Introduction

An intact pedal arch is associated with improved wound healing in critical limb ischemia (CLI).

Endovascular treatment of the pedal arch has good procedural success and patient outcomes in published registries. The small vessel diameter and tortuous anatomy of the foot present unique challenges to endovascular intervention.

Pedal Arch Reconstruction

Arterial revascularization, by a surgical or endovascular approach, is recommended to prevent limb loss in critical limb ischemia (CLI) [1, 2]. Percutaneous transluminal angioplasty has been increasingly used in the treatment of infra‐inguinal arterial occlusive disease. While there are significant limitations in directly comparing endovascular and surgical first strategies for infrapopliteal occlusive disease in CLI, the limited data suggests comparable rates of limb salvage and survival, particularly in those with reduced life expectancy or without a suitable bypass vein graft [3–5].

A major goal of revascularization in CLI is to provide direct flow to the site of a nonhealing arterial wound. This can often necessitate multilevel intervention. Historically, most endovascular interventions were above the level of the ankle, but recent studies have suggested that inframalleolar intervention, including pedal arch angioplasty, may help improve wound healing rates. Therefore, the pedal arch is an important anatomic target in select CLI cases.

In the typical below knee anatomy, the popliteal artery gives rise to the anterior tibial (AT) artery and tibioperoneal trunk, which will in turn supply the peroneal and posterior tibial (PT) arteries. The peroneal artery will extend to the distal leg where it supplies the anterior malleolar and calcaneal branches. The AT courses to the forefoot where it transitions to the dorsalis pedis artery at the level of the ankle joint. The PT bifurcates below the malleolus into the medial and lateral plantar arteries (Figure 12.1), which in turn supply the plantar surface of the foot. Multiple anatomic variants of the below knee vasculature exist, including a trifurcating origin of the three vessels, high origins of the AT or PT, as well as hypoplasia of one or more branches. The absence of the PT is a more common variation, existing in 1–5% of the population [6].

The anterior circulation of the foot includes the dorsalis pedis, lateral tarsal, and arcuate arteries (Figure 12.2). The arcuate artery will typically supply the second, third, and fourth dorsal metatarsal arteries, though anatomy is variable. The posterior foot circulation is composed of the medial and lateral plantar arteries, which connect via the deep plantar arch and give rise to the plantar metatarsal arteries (Figure 12.3) [6].

The pedal arch is the arterial connection between the anterior and posterior circulations of the foot in which the dorsalis pedis and lateral plantar arteries connect via the deep plantar. The pedal arch can have several anatomic variations which are clinically relevant to wound healing (Figure 12.4) [7, 8]. A complete pedal arch, as compared to interrupted pedal arch, has been associated with increased rates of wound healing and shorter time to healing in patients with CLI [9–11]. The presumed benefit of a complete pedal arch is the ability to collateralize adjacent angiosome territories resulting in the observed improvement in healing; however, the association of pedal arch quality and amputation‐free survival for CLI has reported mixed results [10, 12].

Controlled investigations are needed to assess the association of anatomic pedal subtypes on clinical outcomes. While subject to publication bias, initial observational series of pedal arch intervention have been promising. In single center and multicenter registries, endovascular angioplasty of the transpedal arch has resulted in favorable outcomes, with technical success rates of 75–88% [9, 11, 13], limb salvage rate of 88%, and amputation‐free survival rate of 73% at one year [9]. When care is taken to avoid injury to a potential infrapopliteal surgical target vessel, an endovascular first approach has not shown negative impact to surgical pedal bypass outcomes [14].

Endovascular intervention of the pedal arch has been shown to be a safe and effective approach to treatment and has become an important intervention target in select CLI cases. This chapter will focus on the unique challenges and a systematic approach to pedal arch intervention.

Indications for Pedal Revascularization

Current guidelines do not differentiate pedal from infrapopliteal revascularization recommendations in the setting of CLI. The goals of transpedal arch intervention are to improve outflow of the tibial arteries, to improve flow to an adjacent angiosome, and to open a conduit for retrograde intervention of an additional infratibial vessel to achieve in‐line flow in CLI. Procedural failure may result in worsening foot ischemia, so appropriate patient selection is crucial. When care is taken to avoid injury to a potential surgical target vessel, an endovascular first approach has shown to not have a negative impact on surgical pedal bypass outcomes (Figures 12.5 a–h and 12.6a–d) [14].

