Contemporary outcomes after superficial femoral artery angioplasty and stenting: The influence of TASC classification and runoff score

Article Outline

• Abstract
• Methods
  • Intervention
  • Follow-up
  • Secondary interventions
  • Statistical analysis
• Results
  • Demographics and indications
  • Clinical results
  • Secondary interventions
  • Complications
• Discussion
• Author contributions
• Acknowledgment
• References
• Copyright

Objective

A recent randomized trial suggested nitinol self-expanding stents (SES) were associated with reduced restenosis rates compared with simple percutaneous transluminal angioplasty (PTA). We evaluated our results with superficial femoral artery (SFA) SES to determine whether TransAtlantic InterSociety Consensus (TASC) classification, indication for intervention, patient risk factors, or Society of Vascular Surgery (SVS) runoff score correlated with patency and clinical outcome, and to evaluate if bare nitinol stents or expanded polytetrafluoroethylene (ePTFE) covered stent placement adversely impacts the tibial artery runoff.

Methods

A total of 109 consecutive SFA stenting procedures (95 patients) at two university-affiliated hospitals from 2003 to 2006 were identified. Medical records, angiographic, and noninvasive studies were reviewed in detail. Patient demographics and risk factors were recorded. Procedural angiograms were classified according to TASC Criteria (I-2000 and II-2007 versions) and SVS runoff scores were determined in every patient; primary, primary-assisted, secondary patency, and limb salvage rates were calculated. Cox proportional hazard model was used to determine if indication, TASC classification, runoff score, and comorbidities affected outcome.

Results

Seventy-one patients (65%) underwent SES for claudication and 38 patients (35%) for critical limb ischemia (CLI). Average treatment length was 15.7 cm, average runoff score was 4.6. Overall 36-month primary, primary-assisted, and secondary rates were 52%, 64%, and 59%, respectively. Limb salvage was 75% in CLI patients. No limbs were lost following interventions in claudicants (mean follow-up 16 months). In 24 patients with stent occlusion, 15 underwent endovascular revision, only five (33%) ultimately remained patent (15.8 months after reintervention). In contrast, all nine reinterventions for in-stent stenosis remained patent (17.8 months). Of 24 patients who underwent 37 endovascular revisions for either occlusion or stenosis, eight (35%) had worsening of their runoff score (4.1 to 6.4). By Cox proportional hazards analysis, hypertension (hazard ratio [HR] 0.35), TASC D lesions (HR 5.5), and runoff score > 5 (HR 2.6) significantly affected primary patency.

Conclusions

Self-expanding stents produce acceptable outcomes for treatment of SFA disease. Poorer patency rates are associated with TASC D lesions and poor initial runoff score; HTN was associated with improved patency rates. Stent occlusion and in-stent stenosis were not entirely benign; one-third of patients had deterioration of their tibial artery runoff. Future studies of SFA interventions need to stratify TASC classification and runoff score. Further evaluation of the long-term effects of SFA stenting on tibial runoff is needed.

The role of endovascular treatment of femoropopliteal artery occlusive disease continues to evolve. Early experiences with stainless-steel stents showed no benefit over angioplasty alone¹, ², ³, ⁴, ⁵ and stenting was relegated to salvage procedure status in the face of failed angioplasty. More recent randomized studies comparing superficial femoral artery (SFA) angioplasty alone with nitinol stenting have shown a reduced incidence of restenosis with primary stenting.⁶, ⁷ Others have reported⁸ superior patency rates using expanded polytetrafluoroethylene (ePTFE) covered stent grafts (covered stents) compared with angioplasty alone. In addition to angioplasty and stenting, technological advances⁹, ¹⁰, ¹¹, ¹² continue to create new treatment modalities.

With the explosion in endovascular technology, a paradigm shift has occurred in vascular surgery. Reserving open surgery for failures of endovascular therapy, many centers are now using endovascular therapy as a first line treatment¹³, ¹⁴ for chronic lower extremity occlusive disease. A recent randomized trial comparing covered stents with open femoral-popliteal artery bypass¹⁵ found no significant difference in patency rates at 1 year. Another randomized, prospective trial comparing preferential use of endovascular therapy first, vs open surgery¹⁴ demonstrated no significant difference in amputation-free survival at 6 months or in health-related quality of life at 1 year. However, reduced amputation-free survival and increased all-cause mortality were found in the endovascular treatment group after 2 years.

