Heart transplantation is the therapy proven to provide the greatest survival benefit for patients with end-stage heart failure. However, the use of this lifesaving therapy is constrained by the availability of suitable organs. According to U.S. Organ Procurement and Transplantation Network and Scientific Registry of Transplant Recipients data as of January 7, 2011, the number of heart transplantations in the United States in 2010 had decreased to 1,934, after having reached a plateau at approximately 2,100 to 2,200 per year for much of the previous decade. There are presently nearly 3,200 patients awaiting heart transplantation in the United States, of whom almost one third have been waiting for >2 years. Median waiting list times for United Network for Organ Sharing status 1 candidates (the most critically ill of patients awaiting heart transplantation) range from 50 to 80 days, depending on the severity of the patient’s status. Despite recent improvements in the survival time of patients awaiting heart transplantation, the ongoing shortage of suitable donor hearts still represents a significant barrier to the optimal care of patients with end-stage heart failure.
Current recommendations for the selection of donor hearts advise echocardiography to exclude structural abnormalities, including moderate or greater degrees of left ventricular (LV) hypertrophy and significant valvular and congenital cardiac abnormalities. Additionally, screening coronary angiography for all male donors aged >45 years and for female donors aged >50 years is frequently performed; angiography may also be used in younger patients if there is a history of cocaine use or risk factors for coronary artery disease (CAD). It is advised that donor hearts aged >55 years be used only for the most critically ill recipients. However, at present, consensus guidelines for the exclusion of donor hearts do not exist, so practice varies somewhat among transplantation centers. Because of the ongoing critical need for donor hearts, it may be time to reevaluate both the type of donor who we consider for organ donation and the way we screen potential donors for occult cardiac disease.
In this issue of the Journal of the American Society of Echocardiography , Bombardini et al. present a new strategy to increase the pool of donor hearts available for transplantation: pharmacologic stress echocardiography screening of marginal donors. Their analysis included 39 marginal donor hearts undergoing screening for transplantation suitability. A “marginal” donor was defined as >50 years old or <50 years old with risk factors for CAD, defined as a history of cocaine use or three or more classic coronary risk factors. Donors met standard neurologic and physiologic criteria for organ donation eligibility. Potential donors underwent standard resting transthoracic echocardiography. If the results were satisfactory, according to the new strategy, standard pharmacologic stress echocardiography was then performed using standard doses of pharmacologic stressor, but without atropine. Dipyridamole was the first-line agent for inducing stress, with three patients receiving dobutamine because dipyridamole was unavailable, unfamiliar to the operator, or contraindicated. Donor hearts that were excluded because of positive results on stress echocardiography underwent pathologic examination. Recipients underwent coronary angiography with intravascular ultrasound 1 month after transplantation and were followed for a median of 14 months.
The results of the study were encouraging. Of the 39 potential donors included, 28 underwent stress echocardiography (11 were excluded after resting transthoracic echocardiography). Of the 19 hearts that were eligible for transplantation, 16 were transplanted. All 16 donor hearts that had normal results on stress echocardiography were free of significant donor-transmitted coronary atherosclerosis (defined as ≥50% focal and noncircumferential lesions in the proximal segment of one or more major epicardial coronary arteries) at the time of coronary angiography. One-year survival was 94%. Three donor hearts were eligible for transplantation but went unmatched to recipients, and all were found to have CAD that was nonsignificant at pathologic examination. Eight hearts that were excluded from donation on the basis of abnormal results on stress echocardiography all showed significant abnormalities, including extensive CAD in six. Another heart that was abnormal on stress echocardiography was transplanted for emergency reasons in a critically ill recipient and was found to have 75% stenosis of a major coronary artery requiring percutaneous coronary intervention at 1-month angiography. The study was a single-center, proof-of-concept trial with a limited number of subjects, and studies in much larger numbers of patients are needed before definitive evidence will exist. However, the results of the study raise some important questions for the transplantation and echocardiography communities to consider.
Consideration of Marginal Donors
The practice of excluding donor hearts on the basis of age has evolved from older studies demonstrating an increased risk for recipient mortality predominantly during the perioperative period. Transplantation medicine has evolved significantly since that time, including improved immunosuppression therapy, surgical techniques, cardiac allograft vasculopathy monitoring, and national coordination to deliver donor hearts to the neediest patients in the shortest period of time possible. More recent studies have found that with these improvements in transplantation medicine, the perioperative mortality associated with older donors has decreased significantly. Indeed, the mean age of heart donors has steadily risen over the past 20 years. The risks associated with transplanting older hearts must be weighed against the risks of a prolonged waiting period for transplantation. Despite the higher short-term risks, there is clearly a long-term survival benefit for United Network for Organ Sharing status 1 recipients receiving older donor hearts compared with waiting longer for a younger donor to become available. It may be that increased screening and acceptance of marginal donor hearts should continue to be reserved for only the most critically ill patients. Or perhaps older potential recipients with more comorbidities (who would have otherwise been excluded from transplantation eligibility) should also be considered for transplantation with older donor hearts. Further information is needed regarding how survival and quality-of-life outcomes compare with those of patients receiving ventricular assist devices, which are now being more widely used for end-stage heart failure. These important issues will require further exploration as the need for donors leads many transplantation centers to consider increasing their use of older hearts for transplantation.
