Factors associated with early failure of infrainguinal lower extremity arterial bypass

Article Outline

• Abstract
• Methods
  • Database
  • Sample selection
  • Baseline patient demographic characteristics and comorbid conditions
  • Statistical analysis
• Results
  • Age
  • Race
  • Diabetes mellitus
  • Hematocrit
  • Smoking
  • Bypass configuration and early graft failure
    • Popliteal bypass
    • Infrapopliteal bypass
• Discussion
• Conclusion
• Author contributions
• Acknowledgment
• References
• Copyright

Objectives

We analyzed the Veterans Affairs (VA) National Surgical Quality Improvement Program (NSQIP), a large clinical database, to investigate which factors, other than technical, were associated with a higher incidence of early graft failure in infrainguinal bypass.

Methods

Data are prospectively collected in NSQIP from 123 participating VA Medical Centers. All patients from 1995 to 2003 in the NSQIP database who underwent infrainguinal arterial bypass were identified by Current Procedural Terminology (CPT) codes (CPT is a registered trademark of the American Medical Association, Chicago, Ill, Copyright 2007). Data for 30-day graft failure were evaluated by univariate analysis, and multivariate logistic regression was used to control for possible confounders.

Results

The NSQIP database identified 14,788 patients who underwent infrainguinal lower extremity arterial bypasses during the study period, and 723 acute graft failures (4.9%) occurred. On multivariate analysis, compared with patients aged >70 years, patient ages of <50 and 51 to 60 years were significantly associated with early graft failure (odds ratio [OR], 2.2; 95% confidence interval [CI], 1.6-3.0; P < .001; OR, 1.4; 95% CI, 1.2-1.6, P < .001; respectively); age range of 61 to 70 years was not significantly associated with early graft failure. African American race was also associated with early graft failure, and diabetes mellitus had a negative association with early graft failure (OR, 1.4; 95% CI, 1.3-1.5; P < .001; OR, 0.72; 95% CI, 0.58-0.89; P = .002; respectively). Although smoking was a significant factor for acute graft failure on univariate analysis, it was not significant on multivariate analysis. Multivariate analysis of the type of procedure performed revealed that femoral to popliteal bypass with vein or prosthetic graft was associated with better early graft patency than any of the tibial vessel bypass procedures except for popliteal to tibial bypass with autogenous vein.

Conclusion

These data suggest that factors other than technique have an effect on the 30-day graft failure rates of infrainguinal bypasses. These results help the vascular surgeon to predict more accurately early bypass failure rates while planning the procedure and counseling patients about its prognosis.

Patency of infrainguinal arterial bypass grafts is a constant issue of concern for the vascular surgeon. A failed infrainguinal bypass is associated with poor prognosis for the limb in question, particularly if the graft was initially placed for limb salvage.¹, ², ³ This concern regarding patency has led many investigators to identify characteristics associated with infrainguinal bypass failure, leading to the recommendations of increased surveillance and preemptive interventions on vein grafts.⁴, ⁵

Graft failures are traditionally grouped into early and late. Early or acute failure (≤30 days) is believed to be generally related to technical issues or problems related to inflow or outflow arteries and the adequacy of the conduit.⁶ Other factors may result in early graft failure, however. We have recently published our findings regarding the effects of the type of anesthesia on graft failure and found that general endotracheal anesthesia is associated with a higher incidence of early graft failure.⁷ Late failure, or failure especially >6 months, is usually related to intimal hyperplasia or progression of the atherosclerotic process proximal or distal to bypass location.

Prior publications exploring early graft failure have been from smaller, single-institution series. In this study, we used a large, multi-institutional, and well-controlled database in an attempt to identify patient and procedure characteristics that may have an effect on early graft failure.

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Methods 

Database 

Dedicated staff collects detailed perioperative data from Veterans Affairs (VA) Medical Centers in the VA National Surgical Quality Improvement Program (NSQIP) database. This database has been described in detail in prior reports.⁸ In brief, 123 VA Medical Centers in the United States participate in the NSQIP program by prospectively collecting perioperative data and 30-day specific outcomes on surgical patients.

