Cardiac Transplantation and Mechanical Circulatory Support Devices

Indications

Indications for cardiac transplantation include the presence of end-stage heart disease not amenable to standard medical or surgical therapy, New York Heart Association functional class IV heart failure on maximal medical therapy, and an estimated 1-year life expectancy of <50%. This includes patients in cardiogenic shock who require continuous inotropic support or circulatory support, patients with intractable life-threatening arrhythmias unresponsive to more conservative therapies, and patients with refractory angina symptoms from coronary artery disease (CAD) that is not amenable to percutaneous or surgical revascularization. Cardiopulmonary exercise testing, specifically peak oxygen consumption (VO ₂ ) thresholds of <14 mL/kg per minute favors listing for transplantation. Alternatively, a predicted peak VO ₂ <50% may be used as a threshold, especially for women and young patients (younger than 50 years old).

As other therapeutic approaches have improved—from coronary artery bypass grafting to percutaneous interventions to advances in medical therapy for congestive heart failure—patients who need transplantation are generally older and sicker, and have multiple comorbidities. In addition, the spectrum of individuals considered for cardiac transplantation today has been broadened to include older adult patients, children, and newborns. The most common indications for cardiac transplantations in the adult population are cardiomyopathies and end-stage CAD. A minority of transplantations are performed in patients with valvular heart disease, congenital heart disease, and as re-transplantations (e.g., for graft vasculopathy). In children, the leading diagnoses are dilated cardiomyopathies and congenital heart disease.

Potential transplantation patients undergo an intensive screening process by a multidisciplinary team of cardiothoracic surgeons, cardiologists, transplantation coordinators, social workers, dietitians, physical therapists, psychologists/psychiatrists, and financial counselors. The screening ensures not only that the patient needs the transplantation but also that the patient is physically and mentally able to comply with the rigorous posttransplantation medical regimen and has the appropriate social support to undergo transplantation successfully.

Donors

Transplantation donors are individuals who are brain dead but continue to have adequate cardiac function to temporarily support other organ function. Most die of catastrophic intracranial events or trauma. The hearts are carefully evaluated with respect to cause of death, need for cardiopulmonary resuscitation, and use of inotropic support; they undergo ECG and echocardiography to ensure adequate ventricular and valvular function. In men aged older than 45 years, women aged older than 55 years, and patients with other risk factors for CAD, cardiac catheterization and coronary angiography are frequently performed. Donors undergo thorough serological testing to rule out transmissible diseases, and their medical and social histories are evaluated. Donor heart exclusion criteria also include any malignancy with extracranial metastatic potential and systemic sepsis or endocarditis. Ideally, the cardiac donor has not sustained prolonged hypotension or hypoxemia and is younger than 55 years of age. There has been a trend toward more liberal donor selection criteria over the past 15 years, and hearts that have experienced cardiac arrest have successfully been used for transplantation.

Donor–Recipient Matching

Patients accepted for transplantation are placed on a national waiting list maintained by the United Network for Organ Sharing (UNOS). UNOS has a contract with the U.S. government to act as the organ procurement and transplantation network. Patients are evaluated on the waiting list by body size, ABO blood type, medical urgency status, and waiting time.

When a suitable donor is identified, UNOS generates a list that ranks potential recipients by distance from the donor hospital (to minimize the organ ischemic time during travel and implantation), size, ABO blood type, medical urgency, and waiting time. An organ is then offered to a transplantation center of a prospective recipient. If the transplantation physicians believe that the organ is suitable for their patient, arrangements are made to procure the organ and perform the transplantation. On occasion, a potential recipient is precluded from transplantation because of ongoing infection or another potentially reversible contraindication. If the initial center does not accept the organ, it is offered sequentially to all patients on the local list, followed by patients in ever-enlarging geographic circles until the nation is covered. Because of the number of patients actively awaiting transplantation, most hearts are placed within their local or regional areas. Other available organs are likewise matched with potential recipients.

