The treatment of critical limb ischaemia (CLI), a condition that may eventually lead to limb loss in a substantial number of patients, consumes a significant amount of healthcare resources. Distal bypass for limb salvage with autogenous conduit has been considered the procedure of choice for good-risk patients who also have suitable veins and distal target arteries for bypass. However, often one or more of these criteria are not met, and a large number of patients would face a major amputation with unfavourable outcome and poor quality of life.
The endovascular approach offers the advantages of a minimally invasive procedure that only requires local anaesthesia and is associated with shorter procedure time and hospital stay, as well as reduced morbidity rates compared with bypass surgery.
Indications
The decision to perform any endovascular intervention for tibial occlusive disease should be based on clinical grounds rather than diagnostic imaging, as most patients with significant tibial disease are asymptomatic. These asymptomatic patients and claudicants can be treated conservatively with lifestyle changes, an exercise program and sometimes drug therapy; revascularisation is indicated if ischaemic rest pain or ulcerations develop.
Almost all CLI patients are threatened by other co-morbidities related to the generalised atherosclerotic process. This general poor-health status means shorter life expectancy and high-risk for surgery, and, in the authors' opinion, supports the idea that endovascular intervention may soon be considered the primary treatment modality for CLI caused by infrapopliteal occlusive disease.
Endovascular Treatment Strategy
The clinical success of any infrapopliteal intervention for occlusive disease often depends on pre-procedure patient optimisation and achievement of adequate inflow into the infragenicular region by either an endovascular or surgical approach.
The ideal goal would be to restore uninterrupted blood flow down to the foot in at least one vessel.5 When this is not achievable, which is often the case in diabetic patients, therapy is targeted at maximising flow to the trifurcation vessels and geniculate collaterals.
Crossing of the Lesion
Once arterial access is obtained, multi-planar angiography with magnified views of the region of interest is performed.
When passing a lesion seems particularly cumbersome, subintimal lesion passage, (the Bolia technique), offers an effective alternative to the intraluminal approach.
Another alternative approach is the step-by-step laser ablation with a 0.9-1.4mm pulsed excimer laser cath-eter. This short ablation allows the guidewire to be further advanced into the occluded vessel. The laser catheter ablation is generally stopped one to two cm before the end of the occlusion. From here the lesion is best cross-ed with the guidewire in order to prevent dissection.
Lesion Treatment
Percutaneous Transluminal Angioplasty
Infrapopliteal percutaneous transluminal angioplasty (PTA) became feasible with the introduction of low-profile peripheral balloon systems and the use of coronary balloons. After a successful lesion passage, a 5-6F sheath is inserted into the popliteal artery. This provides sufficient support for the balloon catheter to pass the lesion. In order to prevent dissection, hydrophilic-coated balloon catheters with a diameter 2.5-4.0mm are mostly used. A long stenosis is best treated with a gentle PTA using a low-pressure balloon with sizes ranging from eight to 10cm in length and 2.5 to 3.5mm in diameter.
The Bypass versus Angioplasty in Severe Ischaemia of the Leg (BASIL) trial was a randomised trial comparing PTA with bypass in patients with CLI. They found that in the short term, PTA is cheaper than surgery and that 12-month amputation-free survival for bypass and balloon angioplasty as first-line strategy were 68% and 71%, respectively. The published primary patency rates for PTA are less uniform and range from 15% to 70%.
Cutting or Scoring Balloon
The mechanism of peripheral cutting or scoring balloons has been referred to as atherotomy. With these advanced PTA techniques, either atherotomy blades are mounted on the surface of a non-compliant balloon (Peripheral Cutting Balloon, Boston Scientific Interventional Technologies, San Diego, CA, USA), or a nitinol-scoring element encircles a minimally compliant balloon (AngioSculpt, AngioScore,Inc, Fremont, CA, USA). This technique decreases vessel elastic recoil and perivascular injury by focal concentration of the dilating force. Preliminary data show that these devices appear to lower the need for infrapopliteal stents.
Subintimal Angioplasty (SIA)
In some centres, SIA is gaining popularity for long segment occlusions below the knee. The concept of passing a wire into the subintimal space and inflating a balloon to create a channel for blood flow seems to violate the traditional endovascular principles. However, Bolia et al. has reported significant technical and clinical success with this procedure. Nydahl et al. investigated the use of subintimal PTA for restoring blood flow in the infrapopliteal vessels. After one year they reported a limb salvage rate of 85%, even though the subintimal canal was haemodynamically patent in only 53% of the cases. Vraux et al. found comparably low 12-month primary patency rates with a remarkably better limb salvage rate.
Stenting
Stent implantation is generally reserved for cases with a suboptimal outcome after PTA, as only limited evidence is currently available on the need for stenting in the infrapopliteal location. A recent study from the Vienna group demonstrated that the angiographic outcome after stenting is superior to PTA alone in the infrapopliteal vessels. Different stent types have all shown encouraging results: uncoated, stainless steel or nitinol stents, stainless steel stents with a passive or active coating and bioabsorbable magnesium alloy stents.
Excimer Laser
Excimer laser ablation is another treatment modality for recanalising long lesions. Using a wavelength of 308nm, this cold-tipped, pulsed laser often opens occlusions when other interventional endovascular techniques have failed.
Post-procedural Surveillance
Post-operative patient education, focusing on protection of the extremity, wound care management and adoption to a healthier lifestyle cannot be overemphasised. Also, it is the authors' practice to prescribe lifelong clopidogrel (75mg daily) and aspirin (160mg daily).
Standard follow-up visits are planned at one-, three-, six- and 12-month intervals. Duplex investigation for restenosis and flow assessment are performed at the same time, and progress with pain management and wound healing are evaluated.
Conclusion
Limb preservation should be the main goal in patients with CLI due to tibial occlusive disease. With a prompt diagnosis, treatment can be started early and serious consequences may be avoided. Any type of revascularisation that can prevent amputation is the ultimate treatment strategy.
Morbidity and mortality rates associated with an endovascular revascularisation are lower than with surgical bypass; endovascular interventions do not preclude future bypass procedures. Moreover, some patients cannot be treated with surgery because of the infected anastomosis area or the lack of a healthy target vessel. Patency and limb salvage rates after endovascular treatment tend to approach the surgical results.
Patients with CLI require lifelong follow-up to repeatedly assess the status of the limb after intervention. Recurrent symptoms warrant an immediate investigation and an aggressive re-intervention strategy is indicated.
With the advent of minimally invasive techniques for recanalisation of chronically occluded below-the-knee vessels in patients with CLI, a new era has been set and current reporting standards for lower extremity revascularisation may need to be revised.
Acknowledgement
The authors take great pleasure in thanking the staff of Flanders Medical Research Program (www.fmrp.be), with special regards to Koen De Meester and Erwin Vinck, for performing the systematic review of the literature and providing substantial support to the data analysis and the writing of the article.