Sample selection 

Approval to conduct this study was obtained from the Institutional Review Board (IRB) of the Washington, DC VA Medical Center. We queried the database using Current Procedural Terminology (CPT) codes (American Medical Association, Chicago, Ill) for infrainguinal lower extremity arterial bypass procedures from January 1, 1995, to December 31, 2003. The queried CPT codes are listed in Table I. We analyzed the data correlating 30-day graft failure, which was an outcome variable in NSQIP, to various baseline demographic characteristics and comorbid conditions.

Table I. Current Procedural Terminology (CPT) codes queried

Baseline patient demographic characteristics and comorbid conditions 

Patient baseline characteristics included age, sex, and race (African American vs any other race). Clinical characteristics included in the database were history of stroke (with and without a residual deficit), congestive heart failure (CHF), chronic obstructive pulmonary disease (COPD), diabetes mellitus (none vs non-insulin-dependent vs insulin-dependent), need for any assistance with activities of daily living (ADL), American Society of Anesthesiologists (ASA) classification, anesthesia type (spinal vs general endotracheal anesthesia vs epidural), and annual procedure volume at the individual hospital. Current smoking is defined in the NSQIP database as smoking cigarettes ≤1 year of the surgery and current alcohol use as ≥28 alcoholic drinks ≤2 weeks of surgery. Lastly, the database included several preoperative laboratory variables on most patients, including serum albumin, hematocrit, white blood cell count (WBC), platelet count, prothrombin time (PT), partial thromboplastin time (PTT), creatinine, and blood urea nitrogen (BUN).

Statistical analysis 

All of the baseline characteristics were screened for inclusion in the multivariate model using χ² or the Student t test, as appropriate. Any univariate association with a value of P < .25 was included in the initial multivariate model. Multivariate analysis was performed using multivariate logistic regression with hierarchical modeling to account for clustering by region of the country. The final model was checked for goodness of fit using the Hosmer-Lemeshow method. All values of P were two tailed with a significance level of .05. Analyses were conducted using STATA 8.0 software (StataCorp, College Station, Tex).

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Results 

We identified 14,788 patients who had lower extremity surgical bypass procedures during the study period. Baseline demographics are presented in Table II. The patients had the usual demographic pattern for infrainguinal arterial occlusive disease. As would be expected in a VA population, 99% of the patients were men. There were 723 graft failures (4.9%) during the 30-day postoperative period.

Table II. Demographics

Variable	No (%) or average value
Male	14,640(99)
Age, mean ± SD years	66 ± 9.7
Stroke
With neurologic deficit	1477(10)
Without neurologic deficit	976(6.6)
Alcohol use	1715(11.6)
History of smoking	7837(53)
History of CHF	680(4.6)
History of COPD	2706(18.3)
Diabetes mellitus type
Insulin-dependent	3652(24.7)
Oral hypoglycemic medication	2898(19.6)
African American race	2578(17.4)
Albumin, g/dL	3.6
Creatinine, mg/dL	1.4
Blood urea nitrogen, mg/dL	19.4
Hematocrit, %	38
Platelet count, × 103 μL	265
Prothrombin time, seconds	12.8
Partial thromboplastin time, seconds	33.0
White blood count, × 103 μL	8.8

The following clinical factors were not found to be significantly associated with early graft failure by univariate or multivariate analysis: sex, history of stroke, alcohol use, history of CHF, history of COPD, ASA class, need for any ADL assistance, and the volume of procedures preformed at the individual hospital. In addition, the following laboratory values were not found to be associated with early graft failure: albumin, WBC, platelet count, PT, PTT, BUN, or creatinine. The remaining variables discussed in the next sections were found to be associated with graft failure in the multivariate model. All odds ratios (OR) reported were adjusted for anesthesia type, age, diabetic status, African American race, hematocrit, and operation configuration.

