Cardiac Risk of Vascular Surgery
ABSTRACT & COMMENTARY
Synopsis: Recently proposed cardiac risk stratification and management strategies for patients undergoing major vascular surgery are safe, economical, and result in excellent clinical outcomes.
Source: Bartels C, et al. Circulation 1997;95: 2473-2475.
Recently several risk stratification protocols for patients undergoing vascular surgery have been published, including one from the ACC/AHA. However, there is little prospective data about the cost effectiveness of these evaluation and management algorithms. Thus, Bartels and colleagues assessed one of these schema in 203 patients scheduled for abdominal aortic procedures. First, the patients were divided into high- (23), intermediate- (79) or low-risk (101) groups based upon clinical features. Low-risk patients proceeded directly to surgery. Intermediate-risk patients were further stratified by functional capacity, and those able to achieve five METs went straight to surgery. The rest of the patients were treated aggressively, including myocardial revascularization in one patient, or subjected to more extensive cardiac evaluation, including coronary angioplasty in seven; two patients were not operated. Post operative end points in the 201 surgical patients included: 1) cardiac death; 2) myocardial infarction; 3) heart failure; 4) unstable angina; and 5) new arrhythmias. Events 1-3 were considered major. Total mortality was 3.5%, and five of the seven deaths were non-cardiac. The two cardiac deaths (1%) occurred in intermediate- risk patients. Cardiac morbidity was 5%, 10%, and 10% in the low-, intermediate-, and high-risk groups, respectively. Only a diagnosis of coronary artery disease and intraoperative hypotension were significantly associated with cardiac morbidity. Bartels et al conclude that recently proposed cardiac risk stratification and management strategies for patients undergoing major vascular surgery are safe, economical and result in excellent clinical outcomes.
COMMENT BY MICHAEL H. CRAWFORD, MD
The importance of functional status has been advanced by Mangano and Goldman (N Engl J Med 1995;333:1750-1756) and was incorporated into the ACC/AHA Guidelines (Circulation 1996;93:1280-1317), but this concept has not been prospectively tested. Thus, this is the most important information in this study. Functional capacity was assessed by history in those with claudication using the Duke Activity Status Index (Am J Cardiol 1989;64:651-654) or by treadmill testing in the rest. A cut-off level of five METs was used since patients below this level appear to have a poor prognosis in general. The use of functional capacity information was applied differently in this study as compared to the algorithms in the ACC/AHA guidelines. First, low-risk patients with reduced activity levels were not tested further and went directly to surgery. There were no cardiac deaths in this group and morbidity was low (5%). Second, patients in the intermediate-risk group with five METs functional capacity were not evaluated further. This group experienced two cardiac deaths and the same morbidity as the high-risk group (10%). It could be argued that the ACC/AHA approach of further evaluating these patients would have improved the results. Not withstanding these issues, the investigators proved their hypothesis that an evaluation of clinical information and functional status could identify those patients who would profit from further evaluation and treatment, thus avoiding unnecessary, expensive, and potentially risky cardiac testing and therapy in those least likely to benefit from an aggressive approach.
Unfortunately, the paper was concise to the exclusion of other information of potential value. First, we do not learn how many patients had exercise testing and whether the results improved upon the estimated functional capacity by the Duke index. If exercise testing was superfluous, then you could avoid this initial expense. Second, we receive no information on intensive medical therapy and whether this included intraoperative medication with beta blockers or nitrates. Recent data suggest that aggressive perioperative beta blocker therapy may reduce cardiac events in patients undergoing vascular surgery (N Engl J Med 1996;335:1713-1720). Finally, there is no cost analysis, and cost effectiveness cannot be estimated because there is no long-term clinical data. It is conceivable that some of these patients may require further cardiac testing and treatment after hospital discharge, which would have to be considered in estimating cost effectiveness.
At this point, I would consider this study as generally supporting the approach outlined in the ACC/AHA guidelines with the possible caveat that low-risk patients with poor functional capacity may not need further evaluation. All intermediate-risk patients should be evaluated further until it is proven that intermediate-risk patients with good functional capacity are low-risk.
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