Procedural and 3-Year Outcomes of Peripheral Vascular Interventions Performed in Office-Based Labs: LIBERTY 360 Sub-Analysis

Abstract

Objective. Few data are available on the safety of interventions for peripheral arterial disease (PAD) performed in the office-based laboratory (OBL) setting. Thus, the aim of this study was to investigate the short- and late-term outcomes of patients treated in OBL vs hospital settings. Methods. We included patients with PAD treated with any United States Food and Drug Administration approved or cleared devices for distal femoropopliteal and/or infrapopliteal disease. Data were retrieved from the LIBERTY 360 study. A propensity-scored, matched analysis was conducted and hazard ratios with the respective 95% confidence intervals were synthesized to examine the outcomes after interventions at OBL vs non-OBL settings. Results. A total of 710 propensity-scored patients (355 OBL patients and 355 non-OBL patients) with 907 treated lesions (454 OBL lesions and 453 non-OBL lesions), were included. For almost all subjects, balloon angioplasty was the preferred treatment approach (341 [96.1%] in the OBL group vs 353 [99.4%] in the non-OBL group; P<.01), with bail-out stenting necessary in 5.1% of the OBL group and 3.1% of the non-OBL group. Overall, significant angiographic complications occurred in 7.8% of all patients treated, with no differences between the 2 groups. The risk for all-cause death, target-vessel revascularization, and major amputation and death combined was similar between the 2 groups during 3-year follow-up. Conclusions. Peripheral artery endovascular interventions in patients with chronic threatening ischemia or claudication, performed in the OBL setting, are safe and associated with favorable outcomes at 3 years of follow-up. These results demonstrate that treatment at OBLs is comparable to non-OBL settings. Further comparative studies and larger registries are needed to benchmark procedural quality and long-term outcomes.

J INVASIVE CARDIOL 2021;33(5):E365-E377.

Key words: amputation, angioplasty, office-based laboratory, peripheral arterial disease

PAD is associated with numerous comorbidities^1-6 and is correlated with high mortality risk and reduced quality of life.^7,8 Thus, the American College of Cardiology/American Heart Association guidelines recommend revascularization for patients with symptomatic PAD when medical therapy ± exercise programs fail to relieve symptoms.⁹ Although endovascular procedures for PAD are less expensive than surgery due to fewer periprocedural complications and faster recovery (ie, shorter in-hospital stay),^10-12 there is a potential need for endovascular reinterventions, which may reduce the cost difference.¹¹ Moreover, chronic limb-threatening ischemia (CLTI), the most advanced stage of PAD, costs more than $4 billion per year in the United States, representing a growing financial burden on the healthcare system.^8,13 For this reason, there has been a move toward alternative treatment locations to improve patient access to procedures and also potentially reduce procedural costs. A report on interventional radiology procedures showed that treatment in outpatient settings offered significant cost savings.¹⁰ Thus, strategies that are safe and at the same time cost effective (eg, treatment in outpatient or office-based lab [OBL] settings) could have a great benefit on the economy and also contribute to improvements in efficient healthcare services.

Advancements in the medical field have allowed several types of minimally invasive procedures, such as interventions for lower-extremity PAD, to be feasible in the OBL setting. It is thought that the wide application of procedures in the OBL setting might further decrease healthcare expenses, while providing more humanistic care to patients. Thus, over the past decade, OBLs have been increasingly appealing to both patients and physicians, and this movement away from hospitals is estimated at approximately 18% as of 2019.¹⁴ The proposed benefits of OBLs include, but are not limited to: (1) greater autonomy for medical staff and patients; (2) reduced utilization of healthcare resources; and (3) similar prognosis compared with in-hospital therapy (ie, cost effectiveness).

