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Perioperative- and Long-Term Mortality Rates After Major Vascular Surgery: The Relationship to Preoperative Testing in the Medicare Population

Fleisher, Lee A. MD*†‡; Eagle, Kim A. MD§; Shaffer, Thomas MHS; Anderson, Gerard F. PhD†‡

doi: 10.1213/00000539-199910000-00007
CARDIOVASCULAR ANESTHESIA
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Debate continues regarding the value of cardiovascular testing and coronary revascularization before major vascular surgery. Whereas recent guidelines have advocated selective preoperative testing, several authors have suggested that it is no longer necessary in an era of low perioperative cardiac morbidity and mortality. We used data from a random sample of Medicare beneficiaries to determine the mortality rate after vascular surgery, based on the use of preoperative cardiac testing. A 5% nationally random sample of the aged Medicare population for the final 6 mo of 1991 and first 11 mo of 1992 was used to identify a cohort of patients who underwent elective infrainguinal or abdominal aortic reconstructive surgery. Use within the first 6 mo of 1991 was reviewed to determine if preoperative noninvasive cardiovascular imaging or coronary revascularization was performed. Thirty-day (perioperative) and 1-yr mortalities were assessed. Perioperative mortality was significantly increased for aortic surgery (209 of 2865 or 7.3%), compared with infrainguinal surgery (232 of 4030 or 5.8%); however, 1-yr mortality was significantly increased for infrainguinal surgery (16.3% vs 11.3%, P< 0.05). Stress testing, with or without coronary revascularization, was associated with improved short- and long-term survival in aortic surgery. The use of stress testing with coronary revascularization was not associated with reduced perioperative mortality after infrainguinal surgery. Stress testing alone was associated with reduced long-term mortality in patients undergoing infrainguinal revascularization.

Implications Analysis of the Medicare Claims database suggests that vascular surgery is associated with substantial perioperative and long-term mortality. The reduced long-term mortality in patients who had previously undergone preoperative testing and coronary revascularization reinforces the need for a prospective evaluation of these practices.

Departments of *Anesthesiology, †Medicine, and ‡Health Policy and Management, Johns Hopkins Medical Institutions, Baltimore, Maryland; and §Department of Medicine, University of Michigan School of Medicine, Ann Arbor, Michigan

May 28, 1999.

This work was supported in part by a grant from DuPont Pharma Radiopharmaceuticals.

Address correspondence and reprint requests to Lee A. Fleisher, MD, The Johns Hopkins Hospital, 600 North Wolfe St., Carnegie 280, Baltimore, MD 21287. Address e-mail to lfleishe@welchlink.welch.jhu.edu.

Presented in part at the Association of University Anesthesiologists Annual Meeting in Washington, DC, in May 1997, and the Society of Cardiovascular Anesthesiologists Meeting in Baltimore, MD, in April 1997.

Cardiovascular complications continue to be a significant source of morbidity and mortality in high-risk patients undergoing vascular and major nonvascular surgery (1). The American Heart Association/American College of Cardiology and the American College of Physicians have each proposed guidelines for the preoperative evaluation and management of high-risk patients undergoing noncardiac surgery (1,2). Both guidelines advocate the selective use of preoperative noninvasive cardiovascular imaging before major vascular surgery, based on evidence from cohort studies and expert opinion. Ideally, such recommendations should be validated by randomized clinical trials; however, there are currently no such trials published.

Most of the data supporting the value of preoperative testing before major vascular surgery was derived from cohort studies published in the 1980s. Reporting on data collected in the early 1990s, several investigators demonstrated reduced rates of perioperative morbidity and mortality, and suggested that neither preoperative cardiac imaging nor coronary revascularization is necessary (3–5). Yet, other investigators continue to extol the value of preoperative testing in reducing perioperative mortality, and the actual rate of perioperative mortality from nonacademic centers is unknown. Medicare claims files provide information to determine the mortality rate of vascular surgery in a nationally representative unselected population. The primary specific aim of the current investigation was to determine the rate of 30-day and 1-yr mortality after major vascular surgery to evaluate the role for preoperative testing. Since information on the use of preoperative testing is available in the Medicare files, the secondary aim of the current study was to determine the practice pattern of preoperative testing before major vascular surgery and the relationship between mortality and testing (with or without coronary revascularization) before major vascular surgery.

