Baseline clinical characteristics
Regarding the age of patients in the current study ranged from 34 to 80 years, with mean age of (58 ± 8.6) years. The mean age of the sample in the present study is comparable to the mean age of patients enrolled in study by Hoye et al. (2005) (59.8 ± 11.1 years); however, Morino et al. (2010) reported a higher mean age in his study on outcomes of PCI in patients with CTOs (66.9 ± 11 years) [20, 21].
The baseline characteristics and risks factors were comparable between the two study groups.
Angiographic and procedure characteristics
Regarding angiographic procedure in current study, we found that occluded stent just occurred in 2 patients (10%) of BVS group and 4 patients (10%) of EES group at 6 months follow-up without significant difference between both groups. This large percent can be explained by our small sample size.
Our study in comparable with primary end point of absorb III trials which showed target lesion failure (TLF) at 12 months, this trial included 2008 patients (revascularization by BVS was 1322 and revascularization by DES 686) which showed TLF was 7.8% in BVS group and 6.1% in DES group. So absorb III trials provides adequate result of non-inferiority of BVS against DES in treatment of CTO lesions .
Absorb-CTO-registry which included 35 patients with true CTO lesion clearly showed that BVS use in CTO in feasible with good mid-term efficacy and 6 months follow-up by multi-slice computed tomography identifies only 2 cases scaffold re-occlusion without any major adverse event. Safety and feasibility of BVS implantation in CTO has been confirmed in this registry . These results were matched with our study results.
Another Ghost-CTO-registry which included 21 patients who had CTO lesions which treated by BVS and followed up after 1 year by OCT showed overall favorable vascular response and healing profile . These results are also comparable with our study.
In our study, the lesion location of CTOs were in left anterior descending artery (LAD) in 45% of cases, right coronary artery (RCA) in 45% of cases, and left circumflex artery (LCX) in 10% of cases.
In the current study, all patients had initial attempt of wiring through antegrade approach, if antegrade approach was failed, then retrograde approach was tried.
Retrograde approach has been described initially via the bypass grafts and more recently the use of septal collaterals has been described to be safe and efficient. Retrograde approach for recanalization of CTO has gained popularity recently with increased success rates as shown in several case reports and small series of selected patients .
Retrograde approach requires good special devices, such as micro catheters, dedicated guide wires, shorter guide catheters, or longer length guide wires, and should be performed with experienced operators and support staff.
Retrograde approach was successful in 15 (25%) patients, and was failed to cross CTO site in another 5 (4.0%) patients, those 5 patients had another trial of successful antegrade approach. There were no significant differences in respect to angiographic characteristics of the lesion between success and failure groups.
However, the conventional factors such as severe calcification, severe tortuosity, significant side branch at the CTO site and CTO length, which are shown to be independent predictors of successful procedure via antegrade approach in various studies  are not shown to have any significant impact on outcomes during retrograde recanalization in our study.
There was no difference between both groups possibly due to that conventional factors are not important when the retrograde techniques are applied, as the wire manipulation is done in retrograde fashion to gain access to either true or false lumen and to complete the procedure with adjunctive techniques.
Regarding procedure related complication in the current study, there was no reported cases of mortality or stent thrombosis, this might be due to operators experience and use of intense anti-platelet regimen and limited number of patients.
One of the most fatal complications during CTO intervention is coronary perforation and tamponade .
In spite of angiographic coronary perforation was frequently observed during CTO treatment, so evaluating the clinical significance of angiographic perforation is critically important, and goal must be to avoid cardiac tamponade.
In the current study, coronary perforation occurred only in one patient (0.05%) of BVS group and was managed successfully by simple balloon inflation without progressing to cardiac tamponade.
Similar figure was reported by Morino et al. (2010) and they reported incidence of 0.4%. These figures are considered low compared with the previous reports (a range of 0.8% to 1.9%) .
Potential hypotheses to explain low incidence of cardiac tamponade are adequate hemostatic procedures as needed, reduction of prolonged and aggressive antegrade guide wire manipulation. Thanks to the introduction of retrograde approaches. Although a careful evaluation is required, procedural continuation could be considered with angiographic coronary perforation.
Clinical outcome and follow-up
Concerning in-hospital outcome in the current study, there was no reported mortality during hospitalization period, Q wave myocardial infarction developed in 1.6% of study population and non Q wave myocardial infarction developed in 2.4%.
Close figures were reported by Lemos et al. (2004) who reported no death, TLR, TVR or Q wave MI, but incidence of 7.4% of non Q wave MI .
After the introduction of DES, several studies demonstrated that DES markedly reduce the incidence of angiographic restenosis and repeat revascularization in selected patients with relatively noncomplex lesions. In patients with CTO lesions, there are several trials comparing the efficacy of DES with BMS but studies comparing individual DESs against BVS are limited .
Regarding 12-month clinical follow-up in our study, no mortality occurred in all study population in both arms, and at 6 months follow-up unstable angina occurred in 37% with EES and 30% in BVS stent group which agreement with other previous studies from multiple randomized controlled trials (RCT) while revealing no significance between 2 groups about MACE at 12 months follow-up.
Our study shows non inferiority of BVS stent in CTO comparable with EES which matched with absorb III trial. However, our study of small population size limit data to show advantage of BVS on DES.
The knowledge that PCI does not prevent MI or prolong life in stable or stabilized coronary disease is well established. This was reinforced by the COURAGE and OAT trials in which PCI did not provide incremental benefits in hard end points such as MI or mortality above contemporary medical management. However, because COURAGE did not address CTOs specifically and OAT addressed only subacute post-MI occlusions, the generalized ability of these trials to CTO is not clear 
Furthermore, the COURAGE nuclear substudy demonstrated event reduction in patient with moderate to severe ischemia. The CTO populations are often enriched with patients with high ischemic burden who may likely benefit from recanalization .
Coronary BVS are attractive therapeutic option in interventional cardiology; BVS backbone is made of poly-lactoide and coated by thin layer of poly-dilactrole. It releases everolimus and is fully degraded to H2O and CO2 in 2–3 years. BVS seems to offer several theoretical advantage over metallic stent, as it gives temporary mechanical support of vessel wall; therefore, long-term endothelial function and structure are not affected, and a possible future surgical revascularization is not compromised .
Limitations of the study
This study was limited by its small sample size in patients from a two medical centers. Second generation BVS was not used for comparison as it is still under development. We need longer follow up to detect the outcome of BVS.
○ We believe that 1st generation everolimus-eluting bioresorbable vascular scaffold (BVS) stent associated with less complication and less restenosis rate than everolimus-eluting stent (EES) in chronic total occlusion (CTO) recanalization guided by intracoronary imaging.
○ Further follow-up data should be done on a large scale in order to provide evidence for how to follow-up and treat those patients.