Stress Echocardiography as an Alternative to Angiography
As the gold standard for the detection of CAD in potential donor hearts, coronary angiography is not without limitations. These include the risk for organ damage during or shortly after the procedure, as well as cost, invasiveness, and feasibility. Examples of organ damage include injury to the heart itself (such as coronary artery dissection) or damage to the kidneys, which may also be under evaluation for transplantation, from the administration of iodinated contrast dye. Although relatively low, these risks are not trivial, and strategies to minimize or avoid them all together are worth pursuing. Furthermore, the cost differential between coronary angiography and stress echocardiography is not insignificant. The concept of replacing an invasive test that requires transportation to the cardiac catheterization laboratory with one that could potentially be performed at the bedside is appealing; the importance of making the task of determining eligibility easier for those who perform it should not be undervalued. However, the practicality of bedside stress echocardiography requires further evaluation.
In theory, it may seem more convenient to perform stress echocardiography at the bedside rather than transport the donor to the cardiac catheterization laboratory, but this is not a simple undertaking. Stress echocardiography at most centers is performed in echocardiography laboratories with 12-channel electrocardiographic monitoring, often with specially designed beds that facilitate imaging from the cardiac apex. Proper performance of the test requires dedicated, qualified personnel, including the electrocardiography technician, a physician or specially trained registered nurse who administers the stress agent and supervises the test, and the sonographer who performs the imaging.
Moreover, it can be difficult to obtain diagnostic transthoracic images in ventilated patients. In the present study, two of the 28 donors included required transesophageal imaging because of poor transthoracic image quality. Contrast echocardiography is recommended when two or more LV segments are poorly visualized. Contrast was not used in this study, because of concerns about potential pulmonary toxicity precluding lung donation. However, echocardiographic contrast has not been reported to cause lung damage or be harmful to patients without preexisting pulmonary disease, and its use in this setting would likely provide significant benefit for improving endocardial resolution.
The number of such centers globally that have the expertise to provide semiurgent pharmacologic stress echocardiography is difficult to estimate. It is possible that many centers that do not have timely access to coronary angiography will also lack the ability to perform stress echocardiography in a semiurgent manner. Thus, for many medical centers, diagnostic quality stress echocardiography performed in the critical care setting may be as much a barrier to donor evaluation as timely coronary angiography.
Stress Echocardiography as an Alternative to Angiography
As the gold standard for the detection of CAD in potential donor hearts, coronary angiography is not without limitations. These include the risk for organ damage during or shortly after the procedure, as well as cost, invasiveness, and feasibility. Examples of organ damage include injury to the heart itself (such as coronary artery dissection) or damage to the kidneys, which may also be under evaluation for transplantation, from the administration of iodinated contrast dye. Although relatively low, these risks are not trivial, and strategies to minimize or avoid them all together are worth pursuing. Furthermore, the cost differential between coronary angiography and stress echocardiography is not insignificant. The concept of replacing an invasive test that requires transportation to the cardiac catheterization laboratory with one that could potentially be performed at the bedside is appealing; the importance of making the task of determining eligibility easier for those who perform it should not be undervalued. However, the practicality of bedside stress echocardiography requires further evaluation.
In theory, it may seem more convenient to perform stress echocardiography at the bedside rather than transport the donor to the cardiac catheterization laboratory, but this is not a simple undertaking. Stress echocardiography at most centers is performed in echocardiography laboratories with 12-channel electrocardiographic monitoring, often with specially designed beds that facilitate imaging from the cardiac apex. Proper performance of the test requires dedicated, qualified personnel, including the electrocardiography technician, a physician or specially trained registered nurse who administers the stress agent and supervises the test, and the sonographer who performs the imaging.
Moreover, it can be difficult to obtain diagnostic transthoracic images in ventilated patients. In the present study, two of the 28 donors included required transesophageal imaging because of poor transthoracic image quality. Contrast echocardiography is recommended when two or more LV segments are poorly visualized. Contrast was not used in this study, because of concerns about potential pulmonary toxicity precluding lung donation. However, echocardiographic contrast has not been reported to cause lung damage or be harmful to patients without preexisting pulmonary disease, and its use in this setting would likely provide significant benefit for improving endocardial resolution.
The number of such centers globally that have the expertise to provide semiurgent pharmacologic stress echocardiography is difficult to estimate. It is possible that many centers that do not have timely access to coronary angiography will also lack the ability to perform stress echocardiography in a semiurgent manner. Thus, for many medical centers, diagnostic quality stress echocardiography performed in the critical care setting may be as much a barrier to donor evaluation as timely coronary angiography.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
