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Background: Although procedural success rates for treating chronic occlusions are relatively high, dissections and perforations often require stenting. Methods: A fiberoptic guidance system that visualizes lesion characteristics and incorporates a radiofrequency energy source to aid in crossing total occlusions was used in three men and one woman with superficial femoral artery lesions that were 8–50 cm long and 5–144 months old. Results: Five lesions were attempted and successfully crossed, and there were no observed dissections or perforations. Ankle-brachial indexes returned to normal in two of the four patients. The guidance system was useful in visualizing and treating chronic total femoral occlusions.

SUMMARY
Percutaneous treatment of chronic total occlusions may result in dissection or perforation. A fiberoptic guidance system that visualizes lesion characteristics and incorporates a radiofrequency energy source to aid in crossing total occlusions was used to cross five superficial femoral artery lesions, and there were no observed complications.

INTRODUCTION
Recent study of percutaneous intervention in chronic superficial femoral artery (SFA) occlusions indicates crossing the lesion is feasible in 68-100% of cases^1-12 but that flow-limiting dissections and perforations requiring stenting occur at unacceptable rates. Ultimately, restenosis of stents placed across joints or to treat long lesions may limit the overall success of intervention.

A new catheter guidewire system (Safe-Cross™ RF TO Guidewire System, Intraluminal Therapeutics, Carlsbad, CA; Figure 1) uses optical coherence eflectometry, a “forward-looking” fiberoptic guidance technology, to visualize total occlusions. In addition, the system contains a radiofrequency energy source that allows the operator to heat the tip of the guidewire to assist in crossing the occlusion.

Optical coherence reflectometry measures the reflectivity of a scanned beam of near-infrared light to accurately differentiate tissue types, such as plaque, thrombus, and intima.¹³ The technology is based on the variable absorption and scattering of near-infrared light by these different types of tissue. An algorithm accounts for different absorption rates and scattering coefficients as a light beam of known intensity is introduced through the guidewire to illuminate the area adjacent to its tip. A real-time tracing documenting what the forward-looking tip sees is then displayed on the monitor. Red waveforms indicate the vessel wall, while green indicates lumen or plaque. Once in the vessel, the waveform colors are used by the operator to guide the catheter through plaque. Resolution of up to 15 microns is possible and, when the tip of the wire comes too close to the vessel wall, its improper position is reflected in the tracing and an audible signal alerts the operator. The guidewire tip may then be repositioned and maintained in the vessel without fear of perforation or extensive dissection. An added feature of the system is the ability to ablate chronic occlusions with radiofrequency energy, which heats the tip of the guidewire in the lumen or plaque but not when it is directed at the vessel wall.

We present the following report of four patients who are part of the ongoing GRIP (Guided Radiofrequency in Peripheral Total Occlusions) Study in which the safety and efficacy of the Safe-Cross RF TO Guidewire System is being assessed in symptomatic patients with peripheral total occlusions.

MATERIAL AND METHODS
Between March and June 2002, four patients underwent angiography to confirm the diagnosis of a chronic superficial femoral artery occlusion. Occlusion lengths ranged from 8-50 cm, and occlusions were aged 5–144 months. Each patient was brought to the catheterization laboratory after consent was signed. The contralateral groin was prepped and draped in the usual sterile fashion.
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Retrograde contralateral iliofemoral artery access was obtained using a 6F Bright Tip Long Sheath (55 cm) (Cordis/JJIS, Warren, NJ). Using standard crossover techniques, both the guidewire and sheath were advanced into the contralateral femoral artery and to the level of the total occlusion. If the sheath could not reach the total occlusion, then a 5F Glidecath (Meditech/Boston Scientific, Natick, MA) was inserted through the sheath and advanced using a Glidewire (Meditech/Boston Scientific) or Magic Torque wire (Meditech/Boston Scientific) to the proximal edge of the total occlusion.

If the operator was unable to cross the lesion with a conventional wire after 10 minutes, the Safe-Cross guidewire was then inserted through the sheath and placed at the occlusion. The Safe-Cross system comprises a sterile, single-use optical radiofrequency wire that is connected to an optical coherence reflectometry monitor and radiofrequency generator. The radiofrequency wire is 275 cm with a diameter of 0.035”. The radiofrequency generator is capable of transmitting energy between 200 and 500 kHz with sub-second pulses delivered to the wire. The wire cannot be activated when it is directed at the arterial wall.

