Clinical factors associated with long-term mortality following vascular surgery: Outcomes from The Coronary Artery Revascularization Prophylaxis (CARP) Trial

Article Outline

• Abstract
• Methods
  • Screening process
  • Outcomes and statistics
• Results
  • Influence of cardiac risk variables on long-term postoperative survival
  • Clinical identifiers of poor outcome based on presenting vascular problem
  • Multivariate Cox regression analysis and outcome
• Discussion
• Author contributions
• Acknowledgment
• Appendix I. 
• References
• Copyright

Background

Preoperative cardiac risks and clinical indications for vascular surgery are both important determinants of outcome following a vascular operation. Using the nonrandomized cohort from the Coronary Artery Revascularization Prophylaxis (CARP) Trial, we analyzed the predictors of outcome based on the presenting vascular problem and prevalence of comorbid conditions and cardiac risks.

Methods and Results

Between March 1, 1999 and February 28, 2003, 4414 patients were ineligible for randomization in the CARP Trial and their survival was retrieved through the BIRLS system (the Department of Veterans Affairs Beneficiary Identification and Records Locator Subsystem). Surgical indications were either an abdominal aortic aneurysm (N = 1598) or lower extremity ischemia for claudication (N = 1116), rest pain (N = 670), or tissue loss (N = 1030). Patients were screened for major cardiac risks that included a history of angina, congestive heart failure, myocardial infarction, ventricular arrhythmias, pathological q-waves, and diabetes. The absence of multiple cardiac risks, as the sole reason for exclusion from randomization, occurred in 2314 (52.4%) screened patients and their probability of survival at 2.5-year post-surgery was 0.88. This was better than the survival of the remaining excluded patients (N = 2100), which was 0.75 (P < .0001) and the randomized cohort (N = 462), which was 0.80 (P < .0001). By Cox regression analysis, urgent surgery, congestive heart failure, ventricular arrhythmias and creatinine >3.5 mg/dL were significantly associated with long-term postoperative mortality.

Conclusions

Patients without multiple cardiac risks or comorbid conditions have a good outcome following elective vascular surgery. Urgent surgery, creatinine >3.5 mg/dL, congestive heart failure, and ventricular arrhythmias are identifiers of a poor long-term outcome and may justify aggressive strategies for risk-stratification in the postoperative period.

Severe obstructive coronary artery disease is present in a high percentage of patients undergoing vascular surgery.¹, ², ³, ⁴, ⁵ Although screening for multiple intermediate clinical cardiac risk variables is an important component to risk factor stratification in the preoperative period,⁶, ⁷, ⁸, ⁹ the influence of those cardiac risks on long-term postoperative outcome, relative to the nature of the vascular problem and other comorbid conditions has not been prospectively studied in a multicenter trial. The Coronary Artery Revascularization Prophylaxis (CARP) Trial was a clinical trial involving 18 Veterans Affairs Medical Centers, which showed that preoperative coronary artery revascularization prior to an elective vascular operation does not improve long-term postoperative outcome.¹⁰ During the enrollment period, all patients undergoing vascular operations were followed as the registry and the presence of cardiac risks and associated comorbid conditions were enumerated relative to their presenting vascular problem. In the present study, we determined the outcomes of those registry patients according to their presentation for either an expanding abdominal aortic aneurysm or symptoms of lower extremity ischemia. We hypothesized that the absence of multiple preoperative cardiac risk variables as the sole reason for exclusion into the study was an identifier of those patients with the best outcome. We also wished to determine the influence of specific cardiac risk variables and comorbid conditions on long-term postoperative outcome, relative to the nature of the presenting vascular problem.

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Methods 

The Human Rights Committee from the Hines VA Cooperative Studies Program Coordinating Center approved the study protocol and the Cooperative Studies Program Evaluation Committee approved the scientific merit of the research program. The Institutional Review Board (IRB) and Research and Development Committees from participating VA Medical Centers also approved the protocol and screening process.

