Impact of Extravascular Ultrasound-Guided Wiring on Achieving Optimal Vessel Preparation and Patency in Endovascular Therapy for Superficial Femoral Artery Chronic Total Occlusion

Abstract

Purpose. The study aim was to evaluate the impact of extravascular ultrasound-guided (EVUSG) wiring on achieving optimal vessel preparation and patency in endovascular therapy (EVT) for superficial femoral artery (SFA) chronic total occlusion (CTO). Methods. Between April 2007 and January 2019, a total of 239 SFA-CTO limbs were successfully treated with EVT and bailout implantation of self-expandable nitinol stents at our hospital. The study subjects were divided into 2 groups according to the type of guidance strategy used during CTO wiring, ie, the EVUSG group and the conventional angiography guidance (AG) group. Immediately after the initial balloon angioplasty and successful passage of the wire through the SFA-CTO lesions, the EVUSG (65 limbs) and AG groups (174 limbs) were retrospectively evaluated for angiographic dissection patterns. The primary patency rate was also compared between the 2 groups. Results. No significant difference was observed in the balloon diameter at the initial dilation immediately after successful wire passing (3.7 ± 0.5 mm in the EVUSG group vs 3.8 ± 0.5 mm in the AG group; P=.17). The incidence of severe dissection was significantly lower (P<.001) in the EVUSG group (28/65; 43%) than in the AG group (137/174; 79%). The 3-year primary patency rates in the EVUSG and AG groups were 84.5% and 68.4%, respectively (P<.001). Conclusions. EVUSG for SFA-CTO may achieve optimal vessel preparation, defined as an initial balloon angioplasty without severe dissection, and subsequent implantation of self-expandable stents may lead to a better patency rate.

Keywords: chronic total occlusion, extravascular ultrasound, extravascular ultrasound guidance, self-expandable nitinol stent, superficial femoral artery, vessel preparation

Recent advances in endovascular therapy (EVT) have made it the treatment of choice for superficial femoral artery (SFA) disease in patients with peripheral artery disease (PAD). However, whether the selection of device, between stent or balloon, and with or without drugs, actually helps to achieve the final lumen diameter and patency of the target vessel is controversial.¹ Especially, the treatment of long chronic total occlusion (CTO) of the SFA is technically complex, and the patency outcomes remain poor until now.^2,3 Achieving optimal vessel preparation, which means reducing severe dissection after the initial balloon angioplasty, is considered a goal that might lead to better patency rates of SFA lesions.^4,5

Peripheral transluminal angioplasty under extravascular ultrasound (EVUS) guidance (EVUSG) has been reported to be feasible in routine clinical practice.^6,7 The enhanced resolution of ultrasound machines has enabled easy visualization of vessel anatomy, as well as plaque distribution and morphology. EVUSG can reveal the intraplaque morphology and allow changing the wire direction within the plaque even when treating CTOs. However, its impact on vessel preparation and patency after subsequent stent implantation is not well known. We hypothesized that EVUSG could help in penetration of the wire through the central axis of the vessel conduit by providing better intraplaque visualization, which may enable easy achievement of optimal vessel preparation, defined as balloon angioplasty without severe dissection, in SFA-CTO lesions. This study aimed to evaluate the impact of EVUS-guided wiring on achieving optimal vessel preparation and patency after the implantation of self-expandable nitinol stents in EVT for SFA-CTO.

Methods

Study design. Symptomatic patients with PAD with SFA-CTO lesions treated with endovascular percutaneous interventions between April 2007 and January 2019 were collected from a prospectively maintained database and included in this single-center, retrospective cohort study. The database consisted of a series of 402 patients (491 limbs) who underwent EVT for de novo SFA-CTO lesions. Negotiation of the guidewire through the CTO was performed using either EVUSG or AG. EVUSG was used at the time of entering the proximal cap of the CTO and while passing through the occlusion to cross the distal cap of the CTO, making it possible to check the wire position and change direction to remain at the central axis of the CTO and avoid entering into the subintimal space. After negotiating guidewire passage through the CTO, angiography was used next to complete the EVT procedure as in the AG group. The selection of the crossing method of the guidewire through the CTO was at the operator’s discretion.