Donor Procedure

After all the organs are allocated, procurement surgeons arrive at the donor hospital, and a coordinated procedure allows simultaneous procurement of all usable organs, often including the heart, lungs, liver, kidneys, and pancreas, and occasionally, the small intestine. The heart explantation procedure depends on whether only the heart will be used or whether the lungs will also be used separately or as a combined heart–lung transplantation. After initial dissection of the aorta and superior and inferior venae cavae, placement of a cardioplegia cannula in the ascending aorta, and completion of the other initial dissections by procurement teams, the donor is systemically heparinized. The superior vena cava is tied off, the left atrial (LA) appendage is amputated, and the inferior vena cava is partially transected to decompress the heart and prevent ventricular distention. The aorta is then cross-clamped, and cardioplegia is infused while the heart is lavaged with ice-cold saline ( Fig. 34.1 ).

Simultaneously, the other organs are flushed with their own preservative solutions and lavaged with cold saline. After completing the cardioplegia infusion, the superior and inferior venae cavae are transected. If only the heart is to be used, the pulmonary veins and pulmonary arteries are divided at the pericardium, and the aorta is divided. If the lungs are to be used, the LA is divided at the midatrial level, leaving enough cuff of the LA for cardiac implantation and cuffs around the pulmonary veins for lung implantation. The pulmonary trunk is divided at its bifurcation to leave enough length on the pulmonary arteries for the lung implantation. If a combined heart–lung transplantation is planned, the two organs are resected en bloc by dividing the cavae, aorta, and trachea, and dissecting the heart–lung block from its mediastinal attachments. The organs are then stored in ice-cold saline in multiple layers of plastic bags to ensure sterility, and they are packed in an ice-filled cooler for transportation to the transplanting center.

Recipient Procedure

Two approaches to orthotopic cardiac transplantation are widely used. In the traditional Shumway and Lower technique, a biatrial anastomosis is performed, in which the donor and recipient atrial cuffs are sewn together. This technique does not require separate caval anastomoses, and therefore, saves time. An alternative technique, the bicaval technique, was developed in the 1990s and consists of sewing separate caval anastomoses. Purported advantages of this technique are related to improved atrial function, decreased risk of arrhythmia or need for permanent pacing, and decreased tricuspid regurgitation. However, in an outcomes analysis of the UNOS database between 1999 and 2005, no survival difference was identified between recipients of bicaval or biatrial orthotopic cardiac transplantation.

When a heart transplantation recipient is already on left ventricular assist device (LVAD) support, as is increasingly the case, chest reentry and recipient cardiectomy can be more complicated. Reentry via redo sternotomy and VAD explant typically requires additional time, which must be factored into the timing of donor cardiectomy to minimize ischemic time.

Bicaval Technique

The operation is fundamentally the same as the biatrial technique. The differences in cardiectomy include developing the groove between the right and left atria to allow their separation. During excision of the heart, the superior vena cava is divided just above the level of the right atrium, and the inferior vena cava is divided just below the coronary sinus. After the aorta and pulmonary artery have been divided, an LA cuff is then created starting at the dome of the LA, carrying the incision inferiorly above the orifices of the right and left pulmonary veins ( Fig. 34.2 ). During implantation, the LA cuff is sewn in a similar manner. Some surgeons place a vent through the right side of the LA suture line to assist in de-airing and to prevent warm blood from accumulating in the heart during the remainder of the implantation. Next, the recipient and donor inferior venae cavae are anastomosed, followed by the superior venae cavae. The pulmonary artery and aortic anastomosis are then completed similarly. An alternative is to complete the LA, inferior vena cava, and aortic anastomoses, and then release the cross-clamp, completing the remaining right-sided anastomoses with the heart beating and reperfused to decrease ischemic time. Weaning from cardiopulmonary bypass is the same as the biatrial technique.