A particularly challenging condition for percutaneous transluminal angioplasty are chronic total occlusions (CTOs). CTOs are one of the primary causes of procedural failure in peripheral interventions (1-4). Percutaneous negotiation of a guide wire, either intraluminally or subintimally, should be done to recanalize the CTO successfully. However, percutaneous recanalization of long CTOs of the femoropopliteal artery by anterograde methods, using a guide wire and catheter, has only moderate success rates - 40% to 60% - depending on lesion length, calcification, operator experience, and runoff vessels; negotiation failures lead to failure of recanalization of CTOs (5). Therefore, other methods that can enhance the success rate of guide wire negotiation, whether intraluminally or subintimally, are needed.

Since Tønnesen et al. first reported the utility of retrograde popliteal access two decades ago, this approach has been employed in challenging femoropopliteal interventions (6-11). Currently, retrograde subintimal tracking via the popliteal approach, which utilizes the anatomical characteristics of the femoropopliteal artery, delivers an endovascular solution for unsuccessful anterograde CTO crossings (12).

The frontrunner XP CTO catheter (Cordis, Miami, FL, USA) is an intraluminal blunt microdissection device used for the recanalization of CTOs intraluminally. This device has jaws that can separate the plaque, thereby creating a passage through the occlusion for the subsequent placement of a guide wire. The Outback LTD catheter (Cordis, Miami, FL, USA) has been used when subintimal guide wire passage into the true lumen fails; when this device is used, a needle is introduced across the intima into the true lumen to facilitate the reentry process.

A retrograde popliteal approach and these two novel catheter technologies, the Frontrunner and Outback catheters, were used for recanalization of femoropopliteal arterial CTOs, and here, their safety and efficacy is reported.

The Frontrunner catheter was used in five patients. Intraluminal passage of the catheter into the reconstituted artery was successful in four patients, and subintimal passage of the catheter with successful reentry into the true lumen was performed in one patient. The overall technical success rate was 100%. Three patients had CTOs in the SFA, and two patients had a lesion in the distal SFA and popliteal artery. A contralateral approach with the catheter was performed in three patients that had the lesion in the SFA, and an ipsilateral retrograde approach was performed in two patients with the CTO far from the ipsilateral common femoral artery. In one patient with a long CTO in the SFA (20 cm), re-entry into the true lumen was not possible after subintimal passage of the occluded segment; attempts to pull the catheter back to the proximal cap of the CTO and cross the lesion again intraluminally were successful for intraluminal passage. All patients underwent balloon angioplasty with a 4 mm balloon catheter followed by stent placement using a 6-7 mm self-expandable stent after the passage of the guide wire.

In eight of the remaining nineteen patients, the retrograde approach via popliteal arterial access was used. The technical success rate was 100%, and all patients underwent balloon angioplasty followed by stent placement in the same fashion as the cases using the Frontrunner catheter (Fig. 2).

In all eleven patients in which the Outback catheter was used, reentry of the guide wire into the true lumen was successful (100%). Nine patients obtained successful reentry into the popliteal artery; two obtained successful reentry into the SFA (Fig. 3). A contralateral approach of the catheter was used in all patients. One patient had successful reentry into the true lumen using only the hydrophilic guide wire. However, reentry sites achieved with only the guide wire were usually located much more distally over the P2 segment of the popliteal artery; the result of subintimal balloon angioplasty using 5 mm and 6 mm balloon catheters (Cordis, Miami, FL, USA) was suboptimal for stent implantation for the supply of sufficient blood flow. Therefore, the Outback catheter was used to create a new reentry site more proximally for stent placement. The stent placement was performed in the SFA including the newly created reentry site and blood flow was completely restored (Fig. 4). Two patients with femoropopliteal occlusion had some calcifications at the reentry sites; initial attempts to create reentry at those sites failed. Therefore, the Outback catheter was advanced more distally where the calcification was scarce and successful reentry was achieved. In one patient, no catheter could advance over the 0.014 guide wire after successful reentry using the Outback catheter. A 2.0 Fr microcatheter (Terumo, Tokyo, Japan) was advanced over the guide wire, and it was exchanged for a 0.018 guide wire (V18; Boston Scientific, Natick, MA, USA). Subsequent procedures were done using this wire.

In one patient, the Outback catheter was not able to be advanced to the arteries distal to the SFA. Therefore, dilatation with a 4 mm balloon catheter was performed after which the catheter could be advanced. One patient with SFA occlusion had a perforation during the subintimal passage of the guide wire. However, the guide wire and catheter were pulled back to the common femoral artery and subintimal passage through another tract was attempted. The final angiogram, after successful creation of the reentry site and stent placement in the SFA, showed no visible vessel perforation. No distal thromboemolism during or immediately after the procedure was observed.

