Despite advancements in the field of endovascular surgery, bypass surgery is an absolute essential part of vascular surgeons’ armamentarium. Regardless the superiority of venous conduit (3, 4), prosthetic grafts are a viable alternative when the vein is disadvantageous (5), for e.g. in cases of small vein caliber, varicose veins or thrombophlebitis or unavailability because of previous harvesting for coronary or peripheral bypass (6). The initial results of infrapopliteal revascularizations with prosthetic grafts were poor as compared to venous conduits (7, 8, 9). Several strategies have been utilized to improve the performance and patency of prosthetic grafts. Some of these are: venous modifications of the distal anastomosis (MOD) (10, 11, 12, 5), heparin bonding at the luminal surface of PTFE grafts (Hb-ePTFE, Propaten; W.L. Gore & Associates, Inc.) (13, 14), distal AV-fistula (15) and grafts reinforced with rings (16).
MOD are advantageous in decreasing the intimal hyperplasia (17), by improving the flow characteristics (18) and reducing compliance-mismatch and shear stress (19) between relatively rigid prosthetic graft and undersized, delicate, calcified crural vessels. Experimental studies show that the intimal hyperplasia is most prominent at the transition between graft and MOD and least at the recipient artery (20). This spares the artery in an acceptable state for a redo revascularization and may further improve the secondary patency rates (12). The classical MOD were improved with time (21, 22). A boot shaped modification was described in 2000 and was known as St. Mary’s boot (23). The distal vein patch technique (DVPT) showed acceptable long-term results in a series published by Neville et al. (11). We performed the St. Mary’s boot (Supplemental Fig. 2). and the DVPT in 14 and 15 cases respectively. Holdsworth et al. (24) proposed a composite graft, where a segment of an autologous vein is anastomosed to a prosthetic graft and used for the distal anastomosis. We performed this technique in 4 patients. Bridged Bypass technique to improve the distal run-off and the compliance-mismatch was resorted to in 3 patients (25).
The median follow-up of 27 months was comparable to studies conducted by Daenens et al. and Pulli et al. (26, 27). The three groups (PGN, PGY and VG) in this study were comparable in terms of age (p = 0,271) and comorbidities. PGN and VG had significantly higher number of male patients. The most common risk factors were Hyperlipidaemia and Hypertension (28, 12). In 94.5% of patients’ critical limb ischemia was the indication for REBEL. In SCAMICOS (29) pre-existing cardiac illness and previous vascular surgery were the most common risk factors and 94% patients suffered from either rest pain or ulcer or gangrene. In our study out of 48 aneurysm-patients, 25 were asymptomatic. Venous conduit for REBEL was used in 83% (n = 40/48) aneurysm-patients. In 50% (n = 17/36) of patients in PGY group, the vein had already been harvested for a peripheral reconstruction. This was 20% (n = 5/26) in the PGN group. This difference was not significant (p = 0,066) but indicates that more patients in PGY had already undergone previous peripheral bypass surgery. The most common site of distal anastomosis in PGN group was the P3 segment of poplitea artery (69%) and in PGY group the crural arteries (77%). This significant difference (p = 0.002) suggests that PGY group patients the P3 segment was not adequate for distal anastomosis. This may have been because of previous surgery and/or stenting and/or occlusion due to diseased vessel. In 112 tibial bypass procedures presented by Neville et al (28), the patients with prosthetic graft bypass had a higher rate of prior bypass surgery.
The time taken to accomplish REBEL in PGY group was significantly more (p = 0,015) as compared to PGN group. Average duration of REBEL in PGY group was 284 minutes, comparable to VG group (average duration 285mins) but 72 minutes more as compared to the average for PGN group (p = 0.001). The decision regarding the postoperative antithrombotic therapy was not standardized in our study and was dependent on surgeons’ preference, distal outflow, patients’ comorbidities and type of revascularization performed. More than 50% of patients in the PGY group received a combination of AP and OAK. This was significantly higher (p = 0.05) as compared to the both PGN and VG group. Daenens et al (26) administered 160mg of aspirin per day in the postoperative period. Warfarin anticoagulation was only given to patients who received it preoperatively and in redo venous bypass patients.
The patency rates can be compared with the help of Kaplan-meier plots (Fig. 2,3). The primary patency rates for PGY vs PGN were 50% vs 74.2% at 12 months and 36.9% vs 50.1% at 36 months respectively. A similar trend was observed with the assisted primary patency rates. The difference between the PGY and PGN group for both primary patency (p = 0,226) and assisted primary patency (p = 0.74) was not significant. This may have been because of the relatively lower number of patients. A meta-analysis conducted by Albers et al (9) revealed pooled 1- and 2-year primary patency rates of 59% and 48%, respectively, for standard ePTFE grafts used in infrapopliteal procedures. Neville et al. (28) performed 62 femoro-crural reconstructions with Hb-ePTFE and distal vein patch and reported a 1-year primary patency of 75.4%, as compared to 86% for venous grafts. The primary, assisted primary and secondary patency rates at 12 and 36 months for PGN group were comparable to VG (Table 3). The secondary patency rates at 12 and 36 months in PGY group were significantly inferior as compared to VG (59.7% vs 76.1% and 44.6% vs 67.5%; p = 0.017) but were relatively inferior, even though not significant as compared to PGN group (59.7% vs 78.5% and 44.6% vs 59.6%; p = 0.0316). A significantly higher rate of amputation was observed in the PGY group. Amputation-free Survival in PGY group was significantly lower at 12 (62.9% vs 87.6%; p = 0.038) and at 48months (43.4% vs 69.75%; p < 0.001) as compared to the PGN group. The three groups didn’t show any significant difference (p = 0.375) in overall survival (Table 3, Supplemental Fig. 1). In SCAMICOS (29) the primary patency at 36 months was 26% with MOD and 43% without MOD in femoro-popliteal reconstructions and 20% and 17% for femoro-crural reconstructions respectively. The amputation-free survival was better for the revascularizations with MOD both for femoro-popliteal and femoro-crural revascularizations, but this was not statistically significant. Similar to our study, the SCAMICOS (29) could not demonstrate any benefit of MOD for below knee revascularizations with PTFE. A meta-analysis (30) published in 2012 involving 885 patients with below-knee popliteal and crural bypasses. This metanalysis showed no significant improvement for primary patency or limb survival at 3 years for femoro-crural bypasses with venous cuff. In our study, we achieved good patency rates at 1 month (Table 3) for all three groups. These were better for the PGY group as compared to PGN, even though this was not statistically significant. This is an evidence of technical success and expertise of our surgeons. These findings are also in coherence with the reanalysis in the SCAMICOS cohort (31).
Keeping the abovementioned results in mind, we would like to indicate towards the fact that the patients undergoing REBEL with MOD suffer from advanced PAD with prior single or multiple revascularizations (surgical or endovascular). The surgery was more time consuming because of the site of distal anastomosis, possible dissection of the fine crural arteries, vein harvesting and MOD. Because of the poor limb salvage rates, patients undergoing REBEL with MOD would require anticoagulation in addition to AP and demand exhaustive perioperative vascular surgical care, monitoring and decision making.