Angiographic Dissection Patterns and Patency Outcomes After Balloon Angioplasty for Superficial Femoral Artery Disease

Abstract

Purpose: To investigate the angiographic dissection patterns after balloon angioplasty for superficial femoral artery (SFA) lesions, the clinical outcome associated with each dissection pattern, and the predictive factors for severe dissection. Methods: A retrospective, multicenter analysis examined 621 patients (mean age 72.8±9.5 years; 414 men) with 748 symptomatic de novo SFA lesions treated with endovascular therapy. Vessel dissection after the initial balloon angioplasty procedure was graded into 7 types according to a modified version of the coronary artery classification types A to F. Severe vessel dissection patterns were defined as type C or higher. Nitinol stent implantation was performed in 555 (74.2%) lesions for residual stenosis >30% or flow-limiting dissection; 193 lesions (25.8%) were treated with balloon angioplasty only. To determine the clinical outcomes associated with each dissection pattern and identify predictive factors for severe dissection, 2-year follow-up data for the 193 lesions treated with balloon angioplasty only were analyzed for primary patency and clinically driven target lesion revascularization (TLR). Results: No dissection was found in 16% (120/748) of lesions, and types A and B dissections were seen in 19% (142/748) and 23% (172/748), respectively. Dissection grades above type C were observed in 42% of cases, most frequently type D (180/748, 24%) and less often type C (37/748, 5%), type E (67/748, 9%), and type F (30/748, 4%). The bailout stent implantation rate increased according to dissection severity. At up to 2 years, the severe dissection group (types C–F) showed a significantly lower patency rate (p<0.001) and higher clinically driven TLR (p<0.001) compared to the nonsevere group (no dissection and types A and B dissections). Severe dissection was a significant risk factor for restenosis, which rose progressively from types C to F. Multivariate analysis identified a small reference vessel diameter <5 mm (p=0.001), lesion length >15 cm (p=0.001), and chronic total occlusion (p<0.001) as independent predictors of severe dissection. In subgroup analysis, vessels with a small reference diameter and TASC II C and D lesions had a higher prevalence of severe dissection. Conclusion: Severe dissection was found in 42% of cases after PTA. A small vessel diameter and/or TASC II C/D lesions were related to a high incidence of dissection. Severe dissection during procedures employing balloon angioplasty only could affect long-term patency.

Keywords

balloon angioplasty bailout stent dissection patency percutaneous transluminal angioplasty peripheral artery disease restenosis superficial femoral artery target lesion revascularization

Introduction

The application of endovascular therapy (EVT), which has been increasing due to an aging society and improved diagnosis of peripheral vascular disease,¹ is now widely accepted as an effective treatment for symptomatic superficial femoral artery (SFA) disease.² In recent years, nitinol stents have been mainly used for SFA intervention. Pivotal clinical trials of SFA stent placement revealed higher patency rates compared with conventional balloon angioplasty, including balloon angioplasty with a bailout stent.^3,4 However, despite the widespread use of nitinol stents, in-stent restenosis (ISR) still remains a major drawback of stent-based strategies. Above all, nitinol stents are associated with the risk of fracture and thrombosis.⁵

Since the approval of drug-coated balloons (DCB) and various atherectomy devices, the “nothing left behind” approach has been advocated. For nitinol stents, this means as small and as short as possible. Furthermore, 2 randomized controlled trials found that the clinical outcomes of optimal balloon angioplasty without bailout stent implantation were similar to primary nitinol stent implantation.^6,7 However, balloon angioplasty often results in incomplete vessel dilation and/or flow-limiting dissection. In previous studies, the definition of optimal balloon angioplasty and indications for bailout stent implantation were not well defined, and there were no descriptions of dissection patterns following balloon angioplasty.

The aim of this study was to investigate angiographic dissection patterns following balloon angioplasty for SFA lesions, and according to these patterns, identify the clinical predictors of severe dissection based on SFA lesion characteristics.

Methods

Study Design

This was a retrospective, multicenter clinical investigation to analyze vessel dissection patterns after balloon angioplasty and the clinical outcomes related to these patterns in the subset of lesions treated with balloon dilation only (Figure 1). The main inclusion criterion was single or sequential de novo lesions (≥70% diameter stenosis or occlusion) in an SFA segment having a reference vessel diameter (RVD) of 3 to 7 mm. Cases treated by primary stent implantation without balloon angioplasty were excluded, as were ISR cases or those using a DCB or atherectomy device.

