Chapter 281 - Cardiac Transplantation and Prolonged Assisted Circulation Flashcards
Name the current therapeutic options for extraordinary life-extending measures due to advanced heart-failure.
“Current therapeutic options are limited to cardiac transplantation (with the option of mechanical cardiac assistance as a “bridge” transplatation) or permanent mechanical assitance of the circulation.”
Are there any experimental therapies for advanced heart failure?
Yes.
“In the future, it is possible that genetic modulation of ventricular function or cell-based cardiac repair will be option for such patients. Currently, both of the latter approaches are considered to be experimental.”
Briefly explain the history behind cardiac transplantation. How many heart transplants are performed globaly and in the United States?
“Surgical techniques for orthotopic transplantation of the heart were devised in the 1960s and taken into the clinical arena in 1967. The procedures did not gain widespread clinical acceptance until the introduction of “modern” and more effective immunossupression in the early 1980s. By the 1990s, the demand for transplantable hearts met, and then exceeded, the available donor worldwide, acoording to data from the Registry of the International Society for Heart and Lung Transplantation (ISHLT). Subsequently, heart transplantation activity in the United States has remained stable at ~2200 per year, but worldwide activty reported to this registry has decreased somewhat. This apparent decline in numbers may be a result of the fact that reporting is legally mandated in the United States but not elsewhere, and several countries have started their own databases.”
When was the first heart transplant performed?
1967.
Describe the surgical technique for heart transplant as well as the latter technique modifications.
“Donor and recipient hearts are excised in virtually identical operations with incisions made across the atria and atrial septum at mid-atrial level (with posterior walls of the atria left in place) and across the great vessels just above the semilunar valves. The donor heart is generally “harvested” by a separate surgical team, transported from the donor hospital in a bag of iced saline solution, and reanastomosed into the waiting recipient in the orthotopic or normal anatomic position. The only change in surgical technique since this methoed was first described has been a movemenet in recent years to move the right atrial anastomosis back to the level of the superior and inferior venae cavae to better preserve right atrial geometry and prevent atrial arrhythmias.”
Is the transplated heart enervated and, if not, does it respond to physical activity as the normal heart would?
“Both methods of implantation leave the recipient with a surgically denervated heart that does not respond to any direct sympathetic or parasympathetic stimuli but does respond to circulating catecholamines. The physiologic responses of the denervated heart to the demands of exercise are atypical but quite adequate for continuation of normal physical activity.”
Explain the priority system for heart transplant decision in the United States.
In the United States, the allocation of donor organs is accomplished under the supervision of the United Network for Organ Sharing, a private organization under contract to the federal government. The United States is divided geographically into eleven regions for donor heart allocation. Allocation of donor hearts wihin a region is decided according to a system of priority that takes into account (1) the severity of illness, (2) the geographic distance from the donor, and (3) the patient’s time on the waiting list. A physiologic limit of ~3h of “ischemic” (out-of-body) time for hearts precludes a national sharing responsive to input from a variety of constituencies, including both donor families and transplantation professionals.”
Matching is generally based on HLA system.
True or False?
False.
“matching generally is based only on compatibility in terms of AB0 blood group and gross body size.”
“While HLA matching of donor and recipient would be ideal, the relatively small numbers of patients as well as the time contraints involved make such matching impractical.”
What are the patients considered of highest priority?
“At the current time, the highest priority according to severity of illness is assigned to patients requiring hospitalization at the transplantation center for IV inotropic support, with a pulmonary artery catheter in place for hemodynamic monitoring, or to patients requiring mechanical circulatory support - i.e., use of an intra-aortic balloon pump or a right or left ventricular assist device (RVAD, LVAD), extracorporeal membrane oxygenation, or mechanical ventilation.”
“The second highest priority is given to patients requiring ongoing inotropic support, but wihout a pulmonary artery catheter in place. All other patients are assigned a priority accorind to time accrued on the waiting list”
Regarding HLA-matching, one should one use prospective cross-matching before heart transplantation?
“some patients who are “presensitized” and have preexisting antibodies to human leukocyte antigens (HLAs) undergo prospective cross-matching with the donor; these patients are commonly multiparous women or patients who have received multiple transfusions.”
What are the indications and contraindications for heart transplantation?
“Heart failure is an increasingly common cause of death, particularly in the elderly. Most patients who reach what has recently been categorized as stage D, or refractory end-stage heart failure, are appropriately treated with compassionate end-of-life care. A subset of such patients who are younger and without significant comorbidities can be considered as candidates for heart transplantation. Exact criteria vary in different centers but generally take into consideration the patients physiologic age and the existence of comorbidities such as peripheral or cerebrovascular disease, obesity, diabetes, cancer or chronic infection.”
What is the survival rate after heart transplantation?
“A registry organized by the ISHLT has tracked worldwide and U.S survival rates after heart transplantation since 1982. The most recent update reveals survival rates of 83% and 76% 1 year and 3 years after transplantation, respectively, or a posttransplatation “half-life” of 10.00 years. The quality of life of survivors is generally excellent, with well over 90% of patients in the registry returning to normal and unrestricted function after transplantation.”
Which drugs are usually used for imunossupression induction regarding heart transplant?
“Most cardiac transplantation programs currently use a three-drug regimen that includes a calcineurin inhibitor (cyclosporine or tacrolimus), an inhibitor of T cell proliferation or differentiation (azathioprine, mycophenolate mofetil, or sirolimus), and at least a short initial course of glucocorticoids. Many programs also include an initial “induction” course of polyclonal or monoclonal antibodies to T cells in the perioperative period to decrease the frequency or severity of early posttransplantation rejection. Most recently introduced have been monoclonal antibodes (daclizumab and basiliximab) that block the interleukin 2 receptor and may prevent allograft rejection without additional global immunosuppresion.”
How does one detect rejection of the heart allograft?
“Cardiac allograft rejection is usually diagnosed by endomyocardial biopsy conducted either on a surveillance basis or in response to clinical deterioration. Biopsy surveillance is performed on a regular basis in most programs for the first year postoperatively (or the first 5 years in many programs). Therapy consists of augmentation of immunosupression, the intensity and duration of which are dictated by the severity of rejection.”
Survivours of heart transplant might be susceptible to coronary artery disease (CAD). Compare this phenomenon with the “ordinary” atherosclerosis for non-transplanted population.
“Despite usually having young donor hearts, cardiac allograft recipients are prone to develop coronary artery disease (CAD). This CAD is generally a diffuse concentric, and longitudinal process that is quite different from “ordinary” atherosclerosis CAD, which is more focal and often eccentric.”