Of the total cohort, 27 patients (39 limbs) were unable to visit the hospital for clinical follow-up after discharge, 14 patients (14 limbs) had unsuccessful EVT, 5 patients (6 limbs) were treated with drug-coated balloon, 5 patients (5 limbs) were treated with endoprosthesis, and 96 patients (134 limbs) were treated with balloon angioplasty alone. Additionally, from SFA-CTO lesions implanted with bailout self-expandable nitinol stents, cases where EVT procedures were done without angiograms to evaluate the dissection pattern were excluded. Self-expandable nitinol stents were implanted in patients with a residual peak pressure gradient of >10 mm Hg, residual stenosis >30%, and/or flow-limiting dissection after balloon dilation.

Baseline demographics and outcomes were retrospectively evaluated between the EVUSG group (60 patients, 65 limbs) and the conventional angiography guidance (AG) group (142 patients, 174 limbs) (Figure 1). Because the achievement of optimal vessel preparation was evaluated according to the dissection patterns after the initial balloon angioplasty immediately after wire passage to CTO lesions, the EVUSG and AG groups were configured using the angiograms of the limbs obtained after the initial balloon angioplasty. The severity of vessel dissection after initial balloon angioplasty was assessed by 2 experienced vascular interventionists. The primary outcome measure was the 3-year primary patency rate. The 3-year rate of freedom from target-lesion revascularization (TLR) was also compared between the 2 groups. All patients had symptomatic SFA-CTO lesions (Rutherford 2-6) that affected their quality of life despite exercise and optimal medications. EVUSG was defined as the use of EVUS during the recanalization of SFA-CTO, and AG was defined as recanalization of SFA-CTO without using EVUS. CTO was diagnosed when no intraluminal antegrade flow was observed on angiography. The study protocol was designed in accordance with the Declaration of Helsinki and was approved by the ethics committee of the hospital. All patients provided written informed consent.

EVT strategy. After diagnostic angiography of the lower extremity, the decision for EVT was taken in consultation with vascular surgeons, especially for occlusion lengths >20 cm, such as Trans-Atlantic Inter-Society Consensus (TASC) II type D lesions.⁸ Generally, a 6-Fr system approaching from the femoral artery was used. However, if the occluded segment was near the bifurcation of the common femoral artery, the contralateral approach was selected. A .014˝, .018˝, or .035˝ guidewire was advanced through the occlusion with the aid of an over-the-wire balloon or microcatheter. A tip-loaded guidewire was used to cross the distal cap of the CTO. The determination of the strategy (EVUSG or AG) for EVT was left to the discretion of the operator.

With the accumulation of experience and the developments in ultrasound technology, EVUSG became the first-line strategy from April 2012 at the hospital where the study cohort was extracted. EVUS machine (Aplio Series; Canon Medical Systems Corporation) using a 7-8 MHz linear probe was employed, and the image quality was set to obtain a clear image of the guidewire and arterial wall border. Figure 2 shows the details of the technical execution of EVUSG during SFA-CTO crossings. We started using EVUSG for SFA-CTO lesions in 2004 and the other details of the EVUS-guided CTO wiring procedure have been recently reported.⁹ If the antegrade approach failed, a retrograde approach from the popliteal or tibial artery was performed. The re-entry device was used in only 1 case in the AG group. The type of guidewire and support catheter used when crossing the distal cap of the CTO and other details of the devices during the EVT procedure are described below. Once the guidewire had passed through the CTO, the lesion was dilated with an optimal balloon (initial balloon dilation), which can cross the occlusion site and is smaller than the diameter of the distal reference vessel.

Self-expandable nitinol stents were implanted in patients with a residual peak pressure gradient of >10 mm Hg, residual stenosis >30%, and/or flow-limiting dissection after balloon dilation. Stents with a diameter that was approximately 1 mm larger than the reference diameter were used. If necessary, postdilation was performed with an optimal balloon. Dual-antiplatelet therapy (100 mg/day aspirin and 75 mg clopidogrel) was started at least 3 days before EVT and continued for 6 months or longer if there were no contraindications.