Screening process 

The registry patients were screened during the main study involving 18 VA Medical Centers (March 1999 through February 2003). Patients were considered eligible for the study if they were scheduled for an elective vascular operation for either an expanding abdominal aortic aneurysm or severe symptoms of arterial occlusive disease involving the lower extremities. Patients were excluded from consideration if they had minimal cardiac risks to justify coronary angiography, required an urgent or emergent vascular operation that precluded a timely cardiac evaluation or had a severe comorbidity that would diminish the probability of long-term survival. Those comorbid conditions included chronic obstructive pulmonary disease (COPD) as defined by an FEV₁ < 1.0 liters/min, chronic renal failure with a creatinine >3.5 mg/dL, advanced liver disease with an albumin <2.5 g/dL, or prothrombin time >1.5 times normal, metastatic cancer, recent stroke within 3 months, dementia, and unstable angina. Patients were also excluded from consideration of the study if they refused, were enrolled in another research study or had prior coronary artery revascularization without evidence of recurrent angina or ischemia.¹¹ A screening form was filled out on each patient undergoing vascular surgery that enumerated the reasons for exclusion as well as the presence of preoperative cardiac risk variables.⁷ The cardiac risk variables that were listed on the screening form included a history of angina, myocardial infarction, congestive heart failure, ventricular arrhythmias that were treated, diabetes, and pathological q-waves on a baseline electrocardiogram (EKG). To ensure an accurate screening process, the surgery volumes from the monthly vascular surgery logs at each site were compared with the number of patients screened. Overall, >95% of all vascular surgical cases were screened, showing excellent agreement between the data sources.

Outcomes and statistics 

The post-vascular surgical survival was retrieved in 4414 screened registry patients with complete identifiers (names and social security numbers) by using the BIRLS system (the Department of Veterans Affairs Beneficiary Identification and Records Locator Subsystem). The randomized cohort for this sub-study also consisted of 462 of the original 510 randomized patients who underwent their intended vascular operation and had a screening form completed just prior to their operation. Survival curves were generated by the product-limit method and intergroup differences were evaluated by the log-rank test. The Cox proportional-hazards model was used to identify significant univariate identifiers of survival (P < .200) among groups of patients defined by preoperative vascular diagnosis. The clinical variables that were listed on the screening form included cardiac risks and exclusionary criteria from the randomization process (Appendix I).¹¹ The presence of diabetes, prior congestive heart failure, angina, prior myocardial infarction, q-waves on a baseline EKG, and ventricular arrhythmias requiring treatment were obtained from the past medical history, and confirmed by the primary admitting physician. For each of these factors, a Cox model with one independent variable was developed. In addition, Cox regression analyses with backward elimination were performed with multiple independent risk variables and interaction terms to determine the simultaneous influence of cardiac risks on outcome among those patients with urgent surgery or severe comorbid conditions. The need for urgent surgery was a clinical decision by the staff surgeon and was based on the perceived risk of any delay associated with a cardiac work-up relative to the perceived benefit of a timely operation for the vascular condition. All nonurgent operations were considered elective operations. Pair-wise interactions were allowed to enter the model and a P value of .05 defined significance. Hazard ratio estimates and 95% confidence intervals were obtained for risk variables in the models. Data are expressed as means and standard deviations and statistical tests were two-sided.

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Results 

Influence of cardiac risk variables on long-term postoperative survival 

Two thousand, three hundred and fourteen registry patients had minimal cardiac risk, as the only exclusion variable from the randomized cohort and their probability of survival at 2.5 years following surgery was 0.88. Two thousand, one hundred additional patients were excluded for other reasons, and their probability of long-term survival following surgery was 0.75, which was lower than the cohort with no cardiac risks (P < .0001). Four hundred and sixty-two patients from the randomized cohort underwent their intended vascular operation and their probability of survival at 2.5 years following surgery was 0.80, which also was lower than the registry patients with minimal cardiac risk (P < .0001).

The demographics and clinical variables of the randomized cohort, excluded registry patients with minimal cardiac risks and remaining registry patients with other exclusions are shown in Table I. As expected, the registry with low cardiac risk did not have multiple cardiac risks and were not excluded because of either comorbid conditions or urgent vascular operations. A small percentage of patients had a history of prior coronary artery revascularization, but those patients were excluded because of lack of evidence of myocardial ischemia by preoperative stress testing. The Kaplan-Meier survival curves for these groups are shown in Fig 1, and underscore the favorable influence of minimal preoperative clinical cardiac risk variables and comorbid conditions on long-term survival following an elective vascular operation.

