How to Approach Below-the-Ankle Arterial Interventions

Abstract

Critical limb ischemia, also referred to as chronic limb-threatening ischemia, is a major medical problem leading to limb amputations if not managed properly with a multispecialty team. Establishment of sufficient arterial flow to the foot is an integral part of this care. During the past two to three decades, arterial revascularization has become primarily endovascular with open surgical approaches significantly diminished in comparison. As techniques, tools, and experiences of the interventionalist have improved, the ability to recanalize more complex lesions has become more commonplace. We are at an age that even the arteries below the ankle can be accessed for complex interventions and even be recanalized if necessary. This article will discuss common arterial interventions performed below the ankle.

The prevalence of peripheral arterial disease (PAD) is at the rate of 5 to 10% and increases to 15 to 20% in persons older than 70 years. ¹ Approximately 1 to 3% of the PAD population develop critical limb ischemia (CLI). ^{2 3} According to the Rutherford classification, PAD has been grouped into six categories, of which grades 4 through 6 are considered CLI. These include rest pain, minor tissue loss with nonhealing ulcer, or gangrene/major tissue loss. ⁴ In many CLI patients, arterial compromise involves the femoropopliteal and tibio-pedal segments. Aortoiliac recanalization, although at times necessary, are rarely needed in the setting of CLI. Many patients will have complex multilevel disease that involves several segments below the groin. The goal is to establish an inline arterial flow to the foot and wound if applicable. ⁵ The traditional approach in endovascular interventions has been to recanalize the femoral, popliteal, and tibial arteries. However, many patients, especially diabetics, will have occlusive or near occlusive disease below the ankle (BTA). ⁵ In general, below-the-knee (BTK), which includes BTA, interventions should not be pursued for patients with claudication (i.e., Rutherford grade 3 or less). This procedure should almost exclusively be reserved for patients with CLI. Inappropriate BTK or BKA procedural intervention can progress a patient into CLI at an earlier time frame due to the interventions themselves. One of the major challenges with BTA procedures specifically is the lack of dedicated tools for this vascular territory, while tibial artery tools and techniques have significantly increased in recent years. This segment of the peripheral arterial tree is fraught with unique difficulties relative to the more proximal vasculature. Smaller caliber arteries combined with heavy medial calcinosis limits ability to cross the occlusions. There are also no stents designed for use in pedal arteries which makes management of small, heavily calcified arteries more challenging. However, improvement and availability of lower profile devices has allowed interventionalists to successfully recanalize BTA arteries. In addition, during the past 10 to 15 years, pedal access has become a relatively common tool in endovascular management of CLI patients by experienced interventionalists.

As pedal access techniques have surged, allowing operators to revascularize previously considered untreatable patients, so has the ability to improve above-the-ankle outflow with pedal, and even tarsal artery interventions. As a result, interventionalists focused on more targeted, angiosome-directed revascularizations, which have been shown to improve limb preservation rates. ⁶ When the primary issue is forefoot nonhealing wounds, especially in angiosomal watershed territories, an intact or revascularized pedal loop has been of interest and has demonstrated decreased wound healing times. ⁷ It is understood that intact pedal runoffs can increase tibial patency rates as well.

Tools and Techniques

The majority of BTA interventions rely on plain old balloon angioplasty (aka PTA), as the disease burden and lack of significant forefoot runoff vessels are restrictive for other options. More aggressive vessel preparations with scoring, cutting, and other unique adaptations such as lithotripsy and serration angioplasty have been performed. In our experience, plain angioplasty followed by scoring angioplasty has provided good outcomes. Plain angioplasty is almost always necessary prior to scoring angioplasty in severely diseased pedal arteries. For a successful BTA intervention, 0.014″ platform wires, support catheters, and balloons are essential. Atherectomy for vessel preparation has seen growth recently as well. The atherectomy devices that have a low profile option for BTA atherectomy are Orbital (Diamondback, CSI) for circumferential calcium, Directional (Hawk S, Medtronic) for mixed or soft plaque, Rotational (Phoenix, Koninklijke Philips), Excimer Laser (Turbo-Power, Koninklijke Philips and Auryon Laser, AngioDynamics) for mixed plaque morphologies. Due to the small caliber and heavy disease burden within the pedal arteries, atherectomy may help increase compliance and decrease dissections. It should be noted that there is a lack of valuable data to validate use of BTA atherectomy, and its use is operator dependent, mostly with anecdotal evidence and outcomes guiding its use. Distal emboli, particularly to the tarsal arteries, can result in negative procedural and limb preservation outcomes, which will be discussed further in the “Complications” section of this article.