Follow-up and outcome measures. The primary endpoint was the 3-year primary patency, defined as freedom from restenosis (duplex ultrasound peak systolic velocity ratio ≤2.4).¹⁰ The secondary endpoint was freedom from TLR within 3 years after the index procedure. TLR was defined as any reintervention within the target lesion(s) owing to loss of primary patency and the presence of lower-limb symptoms due to PAD.

Definitions. Initial balloon angioplasty was defined as balloon dilation immediately after crossing the guidewire through the SFA-CTO lesion. After the dilation, the dissection patterns were assessed using angiography, following a previous study.^4,11Types A to C were defined as nonsevere dissections and types D to F were defined as severe dissections. A “twisted stent” was defined as a self-expandable stent that was spirally implanted and twisted by at least 360° in the angiogram obtained immediately after implantation as it was originally defined in this study. A representative case is shown in Figure 3A. Calcified lesions were assessed on angiography and were defined as grade 4 in peripheral arterial calcium scoring system (PACSS).¹²Coronary artery disease (CAD) was defined as stable angina with documented CAD, history of percutaneous coronary intervention (PCI), history of coronary artery bypass graft surgery (CABG), or previous myocardial infarction. Cerebrovascular disease (CVD) was defined as a hospital or neurologist report with a diagnosis of transient ischemic attack or ischemic stroke. Below-the-knee runoff was assessed with angiography after the procedure, and poor runoff was defined as ≤1 below-the-knee runoff vessels.

Statistical analysis. Data are presented as values and percentages, or as means and standard deviations. Categorical variables were compared between groups using the χ² or Fisher’s exact test, as appropriate. Continuous variables were compared between groups using Student’s paired t test or Mann-Whitney’s test, according to the normality of data distribution. The primary outcome measure was estimated using the Kaplan-Meier method, and the differences were evaluated with the log-rank test. All statistical analyses were 2 tailed and P<.05 was considered statistically significant. Statistical analyses were performed using SPSS software, version  25.0 (SPSS, Inc).

A Cox proportional hazards model was used to determine the predictors of loss of primary patency. Baseline demographic data (EVUSG, age, female sex, current smoking, hypertension, dyslipidemia, diabetes mellitus, chronic kidney disease, hemodialysis, history of CAD, history of CVD, ankle brachial index [ABI] before EVT, TASC II A to D, critical limb ischemia [CLI], calcified lesion, CTO length >15 cm, reference vessel diameter, poor run-off, guidewire type, support catheter type, intravascular ultrasound [IVUS] usage, distal puncture, predilation balloon diameter, predilation inflation time, postdilation balloon diameter, postdilation inflation time, number of stents, bare-metal stent, drug-eluting stent, stent diameter, stent length, severe dissection, and twisted stent) were included in the univariate model. Factors that were indicated by P<.05 in the univariate analysis (EVUSG, CTO length >15 cm, severe dissection, and twisted stent) were included in the multivariate regression models.

Results

The baseline patient and target-limb/target-lesion characteristics are summarized in Table 1 and Table 2, respectively. No significant differences were found in the baseline demographic characteristics of the patients. The frequency of a CTO length >15 cm was significantly higher in the EVUSG group than in the AG group (89% vs 79%, respectively; P=.047).

Regarding the procedure characteristics (Table 3), according to the type of guidewire and support catheter used when crossing the distal cap of the CTO, .014˝ wire and .018˝ over the wire (OTW) balloons were used as support catheters in all limbs in the EVUSG group. In contrast, the AG group used a significantly higher number of 0014˝ microcatheters (32% vs 0% in the EVUSG group; P<.001) and a significantly lower number of .018˝ OTW balloons as support catheters (65% vs 100% in the EVUSG group; P<.001). The EVUSG group had a significantly lower number of distal puncture procedures (9% vs 35%; P<.001), significantly lower radiation dose (165 ± 145 mGy vs 274 ± 251 mGy; P<.001), significantly lower contrast volume (132 ± 49 mL vs 180 ± 84 mL; P<.001), and significantly shorter procedure time (158 ± 69 minutes vs 190 ± 151 minutes; P=.03) than the AG group. The diameter of the balloon used in the procedure is shown in Table 3, with no significant difference observed between the EVUSG and AG groups (3.7 ± 0.5 vs 3.8 ± 0.5 mm, respectively; P=.17). The postdilation balloon diameter was significantly smaller in the EVUSG group (4.5 ± 0.6 mm vs 5.0 ± 0.6 mm in the AG group; P=.01). The incidence of a “twisted stent” was significantly lower in the EVUSG group (11% vs 46% in the AG group; P<.001).