The institutional review boards of the participating institutions approved the study, which was conducted in accordance with the Declaration of Helsinki. The current study was exempt from informed consent on the grounds that it was a retrospective research work using existing medical records; in fact, relevant information regarding the study is open to the public in accordance with the Ethical Guidelines for Medical and Health Research Involving Human Subjects. The study was registered at the UMIN Clinical Trials Registry (UMIN No. 000014225).

Patient Population

In accord with the inclusion criteria, this analysis included 621 symptomatic patients (mean age 72.8±9.5 years, range 30–96; 414 men) with 748 de novo SFA lesions successfully treated with EVT at 4 centers from January 2010 to July 2015. The baseline patient and lesion characteristics are summarized in Table 1. Most patients had hypertension, more than half had diabetes, and more than a quarter were smokers. The severity of limb ischemia as categorized by the Rutherford classification⁸ ranged from 2 to 6; a third of limbs (262/748, 35.0%) had critical limb ischemia. The mean baseline lesion length was 148.1±92.4 mm. There were 301 (40.2%) chronic total occlusions (CTOs). A total of 348 (46.5%) lesions were classified as TransAtlantic Inter-Society Consensus (TASC II) C/D.

Table 1.

Baseline Patient and Lesion Characteristics.^a

Patient characteristics (n=621)
Age, y	72.8±9.5
Men	414 (66.7)
Hypertension	547 (88.1)
Diabetes	353 (56.8)
Dyslipidemia	326 (52.5)
Obesity	100 (16.1)
Current smoker	171 (27.5)
Chronic kidney disease	408 (66.3)
Hemodialysis	195 (31.4)
Coronary artery disease	350 (56.4)
Lesion characteristics (n=748)
Critical limb ischemia	262 (35.0)
Rutherford classification
Category 2/3	486 (64.9)
Category 4	71 (9.4)
Category 5/6	191 (25.5)
Ankle-brachial indices	0.59±0.3
Dual antiplatelet therapy	602 (80.5)
Lesion length, mm	148.1±92.4
RVD, mm	5.4±1.0
TASC C/D lesions	348 (46.5)
Occlusions	301 (40.2)
Calcification
None	261 (34.9)
Moderate	199 (26.6)
Severe	289 (38.6)
Runoff ≤1 vessel	399 (53.4)

Abbreviations: RVD, reference vessel diameter; TASC, TransAtlantic Inter-Society Consensus.

Continuous data are presented as the means ± standard deviation; categorical data are given as the counts (percentage).

Procedure Protocol

Medications (pre-, peri-, and postprocedure aspirin, clopidogrel, warfarin, heparin, etc) and treatments were administered according to local hospital policy and physician discretion. EVT was performed from either a contralateral or ipsilateral femoral access. The majority of procedures (730/748, 97.6%) were performed using a conventional bare balloon, with nearly two-thirds (472/748, 63.1%) using a 0.018-inch catheter (Table 2). The average balloon size was 4.7 mm and more than half (469/748, 63%) were ≥5 mm. Technical success was defined as <30% residual stenosis. In cases of severe dissection after balloon dilation, the operator selected nitinol stent implantation or additional balloon angioplasty with the same or other size balloon. Commercially available nitinol stents were implanted in 555 (74.2%) lesions; 193 lesions (25.8%) were treated with balloon angioplasty only.

Table 2.

Characteristics of the 748 Procedures.^a

Balloon type and catheter size
Bare	730 (97.6)
Cutting/scoring	26 (3.4)
0.014-inch	159 (21.2)
0.018-inch	472 (63.1)
0.035-inch	118 (15.6)
Balloon size, mm	4.7±0.8
≥6	96 (12.8)
≥5 and <6	373 (49.9)
<5	279 (37.3)
Average inflation time, s	80.7±88
Inflation time ≥2 minutes	230 (30.7)
IVUS use	208 (27.8)
Bailout stents	555 (74.1)

Abbreviation: IVUS, intravascular ultrasound (IVUS) imaging.

Continuous data are presented as the means ± standard deviation; categorical data are given as the counts (percentage).