However, several factors should be taken into account regarding the treatment of patients in OBLs, including quality control and risk abatement. Considering the lack of comparative studies investigating the outcomes of endovascular procedures among patients with lower-extremity PAD, the safety of interventions performed in an OBL setting is still unclear. Thus, the aim of the present study was to investigate the short- and late-term outcomes of patients treated in OBL vs hospital settings and to determine the safety of this approach. We utilized data from the LIBERTY study, which is a modern, real-world cohort of patients with PAD treated with endovascular approaches.¹⁵

Methods

Study design and patient enrollment. LIBERTY was a multicenter, prospective, observational study (ClinicalTrials.gov; identifier: NCT01855412) investigating the clinical outcomes of lower-extremity endovascular interventions in patients with symptomatic PAD. Procedures were performed between 2013 and 2016. A steering committee, including principal investigators, representatives from the study core laboratories, and the sponsor (Cardiovascular Systems, Inc) developed the study protocol, while Cardiovascular Systems, Inc was responsible for effective oversight of the research process. The institutional review board of each site approved the study protocol. Detailed information about the inclusion and exclusion criteria of the LIBERTY study were previously reported¹⁶ and can also be found at https://clinicaltrials.gov/ct2/show/ NCT01855412?cond=NCT01855412&rank=1. The current study included patients with varying degrees of PAD severity treated with endovascular approaches at the discretion of the operator and comparisons were stratified by whether the patients were treated in OBL or non-OBL setting. Angiographic data were adjudicated by SynvaCor/Prairie Educational and Research Cooperative (PERC). Patient demographics and lesion characteristics stratified by OBL vs non-OBL are illustrated in Table 1 and Table 2, respectively.

Study endpoints and statistical analysis. Subjects undergoing procedures in OBL and non-OBL settings were matched 1:1 based on propensity scores, calculated with the Greedy algorithm. Propensity scores with 1:1 nearest-neighbor matching were built through a logistic regression model. The following baseline covariates were considered in the logistic model to obtain the predictive probabilities: Rutherford classification, history of diabetes, history of renal disease, history of coronary artery disease, history of hypertension, history of myocardial infarction, smoker (current/former vs never), chronic total occlusion, total treated lesion length, lesion location, number of wounds on target limb at baseline (1 unit increase), number of target-limb procedures in last 3 years (1 procedure increase), most severe Trans-Atlantic Inter-Society Consensus (TASC) lesion type, previous major amputation of non-target limb, history of previous lower-limb endovascular treatment, and number of target lesions treated (1 lesion increase), lesions with >30% stenosis left untreated at end of procedure, and <50% residual stenosis of all target lesions per subject. Descriptive statistics were used for baseline and lesion characteristics. Categorical variables are presented as absolute and relative frequencies (ie, percentages) and were compared using a Monte Carlo approximation of the Fisher’s Exact test. Numeric data are presented as mean ± standard deviation and/or median with interquartile range (IQR), and were compared using analysis of variance. Discrete data were compared with the Kruskal-Wallis test.

Procedure and lesion success were defined as <50% residual stenosis for treated lesions without significant angiographic complications (flow-limiting dissections [type D-F], perforation, slow/no-reflow, distal embolization, or abrupt closure) per patient (procedure success) or lesion (lesion success); odds ratios were summarized using a logistic regression model. When data from the angiographic core laboratory evaluation were not available, site-reported data were used for the analysis. Incidence of (1) major amputation; (2) all-cause death; (3) target-vessel revascularization (TVR) or target-lesion revascularization (TLR); (4) major adverse event (MAE), defined as death within 30 days of the index procedure, TVR, or TLR, and unplanned major amputation of the target limb; and (5) death or major amputation combined were summarized using Kaplan-Meier survival curves for each group (ie, OBL vs non-OBL). Greenwood’s method was used to obtain the 95% confidence interval (CI) and estimates were compared with the log-rank test. Cox proportional hazard models were synthesized for MAE, death, major amputation, TVR, and combined major amputation or death at 36 months of follow-up. The results are presented as the hazard ratio (HR) and 95% CI. All statistical analyses were conducted by NAMSA. P-values <.05 were considered statistically significant for all tests.

