Excimer Laser Treatment of SFA Occlusions

The combination of excimer laser technology with current interventional devices and advanced recanalization techniques offers certain advantages over standard PTA techniques.

By Giancarlo Biamino, MD, and Dierk Scheinert, MD
 

To view the figures and tables related to this article, please refer to the print version of our May/June issue, page 45.

Chronic atherosclerotic obstructions of the superficial femoral artery (SFA) are a leading cause of lifestyle-limiting claudication, which occurs in approximately 6% to 10% of the population aged 65 years and older.1 Three decades after the clinical introduction of PTA as a recanalization technique in the femoropopliteal segment, a number of factors affecting the primary and long-term success of the procedure have been identified. Short lesion length, minimal vascular disease elsewhere with good peripheral run-off, symptoms of claudication as opposed to limb-threatening ischemia, stenosis rather than occlusion, and the absence of diabetes all correlate with improved primary success and long-term patency.2-4
Unlike other vascular beds, occlusions predominate by a factor of at least three in the femoropopliteal arteries. Furthermore, most femoropopliteal occlusions are long and there is often coexistent multilevel atherosclerotic disease. As a consequence, patients with long chronic occlusions of the SFA are generally not considered good candidates for percutaneous recanalization and surgical bypass has been considered the treatment of choice. Because bypass grafting is associated with a considerable procedure-related morbidity and mortality, surgical intervention is usually reserved for patients with ischemic rest pain or advanced claudication. Consequently, many patients with long, chronic SFA occlusions remain untreated, systematically underestimating the subjective discomfort induced by the disease in the individual patient. Because percutaneous revascularization techniques permit a lower threshold of intervention than surgical procedures, improvement of endovascular recanalization techniques for the treatment of total occlusions is desirable.

The pulsed excimer laser has been extensively evaluated in debulking atherosclerotic material, demonstrating that the photoablative effect of laser light can be used to recanalize total occlusions not amenable to conventional PTA.5-9 Excimer laser debulking of SFA occlusions ablates atherosclerotic and thrombotic material, facilitating subsequent balloon dilation and reducing the risk of thromboembolic events. Furthermore, excimer laser debulking prior to balloon angioplasty allows lower-pressure balloon inflations, which may reduce arterial wall stress and subsequent dissections, resulting in a reduced need for stent placement.

EXCIMER LASER-ASSISTED
RECANALIZATION PROCEDURE
The major challenge in percutaneous treatment of chronic SFA occlusions is to safely navigate the occlusion. The contralateral access with subsequent crossover recanalization of the occlusion is the standard approach for recanalization of long SFA occlusions. After the guidewire is placed into the origin of the SFA occlusion, two different laser techniques may be used to cross the lesion. In the over-the-wire approach, the guidewire is navigated through the lesion, supported by a 4F or 5F multipurpose catheter to an angiographically documented intraluminal distal position. The laser catheter is then activated and slowly advanced over the wire to debulk the occlusion.

As an alternate method of recanalization, laser ablation can be used in a step-by-step manner: The guidewire is first advanced into the origin of the occlusion, the excimer laser catheter is then advanced beyond the guidewire a few millimeters into the occlusion without wire guidance. For further recanalization of the occluded vessel segment, the activated laser catheter is advanced stepwise for a short (<5 mm) distance without wire guidance, followed by further crossing with the guidewire in a step-by-step technique. The last 1 to 2 cm of the occlusion and the patent distal segment of the artery are crossed with the guidewire alone before lasing to avoid dissection.

In both techniques, the advancement of the activated laser catheter must be performed very slowly, not exceeding 1 mm/sec. Fluoroscopic road mapping is used throughout to verify alignment of guidewires and catheters to the vessel lumen. Particular attention is given to thoroughly flushing the vessel with saline before activating the laser to remove contrast medium. Saline more effectively facilitates transmission of the laser light to the atherosclerotic tissue while absorption of ultraviolet light in contrast medium may induce shock waves that can result in dissections of the vessel wall. After the initial pass with the excimer laser catheter (with or without the aid of the excimer laser step-by-step technique), the .035? guidewire is exchanged for an .018? guidewire to allow saline flushing through the wire lumen of the laser catheter during subsequent laser passes. Two to three additional laser passes are performed to maximally ablate the atheroma and thrombus. The ability of the excimer laser to remove atheroma and thrombus allows for the progressive simplification of a complex, diffuse lesion into a focal stenosis that is readily treated by balloon angioplasty (Figure 1A-I).

After excimer laser recanalization, angiographic evaluation of the occluded segment and distal runoff is performed. Balloon angioplasty is then performed on the residual stenosis using low-profile, 5-mm to 7-mm-diameter balloons. Low dilation pressures should be applied for 0.5 minute to 3 minutes. Final angiography, including evaluation of the lower-limb runoff, is performed before the hemostatic sheath is removed.

SUMMARY OF OUTCOME RESULTS
We analyzed the data of 318 consecutive patients (mean age, 64 ± 10.7 years) who underwent excimer laser-assisted recanalization of chronic SFA occlusions (number of lesions = 411; mean occlusion length, 19.4 ± 6.0 cm) during a 1-year period ending December 31, 1996.10 The primary approach (cross-over 89.7%, antegrade 6.6%, transpopliteal 3.6%) to cross the occlusion with a multifiber excimer laser catheter was successful in 342 of 411 lesions (83.2%). A secondary attempt was performed in 44 cases, including use of the transpopliteal approach in 39 cases. Despite the treatment of very long occlusions, the total technical success rate was 372 of 411 (90.5%) (Table 1).