Table I. Differences in clinical variables are shown for randomized patients and the two groups of nonrandomized patients

Clinical variable	Randomized (N = 462)	Registry-low risk (N = 2314)	Registry-other (N=2100)	P value
Demographics
White race	391(84.6%)	1889(84.6%)⁎	1690(84.5%)⁎	P=.992
Male gender	458(99.1%)	2285(98.8%)	310(98.5%)	P=.482
Cardiac risks
MI	194(41.6%)	255(11.0%)	960(45.7%)	P<.001
Angina	177(38.3%)	107(4.6%)	597(28.4%)	P<.001
CHF	45(9.7%)	47(2.0%)	470(22.4%)	P<.001
Diabetes	178(38.5%)	471(20.4%)	899(42.8%)	P<.001
q-waves	83(18.0%)	14(0.6%)	264(12.6%)	P<.001
V arrhythmias	5(1.1%)	5(0.2%)	83(3.9%)	P<.001
≥2 risks	203(43.9%)	0(0%)	1105(52.6%)	P<.001
No ischemia†	0(0%)	248(10.7%)	357(17.1%)	P<.001
Comorbidity
≥1 comorbidity	0(0%)	0(0%)	417(19.9%)	P<.001
Vascular problem
AAA	155(33.6%)	925(40.0%)	673(32.1%)	P<.001
Claudication	164(35.5%)	755(32.6%)	361(17.2%)	P<.001
Rest pain	57(12.3%)	290(12.5%)	380(18.1%)	P<.001
Tissue loss	86(18.6%)	344(14.9%)	686(32.7%)	P<.001
Urgent surgery	0(0%)	0(0%)	1108(52.7%)	P<.001

Registry-low risk refers to those nonrandomized patients who were ineligible because of insufficient cardiac risk while registry-other refers to those nonrandomized patients who were excluded for other reasons. Data was obtained from a surgical screening form that was completed by the research coordinators at each site prior to the vascular operation.

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• Fig 1. 

  Kaplan-Meier survival curves are shown following vascular surgery for those patients excluded from the main trial because of absence of multiple cardiac risks as the only exclusion factor (N = 2314), the remaining patients who were excluded for other reasons (N = 2100) and the randomized cohort (red; N = 462). The 2.5-year survival following vascular surgery in the excluded patients with minimal cardiac risks was 0.88 compared with 0.75 in all of the remaining excluded patients and 0.80 in the randomized patients (P < .0001). Preoperative cardiac risk variables included a history of angina, prior myocardial infarction, previous diagnosis of congestive heart failure, ventricular arrhythmias that have required treatment, pathological q-waves on a baseline EKG and diabetes.

Clinical identifiers of poor outcome based on presenting vascular problem 

Among the excluded patients undergoing surgery for an expanding abdominal aortic aneurysm, the probability of long-term survival at 2.5-years following vascular surgery was 0.83 (Table II). Survival was lower among those patients with an urgent operation or one or more comorbid conditions, particularly creatinine >3.5 mg/dL. The survival was also lower among those patients with two or more cardiac risk variables, with the highest risk associated with congestive heart failure and ventricular arrhythmias.

Table II. Univariate clinical factors associated with reduced survival are shown for the nonrandomized patients undergoing vascular surgery for an abdominal aortic aneurysm