Concerning the dissection pattern (Figure 4), the EVUSG group had a significantly lower incidence of severe dissection than the AG group (43% vs 79%, respectively; P<.001).

The primary and secondary outcomes, which were the 3-year primary patency rate and the 3-year rate of freedom from TLR (Figure 5), respectively, were both significantly higher in the EVUSG group than in the AG group (84.5% vs 68.4% [P<.001] and 86.0% vs 68.6% [P<.001]).

The univariate and multivariate predictors of loss of primary patency are shown in Table 4. In multivariate analysis, EVUSG (hazard ratio [HR], 0.440; 95% confidence interval [CI], 0.211-0.919; P=.03) was an independent predictor of freedom from primary ­patency loss.

Representative cases from the AG and EVUSG groups are shown in Figure 3A and Figure 3B, respectively.

Discussion

The safety and efficacy of EVUSG in EVT have been reported in the early era.^6,7 However, its impact on vessel preparation and long-term patency after the subsequent implantation of self-expandable nitinol stents is not well known.

The key results of the present study show the utility of EVUS-guided EVT for SFA-CTO lesions, as follows: (1) the severity of angiographic dissection after the initial balloon dilation, which represents the status of vessel preparation, was less in the EVUSG group than in the AG group; and (2) implantation of self-expandable nitinol stents after EVUS-guided wiring in SFA-CTO lesions resulted in significantly higher patency and freedom from TLR than after conventional AG wiring.

Although advances in EVT have made this treatment approach the first-line therapy for lower-limb PAD, achievement of long-term patency in more complex lesions, especially SFA lesions such as long CTO, remains poor compared with the patency of vein graft bypass.^2,3 To improve the long-term patency, the selection of finalizing devices during EVT, self-expandable stents, drug-coated balloons, or drug-eluting stents is consistently being studied.^13-15 A recent report has shown that the patency of femoral artery lesions after balloon angioplasty may be affected by the concept of optimal vessel preparation, as assessed according to angiographic dissection patterns, and severe dissection in CTO was reported to be one of the predictors of poor patency.⁴ From the viewpoint of reducing severe dissection to improve the patency of SFA-CTO, EVUSG could better track the guidewire within the plaque and allow it to pass through the central axis of the vessel conduit, which may lead to better vessel preparation, as shown by the less-severe dissection after the initial balloon angioplasty in the EVUSG group than in the AG group.

This study revealed that EVUS-guided wiring could obtain better long-term patency after subsequent self-expandable nitinol stent implantation than conventional AG wiring in EVT for SFA-CTO. The 3-year primary patency rate and the 3-year rate of freedom from TLR were both significantly higher in the EVUSG group than in the AG group (84.5% vs 68.4% [P<.001] and 86.0% vs 68.6% [P<.001]). This finding was speculated to be the result of optimal vessel preparation afforded by EVUS-guided wiring, as shown by the less-severe angiographic dissection pattern after initial balloon angioplasty in the EVUSG group than in the AG group. A histological study of human femoral stenting failure showed that the major cause of stent failure was acute thrombus formation, and other causes included stent under expansion, delayed healing, false lumen stenting, and fracture.¹⁶ Meanwhile, another histological study of the coronary artery showed the lack of a severe medial tear to be an independent predictor of delayed healing after stent implantation.¹⁷ Thus, the relationship between severe dissection during stent implantation and poor patency might be subsequently speculated. Analysis using the Cox proportional hazards model to detect univariate and multivariate predictors of loss of primary patency in our study showed severe dissection as a univariate predictor and EVUSG as a multivariate independent predictor. This finding also supports the relationship between severe dissection and poor patency in stent implantation.