The step-by-step technique was applied in the majority of cases to initially cross the occluded vessel segment. This technique was particularly beneficial to enter flush occlusions without visible proximal stump or to pass a segment that was resistant to crossing with a guidewire. The routine use of this technique may have contributed to the low rate of occlusive arterial wall dissections, with a resultant stent frequency of only 7.3%. Relevant interventional complications were acute reocclusion (1.0%), perforation (2.2%), and embolization/distal thrombosis (3.9%). After intervention, 219 patients (68.8%) could be classified, using Rutherford classification, as category 0, 53 patients (16.6%) could be classified as category 1, and 26 patients (8.2%) could be classified as category 2.

Based on a standard life-table analysis, including primary interventional failures, the primary patency rate after 1 year was 20.1%. Due to the fact that a considerable number of patients without clinical symptoms did not attend the follow-up examinations, the calculated primary patency rate may have been biased toward less favorable results. However, recurrent narrowing after femoropopliteal angioplasty is a relevant problem and restenosis seems to be even more frequent after recanalization of very long chronic SFA occlusions. With an aggressive surveillance program, including functional clinical testing, as well as color-coded duplex ultrasound, restenosis can be detected at an early stage. Timely reintervention on the target lesion can be performed in the majority of cases on an outpatient basis. As a result, eventual reocclusion can be prevented in most patients. With this strategy, we were able to achieve an assisted primary patency rate of 64.6% after 1 year. The performance of repeat recanalization procedures on reoccluded arteries resulted in a 75.1% secondary patency rate (Table 2).

THE PELA STUDY
The Peripheral Excimer Laser Angioplasty (PELA) study is a multicenter, prospective, randomized trial comparing excimer laser assisted PTA vs. PTA alone to treat long, total SFA occlusions. Two hundred fifty-one patients with claudication (Rutherford category 2 to 4) for >6-months duration and total occlusions &Mac179;10 cm in the SFA were randomized (50% laser+PTA, 50% PTA alone) at 13 US sites and 6 German sites. Stenting was optional but discouraged. Clinical success was defined as primary patency (>50% diameter stenosis at 1 year as determined by ultrasound with no reintervention) and no serious adverse event (death, MI, vascular surgical repair, amputation, bypass, acute limb ischemia). Patient enrollment was completed in December 2001 and 12-month follow-up was completed in December 2002. The final report is expected in May 2003, with a PMAS submission to the USFDA shortly thereafter.

Acute procedural results from a preliminary analysis of 189 PELA study patients were similar in both laser and balloon groups. Procedural success was 85% in the laser group and 91% in the PTA group. Total procedural complications were 12.8% and 11.4%, respectively. The only significant difference between the two groups was in the number of stents used. Stents were implanted in 42% of patients in the laser group and 59% of the PTA group. Twelve-month patency rates and functional status were also similar in both groups.11

The acute results from the preliminary PELA analysis are similar to results reported in our series of 411 patients. Table 3 compares the acute procedural data and preliminary 12-month data from our series and the PELA study. In both series, procedural success rates are high, complication rates are low, and there was significant clinical improvement at follow-up.

CONCLUSIONS
The combination of excimer laser technology with current interventional devices and advanced recanalization techniques offers certain advantages over standard PTA techniques. First, in similarly complex lesions, excimer laser debulking prior to PTA results in the need for fewer stents. In-stent restenosis is a much more difficult clinical problem than simply ballooning a focal restenosis in a native vessel. With a similar restenosis rate, the preferred therapy is the one that reduces the number of stents and minimizes the risk of in-stent restenosis, as well as procedural costs. Secondly, excimer laser recanalization of long, total SFA occlusions may result in a significantly lower rate of distal embolization. Although perforations were higher in the laser group of the PELA study, they can be sealed with balloons and stents with virtually no clinical sequela. In contrast, distal embolization occurring in 8% of the cases during conventional PTA recanalization are more challenging to treat and the long-term consequences of this complication are potentially more severe.

As clinical experience, interventional tools, and techniques improve, patency rates associated with the endovascular treatment of long, total SFA occlusions also improve. However, a fairly high frequency of restenosis remains the major limitation of all currently available endovascular techniques. Despite these limitations, an aggressive surveillance program with standardized treadmill testing and color-coded duplex sonography allows for the early detection of reocclusion and the possibility for successful reintervention to maintain the achieved clinical benefit.

Giancarlo Biamino, MD, is Director of the Department of Clinical and Interventional Angiology, University of Leipzig Heart Center, Leipzig, Germany. He is a clinical consultant for Spectranetics. Dr. Biamino may be reached at 49 (0) 341 865 1478; biag@medizin.uni-leipzig.de.

Dierk Scheinert, MD, is Director of the Department of Clinical and Interventional Angiology, University of Leipzig Heart Center, Leipzig, Germany. He holds no financial interest in any product or manufacturer mentioned herein. Dr. Scheinert may be reached at 49 (0) 341 865 1478.

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