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Methods

We used a 5% nationally random sample of the Medicare population for the final 6 mo of 1991 and first 11 mo of 1992 to identify a cohort of patients who underwent elective infrainguinal or abdominal aortic reconstructive surgery. This was the most complete and available database at the initial time of analysis and is coincident with a period in which other investigators have suggested that perioperative morbidity and mortality had greatly improved (3,6). All Medicare beneficiaries aged ≥65 yr and living in any of the 50 states or the District of Columbia with both part A and part B coverage were eligible to be in the study. From this population, the Medicare program creates a research data set by randomly selecting 5% of the population based on the final two digits of the beneficiary’s social security number with the final four digits of the social security number assigned randomly. The entire database included 1.2 million individuals, 62% of whom were female, and 84% of whom were Caucasian.

Two groups of individuals were selected according to the presence of a CPT-4 code for vascular surgery. The first group, known as the indexing group, was selected based on the surgical CPT-4 codes present in the last 6 mo of 1991 and first 11 mo of 1992. To confirm that the surgery had occurred, indexing was initially determined using the physician billing database, and confirmed by an episode of inpatient care for the same CPT-4 code. Patients who underwent both aortic and infrainguinal surgery during the same admission were classified as having undergone aortic surgery. Ruptured aortic aneurysms were excluded from the analysis, but the urgency of the operation could not be determined from the claims data. For each patient, the first episode of vascular surgery in the dataset (beginning in July 1991) was used as the indexing case.

Once the index case was identified, the previous 6-mo period was reviewed to determine if preoperative noninvasive cardiovascular imaging (noninvasive stress testing, including exercise and pharmacologic testing with nuclear imaging or echocardiography, coronary angiography, or assessment of ventricular function) or coronary revascularization (coronary artery bypass grafting [CABG] or percutaneous transluminal angioplasty [PTCA]) was performed, based on the presence of one of the appropriate CPT-4 codes. A 6-mo period before the major vascular surgery was used to assess preoperative testing based on constraints related to access to the dataset (i.e. information on cardiovascular testing prior to this period was not available to the investigators). Patients were categorized according to the extent of preoperative evaluation and intervention based on the hierarchical scheme: preoperative CABG, PTCA, stress test, ventricular function test, and no test. Information on the results of the test are not available in the claims data. The primary outcome was death within 30 days of surgery. Each patient was analyzed once, and the date of the first surgical procedure was used for calculation of 30-day outcome. For those index cases that were performed during the second 6-mo period of 1991, a full 1-yr period of follow-up was available. For this subset of individuals, the primary outcome was death at 30 days and 1 yr after surgery.

The incidence of preoperative testing and interventions is reported as percentages by age cohort. Differences in rates of preoperative testing based on surgical procedure and gender were assessed by χ2 or Fisher’s exact test. Additionally, data were analyzed to detect the existence of any associations between practice patterns and outcome. Differences in mortality rates between groups was determined by χ2 or Fisher’s exact test. P< 0.05 was defined as a statistically significant association.

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Results

Perioperative Outcome

A total of 6895 patients undergoing major vascular surgery were identified for the 17-mo period and defined as the index cases. Aortic surgery was performed in 42% of the cohort (2865 individuals), of which 23% (665 individuals) had a preoperative stress test without revascularization, 21% (614 individuals) had a test of ventricular function, 4% (116 individuals) had a prior CABG, 2% (60 individuals) had a prior PTCA, with the remaining 50% of the patients (1,410 individuals) not undergoing any cardiovascular evaluation in the 6 mo before vascular surgery. Infrainguinal surgery was performed in 58% of the cohort (4030 individuals), of which 8% (338 individuals) had a preoperative stress test without revascularization, 21% (840 individuals) had a test of ventricular function, 2% (86 individuals) had a prior CABG, 1% (54 individuals) had a prior PTCA, and the remaining 68% (2712 individuals) had no preoperative testing.

Stress testing (with or without coronary revascularization) was performed significantly more often in the group who had aortic surgical procedures (841 of 2865 individuals), compared with infrainguinal procedures (478 of 4030 individuals) alone (P< 0.01). Stress testing was performed at a similar frequency between men and women for patients undergoing both aortic and infrainguinal surgeries (data not presented).

