Study design and patient population
In this retrospective study all consecutive patients, who were treated within the 38 months period from September 2017 until October 2020 for CTO by using the Outback® catheter for targeted tibio-peroneal re-entry in subintimal recanalization, were included. Regarding demographic baseline data, age, gender, relevant co-morbidities and clinical stage of peripheral arterial occlusive disease according to Rutherford classification were documented (Hardman et al. 2014; Stoner et al. 2016). In addition, lesion characteristics, such as location and length of the occlusion, the degree of calcification documented as none, mild (< 25% circumference), moderate (25%–50%), or severe (> 50%) and the modified SVS (Society of Vascular Surgery) runoff score were recorded (Stoner et al. 2016). The latter ranges from 1 to 19, with higher values for more severe disease. The patency of the popliteal artery and the three arteries of the lower leg are assessed and any stenoses and occlusions are graduated. A score of 0 corresponds to a vessel with less than 20% stenosis, a score of 1 corresponds to a vessel with 21% to 49% stenosis, 2 corresponds to a vessel with 50% to 99% stenosis, 2.5 corresponds to a vessel that is occluded for less than half of its total length, and 3 corresponds to an occlusion of more than half of the vessel length. The value for the popliteal artery is multiplied by 3 and a value of 1 is added before all 4 vessel values are added. Particular attention was paid to all technical details of the revascularization, like the approach to recanalization, the location of the targeted re-entry as well as the accuracy of the Outback catheter in this respect and the subsequent angioplasty. The technical success of the re-entry manoeuvre itself as well as the overall procedural success defined as successful target vessel recanalization and improvement of wound perfusion were recorded including the achieved modified SVS runoff score. Complications were classified according to the Society of Interventional Radiology (SIR) Classification System for Complications by Outcome (Sacks et al. 2003).
All procedures were performed by one interventional radiologist (CSM) with more than 10 years of experience in vascular interventions and broad expertise in the use of the Outback® catheter, especially in iliac and femoro-popliteal recanalizations. All interventions were performed at a Philips Allura Xper FD 20 angiography system (Philips Healthcare, Best, The Netherlands). An antegrade approach via the ipsilateral common femoral artery was chosen for nearly all procedures. Only in one case the proximal superficial femoral artery had to be used as point of access due to obesity, punctured by ultrasound guidance. Access was gained using a Mini Access Kit (Merit Medical, South Jordan, UT, US) and after initial digital subtraction angiography of the leg arteries a 6 French sheath was introduced for the subsequent intervention. Under roadmap-guidance careful subintimal probing of the occluded vessel segment was performed using either a diagnostic catheter with a short angled tip (Cordis® Tempo® Vertebral Catheter, Cordis - a Cardinal Health Company, Santa Clara, CA, USA) in combination with an 0.035″ hydrophilic guidewire (Radiofocus® Guidewire M Standard Type, Terumo Corporation, Tokyo, Japan), or, in the majority of cases, a low-profile support catheter (0.018″ TrailBlazer™, Medtronic, Fridley, MN, USA) combined with an 0.014″ CTO wire (Hi-Torque Command ES guide wire, Abbott, Chicago, IL, USA). The spontaneous re-entry in the lower leg trifurcation area was unsuccessful in all of the presented cases. In this situation, a retrograde puncture and probing of the target vessel on the lower leg is usually attempted, unless wounds, necroses or extensive edema and inflammation in the pedal or crural access area prevent this. This applied to eight of the presented cases and was already considered during primary probing.
In two cases the distal posterior tibial artery was punctured in a retrograde fashion under ultrasound guidance using a Mini Access Kit. In another case the distal peroneal artery was punctured analogously under fluoroscopic guidance. After successful access, the occlusion was probed using an 0.014″ or 0.018″ Hi-Torque Command guide wire supported by an 0.018″ TrailBlazer catheter. This approach, also known as SAFARI-technique (Subintimal Arterial Flossing with Antegrade-Retrograde Intervention) is mostly successful, but in the three cases presented here no re-entry could be achieved in this way either (Spinosa et al. 2005). Therefore, a modified SAFARI-technique was used by introducing a 2.5 × 40 mm balloon catheter (Pacific Plus, Medtronic, Fridley, MN, USA) from the distal access point without prior placing of a sheath and dilated at the level of the tibio-peroneal trunc. The inflation of the balloon at the desired re-entry point with the following repeated probing with the wire did not lead to a successful re-entry. Hence, the Outback® re-entry device (Outback® LTD or Outback® Elite catheter, Cordis - a Cardinal Health company, Santa Clara, CA, USA) was introduced from the femoral access and placed parallel to the anew inflated balloon, which was then punctured directly. An 0.014″ Hi-Torque Command wire was guided into the balloon. When retracting the balloon, the wire could be pushed and pulled successfully further distal into the posterior tibial or peroneal artery, respectively, and finally out of the patient at the distal access point. Afterwards, a new balloon catheter was advanced from the femoral access by guiding it over the 0.014″ pull-through wire for subsequent angioplasty.
In almost all other cases retrograde pedal or distal-crural access was not possible due to above mentioned reasons. Only in one case retrograde access was avoided despite the absence of wounds in the puncture area, as retrograde probing seemed to be less promising due to an upstream occlusion of a femoro-popliteal bypass anastomosed to the distal P3 segment and severe calcification in the area of the trifurcation. Therefore, an 0.014″ Hi-Torque Command wire was advanced to the point of desired re-entry within the subintimal space. The Outback® catheter was then guided to that position. If a subintimal passage of the Outback® catheter was not possible due to friction, a prior balloon angioplasty with a 2 or 2.5 mm balloon was required. The correct positioning of the Outback® catheter was confirmed either by multiple angiographies in differently angled views or by using the plain fluoroscopy in case of heavily calcified vessels. In most cases, the Outback® needle was not fully deployed due to the smaller crural vessel diameter. In three cases, the shape of the needle was used to penetrate the anterior tibial artery in its proximal bend. The possible feeding of the wire with little to no friction in combination with roadmap guidance displaying the course of the target vessel properly was used to verify a successful re-entry. This was further confirmed by inserting a balloon catheter over the wire with the tip distal of the suspected re-entry point for a careful application of contrast agent. Afterwards, the balloon was used for an angioplasty of the entire subintimal tract and the re-entry point for an extended period. In case of residual stenosis due to dissection, recoil or heavy calcification self-expandable nitinol stents or stent-grafts (Astron Pulsar®, Biotronik, Berlin, Germany; sinus SuperFlex-418®, Optimed, Ettlingen, Germany; Supera®, Abbott, Chicago, IL, USA; GORE® VIABAHN®, W. L. Gore & Associates, Inc., Newark, DE, USA) were deployed to secure the result. In one patient a drug-coated balloon was used instead of placing a stent (IN.PACT® Admiral, Medtronic plc, Dublin, Ireland).
According to their distribution, demographic and clinical baseline as well as follow-up data are given either as median with corresponding range or interquartile range (IQR, 25th – 75th percentile) or as mean with corresponding range. Statistical analysis was performed using R version 3.6 (https://www.r-project.org/). Wilcoxon’s one-sided signed-rank test for paired samples was used to compare the results of the modified SVS runoff score before and after revascularization. A p-value equal to or below 0.05 was considered statistically significant.