Through procedural experience, several techniques can be adapted to overcome difficult BTA revascularization scenarios. Not uncommonly, an interventionalist is able to cross a complex pedal CTO or severely stenotic lesion with a 0.014″ guidewire, but fail to advance any support catheter for wire exchanges, or balloons to perform PTA. In these situations, adjunctive approaches can be performed. More proximal PTA may minimize total friction that may be contributing to the problem. Smaller coronary support catheter use (i.e., Corsair, Asahi) followed by stiffer guidewire exchange may provide the needed support allowing more force to push the balloon. PIERCE or even direct extravascular calcium interruption arterial procedure (DECIAP) techniques have been described, ^{8 9} which involve externally trying to break the calcium by needle punctures into the area. The authors of this article have reservations about this approach as evidence is lacking and the potential for creating additional ulcerations is a possibility. Converting to “flossing” or externalization of the wire may also provide additional ability to advance the balloon. Antegrade pedal access-directed PTA using short shaft pedal balloons or very small profile balloons (1.0, 1.2, and 1.5 mm) is another option for treating challenging lesions. Plantar flexion of the foot in the anterior tibial to dorsalis pedis arteries and in the posterior tibial and plantar artery will allow straightening and limit tortuosity of the anterior tibial/dorsalis pedis arteries and posterior tibial/plantar arteries which can aid in advancing the balloon in some cases. Lastly, the orbital atherectomy system can be used to create a channel in these severely stenotic/occlusive small arteries. However, this approach carries the risk of microemboli in the foot without much reserve and should be applied very carefully with vasodilators and frequent breaks in the application given the high-risk nature of the technique. Another very important point is that the operator should be confident that the distal aspect of the guidewire is indeed intraluminal prior to performing these techniques, otherwise disastrous outcomes may occur.

If attempting pedal loop revascularization and there is difficulty navigating the pedal loop, there are several tips and tricks to improve success. These include obtaining digital subtraction angiography roadmap in the AP projection which may assist via seeing a variable vessel trajectory. Approaching the loop from a different tibial vessel may be required. Direct antegrade access of a tibial vessel in the mid to distal segment may provide the necessary increased support. Finally, use of shapeable guidewires and, in extreme situations, direct first dorsal metatarsal artery access can be of used which can direct the guidewire to either the dorsalis pedis or plantar arteries based on the existing vessel patency and targets. With repetitive attempts, vasospasm may be encountered, and thus liberal use of local nitroglycerin should be considered. Authors of this article use nitroglycerin up to 1,200 μg, with 300 μg slow boluses throughout the course of a single endovascular procedure.

Complications

Interventions of pedal arteries are in general safe and technically successful. But there are complex cases which may result in known complications following more aggressive approaches. One of the most significant and concerning complication is a rupture of the artery. As the lumen of these diseased arteries is often less than 1 mm, angioplasty with a 1.5- or 2-mm noncompliant balloon may result in vessel rupture. Ruptures following PTA differ from a self-limiting wire perforation of a tiny branch, and immediate balloon occlusion, application of external pressure, and possibly embolization of the ruptured segment may become necessary. A second important complication to have an understanding about prior to performing BTA interventions is new microemboli in the background of underlying desert foot anatomy, which can turn a relatively chronic problem into an acute more serious scenario. If no distal flow is seen in the forefoot following orbital (or any) atherectomy, immediate targeted infusion of nitroglycerin (300–400 μg), tissue plasminogen activator (TPA) (2–4 mg), and suction thrombectomy using the 3-Fr penumbra continuous suction thrombectomy device may be helpful. Occasionally, if these efforts fail, overnight thrombolysis with a microcatheter in the effected tibial artery territory may become necessary.

Case Presentations

Figs. 12345 present multiple different patients with below-the-knee interventions using many of the techniques described earlier.

Fig. 1.

A common scenario is the inability to cross the severely stenotic, calcific lesion with a low-profile balloon despite a 0.014″ wire being distal to the lesion. Digital subtraction angiographic image shows severely stenotic/occlusive lesion of the dorsalis pedis artery (red arrow, a ). Native image shows heavy medial calcification (arrows, b ). After failing different catheters and balloons, orbital atherectomy device was used to cross the lesion (red arrow, c ) and angioplasty was successfully performed. Postangioplasty image demonstrates good flow to the distal foot ( d ).

Fig. 2.

