Turning the tide: Evolution of below-the-knee endovascular intervention

As endovascular therapies have become more frequently utilized in the management of patients with atherosclerotic disease, there has been greater interest in applying these treatments to the infrapopliteal vascular beds.^1,2 In particular, advances in peripheral interventional technology with novel and dedicated equipment have created opportunity to address peripheral artery disease (PAD) involving the most distal vascular beds. In part, this treatment paradigm shift is a reflection of the 2015 Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II) updated guidelines, which included new endovascular treatment options for the management of infrapopliteal PAD. ³ However, this area remains relatively ‘data-free’, with the safety and effectiveness of these endovascular approaches (including use of atherectomy, drug-coated balloons, and stents) for treating infrapopliteal PAD undetermined and an area of ongoing investigation.

In this issue of Vascular Medicine, Müller and colleagues sought to address this evidence gap. ⁴ This retrospective single-center study analyzed procedural outcomes of over 300 endovascular procedures performed for infrapopliteal PAD from 2008 to 2018. Included patients had symptoms ranging from claudication to critical limb ischemia (CLI) and encompassed procedures such as balloon angioplasty as well as placement of bare-metal and drug-eluting stents. Infrapopliteal lesions with stenoses greater than 50% were included in the investigation and categorized based on the TASC classification system, ranging from simpler type A lesions to more complex type D lesions. ⁵ Müller et al. also utilized regression models to assess for predictors of the primary outcome of clinically-driven target lesion revascularization.

This study found a very high technical success rate for infrapopliteal endovascular procedures at 96.7%, with no difference when comparing treatment of type A and B lesions to the more complex type C and D lesions (96.5% vs 96.9%, p = 0.837). ⁴ The investigators also reported a low complication rate (7.7%, all related to access site complications) and durable long-term effectiveness, with 77.2% of lesions free from clinically-driven target lesion revascularization at 12 months. Additionally, results from their regression analysis identified several factors predictive of the need for clinically-driven target lesion revascularization, including CLI, distal anatomic lesions, occlusive disease, and TASC D lesions.

A particular strength of the study by Müller and colleagues is the broad patient population included with varying severity of disease (Fontaine classes II–IV). Although infrapopliteal artery intervention is typically reserved for patients with CLI, there are specific scenarios, such as improving outflow after supra-popliteal stenting, that may warrant these adjunct procedures. Additionally, this study furthered prior investigations examining infrapopliteal angioplasty for limb salvage by examining a larger cohort of patients with more diverse use of endovascular devices. ⁶

However, one of the challenges inherent to establishing the effectiveness of these infrapopliteal procedures is the wide variety of devices utilized, ranging from plain balloon angioplasty (which was used for the majority of lesions in this study) to drug-eluting stent placement and atherectomy. With the diversity of device utilization, it is challenging to evaluate specific endpoints related to each individual device and the impact of each device on the composite procedural outcome. As mentioned by Müller and colleagues, this is represented by the ongoing discussion and controversy regarding the utility of drug-coated balloons for infrapopliteal artery disease. ⁷

Overall, the results from the investigation by Müller et al. further support the role for endovascular therapies as a primary modality for the treatment of infrapopliteal PAD. These findings bolster similar results observed in other single-center studies. ⁸ This study is also particularly timely, as there is substantial interest in determining the optimal strategy to manage patients with CLI, which often involves treatment of infrapopliteal artery disease. For instance, the NIH-sponsored BEST-CLI trial (ClinicalTrials.gov Identifier: NCT02060630), which randomized patients with CLI to either a ‘best’ endovascular treatment strategy versus a ‘best’ surgical revascularization strategy, has finished enrollment and is completing follow-up. This clinical trial has the opportunity to substantially impact clinical practice, and having real-world safety and effectiveness benchmarks to compare endovascular treatment outcomes will be useful when understanding the generalizability of the BEST-CLI trial results.

There are numerous areas of investigation that remain in the infrapopliteal PAD space, in particular understanding optimal device and arterial access site strategies. Employing observational research to bridge gaps where randomized trial data are lacking is critical for advancing vascular clinical practice and elevating patient care.