Results

Patient and lesion characteristics. A total of 710 propensity-scored patients (355 OBL and 355 non-OBL) with 907 treated lesions (454 OBL and 453 non-OBL) were included. The majority of patients were males (227 [63.9%] vs 228 [64.2%]), Caucasian (304 [85.6%] vs 284 [80.0%]) and had a significant history of hypertension (336 [94.6%] vs 335 [94.4%]), diabetes mellitus (213 [60.0%] vs 212 [59.7%]), coronary artery disease (228 [64.2%] vs 215 [60.6%]) and smoking history (current smokers, 70 [19.7%] vs 70 [19.7%]; former smokers, OBL: 175 [49.3%] vs 169 [47.6%]), in the OBL vs non-OBL groups, respectively, without any significant differences between the 2 groups. Detailed patient characteristics are presented in Table 1.

Almost half of the cases in the OBL and non-OBL groups had isolated infrapopliteal lesions (P=.60). Above-the-knee lesions alone were present in 37.4% of the OBL group and 36.6% of the non-OBL group (P=.84), while multivessel lesions involving segments below and above the knee were present in 13.4% of the OBL group vs 12.4% of the non-OBL group (P=.69). Target-lesion length was 101.0 ± 103.2 mm in the OBL group vs 99.3 ± 95.6 mm in the non-OBL group, with no statistical difference between the 2 groups (P=.80). The mean preprocedural minimal lumen diameter (MLD) was smaller in the non-OBL group (0.8 ± 0.9 mm in the OBL group vs 0.7 ± 0.7 mm in the non-OBL group; P<.01), corresponding to higher mean preprocedural stenosis among the non-OBL cases (77.6 ± 21.2% in the OBL group vs 80.5 ± 18.2% in the OBL group; P=.03). Predominantly calcified plaques were equally observed in both groups (240/409 [58.7%] in the OBL group vs 256/442 [57.9%] in the non-OBL group; P=.84). The number of run-off vessels (ie, pre and post procedure) was similar among both groups. The lesion characteristics were similar between the 2 groups and are summarized in Table 2.

Procedure characteristics. For almost all subjects, balloon angioplasty was the preferred treatment approach (341 [96.1%] in the OBL group vs 353 [99.4%] in the non-OBL group; P<.01), with bail-out stenting necessary in 18 cases (5.1%) in the OBL group and 11 cases [3.1%] in the non-OBL group (P=.26). Specialty balloons (eg, cutting/scoring balloons) and drug-coated balloons (12 [3.4%] in the OBL group vs 67 [18.9%] in the non-OBL group; P<.001) were more frequently utilized in patients treated in the non-OBL setting. Furthermore, although the overall primary stenting rates were low for both groups, more drug-eluting stents were utilized in the non-OBL setting (11 [3.1%] in the OBL group vs 26 [7.3%] in the non-OBL group; P=.02). In addition, adjunctive technology utilizing atherectomy devices for vessel preparation was used more frequently in patients treated at OBLs (328 [92.4%] in the OBL group vs 238 [67.0%] in the non-OBL group; P<.001). Important procedural characteristics and information about the devices utilized are provided in Table 3.

Overall, significant angiographic complications (ie, flow-limiting dissection, perforation, distal embolization, acute vessel closure) occurred in 7.8% of all patients treated (34/347 [9.8%] in the OBL group vs 20/344 [5.8%] in the non-OBL group ; P=.06). The most common periprocedural adverse event was distal embolization (20/347 [5.8%] in the OBL group vs 13/344 [3.8%] in the non-OBL group; P=.28) followed by iatrogenic perforation (9/349 [2.6%] in the OBL group vs 2/346 [0.6%] in the non-OBL group; P=.06), while abrupt closure occurred in 1.4% of all cases (5/349 [1.4%] in the OBL group vs 5/346 [1.4%] in the non-OBL group; P>.99). Severe dissections (type D-F) occurred in only 2 cases of the OBL group, with no statistically significant difference between groups (2/349 [0.6%] in the OBL group vs 0/346 [0.0%] in the non-OBL group; P=.50). In total, target-lesion success, defined as residual stenosis <50% without any significant angiographic complications, occurred in 360/432 OBL patients (83.3%) vs 382/443 non-OBL patients (86.2%), without any significant difference between the groups (P=.26). Events between the procedure and discharge, including death, TVR, MAE, and major amputation, were not statistically different between the groups. Details about periprocedural angiographic complications and short-term outcomes are presented in Table 4. Almost all patients were discharged on antiplatelet therapy with aspirin and/or clopidogrel; however, more patients in the non-OBL group were prescribed dual-antiplatelet therapy. Information regarding the medical therapy at discharge is presented in Table 1.