The perioperative mortality was significantly increased for aortic surgery (209 of 2865 individuals or 7.3%), compared with infrainguinal surgery (232 of 4030 individuals or 5.8%) (P< 0.05). Mortality was similar between males (242 of 4363 individuals or 5%) and females (153 of 2532 individuals or 6%) (P= NS). Figures 1 and 2 demonstrate the total mortality by age for aortic and infrainguinal surgery, respectively. There is a pattern of increasing mortality with increasing age.

Figure 1

Figure 1

Figure 2

Figure 2

For patients undergoing aortic surgery, stress testing with or without coronary revascularization (combined CABG or PTCA) was associated with significantly reduced perioperative mortality than those who did not undergo any testing (3.8% vs 9.0%, P< 0.01) (Fig. 3). Perioperative mortality was significantly less in those who underwent coronary revascularization, compared with stress testing alone (2.8% vs 4.1%, P< 0.05). Those patients who had a preoperative test of ventricular function had the highest rate of perioperative mortality, which was significantly higher than those who underwent stress testing alone or followed by coronary revascularization (8.1% vs 3.8%, P< 0.01), but not compared with the no-testing group.

Figure 3

Figure 3

For patients undergoing infrainguinal surgery, there was no difference in perioperative mortality in those who underwent stress testing with or without coronary revascularization, compared with those who did not undergo any testing (Fig. 4). Taken separately, patients who underwent stress testing without coronary revascularization had a significantly lower rate of perioperative mortality than no testing (3.6% vs 6.6%, P< 0.05), whereas coronary revascularization was associated with a mortality rate of 8.6% vs 6.6% with no testing (P= NS). Those patients who only had a preoperative test of ventricular function had the highest rate of perioperative mortality, which was significantly higher than those who underwent stress testing (9.3% vs 3.6%, P< 0.01) or no preoperative testing (9.3% vs 6.6%, P< 0.05).

Figure 4

Figure 4

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One-Year Outcomes

A total of 1666 individuals had their indexing surgery between July and December 1991, and had a complete 1-yr of follow-up data available for analysis. A total of 233 patients (14%) died within 1 yr of surgery. The incidence of perioperative and long-term mortality by surgical site and preoperative testing is shown in Table 1. Although aortic surgery was associated with a worse perioperative outcome than infrainguinal surgery, 1-yr mortality was significantly increased in the patients who underwent infrainguinal surgery (16.3% vs 11.3%, P< 0.05). The aortic surgery group who underwent stress testing only or followed by coronary revascularization demonstrated a significantly reduced incidence of combined short- and long-term mortality than the group who did not undergo testing. The infrainguinal surgery group who underwent stress testing without revascularization demonstrated a significantly reduced incidence of combined short- and long-term mortality, compared with the group who did not undergo testing; but no difference was observed from the perioperative perspective. There was no difference in outcome between those who underwent coronary revascularization and those who did not undergo testing before infrainguinal surgery, although the number of patients in the revascularization group was small. Patients who underwent ventricular function testing before vascular surgery had the highest 1-yr mortality.

Table 1

Table 1

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Discussion

Our analysis demonstrates that perioperative mortality in an unselected population of Medicare patients undergoing major vascular surgery in the early 1990s was high (>5% as defined in the guidelines) (1). Higher perioperative mortality rates were observed in aortic, compared with infrainguinal surgery; whereas one-year mortality was significantly increased in the infrainguinal, compared with aortic surgery cohort. Preoperative cardiovascular stress testing with or without coronary revascularization was associated with decreased perioperative and one-year mortality in aortic surgery patients, whereas improved outcome was observed at only one year in infrainguinal patients.

Several recent series have reported much lower rates of perioperative mortality and morbidity (<5%) during the same time period, leading the authors of these studies to propose that risk stratification is no longer necessary in all but highly symptomatic patients (4). Many of these reports are from academic medical centers that use both preoperative risk stratification schemes and intensive perioperative monitoring and interventions, and include both young patients as well as the more typical elderly individuals with advanced vascular disease. The current study has the advantage of including a nationally random sample of elderly patients who underwent surgery in a diverse group of hospitals by a diverse group of surgeons. Including a diverse group of surgeons enhances generalizability of our findings, since multiple studies have demonstrated that perioperative mortality varies according to surgeon volume, and our unselected population would include centers with both high and low major vascular surgical volumes (7). The results of consecutive series of patients reported in the literature may not be generalizable to other institutions, whereas the current series would better reflect national practice.

