Con: Preoperative thallium testing should not be performed routinely before vascular surgery

P ATIENTS WHO HAVE significant cardiac disease do poorly perioperatively. Goldman et al’ proposed the landmark Cardiac Risk Index, believing that if patients could be stratified preoperatively according to their risk of suffering cardiac events, appropriate management would reduce perioperative cardiac morbidity and mortality. Goldman’s Cardiac Risk Index Score was used extensively for cardiac risk assessment, but its limitations were soon recognized. Jeffrey et al? demonstrated that the incidence of cardiac complications in patients who had undergone abdominal aortic procedures was higher than that predicted by the Cardiac Risk Index. A high prevalence of occult asymptomatic coronary artery disease was thought to be the reason for significant cardiac morbidity. Hertzer et al3 reported a 90% prevalence of angiographically proven coronary artery disease, 60% of which was severe, in patients who presented for vascular surgery. Exercise stress testing was of limited value in vascular patients because of their limited exercise tolerance. No reliable way of assessing coronary artery disease was available unless a significant number of cardiac catheterization procedures were to be performed in vascular surgery patients. Concurrently, dipyridamole-thallium imaging (DTI) was introduced in clinical practice as a means of assessing myocardial blood supply. This test had a number of advantages compared with cardiac catheterization. It was noninvasive; was not dependent on the level of exercise achieved by patients; and it defined the location and extent of myocardium at risk (redistribution), permanently damaged (fixed defect), or normal. Absence of redistribution on DTI was reported to signify virtually no risk of sustaining a perioperative myocardial event (negative predictive value, 95% to lOO%).4 With such a high negative predictive value, DTI was rapidly accepted as the most appropriate test for cardiac risk assessment in vascular surgery patients. Should DTI be recommended as a routine preoperative test in patients scheduled for vascular surgery? The author believes that DTI should not be recommended as a routine preoperative test. This conclusion is based on several factors, which are discussed as follows: (I) the true value of the test in cardiac risk stratification, (2) the effect of a positive DTI test on the perioperative management of the patient and overall outcome, (3) the impact of current incidence of the disease and patient outcome on the utility of DTI, and (4) the cost involved. The major shortcomings of most of the initial studies that showed the high negative predictive value of DTI was that they were retrospective and associated with a selection bias. The results were available to the physicians and influenced their anesthetic and surgical management.5 Prospective studies have not supported these retrospective observations.6-Q Mangano et al6 studied 60 consecutive vascular surgery patients who underwent DTI preoperatively. Caregivers were blinded to DTI results, and no significant difference in perioperative ischemia was noted among patients with normal DTI, with fixed defects, or with thallium redistribution.‘j Baron et al,7 in their study of 457 patients who underwent abdominal aortic aneurysm repairs, showed that the presence of clinical evidence of coronary artery disease and old age were the most important preoperative predictors of an adverse cardiac event, rather than thallium redistribution. Similarly, Seeger et al* could not find a significant difference in cardiac complications between patients with positive DTI (redistribution) and negative DTI (fixed or no defect). Roghi et al9 corroborated these findings in 220 vascular surgery patients and reported that redistribution defects had limited sensitivity (38%) and specificity (63%) to predict adverse cardiac outcomes. Positive predictive value and negative predictive value of redistribution were 14% and 87% in their study.g With the benefits of DTI in question, Eagle et ali0 evaluated the advantage of combining clinical indices with DTI results. DTI per se did not enhance the ability to predict perioperative cardiac morbidity in patients who were already assessed by clinical criteria to be at low risk of sustaining cardiac problems (ie, no Eagle’s criteria: Q waves, diabetes mellitus, age > 70 years, angina, ventricular arrhythmias). Similarly, in patients who had three or more of the criteria defined by Eagle, the chance of having significant coronary artery disease and sustaining perioperative events was high. The presence of thallium redistribution raised the risk only from 50% to 64%; and even in the absence of thallium redistribution, the event rate was 33%.t” Eagle et alto suggested that DTI is indicated in determining the myocardium at risk in patients who are at an intermediate risk by clinical criteria (one or two of Eagle’s criteria). Based on the results of DTI, this selective patient population can then be classified as low or high risk. This suggestion has been validated further in a cohort of 1,081 vascular surgical patients by L’italien et al and meta-analysis of DT imaging (19841994) for risk stratification.r*~** These investigations support that DTI has only a limited role in a selective subset of vascular surgery patients, and routine preoperative screening is not advocated. Another factor that the proponents of DTI have promoted arduously is its value in predicting long-term morbidity and mortality. This is an important observation, but it should not be extrapolated to mean petioperative benefit. It is becoming more evident that it may be more prudent to consider DTI in the overall management of coronary artery disease patients, independent of the plans for surgery. The value of DTI in risk stratification in vascular surgery patients has been discussed (see earlier). It is of more limited value when considering the impact of a positive test on perioperative management. The chance of sustaining a pexioperative myocardial infarction is fourfold greater in a patient with a