This latter finding raises concerns over the long-term durability of endovascular therapy, and whether it compromises the arterial runoff. A possible explanation for the inferior long-term results of endovascular therapies in the SFA could be a detrimental effect on the runoff arteries in the lower extremity. A similar scenario was shown when ePTFE grafts were compared with saphenous vein grafts for femoral-popliteal artery bypass. Investigators¹⁶ found a higher incidence of patients presenting with grade II acute ischemia, and deterioration of arterial runoff when ePTFE grafts thrombosed, compared with their vein counterparts. Despite the encouraging results of endovascular therapy in the short term, long-term data are lacking. To date, no studies have evaluated the fate of runoff vessels after stent thrombosis or in-stent restenosis. The purpose of this study was to define outcomes of a large series of carefully followed SFA stents, to determine risk factors, and mechanisms of failure, and to determine whether bare metal nitinol stent (bare stent) or covered stent placement adversely impairs arterial runoff over time.

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Methods 

We retrospectively reviewed the records of patients who underwent stenting of chronic femoropopliteal artery occlusive disease at University Medical Center and the Southern Arizona Veterans Affairs Health Care System in Tucson, Arizona between June 2003 and December 2006. Institutional review board approval was obtained from both institutions. Patients with prior stenting of the femoropopliteal arteries were excluded. Demographic features, comorbidities, indications for intervention, indications for revision, and noninvasive vascular laboratory data were recorded. Angiographic and anatomic data including lesion length, lesion type (stenosis or occlusion), TransAtlantic InterSociety Consensus (TASC I,¹⁸ TASC II¹⁹) classification, and Society of Vascular Surgery (SVS) tibial runoff score were tabulated by a single reviewer (DMI) to prevent interobserver error. The SVS runoff score was calculated from the completion angiogram, so any distal embolization caused from the index endovascular procedure would be included in the patient's baseline runoff score. Results were reported according to the recommended SVS reporting standards.¹⁷

Intervention 

All femoropopliteal endovascular procedures followed general guidelines, with some minor differences that were operator dependent. The majority of procedures were performed in an endovascular suite with fixed imaging. The rest were completed in an operating room with a portable C-arm. Nearly all procedures were performed under local anesthesia and conscious sedation. Contralateral femoral access was preferred, reserving ipsilateral antegrade femoral access for patients found to have focal, isolated distal SFA or popliteal artery occlusive disease. Intravenous heparin was routinely administered. Thrombolysis was used selectively if the interventionalist was concerned about a large thrombus burden.

Lesions were generally crossed with 0.035 inch hydrophilic wires. Lesions were preferentially treated with angioplasty and selective stenting. Balloon inflation times range from 30 seconds to 2 minutes. Stents were reserved for residual stenosis greater than 30% and flow-limiting dissections. Long segment disease and embolic lesions were preferentially stented. The type of self-expanding nitinol stent selected was determined by available inventory and operator preference. Stents were routinely postdilated. If more than one stent was required to treat a single lesion, a minimum of 1 cm overlap was used.

Follow-up 

Postprocedure, patients were administered 150-300 mg of clopidogrel orally (if not previously started), and maintained on 75 mg/day for at least 1 month. Patients also received aspirin indefinitely. Surveillance included ankle-brachial index (ABI) and duplex ultrasound of the stented vessel within 30 days, and every 6-12 months thereafter in concert with clinical examinations. For patients with noncompressible vessels, pulse volume recordings, and toe pressures were routinely obtained. Hemodynamic failure was defined as inability to heal an ischemic ulcer, or an increase in ABI less than 0.15.

Secondary interventions 

When patients presented with stent occlusion, the decision to re-intervene depended on the interventionalist taking care of the patient, the patient's symptoms, and patient preference. Some patients refused to undergo either repeat endovascular procedures or open bypass. As a general rule, an attempt to re-establish stent patency was made if the patient had recurrence of symptoms. Patients presenting with stent failure after two to three endovascular procedures typically were recommended to undergo open revascularization. For in-stent restenosis, the threshold for intervention was a flow disturbance within the stented area associated with a decrease in the ABI and a recurrence of symptoms. If a patient developed a flow disturbance in the region of the stent and it was not associated with a decrease in the ABI, or recurrence of symptoms, then the flow disturbance was observed. Most of these patients presented with recurrent ischemic symptoms. The technique used to revise the in-stent restenosis was determined by the operator. For stent occlusions, thrombolysis was preferred. After thrombolysis, if a residual stenosis was found at the proximal or distal end of the stent, angioplasty with or without additional nitinol stents were typically used. If a long residual in-stent restenosis was present, either atherectomy or placement of a covered stent was usually employed.