This case demonstrates successful pedal loop recanalization from an anterior tibial artery (AT) approach, which may be particularly helpful if the wound is located on the plantar surface of the foot. Given the technically challenging anatomy of the posterior tibial artery (PT) with an absent stump, recanalization of this vessel could be particularly difficult or impossible. On the preintervention angiogram, there was no visible flow to the plantar foot ( a ). Since the AT was the low hanging fruit, the pedal loop was crossed with a wire (arrows, b ). After angioplasty of the loop, the plantar arteries had retrograde perfusion through the AT/dorsalis pedis (DP) arteries ( c ).

Fig. 3.

Patient otherwise active with worsening plantar ulcer planned for below-knee amputation. Initial digital subtraction angiography shows no inflow disease but severe diffuse disease below the ankle ( a ). A challenging issue with this particular case would have been recanalization of both the medial and lateral plantar arteries at the same time. We elected to perform sequential angioplasty each branch and were able to get a good result without compromising either one ( b ). If a 7-Fr sheath is placed, an advanced kissing balloon technique can be performed in this territory as well.

Fig. 4.

This patient had no inflow disease but the AT tapered to complete occlusion above the ankle ( a ). Digital subtraction angiography (DSA) of the foot shows a segment of the plantar artery but otherwise desert foot anatomy ( b ). Attempt to reach the dorsalis pedis artery (DP) from an antegrade approach resulted in a branch perforation with the 0.014″ guidewire (arrow), but at the same time demonstrated a suitable distal target artery ( c ). Synchro Soft 0.014″ Neuro guidewire was used to cross the lesion (arrow, d ). Final DSA shows there was a hibernating artery which responded well to angioplasty ( e ).

Fig. 5.

The patient presented with an ulcer and rest pain. Digital subtraction angiography (DSA) shows desert foot anatomy ( a ). Magnified DSA image from AT injection shows diminutive medial and lateral tarsal arteries ( b ). Postangioplasty with a 2 mm × 8 cm balloon shows overall improvement with a focal residual narrowing (arrow, c ). A 1.5-mm noncompliant coronary balloon was used to treat the residual focal stenosis (arrow, d ). The balloon ruptured under fluoroscopy during inflation and an immediate DSA image was obtained, which showed a large perforation ( e ). The actively bleeding focus was embolized after failed prolonged balloon angioplasty and external compression. Following selective embolization, the patient still had good flow (not shown) and clinically has done well with healing of the ulcer and resolution of rest pain.

Discussion

CLI is considered an epidemic with significant morbidity and mortality and multiple consequences. Patients with CLI commonly present with BTA arterial disease and occlusion of the dorsalis pedis and plantar arteries, which may prohibit distal bypass and prevent the ability to heal minor amputations. ¹⁰ Historically, 73 to 95% of all CLI patients will experience a major amputation at 1 year without prompt revascularization. ⁴ The number of amputations is particularly high in patients with Rutherford grade 5 to 6 diseases with a strong association with diabetes. Palena et al demonstrated that diabetic patients typically presented with a more diffuse pattern of occlusion, often involving multiple pedal branches, with this angiographic appearance previously thought to be too challenging to intervene on. ¹²

With the advent of new techniques and technologies allowing improved access of the pedal arteries and subsequent BTA interventions, historical success rates ranging from 70 to 95% have been achieved. ^{11 12} In particular, our unpublished but regularly reviewed technical success rate is around 95%. This higher-than-expected success rate is likely secondary to our extensive experience performing pedal access in SAFARI procedures for the past 20 years. When Spinosa et al initially described the SAFARI technique, the 1-year patency remained relatively low at 58%. ¹³ However, as multiple centers gained exposure and experience, their technical success rate increased. Similarly, our non-published limb salvage rate of 84% at 12 months, for patients who underwent BTA interventions, is on the high end compared with previous studies reporting a wide range of limb salvage rates from 73 to 92%. ^{2 3 4 5 6 7} The reason for the above-average limb salvage rate is not only due to the volume of cases but also due to the utilization of advanced techniques and devices that allow us to connect antegrade/retrograde access including use of reentry/snare, double-balloon, kissing balloon, and sharp recanalization at or BTK joint, with attention to the concept of angiosomal distribution. As Manzi et al previously mentioned, successful revascularization of the artery directing feeding the ulcer leads to high limb salvage and wound healing rate. ¹¹

Conclusion

In conclusion, BTA intervention is very feasible for experienced CLI interventionalists, but fraught with specific challenges unique to this vascular territory given vessel size and degree of calcification. Performing complex procedures proportional to operator's experience and skill level will allow for better outcomes and less complications.