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Use of Echocardiography in
Cardiac Donor Assessment


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KIRAN K KHUSH, MD, MAS
Assistant Professor, Cardiovascular Medicine
Stanford University School of Medicine
Stanford, California, USA

kiran@stanford.edu


Transthoracic echocardiography (TTE) has proven to be a very useful screening tool for potential cardiac allograft donors, but many questions and controversies remain regarding the best ways to acquire and interpret the images. Such debates are important to highlight as echocardiography is performed in the evaluation of almost all cardiac donors in the United States today.

The utility of TTE as a screening tool for cardiac donors was first studied in 19881, when TTE was successfully performed in all but one of 74 potential donors. Nine hearts with grossly abnormal echocardiograms (severe LV dysfunction, severe valvular disease) were excluded from transplantation and the remaining 64 grafts were successfully transplanted, despite the presence of mild abnormalities (mild hypokinesis, small pericardial effusions) in 18. In the absence of TTE, 29% of these donor hearts would have been excluded based on clinical criteria alone. This study opened the door to the use of TTE to identify donor hearts that can be used for transplantation despite the presence of concerning clinical factors, such as cardiac arrest and chest trauma.

TTE is certainly convenient, as it is non-invasive, can be performed at the bedside with portable equipment, and does not involve the use of ionizing radiation and nephrotoxic contrast dye. Importantly, TTE can provide an accurate assessment of structural abnormalities such as left ventricular hypertrophy (LVH), valvular abnormalities, and congenital heart defects that may be present in organ donors.1,2 LV size and contractile function can be assessed quantitatively using standard techniques,3 and TTE also provides a comprehensive assessment of LV regional wall motion abnormalities (RWMA). Finally, TTE can provide important qualitative assessment of right ventricular contractility.

There are, however, several important problems to consider when performing TTEs on potential organ donors. First, echo is not universally available and delays in organ procurement may result from trying to get a sonographer and/or echocardiographer to perform and interpret the study, which is often required in the middle of the night. Second, acquiring high-quality diagnostic images can be challenging. Organ donors are intubated, mechanically ventilated, unable to change position or breath-hold, and may have chest trauma. In addition, some hospitals may not have newer ultrasound systems with harmonic imaging that can greatly enhance image quality. Moreover, there is wide variability in the ability of sonographers to acquire high-quality images in technically difficult subjects.

A major limiting factor concerns the accuracy of image interpretation and the major impact that this may have on cardiac allograft utilization. Cardiologists have varying levels of experience in interpretation of echocardiograms and may not be familiar with the classic patterns of LV regional wall motion abnormalities that often result after brain death. Neurogenic injury, as is seen after subarachnoid hemorrhage and brain stem death, frequently causes hypokinesis of the basal septum and basal anterior wall, and spares the apex, corresponding to the distribution of myocardial sympathetic nerve endings and catecholamine release. These and other RWMA patterns that do not follow a coronary artery distribution are unlikely to be caused by myocardial infarction. In one study2, 9/40 hearts with severe RWMA were successfully transplanted, with normalization of LV function post-transplant. All of these patients had normal coronary angiograms. In fact, even measurement of LV wall thickness is subject to error in potential donors, as transient myocardial edema may result from the catecholamine storm that accompanies brain death, and may lead to over-calling LVH. A final technical consideration has to do with LVEF measurements. If the interpreting cardiologist chooses to use an M-Mode technique, which emphasizes basal septal contractile function, the result many significantly underestimate the true LV systolic function.4

It is also important to recognize that LVEF is a load-dependent measure of contractility that varies significantly with changes in preload and afterload that often occur after brain death. Metabolic changes, such as hormone depletion, anemia, hypoxemia, and acidosis may also affect LV contractility. Thus, obtaining a TTE at a suboptimal time may result in a falsely low measure of LV systolic function.