Statistical analysis 

Data were entered into an Excel spreadsheet (Microsoft, Redmond, Wash). Statistical analysis was performed using Stata, version 9.2 (Stata, College Station, Tex). Kaplan-Meier survival product limit method was applied to patency rates and limb salvage rate. The Cox proportional hazard model was used to calculate covariates of interest on patency and limb salvage rates. χ² test for independence was used on dichotomous variables, and t test was used for the change in runoff scores. Differences of P < 0.05 considered statistically significant.

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Results 

Demographics and indications 

A total of 95 patients (80% male) underwent stenting of chronic femoropopliteal occlusive disease in 109 legs. The distribution of comorbidities is delineated in Table I. Smoking was defined as active smoking. Chronic renal insufficiency was defined as serum creatinine >1.5 mg/dl. Hypertension was defined as requirement of ≥1 antihypertensive medications. Diabetes mellitus includes both type I and type II. Eight (8%) patients had end-stage renal failure. Indications for intervention included claudication in 71 limbs (65%), ischemic rest pain in 12 limbs (11%), and tissue loss in 26 limbs (24%). Thirty-one patients (28%) underwent adjuvant inflow or outflow procedures, not all were performed concurrently. Thrombolysis was used in 19% of cases. Three patients had undergone previous femoral-popliteal artery bypass, and one patient had a prior angioplasty of the SFA in an area separate from the stent placement. The TASC classifications and runoff scores are summarized in Table II. The frequencies of stent types are listed in Table III.

Table I. Demographic and clinical data

Characteristic	Number
Male	76(80%)
Diabetes mellitus	42(44%)
Tobacco use (active)	34(36%)
Hypertension	80(84%)
Hyperlipidemia	72(76%)
Coronary artery disease	45(47%)
Chronic renal insufficiency	24(25%)
Indication	Number
Claudication	71(65%)
Ischemic rest pain	12(11%)
Tissue loss	26(24%)

Table II. Angiographic anatomic data

Category	TASC I (2000)	TASC II (2007)
A	19(17%)	31(28%)
B	32(30%)	49(45%)
C	46(42%)	17(16%)
D	12(11%)	12(11%)
Runoff score	Number
1-3	42(39%)
3.5-5	15(14%)
5.5-7	32(29%)
7.5-10	20(18%)

TASC, TransAtlantic InterSociety Consensus classification.¹⁸, ¹⁹

Runoff score published by the Society of Vascular Surgery.¹⁷

Table III. Stent data

Primary stent	Number
Viabahn (W.L. Gore & Assoc., Inc., Flagstaff, Ariz)	19(17%)
Luminex (C.R. Bard, Inc., Murray Hill, NJ)	18(16%)
Protégé (EV3, Plymouth, Minn)	16(15%)
Symphony (Boston Scientific, Natick, Mass)	15(14%)
Zilver (Cook Medical Inc., Bloomington, Ind)	13(12%)
Absolute (Abbott Laboratories, Abbott Park, Ill)	6(6%)
Xpert (Abbott)	5(5%)
Smart (Cordis Corp., Miami Lakes, Fla)	3(3%)
Xceed (Abbott)	1(1%)
Mixed (Absolute/Protégé)	1(1%)
Nitinol (not specified)	12(11%)
Total	109

