Applied Radiology

Angioplasty of occlusive lesions within the femoral and popliteal arteries often is utilized when patients present with life-style limiting claudication, rest pain, or now-healing lower extremity ulcers, and also is used as an adjunct to increase blood flow, aiding in healing of wounds following surgery (primarily from amputations). Factors that influence the initial angioplasty outcome and the patency rate at follow-up exam include certain lesion characteristics and the quality of the distal run-off arteries.

Positive predictors of initial and long-term patency include short, segmental lesions (of less than 3 cm) which do not involve the superficial femoral artery (SFA) origin or the popliteal trifurcation; the presence of at least two run-off vessels; performing the procedure for claudication symptoms rather than rest pain or limb salvage; and a good immediate angiographic result with palpable distal pulses. ¹ Negative predictors of continued patency include those procedures performed for limb salvage, one or no distal run-off vessels, or the presence of long segmental stenoses or calcified eccentric lesions, as well as diffuse cardiovascular disease (i.e. diabetes). ¹ Suboptimal results related to technical factors, such as residual thrombotic material, residual stenosis greater than 30%, and focal dissection after angioplasty, also can adversely affect the clinical outcome. ²

The initial success of angioplasty of short segmental lesions of less than 2 cm with two vessel run-off is approximately 83 to 98%. The one-year primary patency rate is reported to be between 60 and 80%; however, this falls dramatically at 5 years, with patency rates of 40 to 60%. ^1,3 Similar results are seen in lesions treated with surgical bypass procedures, where there is an initial success rate of approximately 100% and a 5-year patency rate
of between 50 and 70%. ¹ Additionally, the utilization of balloon angioplasty in longer stenoses or occlusions yields significantly lower primary and secondary patency results. ^1,4

Procedural complications related to percutaneous balloon angioplasty occur in approximately 5 to 10% of cases. ⁴ These are most commonly groin related (hematomas); however, dissections related to guidewire manipulations, vessel perforations, distal embolization, pseudoaneursyms, and acute thrombosis are recognized complications. Meticulous attention to detail and operator experience in performing these procedures should reduce the complication rate.

Within the armamentarium for treatment of infrainguinal stenosis or occlusions are the peripheral atherectomy devices, the most commonly utilized device being the Simpson Atherocath (Mallinckrodt Med. STZ, MO). Atherectomy devices mechanically remove plaque from the wall of diseased vessels, in either an extirpative or ablative fashion. ⁵ Indications for the use of these devices include focal, eccentric, or calcified plaque that fails to respond to balloon angioplasty; post-angioplasty flow-limiting intimal flaps; intimal hyperplasia in graft anastomoses that fails to respond
to balloon angioplasty (including dialysis fistulas); hyperplasia following PTA;
and for "valvectomy" in "in-situ" venous grafts that fail balloon angioplasty. ⁴ Atherectomy at anastomoses have been particularly successful, yielding an initial 100% technical success rate and a 2- to
3-year patency rate of 79%. ⁶

Utilization of an atherectomy device requires an antegrade access and placement through a vascular sheath. The Simpson Atherocath is designed with either a fixed tip guidewire or can be placed over an .018" wire. As with angioplasty, appropriate location within the lesion is essential. At the appropriate position, the support balloon is inflated to oppose the cutting chamber against the lesion. The rotating blade is then advanced through the cutting chamber. The debris is collected in the cutting chamber, and the catheter can then be rotated for additional cuts.

Disadvantages of this device include the need for antegrade access, which can be difficult in obese patients and may preclude its use in treatment of nearby common femoral and proximal SFA lesions. ⁷ High cost, prolonged procedure time, and larger arterotomy sites cause a relatively high incidence of complications. Most of these complications are groin related (hematomas); however, they may include pseudoaneursyms, distal embolizations, vessel dissection, and acute thrombosis.

In regard to initial and long-term patency rates for focal, segmentally treated SFA and popliteal lesions, numerous studies have demonstrated that atherectomy does not result in better long-term patency than does balloon angioplasty. As an example, Vroegindeweij et al demonstrated that atherectomy does
not provide clinical or hemodynamic improvement in comparison with angioplasty at 2- or 3-year follow-up (at 2 years: 52% vs 87%, at 3 years: 34% vs 56%). In addition, they compared angioplasty with atherectomy in a prospective trial and concluded similar angiographic and clinical results. ⁸ From the above, it is apparent that atherectomy should not replace balloon angioplasty in infrainguinal stenosis.

The advent of balloon-expandable stents and the widespread use of these devices in the iliac arteries for the treatment of stenosis and occlusion is well documented; however, their use in the femoral and popliteal system has been less successful. Primary and secondary patency rates vary widely from study to study, and there are many additional factors which contribute to the initial success of the procedure.