Technical Considerations

Pedal arch intervention is best approached via the ipsilateral antegrade approach. The pedal vessels are small in caliber and take a more tortuous course than the larger and more proximal leg vessels. An antegrade approach with a long sheath maximizes the ability to push and transmit torque for wire and catheter manipulation. A long sheath will also allow the use of shorter length catheters, devices, and wires, which can become a significant limitation of alternative access strategies. Placing the sheath in the most distal disease‐free segment of the superficial femoral artery (SFA) can maximize support. A 5 Fr system will enable passage of equipment needed for the small caliber infratibial and pedal vessels, though if there are plans to use a closure device that requires a larger arteriotomy, a 6 Fr system is also commonly used.

Special Considerations of the Pedal Intervention

Defining Pedal Anatomy: Selective angiography via long sheath or through a microcatheter (e.g. 0.035 Navicross – Terumo, or 0.018 Quick‐cross – Spectranetics) is recommended to deliver concentrated contrast injections to the infrapopliteal and pedal vessels for optimal anatomic definition prior to and during intervention. Standard views include AP with shallow cranial and straight lateral views of the foot.

Lumen Crossing: Due to the branch and choke vessels that arise from the pedal arch, subintimal crossing and recanalization can lead to branch occlusion with the risk of tissue or limb loss. Every effort should be made to cross true lumen.

Anticoagulation Strategy: Given small caliber vessels with diminished flow, anticoagulation levels must be judiciously watched with a goal ACT between 250 and 300 seconds to avoid thrombus formation.

Vessel Tortuosity: Tortuosity can be a challenge in small vessels. Difficult to cross lesions may be better defined by taking additional, nonstandard oblique angiographic views for better spatial understanding and directionality of the vessel. In addition, plantar or dorsiflexion of the foot may enable changes in vessel conformation to allow wire or device passage through tortuosity near the ankle [7].

Vasospasm: Small caliber vessels are more prone to vasospasm. Liberal use of intraarterial vasodilators is recommended. Verapamil dosed at 2.5 mg and nitroglycerin dosed at 200 mcg are commonly used and will be most effective when delivered via a microcatheter.

Angioplasty Technique and Balloon Sizing: Bailout stenting below the ankle is not recommended, so care should be taken to achieve optimal angioplasty result. Low pressure, prolonged inflations (e.g. three minutes), and 1 : 1 balloon sizing are recommended. Infrapopliteal vessel sizing can be accomplished using an IVUS catheter if vessel caliber allows. In practice, tortuosity and small vessel caliber prevent the use of intravascular imaging for vessels below the ankle. Most infrapopliteal vessels will measure 1.5–2.5 mm. A 1.5–2.0 mm balloon is most commonly used for the dorsalis pedis, pedal arch, and plantar arteries. Angiography following administration of vasodilators through a microcatheter can aid in estimation of vessel caliber. When there is question of sizing, the smaller of balloons should be chosen to minimize risk of flow limiting dissection or perforation.

Calcification: Calcification of the pedal arch vessels poses a challenge, particularly in tortuous vessels. The pedal arch vessels are not large enough to accommodate scoring balloons. In straight vessel segments, orbital atherectomy can be performed using a 1.25 mm micro crown (Cardiovascular Systems, Inc). Due to short anatomic landing zone and small caliber vessels, distal embolic filter protection is not possible. Similar to coronary intervention, atherectomy runs must be limited in duration, ideally less than 10 seconds, to allow for adequate washout to prevent the no‐reflow phenomenon. Tortuosity increases the risk of vessel dissection or perforation during atherectomy. In such cases, a small coronary balloon can be utilized for focal angioplasty at higher pressure if required for a recalcitrant calcified lesion. Ultimately, calcification with tortuosity increases the risk of the procedure and the operator should reassess the risk and benefit of proceeding.

Summary

The quality of the pedal arch is an important predictor of wound healing in CLI. Advances in endovascular technique have allowed endovascular intervention of the pedal arch to achieve good efficacy and safety outcomes. With appropriate patient selection and technique, the pedal arch can be a valuable intervention target in CLI.