Clinical results 

The mean lesion treatment length was 15.7 centimeters (cm) (range 2-43 cm, standard error = 1.06). An average of 1.9 stents (range 1-5) was used for each limb. The distribution of stent types is shown in Table IV. The mean pre- and postintervention ABI were 0.59 and 0.89, respectively (mean change 0.30). Fifty-five (50%) limbs underwent intervention for native arterial occlusions; 11 (10%) were in the popliteal artery. Two of the 11 stents placed in the popliteal artery crossed the knee joint; the other nine popliteal stents were placed in the above-knee segment. Mean runoff score was 4.6. A total of eight patients (7%) ultimately required amputation (mean 3.1 months), only one underwent open bypass prior to amputation. All of the eight patients that required amputation initially presented with critical limb ischemia. Seven patients (6%) underwent open bypass for stent failure. The average follow-up was 16 months (range 0.25-44). A total of 72 patients were available for follow-up at 1 year and eight patients at 3 years. The primary, primary-assisted, secondary patency and limb salvage rates were 63%, 70%, 78%, 75% at 1 year and 52%, 64%, 59%, 75% at 3 years (see Fig 1, Fig 2). By Cox proportional hazards analysis, hypertension (hazard ratio [HR] 0.35), TASC D lesions (HR 5.5), and runoff score > 5 (HR 2.6) significantly affected primary patency (Table IV). Although gender did not significantly affect primary patency, there was a trend for women (37%) to develop stent thrombosis or clinically significant in-stent restenosis, compared with men (29%). Primary patency rates for TASC A and B lesions vs C and D lesions were calculated for both TASC I (2000¹⁸) and TASC II (2007¹⁹), but were not significantly different (Fig 3, Fig 4).

Table IV. Cox proportional hazard evaluating covariates against primary patency

TASC, TransAtlantic InterSociety Consensus classification.¹⁹

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• Fig 1. 

  Patency data.

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• Fig 2. 

  Limb salvage data (critical limb ischemia only).

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• Fig 3. 

  Patency data stratified by TASC 1 (2000) classification. TASC, TransAtlantic InterSociety Consensus classification.¹⁸

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• Fig 4. 

  Patency data stratified by TASC II (2007) classification. TASC, TransAtlantic InterSociety Consensus classification.¹⁹

Secondary interventions 

A total 33 patients presented with either stent occlusion or stent restenosis. Twenty-one of these patients initially underwent intervention for claudication, four for ischemic rest pain, and eight for tissue loss. Twenty-four patients developed stent occlusion at a mean of 5.2 months after implantation; nine patients developed in-stent restenosis at a mean of 9.9 months after implantation. No specific peak systolic velocity (PSV) threshold criteria were used to mandate repair of in-stent restenosis. Only stents identified to have flow disturbances associated with a decrease in the ABI and recurrence of symptoms underwent angiographic evaluation and secondary interventions. Of the stents that underwent repair of in-stent restenosis, the average PSV was 361 cm/sec (range 220-467 cm/sec). Only one stent had a PSV less than 300 cm/sec; this patient had a decrease in the ABI from 0.9 to 0.68 and recurrence of claudication symptoms. The average decrease in ABI for patients undergoing secondary intervention for in-stent restenosis was 0.43 (range 0.10-0.88).

Of 24 patients with stent occlusion, nine underwent no further endovascular treatment (one bypass, two amputations, six no intervention). The remaining 15 patients with stent occlusion underwent endovascular revision; 10 re-occluded (4.1 months), one underwent amputation (2 months), two developed restenosis, and two required no further revisions. Ultimately, only five of the 15 patients who underwent endovascular revision for stent occlusion were patent at last follow up (15.8 months after reintervention). All nine patients that developed in-stent restenosis remained patent after reintervention; eight remained patent with an average follow-up of 20 months after a single revision, and one required retreatment 6 months later. The endovascular techniques used to treat in-stent restenosis were as follows: 11 covered stents (30%), 8 atherectomies (22%), 6 nitinol stents (16%), 5 angioplasties (13%), and 7 patients that underwent thrombolysis alone (19%). When comparing patients that developed stent occlusion with patients that developed in-stent restenosis, the two groups were similar. Patients that developed stent occlusion had a mean treatment length of 19.1 cm, an average runoff score of 1.8, and had claudication as the indication in 63% of patients. Patients that developed in-stent restenosis had a mean treatment length of 12.4 cm, a mean runoff score of 1.8, and had claudication as the indication in 67% of patients.

We analyzed the patients' presenting symptoms when stent occlusion or restenosis was diagnosed. Eight of the 33 patients (24%) presenting with either stent occlusion or restenosis, had grade II acute ischemia (pain with or without neurologic impairment). The remaining 25 patients that presented with either stent occlusion or restenosis presented with recurrence of their original symptoms, but not acute grade II ischemia. None of the patients that underwent secondary intervention were asymptomatic. Among the eight patients that presented with acute grade II ischemia, four initially underwent intervention for claudication. Seven patients had stent occlusion, and one had a long segment, high grade stenosis. Following reintervention, six (75%) presented a second time with recurrent stent failure, three of whom presented again with grade II ischemic symptoms. Only two of the eight stents ultimately remained patent at long-term follow up. Among the remaining 25 patients that presented with stent failure and did not have grade II ischemia, 16 underwent endovascular revision; only six (37%) presented a second time with stent failure (two with acute grade II ischemia), and nine (56%) ultimately remained patent at long-term follow up.