Age 

Patients were divided into four groups by age: <50, 51 to 60, 61 to 70, and >70. Patients aged <50 years were found to have an 8.2% early graft failure rate, which was significantly higher (P < .001) than the failure rate of 4.4% in patients >70 years. In addition, when placed in a multivariate model with age >70 years as the referent, patients <50 years had two times the odds of graft failure and patients aged 51 to 60 years had a 40% higher chance of graft failure. In contrast, patients aged 61 to 70 years did not have significantly higher odds of graft failure compared to those >70 years (Table III).

Table III. Age and early graft failure

CI, Confidence interval; OR, odds ratio.

Race 

A total of 173 (6.7%) graft failures occurred in 2578 bypass procedures performed in African Americans. In comparison, 550 (4.5%) graft failures occurred in 10,602 procedures performed in Caucasians. In our multivariate model, we combined all other races (1608 patients who were Hispanic, Asian, and others) with Caucasians because these individual races were too small in number for meaningful multivariate analysis. When we compared the African American group with Caucasian patients, we found that African Americans had an increased OR of 1.4 (95% CI, 1.3-1.5) in the likelihood of having early graft failure (Table IV).

Table IV. Race and early graft failure

CI, Confidence interval; OR, odds ratio.

Diabetes mellitus 

There were 8238 nondiabetic patients, 3652 patients with insulin-dependent diabetes mellitus, and 2898 patients with non-insulin-dependent diabetes. There were 448 early graft failures in the non-diabetic patients (5.5%), 161 early graft failures in patients with insulin-dependent diabetes (4.4%), and 114 early graft failures in patients with non-insulin-dependent diabetes (4.0%). The higher percentage of failures in the nondiabetic patients was significant on univariate analysis (P < .003). In addition, multivariate analysis using nondiabetic patients as the referent group showed a 28% lower chance of graft failure in patients requiring insulin and in those taking oral medication, and both these comparisons were statistically significant (Table V).

Table V. Diabetic status and early graft failure

CI, Confidence interval; OR, odds ratio.

Hematocrit 

The mean hematocrit was 38% for the group, and patients with a higher hematocrit did better with regards to early graft failure vs those with a lower hematocrit. Indeed, for every 1% decrease in the hematocrit <38%, the odds of graft failure increased by 2% (OR, 0.98; 95% CI, 0.98-0.99; P < .001).

Smoking 

Patients with a history of smoking had an early failure rate of 5.4%, and nonsmokers had a graft failure rate of 4.4%. On univariate analysis this difference was significant (P = .009); however, when placed in our multivariate model, the difference was not found to be statistically significant.

Bypass configuration and early graft failure 

A total 8310 femoral–popliteal artery bypass procedures were done. In 4010 patients, the bypass was done with translocated or reversed vein (TLV/RSV), and 154 had acute graft failures (3.8%). An in situ femoral–popliteal artery bypass was done in 795 patients, and 32 had acute graft failures (4.0%). Finally, 3505 patients underwent a femoral–popliteal artery bypass with prosthetic grafts and had 125 early graft failures (3.6%). The difference between these three graft types on univariate or multivariate analysis was not statistically significant (Table VI). The difference in graft failure between above and below the knee configurations could not be analyzed because the group of femoral popliteal bypasses in NSQIP included both types.

Table VI. Femoral to popliteal bypass: vein vs prosthetic and early graft failure

Procedure	Total	Graft failure	Percent	ORa	95% CI	P
Fem-pop bypass
With vein (RSV/TLV)b	4010	154	3.8	Ref	Ref	Ref
In situ	795	32	4.0	1.1	0.99-1.3	.07
With prosthetic	3505	125	3.6	0.91	0.74-1.1	.34

CI, Confidence interval; OR, odds ratio; RSV, reversed saphenous vein; TLV, translocated saphenous vein.