Follow-up

Clinical evaluations were made at 1, 6, and 12 months and every 6 months thereafter. Lesion patency was assessed using duplex ultrasound as defined below, with patency decisions based on the consensus of experienced sonographers at the individual institutions.

Evaluation of Vessel Dissection

Quantitative angiographic data obtained before and immediately after EVT were analyzed at each catheterization laboratory using CAAS software (versions 5.5–5.7; Pie Medical Imaging, Maastricht, the Netherlands). The severity of vessel dissection after the initial balloon angioplasty procedure was assessed through consensus of 2 experienced vascular interventionists who examined a single anteroposterior view. If several dissection patterns were evident in a single lesion, the worst was used for the analysis. Six grades of dissection (A-F) were employed (Figure 2) according to the criteria for coronary artery dissection.⁹ Type A was defined as dissection with minor radiolucent areas, type B as linear dissection, type C as dissection with contrast outside the lumen, type D as spiral dissection, type E as persistent filling defects, and F as total occlusion without distal antegrade flow. Severe vessel dissection patterns were defined as type C or higher.

To determine the clinical outcomes associated with each dissection pattern and identify predictive factors for severe dissection, 2-year follow-up data for the lesions treated with balloon angioplasty only were analyzed for primary patency and clinically driven target lesion revascularization (TLR). Primary patency was defined as an at-rest peak systolic velocity ratio <2.5 by duplex ultrasound without any reintervention.¹⁰ Clinically driven TLR was defined as reintervention performed for >50% stenosis as identified by duplex ultrasound with recurrent clinical symptoms. Moderate and severe calcification were defined as grades 3 and 4, respectively, according to the proposed Peripheral Arterial Calcium Scoring System.¹¹

Statistical Analysis

Continuous variables are presented as mean ± standard deviation and discrete variables as numbers (percentage) unless otherwise stated. Estimates of the primary patency and clinically driven TLR rates were calculated using the Kaplan-Meier method; intergroup differences were assessed with the log-rank test.

The association of dissection patterns with restenosis was analyzed in a mixed effects Cox regression model in which intersubject variability was estimated using random effects analysis; outcomes are presented as the hazard ratios (HRs) with 95% confidence intervals (CIs). The predictive factors for severe dissection patterns were explored using the generalized linear mixed model with a logit-link function in which intersubject variability was estimated by random effects analysis; the outcomes are given as the odds ratios (ORs) with 95% CI. The candidate predictors were hemodialysis dependence, RVD, lesion length, CTO, severe calcification, use of a large 0.035-inch balloon catheter, vessel to balloon size ratio <1.0, long inflation time (≥2 minutes), and use of intravascular ultrasound (IVUS) imaging. Estimates of the prevalence of severe dissection patterns in the subgroups stratified according to the TASC II classification¹² and the RVD were calculated by applying a generalized linear mixed model with a logit-link function. Differences achieving p<0.05 were considered statistically significant.

All statistical analyses were performed with JMP statistical software (version 10.0; SAS Institute, Cary, NC, USA), except for the Cox regression model with mixed effects and the generalized linear mixed model with a logit-link function, which were performed using R software (version 3.1.0; R Foundation for Statistical Computing, Vienna, Austria; http://www.r-project.org )

Results

Vessel Dissection Patterns

As shown in Figure 3A, the majority of lesions had no dissection (120/748, 16%) or dissections of types A (142/748, 19%), B (172/748, 23%), or D (180/748, 24%), whereas types C (37/748, 5%), E (67/748, 9%), and F (30/748, 4%) were rare. The bailout stent implantation rate increased with dissection severity (Figure 3B).

Clinical Outcomes According to the Dissection Pattern

Figure 4 shows the HRs for restenosis according to the dissection pattern in the 193 balloon dilation–only lesions with type A dissection as the reference. Unadjusted HRs for restenosis were greater for severe dissection from type C or higher, while the risk increased with the severity from types C to F. The Kaplan-Meier analysis (Figure 5) examined the clinical outcomes up to 2 years; the severe dissection group (types C–F) showed a significantly lower patency rate (p<0.001) and higher clinically-driven TLR rate (p<0.001) compared with the nonsevere group (no dissection and types A and B dissections).