	Number of patients	2.5-year survival	Hazard ratio (95% CI)	P value
Abdominal aortic aneurysm	1598	0.83	—	—
Cardiac risks⁎
None	865	0.85	Reference	—
One	410	0.84	0.97(0.73,1.29)	.84
Two or more	323	0.77	1.36(1.04,1.79)	.03
CHF	151	0.60	2.58(1.94,3.44)	<.01
V arrhythmias	30	0.62	2.38(1.30,4.35)	<.01
Diabetes	226	0.77	1.38(1.03,1.85)	.03
q-waves			0.70(0.42,1.19)	.19
Urgent surgery	323	0.74	1.87(1.46,2.39)	<.01
Comorbidity†
None	1443	0.84	Reference
One or more	155	0.71	2.13(1.58,2.86)	<.01
Creatinine >3.5 mg/dL	22	0.40	4.00(2.19,7.32)	<.01
Metastatic cancer	45	0.69	1.74(1.02,2.97)	.04
Severe dementia	19	0.51	3.43(1.77,6.67)	<.01
Liver disease	20	0.61	2.48(1.23,5.00)	.01
COPD (FEV1 < 1 liter)	31	0.70	1.59(0.82,3.08)	.17

Among the excluded patients undergoing surgery for ischemic symptoms of the lower extremity, the probability of long-term survival at 2.5-years following vascular surgery was 0.80 and was dependent upon the presenting symptom of either claudication, rest pain or tissue loss (Table III). Univariate analysis revealed that long-term survival was worse in those patients with an urgent operation or one or more comorbid conditions, particularly creatinine >3.5 mg/dL. Long-term survival was also worse with each increment in the number of cardiac risk variables, with the highest risk associated with congestive heart failure and ventricular arrhythmias.

Table III. Univariate clinical factors associated with reduced survival are shown for the nonrandomized patients undergoing vascular surgery for lower limb ischemia

	Number of patients	2.5-year survival	Hazard ratio (95% CI)	P value
Lower limb ischemia	2816	0.80	—	—
Claudication	1116	0.90	Reference
Rest pain	670	0.82	1.62(1.29,2.04)	<0.01
Tissue loss	1030	0.69	2.80(2.31,3.39)	<0.01
Cardiac risks⁎
None	1130	0.85	Reference	—
One	904	0.80	1.36(1.11,1.65)	<.01
Two	438	0.77	1.63(1.30,2.04)	<.01
Three	220	0.71	1.86(1.41,2.46)	<.01
Four or more	124	0.66	2.47(1.81,3.38)	<.01
CHF	366	0.65	2.07(1.71,2.50)	<.01
Diabetes	1144	0.76	1.47(1.26,1.72)	<.01
MI	761	0.76	1.30(1.10,1.53)	<.01
V arrhythmias	58	0.69	2.01(1.34,3.02)	<.01
Angina	464	0.75	1.23(1.01,1.49)	.04
Urgent surgery	785	0.73	1.64(1.40,1.93)	<.01
Comorbidity†
None	2554	0.82	Reference
One or more	262	0.59	2.59(2.11,3.18)	<.01
Creatinine >3.5 mg/dL	106	0.46	3.15(2.37,4.19)	<.01
Metastatic cancer	35	0.53	3.01(1.88,4.82)	<.01
Severe dementia	36	0.54	2.87(1.74,4.71)	<.01
COPD (FEV1<1 liter)	24	0.74	1.53(0.76,3.06)	.236
CVA within 3 months	15	0.57	2.12(0.95,4.74)	.07

Multivariate Cox regression analysis and outcome 

Cox regression analyses were done separately for patients presenting with an expanding abdominal aortic aneurysm and symptoms of lower limb ischemia. Among the patients presenting with an expanding aortic aneurysm, identifiers of poor outcome included urgent surgery, dementia, creatinine >3.5 mg/dL, congestive heart failure, and ventricular arrhythmias with borderline significance (Fig 2). Among patients with symptoms of lower limb ischemia, tissue loss, rest pain, and urgent vascular surgery were associated with an increased risk of death along with metastatic cancer, dementia and creatinine >3.5 mg/dL. Cardiac risks that predicted a worse outcome were congestive heart failure and ventricular arrhythmias (Fig 3).

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• Fig 2. 

  The clinical variables that were associated with an increased risk of mortality at a median of 2.5 years following vascular surgery, as determined by the Cox regression analysis, are shown for those patients presenting with an expanding abdominal aortic aneurysm along with the hazard ratios and 95% confidence intervals.

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• Fig 3. 

  The clinical variables that were associated with an increased risk of mortality at a median of 2.5 years following vascular surgery, as determined by the Cox regression analysis, are shown for those patients presenting with symptoms of lower limb ischemia, along with the hazard ratios and 95% confidence intervals.