There were 6478 tibial vessel bypass procedures included. Femoral–tibial artery bypass with prosthetic graft was associated with the highest incidence of early graft failure (8.2%). In contrast, autogenous vein popliteal–tibial artery bypass was associated with the lowest incidence of early graft failure (4.7%). In addition, early graft failure occurred in only four (3.7%) of the 109 popliteal–tibial vessel bypasses with prosthetic graft; however, this group was too small to place within the multivariate model. Thus, in the multivariate analysis using femoral–popliteal artery bypass as the referent group, all tibial artery bypass procedures, with the exception of popliteal–tibial artery bypass with vein, were associated with higher odds of 30-day failure (Table VII). Adjuvant techniques used to improve patency of prosthetic infrapopliteal bypasses, such as distal arteriovenous fistula or addition of vein cuff or patch at distal anastomosis, could not be queried in NSQIP because add-on codes for these techniques were only recently added to CPT.

Table VII. Tibial vessel bypass and early graft failure

Procedure	Total	Graft failure, no.	Percent	ORa	95% CI	P
With vein (RSV/TLV)
Femoral–tibial	3344	211	6.3b	1.7	1.5-2.0	<.001
Popliteal-tibial	848	40	4.7	1.3	0.85-2.0	.22
In situ
Femoral–tibial	1312	90	6.9b	1.9	1.7-2.2	<.001
Popliteal–tibial	192	12	6.3b	1.7	1.2-2.3	.001
With prosthetic
Femoral–tibial	673	55	8.2b	2.2	1.7-2.8	<.001
Popliteal–tibial	109	4	3.7	…c	…	…

CI, Confidence interval; OR, odds ratio; RSV, reversed saphenous vein; TLV, translocated saphenous vein.

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Discussion 

Several reports in the literature have focused on technical issues and underlying physiologic factors as the culprit in early infrainguinal bypass failure.⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁴, ¹⁵ In this study, we were able to identify from a large database the following factors to be associated with a higher risk of early graft thrombosis: patients aged <60 years, African American patients, nondiabetic patients, and patients with lower hematocrit levels. In addition, although no difference in the risk of early graft failure was found between femoral–popliteal bypass with vein or prosthetic grafts, all types of tibial vessel bypass procedures were associated with a higher chance of early graft failure compared with femoral–popliteal artery bypass with vein, with the exception of a popliteal–tibial vessel bypass with autogenous vein.

The finding in this study that patients aged <60 years, and particularly those <50 years, have higher incidence of early graft failure has important clinical implications on the management of lower extremity vascular disease. The term virulent disease has been used in smaller series to describe an aggressive form of atherosclerosis that appears in young patients; some reports have indicated that such virulent disease maybe associated with an underlying hypercoagulable state in these patients.¹⁶ Numerous studies have found a poor prognosis for this virulent disease because these patients have higher rates of graft failure, reoperations, and amputations.¹⁷, ¹⁸, ¹⁹, ²⁰, ²¹, ²², ²³

Saltzberg et al¹⁷ studied outcomes in lower extremity revascularization in young diabetic patients and found a 30-day graft failure rate of 11.1%. They postulated that this may be a result of a more aggressive treatment taken in these younger patients with an attempt to perform a bypass to a suboptimal distal target rather than perform a primary amputation.¹⁷ Although this report blamed the inferior results on aggressive surgical behavior, other investigators have attempted to identify other risk factors for graft failure in young patients, such as hypercoagulable states. Eldrup-Jorgenen et al²⁴ studied 20 patients aged <51 who underwent a lower extremity bypass. Four of these patients had a bypass failure, and all four had a known hypercoagulable disorder. Curi et al²⁵ have also suggested that the grafts of patients with a hypercoagulable state have inferior long-term patency; in their series, patients with hypercoagulability were also younger. Thus, younger patients presenting with lifestyle-limiting claudication or tissue loss should be evaluated for hypercoagulability before proceeding with revascularization.²⁶

Our study noted that African American patients were more likely to have an early graft failure compared with all other races. In a study by Huber et al,²⁷ African Americans in Florida were significantly more likely to undergo amputation rather than revascularization compared with Caucasians, and they concluded this was likely due to differences in the severity of disease or disease distribution. More recently, Chew et al²⁸ found poorer primary patency and limb salvage rates in African American patients, who had a 30-day graft failure rate of 12% compared with 5% in Caucasians.

