Current And Emerging Options For Intervention In CLI
Treatment for peripheral arterial disease (PAD) and particularly critical limb ischemia (CLI) involves the collaboration of a multidisciplinary team and consideration of both new and existing interventions. These authors explore the potential of catheter-based interventions and other technologies to salvage limbs.
As surgical treatment options become increasingly more consumer driven, it is imperative that practitioners step back and review the role of historic and proven treatments in comparison with new and innovative technology. When it comes to the treatment of peripheral arterial disease (PAD), we find ourselves in the “eye of a storm” characterized by rapid advances in minimally invasive technology.
The treatment of PAD necessitates a collaborative and multidisciplinary approach. This involves podiatrists and vascular practitioners employing the most effective surgical and wound care strategies. The common goals of practitioners in managing this challenging condition should be consistently high rates of wound healing and limb salvage.
For the past five years, it has been increasingly more common for patients to enter the office with a clear expectation about whatever treatment is appropriate for their given malady. Access to Internet-based sources of medical information, direct to consumer advertising and local news health reports are some of the more common sources of patient education. Direct to consumer marketing has been a very effective tool in increasing public awareness of disease states and the medical products that treat them. To be fair, in our experience, most patients are very reasonable when the physician’s ultimate recommendation differs from their preconceived expectation.
Our multidisciplinary wound care center, the Penn Wound Care Center (part of the University of Pennsylvania Health System) has a collaborative team model. The multidisciplinary model, directed by our expert podiatric colleagues, has been and continues to be the most important factor responsible for an excellent rate of limb salvage in patients with PAD.
Re-Examining The Goals Of Revascularization
In regard to the treatment of severe chronic limb ischemia (CLI) associated with significant tissue loss, the primary goal for the revascularization is guided by an unambiguous, longstanding vascular surgical dictum: Provide maximal, sustained blood flow directly to the wound bed. Once this occurs, our podiatric colleagues have the best chance of healing a wound. Of course, the healing may take place over a long period of time and require meticulous wound care.
In the rush to utilize innovative catheter-based technology and apply it broadly in the treatment of PAD, there is a concern that we have forgotten the ultimate goal of advancing patient care. In this case, our goal is to heal wounds. If we are able to merge the goal of healing a wound with a catheter-based technology, this creates a mutually beneficial circumstance. However, we must never lose sight of the fact that healing the wound is the primary goal.
Historically, in the treatment of CLI, our best indicator of success following open surgical revascularization has been the restoration of a palpable pulse in the foot. There is no difference in what type of bypass one performs as long as pulsatile and direct inline flow to the wound bed is the desired and attained goal.
In the case of the longstanding diabetic patient with non-compressible and calcified vessels, the graft pulse may not be palpable. In these cases, the acceptable surrogate findings have been the return of normal pressure waveforms by noninvasive testing and the intraoperative confirmation of brisk bleeding by our podiatric colleagues at the time of debridement or resection.
Somewhere along the line, we have diverged from the principle of a graft pulse as we increasingly rely upon minimally invasive technology to revascularize patients with severe CLI. I hear discussions of “partial revascularizations” with the idea that “We will see how that works.” However, without the prompt, complete and sustainable restoration of blood flow to the wound bed, are we losing opportunities to salvage the maximal amount of at risk tissue? Surely, catheter-based interventions have the opportunity to improve blood flow but questions remain. How much improvement do such interventions provide? For how long will the improvement last? Are we immediately able to identify failure of our catheter-based intervention in a way that allows timely re-intervention?
Weighing The Various Limb Salvage Options
In the infrainguinal region, the various options for limb salvage range from catheter-based intervention with various therapeutic devices to traditional open surgical bypass.
The concern about patency associated with angioplasty, stenting and atherectomy of infrainguinal blood vessels is an ongoing and controversial topic. There is a shortage of good clinical data for many of the available devices. Much of the available data are from anecdotal or single center experiences.
There is a developing body of data regarding self-expanding bare metal stents in the femoral popliteal anatomy for the important one- to two-year follow-up period. McKinsey and colleagues reported a single center registry experience using directional atherectomy to treat 579 lesions in patients with lower extremity ischemia.1 This study reported that primary patency for all lesions at 12 and 18 months was 62.2 percent and 52.7 percent, respectively. These results are mediocre at best. Unfortunately, no large, prospective, randomized trials exist with any available atherectomy technology.