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Discussion 

The principal finding of this nonrandomized cohort of the Coronary Artery Revascularization Prophylaxis (CARP) Trial is that the absence of multiple preoperative cardiac risk variables, comorbid conditions, and need for an urgent operation predicts those patients with the best long-term prognosis at 2.5 year following vascular surgery. These patients comprised over 50% of the nonrandomized registry from the CARP Trial and demonstrate that a conservative approach to preoperative risk assessment is associated with a favorable outcome in selected patients at low risk.

An additional finding is that urgent vascular operations and a comorbid condition, particularly creatinine >3.5 mg/dL, were predictive of a worse outcome and along with congestive heart failure and ventricular arrhythmias, were identifiers of those patients with the highest long-term risk of death following the vascular surgery. Although patients in need of an urgent vascular operation may not be deemed suitable for the delays associated with preoperative risk assessment, their poor outcome might justify an additional strategy of risk factor stratification following vascular surgery and prior to discharge from the hospital. This is particularly relevant to those patients with modifiable clinical risks, such as a history of congestive heart failure and ventricular arrhythmias, which have been associated with improved outcomes with additional therapies. The most important comorbid condition with a worse long-term outcome was chronic renal failure, among those patients with a creatinine >3.5 mg/dL. These patients were ineligible from the randomization process but the degree of coronary artery disease may be an important, potentially modifiable determinant of their outcomes that may need to be addressed, particularly in the postoperative period.

Over the past several decades, longitudinal studies of patients undergoing elective vascular operations for either an expanding aortic aneurysm or for lower extremity arterial occlusive disease have emphasized the importance of coronary artery disease as the major determinant of long-term survival following the operation.¹, ³, ¹² Severe obstructive coronary artery disease is present in more than 50% of patients scheduled to undergo vascular surgery¹ and is the major cause of death both early and late following the vascular operation.², ³, ⁴, ⁵ The randomized cohort of patients with severe vascular disease from the CASS trial showed a survival benefit in favor of bypass surgery compared with medically treated patients who were risk-adjusted, supporting a beneficial effect of preoperative coronary artery revascularization.¹³ However, the randomized cohort of the CARP trial showed that an aggressive strategy of coronary artery revascularization with either bypass surgery or percutaneous coronary interventions (PCI) prior to vascular surgery does not improve long-term survival.¹⁰ Since the CASS trial, the potential impact of advanced medical therapy on improving outcomes in patients with coronary artery disease cannot be overemphasized. The wide spread use of beta-blockers, antiplatelet agents, angiotensin converting enzyme inhibitors, and statins in the randomized cohort of the CARP trial throughout the follow-up period may have improved the outcomes in all patients and diminished the long-term survival differences between an initial aggressive vs conservative preoperative strategy. Moreover, in the perioperative period, beta-adrenergic blocking agents, a therapy that has demonstrated improved outcome among vascular patients undergoing surgical procedures,¹⁴, ¹⁵ were judiciously administered to all study patients. This therapy as well as use of statins¹⁶, ¹⁷ provide protection at the time of the surgery and during long-term follow-up and support a conservative approach toward most patients prior to vascular surgery.¹⁸ The advancement of these medical therapies as well as more accurate means of diagnosing and managing patients with acute coronary syndromes may have potentially altered the natural history of patients with advanced peripheral vascular disease so that postoperative causes of morbidity and mortality relate more to chronic illnesses. In the postoperative period, recognition and management of high-risk characteristics such as congestive heart failure and predisposition to ventricular arrhythmias will undoubtedly improve long-term survival, even among those individuals who might not be considered candidates for placement of defibrillators. Although many individuals with heart failure and a history of ventricular arrhythmias might not be deemed suitable candidates for placement of defibrillators, pharmacological therapies including beta-blockers, angiotensin converting enzyme inhibitors (ACEI), statins, and aldosterone inhibitors can certainly improve their long-term outcomes, if those high-risk characteristics are properly identified in the postoperative period.