Outcomes in follow-up. At baseline, the median ankle-brachial index (ABI) was higher in OBL vs non-OBL patients (0.83 [IQR, 0.67-1.02] in the OBL group vs 0.74 [IQR, 0.59-0.93] in the non-OBL group; P<.001). However, the median Rutherford classification between the 2 groups was not statistically different (P=.33). Median periprocedural (within 30 days) ABI was improved compared with preprocedural values of each group, without any difference between the OBL vs non-OBL cases (0.99 [IQR, 0.86-1.10] in the OBL group vs 0.96 [IQR, 0.82-1.08] in the non-OBL group; P=.35). At 2-year follow-up, the median ABIs remained statistically similar between the groups (0.97 [IQR, 0.86-1.07] in the OBL group vs 0.92 [IQR, 0.75-1.06] in the non-OBL group; P=.05), although a strong trend for better ABI was observed among patients treated at OBLs. However, the 2-year median Rutherford classification was statistically better in the OBL group (1.00 [IQR, 0.0-2.0] in the OBL group vs 1.00 [IQR, 0.0-3.0] in the non-OBL group; P<.01). The OBL group at 2 years of follow-up had more asymptomatic or minimally symptomatic patients (Rutherford class 0-1) compared with the non-OBL group, while patients with CLTI were equally distributed between the 2 groups. Detailed information regarding the Rutherford class and the ABI values at several time points during follow-up are presented in Supplemental Table S1.

The risks of death (HR, 0.75; 95% CI, 0.50-1.11; P=.15), major amputation (HR, 0.69; 95% CI, 0.31-1.56; P=.37), TVR (HR, 1.06; 95% CI, 0.80-1.42; P=.68), and MAE (HR, 1.13; 95% CI, 0.85-1.48; P=.40) at 36 months were similar between the 2 groups, without any statistical difference detected. The combined risk of major amputation and death was also not different between the 2 groups (HR, 0.78; 95% CI, 0.54-1.12; P=.18) during a follow-up period of 3 years. The 36-month survival rate was estimated to be 85.8% (95% CI, 81.8-89.8) for the OBL group and 80.9% (95% CI, 76.4-85.5) for the non-OBL group (log rank P=.15) (Figure 1). The 36-month freedom from major amputation was 96.7% (95% CI, 94.7-98.8) in the OBL group and 95.4% (95% CI, 93.0-97.8) in the non-OBL group (log rank P=.37) (Figure 2). The 36-month Kaplan-Meier curves of freedom from TVR/TLR were similar between the 2 groups as well (67.9% [95% CI, 62.5-73.3] in the OBL group vs 69.8% [95% CI, 64.4-75.1] in the non-OBL group; log rank P=.68) (Figure 3). During 3 years of follow-up, MAE rate was 35.1% (95% CI, 29.6-40.6) in the OBL group and 31.8% (95% CI, 26.5-37.2) in the non-OBL group. No difference was observed between the 36-month Kaplan-Meier curves of freedom from MAE in the 2 groups (log rank P=.40) (Figure 4).