Comparing stent types, the mean lesion treatment length was 25.4 cm in patients that had covered stents placed at their initial intervention, and 13.7 cm in those who had bare stents placed. Claudication was the indication for the initial intervention in 17 (89%) of patients that had covered stents placed, and tissue loss in two (11%). In contrast, claudication was the indication in 54 (60%) patients that had bare stents placed, rest pain in 12 (13%), and tissue loss in 24 (27%). The SVS runoff scores were 3.92 and 4.79 in patients with covered stents and bare stents, respectively. In patients that presented with either initial stent occlusion or restenosis, patients that had covered stents were statistically more likely to present with acute ischemic symptoms (Fisher exact, P = .047) than patients with bare stents. The primary patency rates between covered stents and nitinol stents were not significantly different (P = .48), but because of the small number of covered stents, the standard error became greater than 10% after 2 months.

We also analyzed the arterial runoff in patients presenting with either stent occlusion or stenosis. Of the 24 patients who underwent endovascular revision for either occlusion or restenosis, 22 had adequate visualization of the tibial arteries to determine the runoff score. An additional patient with untreated stent occlusion underwent angiography and had sufficient visualization of the tibial arteries to determine the runoff score. Eight patients (35%) had worsening of their runoff score from an average score of 4.1 to 6.6 (P = .002). The deterioration in the runoff score occurred an average 12 months (range 2-24 months) after the initial runoff score had been calculated from the completion angiogram. Among these eight patients, five presented with occlusion, and three presented with stenosis. The average lesion treatment length was 17 centimeters. Only one of these eight patients had a covered stent.

We also reviewed the angiograms of the 24 patients that underwent endovascular revision to see if stent fracture had occurred. Only two stent fractures were identified, both were Luminex stents. One was the stent that became infected and required removal. It was placed in the above knee popliteal artery, did not cross the knee joint, and was removed 3 months after implantation. The other stent was placed in the distal superficial femoral artery and was associated with stent occlusion 14 months later.

Complications 

A total of 36 complications (Table V) were identified in 30 patients (28%). The most common complications were early (on table or <30 days) thrombosis (9%), hemodynamic failure (6%), and perforation (5%). Hemodynamic failure was defined as either as an increase in ABI less than 0.15 (three patients), or a failure to heal ischemic ulcers, which occurred in four (4%) patients with tissue loss. All other patients improved their symptoms. All five perforations were treated by endovascular methods (three covered stents, two coils). Three patients (3%) died (12, 18, and 18 days postprocedure). All three patients that died within 30 days of stent implantation were treated for tissue loss. These patients were ill prior to the procedure, died at home, and did not sustain any other known complication in the periprocedure period. Of the two infectious complications, one patient developed an infected stent requiring stent removal, and open bypass. The other developed a peri-stent abscess that was drained percutaneously and resolved. This patient had bacterial endocarditis that likely preceded stent placement. Both of the infectious complications occurred in patients that had bare nitinol stents.

Table V. Complications (≤30 days)

Complication	Number
Early thrombosis	10(9%)
Hemodynamic failure	7(6%)
Perforation	5(5%)
Death ≤30 days	3(3%)
Pseudoaneurysm	2(2%)
Hematoma	2(2%)
Distal embolization	2(2%)
Deep venous thrombosis	2(2%)
Infection	2(2%)
Acute renal failure	1(1%)

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Discussion 

The range of reported outcomes for endovascular treatment of femoropopliteal artery occlusive disease fluctuates widely. With the recent explosion of technological advances, numerous treatment options are available, and no single algorithm is widely accepted. Since treatment preferences vary by providers and region, comparisons with the literature are difficult. Reported series may differ with respect to whether angioplasty and selective stenting vs primary stenting is the preferred treatment, the average lesion treatment length, and whether technical failures are included in patency data. Other series have reported restenosis⁶, ⁷, ²⁸ rates instead of patency rates. Furthermore, some reports mix iliac or tibial artery occlusive disease with femoropopliteal disease, making comparisons even more challenging. Clearly, lesion length has been demonstrated to affect patency,¹⁸, ¹⁹, ²⁰ with long lesions faring poorly compared with short focal ones. Similarly, nitinol stents have been found to have superior patency²¹ compared with the older stainless steel devices.

