team is ready.

Ventricular assist devices
These are removed at the start of the recipient procedure, after opening the chest, and may take additional time 2 or 3 hours compared with the 20 minutes it takes to remove a ‘normal’ heart.

Congenital heart disease
The success of neonatal surgery for congenital heart disease has led to an increasing number of patients coming to require heart transplantation in later life. Many have unconventional anatomy, clear delineation of which is essential before surgery. Some procedures, such as in patients who have had surgery for transposition of the great vessels, may need cannulation of the femoral vessels instead to facilitate cardiopulmonary bypass. Additional lengths of aorta and SVC may be needed to cope with anatomical abnormalities. However, there is no condition, including dextrocardia, that precludes transplantation.

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