At baseline, 57/355 OBL patients (16.1%) and 86/355 non-OBL patients (24.2%) were seeing a wound-care specialist for wounds on the target limb. At 6-month follow-up, 24/272 OBL patients (8.8%) and 39/278 non-OBL patients (14.0%) were seeing a wound-care specialist for wounds on the target limb (P=.06). Among patients who had wounds at baseline, 23/47 OBL patients (48.9%) and 43/81 non-OBL patients (53.1%) had complete wound healing at 6-month follow-up (P=.72). At 12-month follow-up, 20/249 OBL patients (8.0%) and 28/255 non-OBL patients (11.0%) were seeing a wound-care specialist for wounds on the target limb (P=.29). Out of the patients who had wounds at baseline, 32/46 OBL patients (69.6%) and 56/73 non-OBL patients (76.7%) had complete wound healing at 12-month follow-up (P=.40). At 24-month follow-up 9/194 OBL patients (4.6%) and 13/213 non-OBL patients (6.1%) were seeing a wound-care specialist for wounds on the target limb (P=.66). Out of the patients who had wounds at baseline, 37/37 OBL patients (100%) and 63/65 non-OBL patients (96.9%)had complete wound healing at 24-month follow-up (P=.53).

Discussion

This study utilized data from the multicenter LIBERTY 360 trial to compare the outcomes of endovascular treatment modalities for PAD performed in OBL vs non-OBL settings.¹⁵ This was a propensity-score matched analysis; as such, there were only a few differences between the groups in terms of baseline and procedural characteristics. Our study was based on real-world data and indicated that patients with similar baseline and lesion characteristics could safely undergo endovascular procedures in an OBL vs non-OBL setting, without being at higher risk for procedural complications or death. The procedure success rate for OBL patients was 81.8%, with angiographic complications occurring in 9.8% of cases, while only 1 MAE occurred in a patient during the time interval between the procedure and discharge.

The number of OBLs suitable for endovascular procedures has been increasing in the United States since the reimbursement rates for OBL treatment were modified in 2008. As such, elective endovascular procedures have been increasingly performed in non-hospital settings.¹⁷ The OBL setting offers an improved and more efficient environment for patients, reduced overall healthcare resource utilization, and greater autonomy for the medical staff. However, despite the large number of procedures performed in the OBL setting, data regarding the complication rates, effectiveness, and overall efficiency of OBL endovascular procedures are sparse. Therefore, it has been questioned whether it is safe for patients to undergo interventions in a non-hospital setting and whether the standard of care is met, either due to limited equipment for the treatment of potential complications, or due to the possibility of overuse of care.¹⁸

Struk et al studied 141 outpatient vs 84 inpatient arterial interventions and reported complication rates of 5% and 8.3%, respectively.¹⁹ Similarly, a prospective study of almost 2700 procedures performed in an outpatient setting showed a major complication rate (including hematoma requiring surgical intervention) of 3.6%.²⁰ The angiographic complication rate (ie, severe dissection, perforation, distal embolization, abrupt closure, slow/no-reflow) of the present study, which limits the endovascular interventions to only procedures performed for the treatment of symptomatic PAD, is 9.8% in the OBL group vs 5.8% in the non-OBL group, with no statistically significant difference between the groups. Interestingly, only 1 patient from the OBL group experienced an MAE during the time interval between the procedure and discharge. Additionally, previous studies reported a periprocedural complication rate after endovascular interventions in OBLs ranging from 0.1%-16%.^19-23 The high heterogeneity of the reported complication rates is likely attributable to lack of standardized reporting modalities, the variable definitions used for procedure-related complications, and the different treatment modalities utilized. However, as demonstrated by our real-world study, the overall incidence of periprocedural major events, including death, major amputation, and TVR, after endovascular procedures for PAD is low at OBLs.

A previous study including almost 240 cases of arterial interventions performed in an outpatient practice showed a periprocedural complications rate of 8%, with most serious adverse events occurring within 4 hours of the index procedure.²² Therefore, the authors conclude that interventional procedures can be safely performed on an outpatient basis.²² Additionally, further studies have provided evidence that patients can be safely discharged on the same day after peripheral or coronary endovascular procedures.^20,24-26 Therefore, we believe that endovascular procedures for PAD can be performed safely in an OBL setting, with promising outcomes when the patients are observed for an extended period of time (eg, at least 4 hours) before discharge.^20,21,27-29 Furthermore, as most adverse events have been related to bleeding, clinical strategies that include minimizing the sheath size by selective stenting and using access-site closure devices in the OBL setting could further decrease the bleeding complications, while improving patients discomfort.^21,23,30,31 Therefore, we believe that with established protocols for arterial endovascular interventions suitable for an OBL setting, the clinical practice may be further improved.