Despite the difficulties interpreting the literature, our results are comparable with other similar series (see Table VI). Some reports demonstrated primary patency rates of 70%-85% at 1 year with angioplasty²², ²⁴ or stenting.²⁷ These series describe treatment for relatively short lesions. Our series consisted of long (nearly 16 cm) segment disease, among the longest reported in the literature. Two other reports²⁵, ²⁶ of femoropopliteal stenting for long (16 cm) segment disease demonstrated similar results, 56%, and 54% 1 year patency vs 63% in our study.

Table VI. Comparative results of published series on endovascular therapy for femoropopliteal artery occlusive disease

Series	Number treated	Average lesion length	Primary patency	Technical failures included	Factors effecting patency (RR)
Johnston 199222 (PTA only)	254	<10cm	70% 1 y	4%	Runoff
			57% 2 y
			50% 3 y
			43% 5 y
Jamsen 200223 (PTA only)	218	5.2cm	46% 1 y	16.5%	Runoff
			25% 5 y
Clark 200424 (PTA only)	219	4cm	87% 1 y	5%	Runoff (8.5)
			80% 2 y		Diabetes (5.5)
			69% 3 y		Renal failure (4.0)
			55% 5 y
Cheng 200325 (Stent only)	73	16cm	56% 1 y	0%	Indication
			35% 2 y		Lesion > 10 cm
			22% 4 y
Sabeti 200526 (Stent only)	65	16 cm (all greater than 5 cm)	54% 1 y	0%	Diabetes (3.8)
Lugmayr 200227 (Stent only)	54	3-4cm	87% 1 y	0%	Diabetes
			85% 2 y
			76% 3 y
Ihnat	109	15.7cm	63% 1 y	0%	Runoff (2.6)
			52% 2 y		TASC D (5.5)
			52% 3 y

PTA, Percutaneous transluminal angioplasty; RR, relative risk; TASC, TransAtlantic InterSociety Consensus classification.¹⁹

The factor most strongly associated with stent failure was a TASC D lesion. We calculated both the original TASC I¹⁸ and the revised TASC II¹⁹ classification for all treated lesions. Results after endovascular therapy for TASC D lesions were significantly inferior when using both the original TASC I (HR = 5.2) as well as the revised TASC II (HR = 5.5) classifications. The revised TASC classification essentially increased the numbers of A and B lesions, and decreased the number of C lesions, but did not change the D lesions. In our series, TASC B and TASC C lesions were not statistically more likely to fail, compared with TASC A lesions. This is possibly a type II statistical error due to insufficient numbers. When TASC A and B were compared against TASC C and D (Fig 3, Fig 4), the patency rates showed a trend toward improved patency with TASC A and B, but this was not statistically significant, again most likely due to insufficient numbers.

In our series, poor arterial runoff was associated with a higher risk of stent failure. This finding has been previously reported in larger series²², ²³, ²⁴ for angioplasty, but not in smaller series with stenting.²⁷ The association of poor arterial runoff with stent failure makes intuitive sense, and has also been shown for arterial bypass grafts.²⁹, ³⁰ Others have found diabetes²⁴, ²⁶, ²⁷ and renal failure²⁴ to be associated with decreased patency, associations which we were unable to confirm. Our series did show that patients with hypertension had a decreased risk of stent failure. This association has not been previously described. In our series, 84% of patients were taking at least one antihypertensive medication. Perhaps this finding indicates overall improved control of atherosclerotic risk factors.

One-third of the 23 patients with stent failure had deterioration of their runoff vessels. We were not able to identify any reports in the literature that evaluated the incidence of progression of outflow disease after SFA stenting. The SVS runoff score ranges from 1 through 10, with 10 being the worst (high resistance). In our series, the reduction in runoff score is the equivalent of going from two-vessel runoff to one-vessel runoff. While this may seem clinically insignificant at first, this series does not have long-term follow-up. If the reduction of runoff vessels continues over time, it may raise concerns about the long-term impact of endovascular stenting in the femoropopliteal arteries. Since the deterioration of runoff score occurred over 12 months, it most likely was due to recurrent thromboembolism from a long, stented segment instead of atherosclerotic disease progression. We do not have angiographic information for the patients that did not develop stent occlusion or hemodynamically significant in-stent restenosis, so we cannot know if this phenomenon is solely associated with stent failure and revision or if it occurs in widely patent stents as well.

