Cardiovascular Risk Evaluation before Kidney Transplantation

Abstract

Candidates for kidney transplantation undergo an extensive evaluation of health status before surgery (1). An important component is a rigorous consideration of the subject’s cardiovascular health. Among the reasons that cardiac disease is particularly relevant to the pretransplant evaluation is the need to fully assess and manage perioperative risk. There are excellent published clinical practice guidelines that link evidence to specific recommendations for the cardiac evaluation of patients undergoing noncardiac surgery (2). Although written for general patient populations, many of these principles can be applied directly to the potential renal transplant recipient. Beyond perioperative risk, the potential transplant recipient has other characteristics that make cardiac evaluation important. First, cardiovascular disease is the major cause of death in this population (3). Almost half of deaths within 30 d of transplantation are due to cardiac events (4). Second, the long-term posttransplant need for immunosuppressive medications may complicate the process of atherosclerotic risk reduction (5). Both steroids and calcineurin inhibitors can increase BP and aggravate dyslipidemia. In addition, clinicians may tend to under-treat with statin drugs because of interactions with calcineurin inhibitors. Third, kidneys for living or cadaver transplants are a precious and scarce resource. Because cardiovascular death is a major reason for eventual graft loss, the balance of risk and benefit for decisions related to cardiac testing may be shifted with this difficult resource utilization/ethical issue in mind. In this editorial I will consider issues that affect the cardiovascular presurgical evaluation of patients who seek renal transplantation. I will place particular emphasis on difficult issues in clinical decision making with respect to the high-risk candidate. The American College of Cardiology (ACC) recommends a stepwise approach to the selection of tests for risk assessment before noncardiac surgery (2). For elective surgery, physicians are asked to determine the level of clinical predictors of risk, much as discussed above, and to categorize patients as having minor, intermediate, or major predictors. It is recommended that patients in the major group go directly to coronary angiography; patients with intermediate predictors should be stratified on the basis of functional status; the ACC recommends that patients with good function proceed to surgery, with poorfunction noninvasive stress testing recommended. The American Society for Transplantation has guidelines refined more specifically for pretransplant evaluation, recommending risk stratification and noninvasive stress testing for candidates at high cardiac risk (1). Decisions as to selection of cardiac testing pathways involve consideration of the complex interplay of test performance characteristics applied to the individual patient. This is the discipline of analytic clinical decision making. The clinician must weigh (1) the accuracy of noninvasive tests (sensitivity and specificity), in light of (2) the individual patient’s risk profile (pretest probability) to understand how well the test will be able to exclude the presence of significant disease (negative predictive value). Positive predictive value, the likelihood that a positive test result predicts actual disease, may be a less important characteristic when trying to rule out the presence of cardiac disease before transplantation. Noninvasive cardiac tests (specifically dipyridamole thallium/sestamibi scintigraphy [DSS] or dobutamine echocardiography [DE]) have been fairly well studied in patients with ESRD. A recent meta-analysis found that transplant candidates with positive noninvasive stress tests may have a greater risk for future cardiac events. For prediction of cardiac death the pooled results indicated a sensitivity of 80%, but a specificity of only 59% (6). For prediction of coronary stenoses in this patient population, most studies have found these tests to have suboptimal accuracy, with sensitivity and specificity 60% (7–11), with some exceptions (12,13). It is my opinion that the study with the greatest evidentiary value was one recently reported by De Lima et al. (8). These investigators studied 126 renal transplant candidates, performing coronary angiography as well as both key noninvasive tests. The primary finding was that DSS had a sensitivity and specificity of only 58% and 67%, respectively, and DSE had a sensitivity of only 44%, with a better specificity of 87%. Furthermore, patients were followed for 4 yr to determine cardiac outcomes. But similar to the results for cardiac stenoses, the noninvasive tests performed with similar poor accuracy for the prediction of future cardiac events. Only coronary angiography was able to reasonably predict patients at risk. The authors concluded that noninvasive testing was probably insufficient for high-risk transplant can