As a matter of disclosure, we are comfortable offering all of these options and do not believe we are partial to any single modality. What does appear to be clear at this point in time is that the patency of open vascular reconstructions using appropriate vein conduit with well selected inflow and target outflow vessels provides a substantial advantage with regards to patency and durability in comparison to the available catheter based approaches, especially in the infrapopliteal arteries. The infrapopliteal level, in many cases of CLI, must undergo revascularization to establish direct inline flow to the wound bed.
In our experience, there is a management dilemma when our podiatric colleagues call and note that wound healing has stalled after we have performed a minimally invasive infrapopliteal revascularization (angioplasty, stenting or atherectomy of a tibial level vessel). When one does not achieve palpable pulses after using a catheter-based modality in a partial revascularization, we do not know if the revascularization has failed. Noninvasive examination, including ultrasonography, magnetic resonance imaging (MRI), computed tomography angiography (CTA) and pulse volume recording (PVR), is minimally helpful for detecting subtle but clinically relevant disease recurrence.
Ultimately, the dilemma frequently leads us to repeat the invasive contrast arteriography, exposing the patient to cumulative radiation and risks like contrast nephropathy. If a repeat catheter-based intervention is possible, the same concerns arise regarding long-term patency of the subsequent re-intervention. With a tibial bypass, failure does occur. However, there is never a question of the patency of a tibial bypass. The bypass is either open or it is closed.
Key Insights On Catheter-Based Interventions
To be clear, catheter-based interventions certainly have an appropriate role in the treatment of infrainguinal PAD, including presentations of CLI with significant tissue loss. The inadequacy or unavailability of an autogenous vein conduit necessary to perform a tibial level revascularization may be a relative contraindication to an open bypass.
However, heparin-bonded prosthetic conduits have recently demonstrated impressive patency rates in comparison to previous prosthetic conduits. In the absence of a vein conduit, catheter-based treatment may be an option to improve tibial blood flow. The caveat is that diligent post-revascularization follow up is essential and, at the first sign of stalling or regression of wound healing, re-imaging is necessary.
When adequate vein length is not present, a catheter-based intervention can shorten the length of vein necessary to revascularize infrapopliteal vessels directly to the wound bed. This is permitted by minimally invasive treatment of the femoral-popliteal arteries. In the femoral-popliteal anatomy, various catheter-based modalities including self-expanding stents yield acceptable patencies (50 to 60 percent at two years). The concern in this configuration is that there is a distal vein bypass dependent upon the sometimes unpredictable restenosis pattern of a femoral popliteal stent.
For patients suffering from lifestyle limiting claudication, percutaneous revascularization offers a less morbid solution to their illness while preserving vein conduit for future infrainguinal or coronary revascularization. In the absence of severe tissue loss, vascular surgeons may perform palliative percutaneous interventions and can often repeat these interventions on the femoral and popliteal arteries when and if failure does occur for the patient who develops new symptoms.
For patients with rest pain or small superficial ulcerations, our decision-making is guided by the premise that these pathologies may not require the durability of traditional open bypass patency necessary to heal CLI with significant tissue loss. Additionally, these patients will frequently carry a high-risk operative profile that one must carefully consider. With CLI and rest pain, even an incremental increase in perfusion will often ameliorate the patient’s pain. In the case of superficial ulcerations, revascularization of a single level or “partial revascularization” frequently permits wound healing to occur, provided one implements diligent wound care.
Catheter-based options for revascularization of CLI currently play an important role. Available technology continues to improve and leads to significant innovations. These innovations include biodegradable stents, drug eluting balloons and stent platforms. They hold great promise to improve our options in the infrapopliteal territory. We must have clearly articulated treatment goals that are communicated with our multidisciplinary teams as we set out to successfully manage the challenging process of severe limb threatening ischemia.
Dr. Kirksey is affiliated with the Department of Vascular Surgery at the University of Pennsylvania School of Medicine in Philadelphia.
Dr. Troiano practices at the Center for Foot and Ankle Disorders in Philadelphia.
1. McKinsey JF, Goldstein L, Khan HU, et al. Novel treatment of patients with lower extremity ischemia: use of percutaneous atherectomy in 579 lesions. Ann Surg 2008; 248(4):519-28.