When the guidewire position was confirmed in the lumen, radiofrequency energy was applied as needed to the occlusion (see Table 1) to facilitate crossing the lesion. The Glidecath was then advanced as the Safe-Cross guidewire crossed the lesion. Once the Glidecath was past the distal portion of the occlusion, the Safe-Cross guidewire was removed. Careful injection of contrast dye through the Glidecath helped confirm the intraluminal position of the Glidecath. Before the Glidecath was removed, guidewire access was once more obtained with either a Glidewire or Magic Torque wire. Routine balloon angioplasty was then performed.

RESULTS
The lesion characteristics and results of intervention in three men and one woman are summarized in Table 1 and shown in Figures 2–4. A total of five vessels (three in left SFAs and two in right SFAs) were treated with the Safe-Cross system, and all target lesions were successfully crossed. There were no observed dissections or perforations. Ankle-brachial indexes (ABIs) ranged from 0.38 to 0.72 before treatment, and all cases showed an improvement in ABI following the procedure — in two of the four patients, ABIs returned to the normal range.

^DISCUSSION
In this small series, all patients had chronic superficial femoral artery occlusions and lifestyle-limiting claudication. The rationale for revascularizing chronic coronary occlusions has been a subject of much debate.¹⁴ As with coronary occlusions, treating peripheral occlusions is meant to improve clinical symptoms and decrease the need for vascular bypass surgery. A reduced likelihood of critical limb ischemia and amputation is expected, and avoiding vascular bypass surgery spares saphenous veins for use in coronary artery bypass surgery.

Success in percutaneous revascularization of total occlusions is hampered by difficulties in crossing lesions. While acute and sub-acute total occlusions may be treated using thrombolysis or fibrinolysis in addition to angioplasty and stenting, such therapies have little impact on chronic occlusions and may prolong the procedure, increasing the risk of serious bleeding complications.¹⁵ Hydrophilic wires may be useful in crossing chronic occlusions, but distal perforation is a potential complication.

Other treatment options for chronic total occlusions have also been studied. Before the stent era, Bolia and colleagues^>16 used a wire loop to form a subintimal dissection of the occluded vessel. By pushing the loop and the catheter towards the distal, patent part of the vessel, the wire moved down freely into the subintimal space. Then, the catheter was brought down, the wire was removed, and intraluminal alignment of the catheter was checked by contrast injection. Preventing damage to the first major collateral artery required that the site of re-entry not be too distal. After re-entry into the true patent distal lumen was confirmed with contrast, heparin was given, and the new lumen was dilated in a standard fashion.

More recently, the excimer laser wire has been used successfully as an adjunct to conventional means for chronic occlusion angioplasty.¹⁷ In contrast to early lasers that used continuous-wave irradiation, the excimer laser is a pulsed-wave system that induces photoablation during an athermic process. The system uses xenon chloride (308 nm) as the source of energy. At this wavelength, ablation of the irradiated tissue causes a rapid, predominantly local “microexplosion” with energy densities of about 3 to 6 J/cm2. The excimer laser beam has a small penetration depth and extremely short pulse duration; thus, thermal damage induced by the excimer laser is minimal even when high-energy densities are used.

On a larger scale, the GRIP trial was a prospective, multi-center registry of 14 sites in the United States in which a total of 75 chronic total occlusions in 72 patients were treated with the Safe-Cross Optical Coherent Reflectometry System.¹⁸ The study focused on long chronic total occlusions in peripheral arteries with a mean vessel diameter of 5.7 mm with a mean lesion length of 12.8 cm. Moreover iliac, femoral, and popliteal long chronic total occlusions were attempted in the GRIP trial. Multiple investigators utilizing the Safe-Cross Optical Coherent Reflectometry System were successful in crossing 76.0% of the chronic total occlusions in patients that failed conventional wire crossing (minimum 10 minutes of fluoroscopic time). Clinical success occurred in 75% of these patients. Complications consisted of a single dissection >= Grade C (1.3%). No clinical perforations or distal embolization occurred in any of the patients in the GRIP trial.

CONCLUSION
Percutaneous treatment of peripheral vascular disease has rapidly become the therapy of choice. Chronic total occlusions, however, remain a therapeutic challenge. In this small series of patients with chronic superficial femoral occlusions and claudication, the Safe-Cross system was used successfully to cross the total occlusions, and there were no observed complications. The results of this study paralleled both the clinical success rate and the low complication rate in the larger GRIP trial.

The authors can be contacted at romas@cox.net

Dr. Heuser discloses he is a consultant for Intraluminal Technologies.