A trend toward poorer patency existed in patients who presented with stent occlusion compared with in-stent restenosis. Although these numbers are small, only one-third of patients treated for stent occlusion maintained stent patency by the end of the study period, compared with 100% of patients treated for in-stent restenosis. This raises the question of whether patients presenting with stent occlusion could undergo secondary intervention prior to occlusion and positively impact long-term patency, similar to vein graft stenosis. Currently, our practice is to perform ABI and duplex ultrasound on the day following the endovascular procedure, at three months, and every 6 months thereafter. Despite general adherence to this protocol, some patients thrombose their stents in proximity to a normal duplex ultrasound. In fact, seven (28%) of the secondary procedures for stent occlusion in this series demonstrated no detectable stenotic lesions once thrombolysis was complete (six had previously been treated with covered stents). Consequently, we believe some patients may thrombose their stents with little or no warning while others will gradually develop a stenotic lesion that can be detected on surveillance duplex. More frequent follow-up would be unlikely to yield benefit in the former group. In our experience, the latter group frequently develops recurrent symptoms prior to stent occlusion. Elucidation of the optimal frequency for follow-up will require further study.

Similarly, a trend was noted toward decreased patency in patients who presented with acute grade II ischemia from stent failure, compared with patients treated for recurrent symptoms from stent failure, and did not have acute grade II limb ischemia. Despite the small numbers, only 25% of patients who presented with acute limb threat maintained patency by the end of the study period, compared with 56% of patients treated for recurrence of symptoms from stent failure, who did not have limb threat. We are now more likely to perform open bypass on patients who present with acute limb threat (acute grade II ischemia) after stent failure.

We found patients with covered stents were statistically more likely than those with bare stents to present with symptoms of acute (grade II) ischemia when presenting with stent occlusion or restenosis. Similarly, ePTFE femoral-popliteal artery bypass graft failure¹⁶ is associated with a higher incidence of acute grade II ischemia. In our series, the groups were not similarly matched. While the ePTFE covered stent-graft group had a higher incidence of claudicants (89% vs 60%), and a slightly better mean runoff score (3.9 vs 4.8), the lesion treatment length was nearly twice as long as the bare metal nitinol stents (25.4 vs 13.7 cm). Interestingly, in the ePTFE group, only one patient (5.3%) had deterioration in the tibial runoff vessels, compared with seven patients (7.7%) in the bare metal stent group. Perhaps the association with acute grade II ischemia is more related to loss of collaterals, and acute thrombosis of a long stented segment, and not related to the ePTFE. Another possibility is that the thrombus burden extends distally into the tibial arteries, causing the grade II ischemia, but then reverts to its baseline patency with prompt thrombolysis. With eight different stent types in addition to the ePTFE covered stent grafts, this series is not large enough to perform any additional subgroup analysis regarding the influence of stent type.

Our practice has also shifted over time. We are now less likely to pursue endovascular treatment techniques in patients with TASC D lesions, patients with poor tibial artery runoff, and patients with extensive tissue loss. Furthermore, in patients considered to be very poor candidates for open bypass, we are more likely to recommend primary amputation instead of an endovascular attempt in those with complex lesions (such as TASC D) or severe tissue loss. Most of our patients that underwent amputation after failed endovascular attempt would now undergo primary amputation. Other investigators³¹ have reported similar findings. We have also adopted a general policy of performing only two endovascular attempts to revascularize a leg. After two endovascular therapeutic failures over a short period of time we convert to open bypass.

The weaknesses of this study include its retrospective nature, the lack of randomization, the lack of a clear protocol for endovascular therapies, and the lack of a standardized algorithm in choosing endovascular treatment as opposed to open surgical revascularization. Since we retrospectively searched our database for patients that had stents implanted into the superficial femoral or popliteal arteries, data regarding initial technical failures is lacking. Table III.

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Author contributions 

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The authors acknowledge Jose Guillen for his help with statistical analysis and Shemuel B. Psalms for assistance with data collection.

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References 

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