The primary treatment of isolated segmental stenosis within the superficial femoral and the popliteal arteries continues to be percutaneous transluminal angioplasty. The use of stents within these vessels often is performed to improve the immediate results of PTA, in particular to prevent immediate technical failures. ⁹ Despite the initial high rate of technical success with stents, results have been discouraging regarding long-term patency (restenosis remains a significant problem). ⁹ Nevertheless, stenting of the femoropopliteal vessels is performed by some interventionalists for residual stenosis after angioplasty, in acute occlusion or thrombosis, post PTA flow-limiting dissections, in calcified lesions not responsive to angioplasty, and in those cases where stenting of an obstructing lesion may increase inflow in an attempt at limb salvage. ^4,10

Regarding the initial and long-term success of stent placement, publicized results have been inconsistent and, at times, conflicting. However, it is apparent that focal stenosis (of less than 4 cm) treated with short stents demonstrated longer primary and secondary patency than longer lesions (the 2-year primary patency rate for stents of less than 4 cm is approximately 60%, while it is approximately 30% for longer lesions). ¹¹ Also, stenotic lesions have demonstrated better primary and secondary patency than lesions of an occlusive nature (the 2-year patency for stenosis is approximately 73% vs 33% for occlusions). ¹¹ In regard to the efficacy of primary stenting of lesions within the SFA and popliteal vessels versus angioplasty, it is apparent that stent placement does not improve the clinical or hemodynamic outcome. ¹² As an example, a prospective study of primary stenting versus balloon angioplasty demonstrated that the primary patency rate at 1 year was slightly less for the stented group (approximately 63% for the stented group and 74% for the angioplasty group). ¹²

As described above, there are certain factors which influence the patency of stented infrainguinal vessels. These include the length of the stenosis, whether the area stented is a stenosis or an occlusion, the number of stents utilized (use of a greater number of stents has a much lower primary patency), and the existence of comorbid processes, such as diabetes mellitus and diffuse peripheral vascular disease. ^9,13 As with angioplasty, the presence of two vessel runoff greatly influences the primary patency rate. Smoking negatively influences the outcome of the procedure, as does small vessel diameter. ^9,13 Additionally, the placement of stents across joints is often associated with a poor result secondary to compression.

The incidence of complications with PTA and stent placement is relatively low and there is a high initial success rate. Groin complications are the most common and include hematomas and pseudoaneurysms. Acute thrombosis, pain, sepsis, vessel rupture, and stent compression also are recognized complications. Dissections may occur and may require stent placement if they are flow-limiting.

The most recent tool under investigation for treatment of infrainguinal occlusive disease is the stent graft. As of this date, stent grafts have been utilized primarily in the aorta and iliac vessels; however, this has been expanded to the infrainguinal region for the treatment of claudication and limb threatening ischemia. ¹⁴ These conduits have been utilized in long segmental occlusive disease, complex lesions unlikely to be successfully treated with other endovascular techniques, for the exclusion of aneurysms, and as an alternative to uncovered stents for failure of primary angioplasty. ¹⁵ A variety of devices are under investigation, but most utilize a self-expanding metallic stent covered with a synthetic graft material. It is postulated that lining the stent with a synthetic graft material reduces the incidence of restenosis and excludes thrombus and/or plaque from the lumen. ¹⁶

Numerous studies are now being performed to evaluate the patency rate of covered versus non-covered stents. The initial results of patency have varied; however, this technique of percutaneous endovascular repair appears feasible. ¹⁵

In a study of endovascular grafting of SFA stenosis, occlusions, complex lesions, and angioplasty failures, the initial success rate was nearly 100%, with a primary patency of 72% and a secondary patency of nearly 84%. ¹⁵ The mean length of these lesions was approximately 20 cm. In another study, the stent graft system was used in patients with similar or shorter lesions and demonstrated 6-month to 1-year primary patencies ranging from 59 to 70%, with secondary patencies from 70 to 85%. In each study, the initial technical success rate was nearly 100%. ^17,18 As attested to by the above, the stent graft system is technically highly successful; however, additional clinical trials are necessary to evaluate their clinical utility.

The incidence of complications occurring during stent graft placement within the femoral and popliteal system is relatively high. However, refinement of the techniques and continued user experience will undoubtedly reduce their occurrence. The most common complications are hematomas and pseudoaneurysms. Technical problems occasionally require conversion to a femoral bypass procedure. Distal embolization, acute graft occlusion/
thrombosis requiring lytic therapy, perigraft leak, and distal dissections related to guidewire manipulations also occur infrequently. The operative mortality is low. ¹⁵

The percutaneous treatment of vascular disease has expanded the role of the interventional radiologist. The utilization of percutaneous transluminal angioplasty in short focal lesions of the superficial femoral arteries has both short- and long-term patency rates approaching those of classical surgical bypass procedures. ¹ Atherectomy devices, of which there are many, have slightly lower primary patencies and have a higher incidence of complications. Therefore, it should not replace angioplasty as the initial percutaneous treatment modality for infrainguinal lesions. Atherectomy is, however, effective in the treatment of graft intimal hyperplasia and eccentric calcified stenosis when balloon angioplasty has failed, or for treating post-angioplasty dissection flaps. ^4,5,6

Primary stenting of SFA lesions does not improve the clinical or hemodynamic outcome in comparison with balloon angioplasty, ¹² and probably results in a slightly lower primary and secondary patency rate. ¹² However, stents are effective in the treatment of suboptimal angioplasty results, including residual stenosis, flow-limiting dissections, and calcified lesions that fail to respond to balloon angioplasty. ^4,10 Finally, the use of covered stents for a variety of SFA lesions is an attractive idea with the potential to further expand endovascular therapy. Early results attest to its feasibility; however, additional clinical trials are necessary to define its role in the percutaneous management of femoral lesions. AR