Cardiac Risk Stratification for High-Risk Vascular Surgery
Background The best strategy for cardiac risk assessment before high-risk vascular surgery remains controversial. A cardiac risk stratification protocol was evaluated in patients undergoing high-risk vascular surgery. Our investigation paralleled the elaboration of the American College of Cardiology/American Heart Association (ACC/AHA) Guidelines for Perioperative Cardiovascular Evaluation for Noncardiac Surgery and is highly comparable to the proposed guidelines.
Methods and Results A cardiac risk stratification protocol was evaluated prospectively in 203 patients scheduled for aortic surgery. Key points of the study were cardiac mortality/morbidity and cost-effectiveness. Patients were stratified into low (n=101), intermediate (n=79), and high (n=23) cardiac risk after clinical predictors. After stratification, the degree of estimated functional capacity assessed by treadmill exercise and daily living activities and expressed by metabolic equivalents (METs) was critical for further cardiac evaluation. In intermediate-risk patients with an estimated functional capacity <5 METs and in all high-risk patients, noninvasive cardiac testing and/or subsequent medical care were performed. Noninvasive testing was considered necessary in 41 patients, coronary angiography in 7, and myocardial revascularization in 1. Overall hospital mortality was 3.5%. Cardiac mortality and morbidity were 1% and 12.4%, respectively.
Conclusions Cardiac risk stratification for high-risk vascular surgery patients, according to a protocol similar to the ACC/AHA Guidelines for Cardiovascular Evaluation for Noncardiac Surgery, demonstrated excellent clinical outcome. This approach appears to be a safe and economical strategy for preoperative cardiac evaluation.
Coronary artery disease is commonly associated with vascular disease and is the leading cause of morbidity and mortality after vascular surgery.1 Routine clinical evaluation seems to be neither sufficiently sensitive nor specific enough for cardiac risk estimation, especially in a patient group frequently unable to exercise because of lower-extremity claudication.2 3 4 Various cardiac evaluation procedures have therefore been recommended, including preoperative coronary angiography and prophylactic myocardial revascularization procedures.5 6 Although this approach resulted in a low frequency of cardiac complications, mortality is augmented by the risks of invasive diagnostic procedures and coronary artery surgery itself.7 Also, medical expense increases significantly when such combined procedures are used. Higher costs may be justified if specialized cardiac testing and further treatment improve patients’ clinical outcome. However, it remains to be determined which, if any, of the subgroups of patients scheduled for aortic surgery require such an approach. Therefore, the optimal procedure for cardiac risk assessment and further treatment remains uncertain.
The ACC/AHA Guidelines for Perioperative Cardiovascular Evaluation for Noncardiac Surgery were recently published.6 Parallel to the development of these guidelines, we prospectively evaluated a preoperative cardiac risk assessment protocol similar to the ACC/AHA guidelines for patients undergoing high-risk vascular surgery.
Between June 1994 and August 1995, 201 patients underwent major aortic reconstruction (159 men, 42 women; mean age, 64±8 years). Operations had been cancelled in two patients because of untreatable CHF or disabling chronic obstructive pulmonary disease. The indication for surgery was abdominal aortic aneurysm in 109 patients and aortoiliac occlusive disease in 94.
First, functional capacity was assessed by a detailed history using an activity questionnaire scale.8 Patients were stratified into low, intermediate, and high cardiac risk according to clinical predictors (Table 1⇓).
In a second step, all patients had ergometric measurements on a treadmill. Because the treadmill exercise protocol was designed primarily to assess the walking distance, speed and grades of the treadmill were kept constant (2 km/h=1.24 miles/h, 5% grades). Patients who did not suffer from claudication had to fulfill at least 5 METs.
The algorithm used for cardiac stratification is depicted in the Figure⇓. Before surgery, no further cardiac evaluation was performed in low-risk patients and intermediate-risk patients able to exercise at a functional capacity level of ≥5 METs. If treadmill exercise revealed a functional capacity of <5 METs, cardiac workup was initiated in intermediate-risk patients. Noninvasive testing included exercise ECG and stress 201Tl scintigraphy. Patients considered to be at high cardiac risk underwent further cardiac evaluation and/or subsequent medical care. In high-risk patients with inadequate medical treatment of CHF or significant arrhythmias, medical treatment was intensified. If clinical improvement could be achieved, patients proceeded to the operation without further testing.
On postoperative days 1, 3, and 7, cardiac isoenzymes were measured, and a 12-lead ECG was recorded. All measurements were repeated whenever necessary, at the discretion of the treating physician. Adverse cardiac outcome included (1) cardiac death, (2) myocardial infarction, (3) acute CHF, (4) unstable angina, and (5) new arrhythmias requiring treatment. Major morbidity was defined if any of events 1 through 3 occurred.
Data were analyzed with SPSS for Windows. Categorical variables were analyzed by means of two-tailed χ2 test or Fisher’s exact test, where appropriate. Multiple logistic regression analysis was performed with total or major cardiac morbidity as the dependent variable and the clinical risk factors as predictive variables. A value of P<.05 was considered significant. Continuous values are expressed as mean±SD.