In summary, among the registry from the CARP trial, the absence of multiple preoperative cardiac risks, as the only reason for exclusion from the randomized trial, identified those patients with the best long-term prognosis following elective vascular surgery. The subsets of patients with a severe comorbidity, notably creatinine >3.5 mg/dL as well as the need for an urgent operation had an increased risk of death and along with congestive heart failure and ventricular arrhythmias, are identifiers of poor outcome following vascular surgery. These findings might justify an aggressive strategy for risk stratification in the postoperative period, targeting those individuals with urgent operations, creatinine >3.5 mg/dL, congestive heart failure, and ventricular arrhythmias.

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Author contributions 

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This study was supported by the Cooperative Studies Program of the Department of Veterans Affairs Office of Research and Development.

Site Investigators – M. Icenogle, M. Langsfeld, S. Pett, (Albuquerque); K. Mavromatis, A. A. Salam, J. D. Vega, (Atlanta); J. Jean-Claude, G. Pinault, J. Ortiz, (Cleveland); P. Frenkel, M. Jessen, J. G. Modrall, (Dallas); W. Krupski, B. Hattler, (Denver); J. Gray, K. Morris, W. Wolfe, (Durham); R. Kerensky, S. Lind, M. Staples, (Gainesville); A. Greene, S. Lalka, T. Sharp, (Indianapolis); M. Moursi, Y. W. Aude, T. Antakli, (Little Rock); G. Pierpont, S. Santilli, (Minneapolis); M. Amidi, S. Muluk, F. Sonel, M. Zenati, (Pittsburgh); J. Edwards, G. Larsen, P. Ravichandran, (Portland); G. Chilton, E. Sako, M. Sykes, B. Toursarkissian, (San Antonio); J. Rapp, M. Ratcliffe, K. Shunk (San Francisco); T. R. Kohler, K. Lehmann, (Seattle); M. Back, D. Novitzky, M. A. Siddique, (Tampa); S. Goldman, D. Morrison, G. Sethi, A. Westerband, (Tucson); D. Baker, R. Ebrahimi, F. Esmailian, B. Singh, (West Los Angeles); D. DePinto, F. Littooy, H. Loeb, (Hines); T. Gavin, K. B. Ramanathan, D. Weiman, (Memphis); S. Khuri, G. Sharma, (West Roxbury); Endpoint Committee – (confirmed endpoints, based on pertinent hospital records): K. Weir, R. Kelly, J. Davenport: Cooperative Studies Program Coordinating Center, Hines, IL – N. Ellis, T. Moritz. W. Henderson, D. Reda, L. Thottapurathu. Clinical Coordinator – C. Jaenicke; Angiography Core Lab – (reviewed all angiograms): K. Weir. Specimen Testing Core Laboratory – (validated perioperative cardiac enzymes): F. Apple (Hennepin County Medical Center). Good Clinical Practice – C. Haakenson. Study Coordinators – D. Robertson (Albuquerque); D. House, (Atlanta); G. Webbs, (Cleveland); A. Swann, (Dallas); W. Klenke, (Denver); K. Swails, (Durham); J. Brown, (Gainesville); M. Rusomaroff, (Indianapolis); R. Pacheco, (Little Rock); J. Weigenant, (Minneapolis); M. DiTommaso, (Pittsburgh); S. Perez, (San Francisco); A. Sorley, (Seattle); A. Esquivel, (San Antonio); S. Thomas, (Tampa); A. Morgan, K. Zadina, (Tucson); L. Cole, (West Los Angeles); J. Maggio, (Hines); R. Thomas, (Memphis); J. Bannister, (West Roxbury); Executive Committee–E. McFalls (Chairman), H. Ward (Co-Chairman), C. Jaenicke, T. Moritz, S. Goldman, W. Krupski, F. Littooy, D. Reda; Data and Safety Monitoring Board – (had nine interim analyses, at 6-month intervals, and made recommendations about the continuation of the trial): N. Hertzer. B. J. Gersh, F. Grover, R. Chappell.

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Appendix I. 

Screening form variables that were entered into the Cox Regression Analysis

Cardiac Risk Variables

Urgent Vascular Surgery

Comorbid Conditions

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