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.

       Recent study of percutaneous intervention in chronic superficial femoral artery (SFA) occlusions indicates crossing the lesion is feasible in 68–100% of cases1–12 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.

Figure 1

The Safe-Cross system, which includes a monitor, sheath, catheter, and guidewire.

       A new catheter guidewire system (Safe-Cross RF TO Guidewire System, Intraluminal Therapeutics, Carlsbad, Calif.) (Figure 1) uses optical coherence reflectometry, 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

Figure 2a

Figure 3a

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

Figure 2b

Figure 3b

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.

Figure 2c

Figure 3c

       Retrograde contralateral iliofemoral artery access was obtained using a 6 F Bright Tip Long Sheath (55 cm) (Cordis/JJIS, Warren, New Jersey). 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 5 F Glidecath (Meditech/Boston Scientific, Natick, Mass.) 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. These wires were first used in all initial attempts to cross the total occlusions before the utilization of the Safe-Cross RF TO Guidewire System.
       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

Figure 2d

Figure 3d

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 in. 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 (Meditech/Boston Scientific) or Magic Torque wire (Meditech/Boston Scientific). Routine balloon angioplasty was then performed.

Figure 2e

(A) Left SFA occlusion near the femoral bifurcation (Patient #3, Left SFA).(B) Safe-Cross guidewire tip across the initial part of the left SFA occlusion (Patient #3, left SFA).(C) Safe-Cross guidewire tip further advanced distally in the left SFA occlusion (Patient #3, left SFA). (D) Post-angioplasty angiogram confirming a patent left SFA (Patient #3, left SFA).(E) Post-angioplasty angiogram confirming a patent left popliteal artery (Patient #3, left SFA).

Figure 3e

(A) Right SFA occlusion at the femoral bifurcation (Patient #3, right SFA) (B) Distal end of the right SFA occlusion with right popliteal artery filling in via collateral vessels (Patient #3, right SFA).(C) Safe-Cross guidewire tip across the right SFA occlusion and positioned in the distal right SFA (Patient #3, right SFA).(D) Safe-Cross guidewire tip completely across the right SFA occlusion and positioned in the right popliteal artery (Patient #3, right SFA). (E) Post-angioplasty angiogram confirming a patent right SFA (Patient #3, right SFA).

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. All occlusions were hard, fibrotic lesions and calcified. 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. The Safe-Cross RF TO Guidewire System allowed the chronic total occlusions (CTOs) to be crossed within the true vessel lumen and as a result the guidewires were never passed subintimally. In crossing some of the CTOs greater guidance flexibility was required. If the guidewire would not torque correctly, then a straight or angled Glidecath was utilized to assist in crossing the CTO. Utilization of the 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. In all of the CTOs, adequate results with angioplasty alone were obtained and thus none of the lesions required the placement of a stent.

Figure 4a

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

Figure 4b

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 subacute 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

Figure 4c

studied. Before the stent era, Bolia and colleagues16 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.

Figure 4d

(A) Total occlusion at mid-level of left SFA (ruler marker 122) (Patient #2).(B) Safe-Cross guidewire tip across the total occlusion (positioned between ruler markers 200 and 210) (Patient #2). (C) Post-angioplasty angiogram confirming a patent mid-level left SFA (Patient #2). (D) Post-angioplasty angiograms confirming a patent left distal SFA and popliteal artery (Patient #2).

       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.
       The results of other studies have further demonstrated the safety and efficacy in utilizing the Safe-Cross RF TO Guidewire System to cross CTOs in various settings. OCR and RF ablation has been successfully utilized in crossing native coronary CTOs with a 60% success rate.18 The same system has also been used for the successful recanalization of long occlusive in-stent restenosis which failed conventional guidewire crossing.19

Conclusions
       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. Additional study is needed to fully assess the safety and utility of this technology in the treatment of chronic occlusions, and we await further results from the ongoing GRIP Study.