Predictive Factors of Severe Vessel Dissection

Multivariate analysis using a Cox hazards model identified a small reference vessel diameter <5 mm (p=0.001), lesion length >15 cm (p<0.001), CTO (p<0.001), and IVUS usage (p=0.045) as independent predictors of primary patency (Table 3). Other procedure factors, balloon type, balloon size, and inflation time were not predictive of severe dissection in this study. These findings indicate that severe (long or occluded) lesions as well as a small RVD may result in a higher risk of severe dissection. Indeed, as shown in Figure 6, subgroups with a small RVD and a high-grade TASC II class had a higher prevalence of severe dissection.

Table 3.

Predictive Factors for Severe Dissection After Balloon Angioplasty.^a

	Unadjusted OR^a	Adjusted OR^a
Hemodialysis	0.63, 0.43 to 0.93, 0.019	1.09, 0.68 to 1.75, 0.714
RVD (vs ≥6 mm)	1.00 (Reference)	1.00 (Reference)
≥5 and <6 mm	1.64, 1.07 to 2.52, 0.024	1.82, 1.12 to 2.98, 0.016
<5 mm	3.66, 2.20 to 6.10, <0.001	2.96, 1.55 to 5.65, 0.001
Lesion length (vs ≤5 cm)	1.00 (Reference)	1.00 (Reference)
>5 and ≤15 cm	3.36, 1.78 to 6.32, <0.001	2.46, 1.29 to 4.72, 0.006
>15 cm	15.4, 7.32 to 32.3, <0.001	5.37, 2.63 to 11.0, 0.001
Chronic total occlusion	9.25, 5.24 to 16.3, <0.001	5.16, 3.03 to 8.78, 0.001
Severe calcification	0.71, 0.50 to 1.01, 0.059	0.70, 0.45 to 1.09, 0.113
0.035-inch balloon	0.54, 0.33 to 0.88, 0.013	0.59, 0.33 to 1.06, 0.078
Vessel:balloon size <1.0	2.30, 1.46 to 3.62, <0.001	1.32, 0.72 to 2.41, 0.367
Inflation time ≥2 minutes	1.19, 0.81 to 1.75, 0.379	0.99, 0.63 to 1.57, 0.968
IVUS usage	1.82, 1.24 to 2.67, 0.002	1.59, 1.01 to 2.50, 0.045

Abbreviations: IVUS, intravascular ultrasound; OR, odds ratio; RVD, reference vessel diameter.

Data are given as the ORs for severe dissection, 95% confidence intervals, and p values obtained from the generalized linear mixed model with a logit-link function in which intersubject variability was treated as random effects. The adjusted ORs were obtained from a multivariate model containing all the variables listed in the table.

Discussion

This study classified the dissection patterns after balloon dilation in SFA lesions and investigated the predictive factors for severe vessel dissection along with the clinical outcomes according to these patterns. About half of all cases (42%) exhibited severe dissection from types C to F. The primary patency rate of severe dissection was significantly lower and clinically driven TLR was significantly higher compared with cases that showed no or nonsevere dissection.

These results underscore the inherent risks of balloon angioplasty in patients with severe occlusive disease. Balloon angioplasty works by mechanical dilation and disruption of the artery and atherosclerotic plaque. This forced dilation of stenotic vessels has inherent risks that result in plaque fracture, intimal splitting, and localized medial dissection. Such injuries may extend not only outward but also longitudinally for varying distances into the media and may even invade the adventitia, resulting in frank perforation. Thus, the basic mechanism of dilation in balloon angioplasty can be the cause of vessel injury, resulting in either major or minor dissection, which negatively impacts clinical outcomes.^9,13

In general, severe dissection (eg, types E or F) may result in marked flow limitation or stopped flow, which can be expected to cause poor patency, so stent implantation is needed as a bailout procedure. However, there is no solid definition of dissection in SFA interventions. Given that there are conflicting views on optimal strategies for SFA angioplasty, the potential of severe dissection can adversely affect long-term patency.

Nitinol stents, DCBs, and atherectomy device trials have shown mixed results using the frequency of adjunct stent implantation as one of the definitions for severe dissection. These results are based on the fact that an objective definition of severe dissection has yet to be made. Earlier randomized trials comparing nitinol stents to percutaneous transluminal angioplasty (PTA) found higher acute failure and bailout stent rates in the PTA arm. In the Zilver PTX randomized study, 50% of cases exhibited acute PTA failure and required bailout stent implantation,⁶ whereas in the RESILIENT randomized trial,⁷ 40.3% required bailout stent implantation due to either flow-limiting dissection (38%) or residual stenosis >30% (62%). Similarly, the ASTRON and ABSOLUTE studies reported 26% and 32% bailout stent implantation rates, respectively.^2,3 The main reason was due to the high rates of flow-limiting dissection (15% and 18%, respectively).