Fortunately, there are several strategies that can be used to improve the quality of TTEs in potential cardiac donors. Intravenous injection of agitated saline can improve visualization of the right ventricle and enhance the tricuspid regurgitation signal, thereby facilitating measurement of pulmonary artery systolic pressure. Use of commercially available ultrasound contrast agents such a Definity® improves LV endocardial border definition and can enable accurate measurement of the LVEF and assessment of RWMA. These agents can be carried and administered by donor management personnel at any hospital.

It would also be possible for donor management personnel, such as coordinators from organ procurement organizations, to carry light-weight, portable, high-quality ultrasound systems with harmonic imaging capability to any donor hospital. These personnel could also be trained to acquire a limited set of echocardiographic images that would be adequate in most cases. Moreover, "core" interpretation of donor TTEs by expert reviewers would be highly desirable and should certainly be feasible in the era of electronic image transfer.

Clearly a challenge in performing donor echocardiography is the ability to distinguish those donors with abnormal cardiac function that is likely to be transient from those that may fail the recipient. There is some evidence that dobutamine stress echocardiography may be useful5,6 but this approach has not been widely adopted. Instead, serial echocardiography can be highly informative. This strategy reassesses ventricular function after optimization of loading and metabolic conditions. In a prospective study of 49 donors hearts with reduced ejection fraction (EF<50%) or RWMA sufficient for the organs to be initially rejected, prolonged donor management resulted in improvement in EF or RWMA in 38 donors, resulting in the successful transplantation of 34 donors hearts.7

In summary, echocardiography is the best imaging method available for assessing anatomic and functional abnormalities in potential cardiac organ donors. Transplant personnel, however, should be aware of the important limitations of this technique and should implement strategies to improve its accuracy and utility in donor evaluation.



Disclosure Statement: The author has no conflicts of interest to disclose.

References:

  1. Gilbert EM, Krueger SK, Murray JL, Renlund DG, O'Connell JB, Gay WA, Bristow MR. Echocardiographic evaluation of potential cardiac transplant donors. J Thorac Cardiovasc Surg. 1988;95(6):1003-1007.
  2. Seiler C, Laske A, Gallino A, Turina M, Jenni R. Echocardiographic evaluation of left ventricular wall motion before and after heart transplantation. J Heart Lung Transplant. 1992;11(5):867-874.
  3. Lang RM, Bierig M, Devereux RB, Flachskampf FA, Foster E, Pellikka PA, Picard MH, Roman MJ, Seward J, Shanewise JS, Solomon SD, Spencer KT, Sutton MS, Stewart WJ. Recommendations for chamber quantification: a report from the American Society of Echocardiography's Guidelines and Standards Committee and the Chamber Quantification Writing Group, developed in conjunction with the European Association of Echocardiography, a branch of the European Society of Cardiology. J Am Soc Echocardiogr. 2005;18(12):1440-1463.
  4. Zaroff J. Echocardiographic evaluation of the potential cardiac donor. J Heart Lung Transplant. 2004;23(9 Suppl):S250-252.
  5. Bombardini T, Gherardi S, Arpesella G, Maccherini M, Serra W, Magnani G, Del Bene R, Picano E. Favorable short-term outcome of transplanted hearts selected from marginal donors by pharmacological stress echocardiography. J Am Soc Echocardiogr.24(4):353-362.
  6. Leone O, Gherardi S, Targa L, Pasanisi E, Mikus P, Tanganelli P, Maccherini M, Arpesella G, Picano E, Bombardini T. Stress echocardiography as a gatekeeper to donation in aged marginal donor hearts: anatomic and pathologic correlations of abnormal stress echocardiography results. J Heart Lung Transplant. 2009;28(11):1141-1149.
  7. Zaroff JG, Babcock WD, Shiboski SC, Solinger LL, Rosengard BR. Temporal changes in left ventricular systolic function in heart donors: results of serial echocardiography. J Heart Lung Transplant. 2003;22(4):383-388.