1. Belli AM, Cumberland DC, Procter AE, Welsh CL. Total peripheral artery occlusions: Conventional versus laser thermal recanalization with a hybrid probe in percutaneous angioplasty — Results of a randomized trial. Radiology 1991;181:57–60.
2. Dorros G, Lewin RF, Sachdev N, Mathiak L. Percutaneous atherectomy of occlusive peripheral vascular disease: Stenosis and/or occlusions. Cathet Cardiovasc Dis 1989;18:1–6.
3. Jahnke T, Voshage G, Muller-Hulsbeck S, et al. Endovascular placement of self-expanding nitinol coil stents of the treatment of femoropopliteal obstructive disease. J Vasc Radiol 2002;13:257–266.
4. Karch LA, Mattos MA, Henretta JP, et al. Clinical failure after percutaneous transluminal angioplasty of the superficial femoral and popliteal arteries. J Vasc Surg 2000;31:880–888.
5. Lammer J, Pilger E, Decrinis M, et al. Pulsed excimer laser versus continuous-wave Nd:Yag laser versus conventional angioplasty of peripheral arterial occlusions: Prospective, controlled, randomized trial. Lancet 1992;340:1183–1188.
6. Masti PJ, Manninen HI, Soder HK, et al. Percutaneous transluminal angioplasty in femoral artery occlusions: Primary and long-term results in 107 claudicant patients using femoral and popliteal catheterization techniques. Clin Radiol 1995;50:237–244.
7. Muller-Buhl U, Strecker EP, Gottmann D, et al. Improvement in claudication after angioplasty of distal ostial collateral stenosis in patients with long-segment occlusions of the femoral artery. Cardiovasc Intervent Radiol 2000;23:447–451.
8. Nicholson T. Percutaneous transluminal angioplasty and enclosed thrombolysis versus Percutaneous transluminal angioplasty in the treatment of femoropopliteal occlusions: Results of a prospective randomized trial. Cardiovasc Intervent Radiol 1998;21:470–474.
9. Odink HF, de Valois HC, Eikelboom BC. Femoropopliteal arterial occlusions: laser-assisted versus conventional percutaneous transluminal angioplasty. Radiol 1991;181:61–66.
10. Zdanowski Z, Albrechtsson U, Lundin A, et al. Percutaneous transluminal angioplasty with or without stenting for femoropopliteal occlusions? Int Angiol 1999;18:251–255.
11. CATS Protocol #990-930-B, dated 12/14/01. Final Clinical Report.
12. In vivo evaluation of a OCR guided 0.014 in. radio frequency guidewire in renal artery with stents in porcine model. Final Report No. ARF03162001.
13. Morales PA, Heuser RR. Chronic total occlusions: Experience with fiber-optic guidance technology — Optical coherence reflectometry. J Intervent Cardiol 2001;14:611–616.
14. Puma JA, Sketch MHJ, Tcheng JE, et al. Percutaneous revascularization of chronic total occlusions: An overview. J Am Coll Cardiol 1995;26:1–11.
15. Olin JW and Graor RA. Thrombolytic therapy in the treatment of peripheral arterial occlusions. Ann Emerg Med 1988;17:1210–1215.
16. Bolia A, Miles KA, Brennan J, et al. Percutaneous transluminal angioplasty of occlusions of the femoral and popliteal arteries by subintimal dissection. Cardiovasc Intervent Radiol 1990;13:357–363.
17. Meier B. Chronic Total Occlusion. In: Topol EJ, ed., Textbook of Interventional Cardiology, 3rd Edition. Philadelphia: WB Saunders, 1999, pp280–296.
18. Chen, et al. Recanalization of chronic and long occlusive in-stent restenosis using optical coherence reflectometry-guided radiofrequency ablation guidewire. Cathet Cardiovasc Intervent 2003; 59: 223–229.
19. NG, W. Initial experience and safety in the treatment of chronic total coronary occlusions with a new optical coherent reflectometry-guided radiofrequency ablation guidewire. Am J Cardiol 2003; 92:732–734.