This study also demonstrated that there was no difference in late-term outcomes of patients undergoing endovascular procedures for PAD in OBL vs non-OBL settings. Although there were slight differences in the techniques used between the 2 groups (eg, atherectomy was more commonly utilized in the OBL group; drug-eluting technology was more commonly utilized in the non-OBL setting), the overall survival, freedom from MAE, and freedom from major amputation/death were not different. Thus, our study indicated that endovascular procedures performed at OBLs are not inferior to procedures performed at hospitals for similar populations, in terms of late outcomes. However, appropriate patient selection for OBL treatment is crucial in order to optimize the treatment outcomes and patient prognosis. Furthermore, risk management plays an important role in avoiding complications and improving procedural success. Therefore, standardized protocols for the management of potential periprocedural complications and specific treatment strategies after a procedure failure should be developed in every OBL, depending on available resources. Last, organizational accreditation is a cornerstone for providing the standard of care, as a review process for clinical practices in OBLs has not yet been established. OBL accreditation will ensure optimal oversight and professional treatment that meets all standards of care, is equitable to hospital care, and offers a low MAE rate.

Study limitations. The LIBERTY 360 study was a multicenter, core-laboratory adjudicated study with data about patients that were typically excluded from large clinical trials. However, our results should be interpreted in the context of several limitations. First, this is a post hoc analysis of data retrieved from the LIBERTY 360 study, which was an observational, non-randomized study of endovascular therapies, sparing open surgery.¹⁵ Second, site and patient participation bias may have occurred due to the requirement for extensive testing. Third, the outcomes might have been affected by the various devices used and the preferred treatment algorithms among the physicians (eg, atherectomy, drug-eluting technology utilization, etc) in the different treatment settings (ie, OBL vs non-OBL, inpatient/outpatient). Moreover, this study was sponsored by a company promoting atherectomy; as such, bias could be attributed to the extensive use of orbital atherectomy. Last, the lesion location exhibited high heterogeneity, and sensitivity analyses for lesions limited to infrapopliteal or femoropopliteal segment could not be synthesized. Further studies should compare endovascular procedures among similar populations performed in OBL vs non-OBL settings.

Conclusion

Endovascular procedures performed in an OBL setting for the treatment of PAD were non-inferior to interventions performed in a non-OBL setting in terms of short- and long-term outcomes. Appropriate patient selection and standardized treatment algorithms based on individual OBL resources may further improve the prognosis of patients undergoing treatment at OBLs. However, further comparative studies are needed in order to evaluate our results and to determine the safety of undergoing endovascular procedures in a non-hospital setting.

Acknowledgments. All authors had unrestricted access to the datasets and can take responsibility for the integrity of the data and the accuracy of the data analysis. The authors also thank Ann Behrens, BS, and Brad J. Martinsen, PhD, of Cardiovascular Systems, Inc, for editing and critical review of this manuscript.

From the ¹Division of Cardiology, Rocky Mountain Regional VA Medical Center, University of Colorado, Denver, Colorado; and ²Premier Surgical Associates, Vascular Division, Knoxville, Tennessee.

Funding: This work was supported by Cardiovascular Systems, Inc.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Pliagas reports consultant income from Cook, Philips, Cardiovascular Systems, Inc, and Medtronic. Dr Giannopoulos reports consultant income from Abbott Vascular, Boston Scientific, Cardiovascular Systems, Inc, Gore, Medtronic, Philips, PQ Bypass, and Shockwave. The remaining authors report no conflict of interest regarding the content herein.

Manuscript accepted November 5, 2020.

Address for correspondence: Ehrin J. Armstrong, MD, MSc, University of Colorado, 1600 N. Wheeling Street, Aurora, CO 80045. Email: Ehrin.armstrong@gmail.com

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