We also included 30-day perioperative outcomes, whereas most reports focus on inhospital death. Although most of the morbidity has previously been reported in the first three days and/or during the hospital admission for the initial surgical procedure, very few reports focus on mortality beyond the initial admission. With the trend toward cost containment, patients are frequently discharged early before all of the effects of the surgical stress have abated; however, the patient is concerned with total morbidity and mortality related to the surgical intervention. Many of these patients may be readmitted for the initial diagnosis, but additional mortality during any subsequent admission would not be included in the “perioperative period.” A longer time horizon allows better assessment of long-term risks and benefits of certain procedures. The current study more accurately reflects overall mortality.

Perioperative mortality was correlated with increasing age, but not gender. Advanced age (>70 years) has been shown to be a risk factor for perioperative cardiac morbidity and mortality in multiple studies; although it has not been evaluated in incremental steps, as in the current analysis (8,9). The implications for mortality of age impacts on the decision to perform preoperative testing and interventions. We observed a marked increase in perioperative mortality for vascular surgery with increasing age, suggesting that older patients might accrue the greatest benefit by identifying occult disease. However, mortality related to coronary revascularization also increases with age and the potential life-prolonging effects decrease, suggesting that any long-term benefit of coronary revascularization in the oldest group may not be realized. The optimal management strategy for such patients may be cancellation of elective surgery if preoperative testing demonstrates significant risk. In contrast, younger patients demonstrated a lower risk of vascular surgery, suggesting a lower perioperative benefit from prior coronary revascularization. In these patients, perioperative mortality may be similar or lower for proceeding directly to vascular surgery, compared with the combined mortality for coronary revascularization and vascular surgery, but a potential life-prolonging effect of the coronary revascularization should be observed. Therefore, age-specific information is critical to the decision process regarding the optimal strategy and should be included in decision models dealing with this question.

Although many of these patients may have undergone cardiac evaluations prior to the indexing surgical procedure, the incidence of testing in our aortic population (29%) is similar to that described by Bartels et al. (10) in which testing was determined based on protocols similar to the American Heart Association/American College of Cardiology guidelines. In that series, 20% of patients underwent diagnostic testing. However, the incidence is lower than suggested by other reports. For example, Eagle et al. (8) proposed that testing only be performed in the subgroup of patients with 1–2 clinical risk factors, which compromised 58% of their population. Importantly, age over 70 years is one of the risk factors. Sixty-eight percent of our population was over 70 years of age, suggesting that this would be the minimum rate of preoperative testing according to the criteria suggested by Eagle et al. (8). The lower rates of testing may reflect more selective testing than previously proposed or cardiac evaluations prior to the current index.

Preoperative testing is used less often in patients undergoing infrainguinal surgery, compared with aortic reconstruction, despite previous literature to suggest that they have a greater number of risk factors and more occult disease (11,12). There are several potential etiologies for the difference in referral. Infrainguinal procedures are often performed for lower extremity ischemia on a semiurgent basis, and interventions based on testing, such as coronary revascularization, may not be an option. Patients with lower extremity ischemia frequently undergo multiple revascularization procedures and may have undergone testing before a surgery performed prior to July 1991. Patients with lower extremity procedures may have undergone cardiovascular evaluation and coronary revascularization before the current indexing procedure because of more advanced cardiac symptomatology, although there is no evidence to support such a claim. Finally, physicians may not refer patients undergoing infrainguinal procedures for further testing based on an impression that such procedures have a low incidence of perioperative morbidity and mortality. Our results support a lower, but still significant, perioperative mortality rate for infrainguinal patients; however, a longer perspective should be considered based on the very high one-year mortality.