We have studied race as a risk factor in infragenicular occlusive disease and found that when disease severity scores were compared between Caucasians and African Americans, African Americans presenting with symptomatic lower extremity peripheral arterial disease had more advanced occlusive disease in the infragenicular distribution.²⁹ It is possible that this advanced disease in this distribution may lead to higher incidence of early graft failure in this patient population.

Of interest was that patients with diabetes in our study had a lower incidence of early graft failure compared with nondiabetic patients. Other series have also shown that diabetic patients have better outcomes after infrainguinal bypass procedures.³⁰, ³¹ Pomposelli et al³² investigated their experience with dorsalis pedis bypass procedures, 92% of which were performed on diabetic patients, and found the 30-day graft failure rate was 4.2%, which was almost identical to our findings. They commented on the pattern of disease frequently found in diabetic patients in whom the aortoiliac segment and superficial femoral arteries are usually spared, thus allowing for more distal inflow sites and shorter segments of vein conduit for the bypasses.

Similarly, Rutherford et al³¹ found in a series of patients who were classified as difficult distal bypass procedures that diabetic patients fared better with regards to patency compared with nondiabetic patients. The diabetic patients in that series had more autogenous vein grafts and less tobacco use, but even taking these variables into account, diabetic patients who underwent femoral–tibial artery bypass with vein had an “unexplained advantage” with regards to patency.

Patients with a higher hematocrit also had a lower incidence of early graft failure. This may not be clinically relevant, however, because the level of benefit for an increase in the hematocrit by 1% (ie, 38% to 39%) was a decrease in graft failure by only 2%. Thus, we believe that although this difference is statistically significant, it may not be clinically relevant.

Finally, we found that the incidence of early graft failure was not significantly different for femoral–popliteal bypass procedures done with either prosthetic or vein grafts. Numerous studies have found equivalent patency rates for bypasses done with prosthetic and autogenous conduits in the above knee position but worse patency in the below knee position.³³, ³⁴ Unfortunately, because the database is queried by using CPT codes, we could not separate the femoral–popliteal bypasses into above knee and below knee popliteal artery targets for subgroup analysis. We also found that all infrapopliteal bypass procedures had worse early failure rates compared with femoral–popliteal bypass procedures performed with autogenous vein, with the exception of a popliteal–tibial artery bypass with vein. This may be the result of a more distal inflow site requiring a shorter segment of autogenous vein for the bypass. As expected, the femoral–tibial vessel bypass with prosthetic grafts had the highest early failure rate, 8.2%.

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Conclusion 

Although some of the patient factors identified in this study cannot be modified, such as the patient’s diabetic status or race, perioperative management could be adjusted with an understanding of the risk of early graft failure posed by these patients’ conditions. In a patient aged <50 years, optimal nonoperative management and hypercoagulability studies would be warranted before proceeding with an infrainguinal bypass procedure. Although there is a tendency to operate on young patients with claudication to return them to full active walking status, this may not be the most appropriate strategy in light of our results, and the surgeon should be less rather than more aggressive in the surgical management of these patients. Furthermore, bypass especially to the tibial arteries should be strictly reserved for limb salvage situations and every effort should be expended to use an autogenous vein from the most available distal inflow source. Considering these patient characteristics while formulating treatment options and presenting their prognosis to patients would optimize care of patients and their understanding of their disease and the proposed management.

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Author contributions 

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We thank Chris Abularrage, MD, Jonathan Weiswasser, MD, Subodh Arora, MD, Gilbert Aidinian, MD, and Eric Adams, MD.

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