Chronic occlusions account for a significant portion of peripheral vascular lesions and have historically represented a serious technical challenge to endovascular interventionalists using conventional guide wires and catheters (13). Recently, new technologies and methods have been introduced for recanalization of CTOs. Subintimal recanalization with distal re-entry has been advocated as a solution to the problem of unsuccessful passage through multisegmented long calcified occlusions. London et al. (14) reported a 90% technical success rate for SFA subintimal angioplasty in a series of patients with a mean occlusion length of 15 cm. This approach, however, has been limited in some cases by the lack of controlled re-entry into the true lumen of the target vessel. In addition, true lumen re-entry using hydrophilic wires and catheters is not achieved until subintimal passage to a site significantly remote from the level of vessel lumen patency; this causes subintimal angioplasty or stenting to extend beyond the occluded segment. In fact, in the present study, one case occurred in which the creation of a new reentry site proximal to the remote reentry site created by the traditional subintimal technique allowed the stent to be placed, overcoming the suboptimal subintimal balloon angioplasty. Some surgeons report using retrograde popliteal access (15) for subintimal recanalization or a "kissing catheter" or "wire pull-through" technique (16, 17), which requires two access sites (femoral and popliteal). After femoral access and catheter or guide wire advancement through the subintimal plane around the occlusion, the patient is placed in a prone position, and the popliteal artery is accessed. A catheter is advanced then through the popliteal artery in the same subintimal plane to meet the initial catheter. Our study also had a 100% technical success rate in cases with failure of advancement of the guide wire into the true lumen. However, this retrograde approach technique causes patients discomfort, a complicates the access site, and is technically feasible only for the superficial femoral artery (18). Therefore, new instruments, such as the Outback catheter, that can enhance the reentry success rate, have been needed; the purpose of using this reentry catheter is to overcome the above limitations and problems that prolong the procedure and increase the amount of exposure of the patient to radiation while achieving true lumen access in a controlled manner.

The results of our study demonstrate that use of a reentry catheter significantly improves the outcome of endovascular treatment in patients with femoropopliteal occlusions, with no additional risks or complications. Etezadi et al. (13) reported that true lumen reentry was achieved in 87% and 91% of patients with femoropopliteal and aortoiliac occlusions, respectively, and the overall technical success rate with the device was 88%. Hausegger et al. (19) reported that eight of ten patients had successful true lumen reentry with the prototype of the Outback catheter; two technical failures occurred in heavily calcified arteries. Wiesinger et al. (18) reported a 50% success rate of reentry (5/10 patients). Although, in our study, the number of patients was fewer than in previous studies, reentry was achieved in 100% of cases. It has been suggested that heavy calcification of the vessel wall is a contributing factor to reentry failure (13). In our study there were two cases that failed reentry at the initial puncture site with the Outback catheter due to calcification; successful reentry was achieved after puncture at a more distal site with scarce calcification. Although the amount of calcification was not specifically evaluated, based on the limited experience in this study, it may be necessary to avoid calcification that interferes with successful reentry at heavy calcification sites. Decreases in procedure time and radiation exposure have been suggested as additional benefits of the use of reentry catheters; these factors were not evaluated in our study. Therefore, additional prospective studies with the assessment of calcification, procedure time, and radiation hazard are needed.

The Outback catheter could not be advanced to the target lesion and the angiographic catheter could not be advanced over the reentry site after successful reentry of the 0.014 inch guide wire into the true lumen. This might be explained by the presence of a thick intima or heavy calcifications. Based on the limited experience of this study, such problems can be overcome technically by pre-balloon dilatation or use of a microcatheter. The durability of the subintimally created channels is currently a topic of debate. Only a few studies on the efficacy of subintimal angioplasty in the treatment of very long lesions extending over multiple limb segments have been undertaken thus far. The initial relatively high long-term patency rate reported by Bolia's group has not been reproduced by most other studies (20-23). Although some recent investigations suggest that the subintimal technique is effective, no randomized study comparing subintimal angioplasty with intraluminal angioplasty has yet been performed (24, 25). Therefore, some surgeons still prefer intraluminal angioplasty to the subintimal technique.

The Frontrunner catheter, a relatively new device, is thought to selectively cause disruption of plaques and the adventitia and is designed to improve the technical success of traversing complex lesions. Although it sometimes creates extraluminal passages along subintimal planes in CTOs, the passage created by the Frontrunner device is frequently intraluminal (26). The Frontrunner catheter is safe and effective to use; however, few reports are available on the results of peripheral arterial CTO. Charalambous et al. (27) reported a 65.4% success rate of recanalization using the Frontrunner for the SFA; the main reasons for failure were inability to cross the lesion due to heavy calcification, similar to the studies using the Outback catheter. In our study, the success rate using the Frontrunner catheter was 100%. Although the number of patients was small and calcium in the lesions was not assessed, our study included only patients with failure of guide wire advancement into the CTO. In fact, this advancement failure can make it difficult to use any tools or methods to achieve reentry. The Frontrunner catheter could pass this lesion and successful recanalization could be achieved via this catheter. Occasionally, the Frontrunner catheter was advanced into the subintimal tract in the femoropopliteal artery and did not obtain successful reentry into the true lumen. This occurred in one case, and several attempts to use the Frontrunner catheter again after pulling it back into the proximal cap of the CTO resolved the problem.

In conclusion, these various methods using a retrograde approach and a Frontrunner or Outback catheter for recanalization of CTOs are promising. Although the study sample was small, appropriate use of these approaches appear to be safe and effective options after failed recanalization of CTOs of the femoropopliteal arteries by conventional methods using guide wires and angiographic catheters.