We observed an improved perioperative and one-year survival in aortic surgery patients who underwent stress testing or coronary angiography with or without subsequent coronary revascularization, compared with those who did not. This analysis reflects those patients who were referred for a preoperative evaluation and survived the coronary revascularization procedure. Since the indications for surgery are not available in the database, the number of patients who died after prophylactic coronary revascularization is not known. Therefore, there is risk of additional mortality that must be included in the decision to perform preoperative testing for the purpose of coronary revascularization. Two previous decision analyses emphasize the importance of this short-term tradeoff and suggest that the best strategy is very institution-specific (13,14). Particularly when incorporating the one-year mortality data to the previously published decision model by Fleisher et al. (13), the use of preoperative testing and coronary revascularization could be the optimal strategy in the overall Medicare population, although preoperative coronary revascularization would not be indicated at selected institutions with very low overall mortality (<3%). The benefits of preoperative testing without revascularization also deserve comment. Patients with evidence of myocardial ischemia and/or dysfunction, but not revascularized, are treated with aggressive medical therapy. This may include β-blockers, more careful perioperative monitoring, and angiotensin-converting enzyme inhibitor for patients with poor ventricular function. Furthermore, long-term treatment with aspirin and cholesterol-lowering drugs in at-risk patients might also improve outcomes in such patients.

The use of preoperative stress testing or coronary angiography with or without coronary revascularization was not associated with improved perioperative survival in patients having infrainguinal surgery, but was associated with improved one-year survival. Of note, coronary revascularization was not associated with improved survival, compared with a no-testing strategy in this cohort of individuals. This may reflect the small sample size of this group or may reflect the underlying risk of the patients. Several recent series have suggested that patients undergoing infrainguinal surgery have a greater degree of coronary artery disease and perioperative cardiac morbidity than aortic surgery patients (15,16). We were unable to determine this difference from our administrative dataset, and a prospective evaluation would be required to determine if there are subsets of patients who would accrue a benefit. However, the negative findings in the infrainguinal group suggest that the perioperative benefit from coronary revascularization may be small or nonexistent.

Patients who only underwent an assessment of ventricular function before vascular surgery had the highest incidence of perioperative and long-term mortality for both aortic and infrainguinal surgery. One study demonstrated that the use of echocardiography before noncardiac surgery does not provide additional information beyond the clinical history (17). The American Heart Association/American College of Cardiology does not endorse the use of echocardiography to assess ventricular function except for patients with dyspnea of unknown etiology (1). We suspect that patients who underwent such testing had known cardiovascular disease, particularly congestive heart failure. Although we have no evidence to support such a possibility, this would make intuitive sense, given the strong association of poor ventricular function with poor short- and long-term outcomes.

Our study has several limitations. Most importantly, analysis of an administrative dataset can only demonstrate associations and not cause and effect. Additionally, selection criteria for performing preoperative cardiac imaging is unknown. Specifically, we did not determine the individual patient’s comorbidities, history of previous cardiac evaluation, and exercise tolerance, all of which have been proposed as determinants of the appropriateness and value of preoperative cardiac testing. We also could not determine surgeon or institution-specific rates of perioperative mortality, although long-term mortality should not have been influenced by this factor. We attempted to determine if the groups had similar age and gender profiles, but were unable to accurately assess the presence of other risk factors (prior myocardial infarction, congestive heart failure, diabetes). Our rate of mortality may underestimate the actual rate, since only in-hospital deaths are included in the claims data; however, such a potential bias would only strengthen our conclusions that the current rates of 30-day and one-year mortality are high. Our analysis focused on mortality and not on perioperative cardiac morbidity. An analysis for the presence of perioperative acute myocardial infarction was attempted based on the presence of the appropriate ICD-9-CM code. Based on the poor surveillance for perioperative myocardial infarction, we chose to focus solely on the solid outcome of mortality. The categorization with respect to preoperative testing was based on a prior six-month period. This cutoff was based on time constraints related to the dataset and appears reasonable with regard to testing directly related to the planned surgical procedure. Many of these individuals may have had cardiovascular testing and interventions before the six-month period and therefore would be misclassified. Finally, we cannot determine the cause of death, and therefore some of the patients may have died from noncardiac etiologies.

In summary, the cohort of patients who underwent preoperative stress testing with or without coronary revascularization had a lower mortality rate, compared with those who did not undergo any evaluation, particularly when evaluated from a one-year perspective. Considering the rate of mortality observed, this work supports the need for a randomized trial to determine the value of preoperative cardiovascular testing, assessing both perioperative and long-term outcomes.

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References

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