Moreover, the suboptimal vessel preparation in the AG group might have resulted in the occurrence of a “twisted stent” during the expansion of the self-expandable stent, which indicates acute suboptimal stent expansion. Additionally, the postdilation balloon diameter was significantly smaller in the EVUSG group because of more optimal stent expansion than in the AG group, and the reduced injury to the vessels around the stent might have led to less neointimal hyperplasia growth.^18-20 EVUSG could better track the guidewire within the plaque and can allow it to pass through the central axis of the vessel conduit, which may lead to better vessel preparation and better long-term patency. In previous studies on SFA-CTOs, the 12-month primary patency rate was 78% after the implantation of self-expandable bare nitinol stents,²¹ and 65% and 55% after intraluminal and subintimal implantation of drug-eluting stents, respectively.²² The present study showed a higher primary patency rate than previous studies, especially in the EVUSG group, which may indicate that optimal vessel preparation, as shown by less-severe dissection after initial ballooning in SFA-CTO lesions, leads to better patency even after the implantation of self-expandable nitinol stents. A gentler approach to avoid severe dissection after balloon angioplasty might be finalizing the procedure with drug-coated ballooning with spot stenting; however, finalizing with drug-coated ballooning alone without stenting might also be possible. Further studies are needed with respect to the combination of debulking devices that are not suitable for subintimal angioplasty as opposed to intraplaque angioplasty.

According to the types of guidewire and support catheters that were used when crossing the distal cap of the CTO, .014˝ wire and .018˝ OTW balloons were used as support catheters in all SFA-CTO lesions in the EVUSG group. This is because the SFA is a relatively straight vessel and EVUS can easily detect the tip of a stiff .014˝ guidewire. Advancing the OTW balloon as a support catheter and simultaneously dilating CTO lesions with an OTW balloon and crossing the wire can be performed safely under EVUS guidance until the distal cap of the CTO.

Because of the EVUSG during the procedure of CTO wiring, the time of radiation exposure and the volume of contrast medium can be reduced compared with conventional AG wiring. Consequently, complications such as radiation injury and contrast-induced nephropathy could be reduced in patients undergoing EVUS-guided EVT. Additionally, because EVUSG during CTO wiring could allow intentional penetration of the distal true lumen with an antegrade stiff wire throughout CTOs, a retrograde wire from the distal puncture site is not always necessary. These characteristics of EVUS-guided EVT have the possibility of allowing a less-invasive procedure than conventional AG-EVT for SFA-CTOs.

Study limitations. This was not a randomized study, and the sample size was small, which may have affected the results. The EVUS guide was used at the discretion of the operator. Both procedures were performed by experienced operators and the main operator was the same. It is not a general procedure, and there is a learning curve for EVUSG in SFA-CTO. This study did not attempt to correlate operator proficiency with procedure success. IVUS is not a routinely performed technique. A prospective randomized study with IVUS assessment is required to confirm the advantages of EVT combined with EVUSG. Re-entry catheter was not available until 2016; the procedure time may have been less in the AG group if it was used.

Conclusion

EVUSG could lead to the penetration of the wire through the central axis of the vessel conduit by providing better intraplaque visualization, which may enable easily achieving optimal vessel preparation, defined as balloon angioplasty without severe dissection, in SFA-CTO lesions. Further, subsequent implantation of self-expandable stents may lead to a better patency rate.

Affiliations and Disclosures

From the Division of Cardiology, Saiseikai Yokohama City Eastern Hospital, Yokohama, Kanagawa, Japan.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript accepted April 12, 2022.

The authors report that patient consent was provided for publication of the images used herein.

Address for correspondence:  Yasunari Sakamoto, MD, Division of Cardiology, Osaki Hospital Tokyo Heart Center, 5-4-12 Kitashinagawa, Shinagawa-ku, Tokyo, 141-0001, Japan. Email: cbc08282@hotmail.co.jp

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