In contrast, the bailout stent implantation rates in the DCB trials were relatively low. The IN.PACT SFA and LEVANT 2 randomized control trials compared DCB to PTA, but only successful PTA cases were randomized.^14,15 In these studies, acute PTA failure rates before randomization were low (2% and 9%, respectively). Moreover, they reported very few cases of severe dissection following DCB or conventional balloon angioplasty. In the IN.PACT study,¹⁴ types D to F dissection occurred in 0.0% of the DCB group and only 0.9% of the PTA group. In fact, bailout (equal to provisional stent implantation) was required in only 7.3% of the DCB group and 12.6% of the PTA group. Similarly, in the LEVANT2 trial,¹⁵ types D to F dissection did not occur in either arm, and provisional stent implantation rates were only 8% and 11% for the DCB and PTA arms, respectively (p=0.022). In contrast, the Passeo-18 randomized controlled trial comparing DCB to standard PTA without predilation found a significantly lower bailout stent implantation rate in the DCB arm than the standard PTA arm (6.7% vs 26.7%; p=0.038) but a higher dissection rate in the DCB arm (57.5% vs 48.5% in the standard PTA arm).¹⁶

Thus, DCB was shown to improve the patency rate compared with standard PTA without a higher incidence of severe dissection. Another analysis of the THUNDER trial found that DCB treatment in any grade of dissection showed less late loss of patency than standard PTA treatment.¹⁷ From our findings, patients who most often needed stents were type C or those with more severe forms of dissection. However, contrary to our findings, patients treated with DCBs who had either types C or D dissection showed fairly good patency without stent placement. The reasons for such high patency following DCB treatment despite types C or D dissection remain unclear.

Atherectomy devices can reduce the incidence of severe dissection and potentially minimize stent use in femoropopliteal lesions, but clinical outcomes are influenced by the choice of a specific atherectomy device. The CALCIUM 360 trial found that orbital atherectomy plus PTA reduced the rate of severe dissection compared with standard PTA alone.¹⁸ McKinsey et al¹⁹ reported 18% flow-limiting dissection and 8% provisional stent implantation rates using the SilverHawk atherectomy device. In the Jetstream (Pathway PV system) trial,²⁰ 10% dissection and 7% stenting rates were documented. The bailout stent rate using the excimer laser system in the CELLO study was somewhat higher, with 23% of patients receiving a stent due to flow-limiting dissection and suboptimal technical and/or angiographic results.²¹

Fitzgerald et al²² have reported a higher incidence of dissection or plaque fracture immediately after balloon dilation if the lesion was calcified. In our study, calcification was not predictive of dissection as long as an optimally sized balloon was used. The main reason is that calcified lesions limit expansion of the balloon, thus, actually reducing the risk of dissection.

More precise assessments of dissection following balloon angioplasty are required to clarify these contradictory results. To reduce the severe dissection after balloon dilation, further analysis will be needed regarding the balloon angioplasty strategy based on this dissection pattern evaluation. Future studies of dissection should also use multiple diagnostic modalities, including IVUS and/or optical coherence tomography to make a more objective and comprehensive evaluation of dissection after balloon angioplasty.

Limitations

This study shares the limitations of all retrospective, nonrandomized investigations, including selection bias. The strategy after postangioplasty dissection, that is, stent implantation or additional balloon angioplasty, depended on the physician’s decision to a certain degree. Second, there was no core laboratory and only single angiographic views were analyzed. These factors may have influenced the results.

Conclusion

Balloon angioplasty for SFA disease resulted in severe dissection in 42% of the cases investigated. Long lesions, small vessel diameter, and total occlusion were the independent predictors of severe dissection. In cases with severe dissection, the balloon-only procedure is of limited efficacy in terms of midterm patency. Precise assessment of dissection patterns after angioplasty is necessary to maximize the effects of the balloon-only procedure.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest regarding the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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