Prevalence of estimated cardiac risk and further management are depicted in the Figure⇑. Forty-one patients underwent noninvasive testing. Seven coronary angiographies and one myocardial revascularization were performed. In 13 high- and 23 intermediate-risk patients, subsequent medical care improved CHF, arrhythmias, or arterial hypertension.
Total mortality rate was 3.5% (7/201). Two patients (1%) of the intermediate-risk group died of cardiac causes. No cardiac death occurred in the other subgroups. Noncardiac mortality (n=5) was due to multiorgan failure, stroke, sepsis, and surgery-related problems.
Cardiac morbidity (12.4%) is indicated in Table 2⇓. There was no significant difference between groups for overall cardiac morbidity or major cardiac morbidity (5%, 10%, and 10% for low-, intermediate- and high-risk groups, respectively). Univariate analysis revealed a diagnosis of coronary artery disease (P<.05) and episodes of intraoperative hypotension (P<.01) as significantly associated with cardiac morbidity. There was no overall significance for the models derived from multiple logistic regression analysis (P=.17 and P=.08, respectively).
Patients undergoing major vascular surgery often present a special challenge for cardiologists, vascular surgeons, and anesthesiologists. The physical impairment imposed by claudication may mask the clinical manifestation of coronary artery disease in these patients. The limitations of cardiac risk scores have resulted in an excessive use of preoperative testing and further treatment in the 1990s. The various cardiac testing procedures have strengths and limitations that were recently discussed extensively.6 Preoperative myocardial revascularization seems to be effective in lowering perioperative cardiac morbidity.5 However, no randomized or controlled trial has assessed the overall benefit of prophylactic myocardial revascularization to lower perioperative risk in patients undergoing major aortic surgery. The potential financial expenditures expected from an increased number of vascular surgery procedures in older high-risk patients has recently been outlined.6 9 The main problem is to determine the perioperative risk in these patients while avoiding unnecessary, expensive, and potentially dangerous cardiac evaluation. No test should be performed unless it is likely to influence patient treatment.6
The algorithm studied is based on the assumption that defining clinical predictors and estimating the functional capacity of the patient will correctly identify patients in whom further cardiac evaluation may be profitable. The clinical predictors used were comparable to the ACC/AHA guidelines. Because patients with azotemia (unpublished data) seem to be at higher risk of perioperative events, azotemia was classified as an intermediate clinical predictor. Functional status appears to be an important predictor of major complications in patients undergoing high-risk vascular surgery. Functional status can be estimated from various activity scores or from treadmill exercise protocols.8 10 Patients with a MET level <5 appear to be at increased perioperative risk.10 11 However, patients with moderate or excellent functional status are at low risk when undergoing high-risk vascular surgery.10 In the reported protocol, functional capacity was assessed by estimation of METs from a daily living activity questionnaire and/or treadmill exercise protocol. In contrast to the ACC/AHA guidelines, our algorithm did not warrant further noninvasive testing if a patient with intermediate clinical predictors reached a functional capacity of ≥5 METs. The two cardiac deaths in the patient collective studied occurred in this subgroup. Whether these two deaths could have been avoided by preoperative noninvasive evaluation of intermediate-risk patients with good functional capacity remains uncertain. However, these results support the proposed stratification of patients with intermediate clinical predictors scheduled for high-risk vascular surgery as indicated in the ACC/AHA consensus document.
In patients considered to be at low cardiac risk, no further cardiac evaluation was performed whether these patients reached a functional capacity of 5 METs or not. This is in contrast to the ACC/AHA guidelines. However, no cardiac death and low cardiac morbidity occurred in this subgroup. This approach is supported by Paul et al,12 who were able to exclude the presence of severe or critical coronary artery disease by the absence of clinical markers. They conclude that low-risk patients can be easily identified and may proceed to surgery without further testing. Further studies with a larger patient collective are warranted to decide whether noninvasive testing is appropriate in patients considered to be at low cardiac risk and with limited functional capacity.
Our results indicate that low cardiac mortality and morbidity for patients undergoing high-risk vascular surgery can be achieved by selected use of cardiac testing, amelioration of medical therapy, and invasive treatment according to an algorithm comparable to the ACC/AHA guidelines.
Limitations of the Study
After patients were discharged from the surgical intensive care unit, routine monitoring of possible ischemic cardiac events in the patient group studied was performed only by measurement of cardiac isoenzymes and detected by 12-lead ECG. The incidence of myocardial ischemia could have been underestimated in our study. Since no control group exists, statistical data have to be interpreted cautiously.
Our study did not evaluate the long-term outcome of the patients. Because long-term survival in vascular patients is determined primarily by cardiac events,13 cardiac evaluation and subsequent treatment may be necessary after vascular surgery. In our opinion, this consideration should be kept in mind if cost-effectiveness is discussed for preoperative cardiac evaluation for patients undergoing vascular surgery.
Selected Abbreviations and Acronyms
|ACC/AHA||=||American College of Cardiology/American Heart Association|
|CHF||=||congestive heart failure|
- Received February 17, 1997.
- Revision received April 1, 1997.
- Accepted April 2, 1997.
- Copyright © 1997 by American Heart Association
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