This was an observational, non-randomized, retrospective, single-arm study carried out in real-world patients at three clinical centres of India. A total of 419 consecutive patients’ data was collected in the study, who underwent treatment for coronary lesions by implantation of Flexinnium stent, between April 2013 and December 2014. Before the discharge of the patient from the hospital, data release consent was taken from every patient, which is the practise of associated hospitals, irrespective of any study to be conducted in future. Baseline clinical data with procedural outcomes, patients were obtained from medical records and follow up data were recorded prospectively. The study was approved by the Institutional Review Board or Independent Ethics Committee.

The patients were included for analysis if: 1) patient’s age was 18 years or above; 2) patients had stable, unstable angina or acute recent myocardial infarction, and 3) were undergoing coronary intervention with the study stent. The patients were excluded if they declined to give consent for data release or if they had any allergy to aspirin, clopidogrel, ticlopidine, heparin and cobalt chromium.

The Flexinnium coronary stent system comprises L605 Co-Cr alloy positioned on balloon catheter amid two radiopaque markers. High tensile properties of Co-Cr alloy lead to thinner struts without compromising the radial strength. The Co-Cr alloy has been preferred as it retains the properties of biocompatibility, radiopacity, strength, non-ferromagnetism, and high corrosion resistance. Flexinnium has been developed with a very flexible ‘S-link’ that allows the stent to be more flexible hence, more deliverable as it travels through vessels during implantation. Strut is ultrathin with a thickness of 60 µm. Flexinnium stent is available in different lengths i.e., 8, 12, 16, 20, 24, 28, 32, 36, 40, 44 and 48 mm and different diameters i.e., 2.0, 2.25, 2.5, 2.75, 3.0, 3.5, 4.0, and 4.5 mm.

All patients were given a loading dose of 300 mg of aspirin and clopidogrel (300 mg) or prasugrel (60 mg) or ticagrelor (two tablets each of 90 mg). The procedural anticoagulation was brought about either with heparin or bivalirudin. The intra-procedural glycoprotein IIb/IIIa- inhibitor was administered based on the investigator’s decision. The procedure was performed as per standard treatment guidelines of every participating centre. Dual antiplatelet therapy (aspirin 75-300 mg daily indefinitely and clopidogrel 75 mg daily or prasugrel 10 mg daily or ticagrelor 90 mg twice daily for at least 1 month) was administered to all patients after the procedure.

Occurrence of any MACE was the primary end-point of the study. The MACE was defined as a miscellany of cardiac death, MI (Q-wave and non-Q-wave), TLR and TVR. The occurrence of ST was also analysed as safety endpoint as per the Academic Research Consortium. These endpoints were observed at in-hospital stay, 30 days, six months and 12 months follow up. The secondary endpoints will be measured at 24 months.

Any death due to a cardiac cause (such as myocardial infarction, low-output failure, lethal arrhythmia), unwitnessed death and death of unknown reason, and all procedure-related deaths, involving those linked to concomitant treatment, were classified as cardiac death [14]. The MI was defined by rise of cardiac troponin (cTn) values [>5 × 99^th percentile upper reference limit (URL)] in patients who have normal baseline values (≤99^th percentile URL) or a increase of cTn values >20% when the baseline values are elevated and are stable or declining [15]. Pathological Q waves are defined as per amplitude, location, and depth if appear in at least two contiguous leads. A TLR was described if restenosis was within the stent or in subsequent 5 mm of distal or proximal segment. A TVR was considered when there was stenosis in any segment of the treated vessel. A ST was considered acute when it occurred within 24 hours, sub-acute when it occurred between 1 and 30 days, and late when it occurred after 30 days. A definite ST was defined by symptoms suggestive of an acute coronary syndrome and angiographic or pathologic confirmation of stent thrombosis. A probable ST was described as unexplained death in 30 days or target vessel MI without angiographic confirmation of ST. A possible ST was described as any unexplained death after 30 day [14].

Clinical follow up or telephonic follow up were scheduled at 30 days, 6 months and 12 months. Follow up data were obtained relating to current clinical status, prior hospitalisation and incidence of any adverse events. Further follow up is scheduled to be taken at 24 months.

Continuous variables were presented as mean ± standard deviation and categorical variables as counts and percentages. The event free survival curve was calculated according to the Kaplan-Meier method. All data were analysed using the Statistical Package for Social Sciences (SPSS; Chicago, IL, USA) program, version 15.

A total of 419 patients were enrolled in the study. [Table/Fig-1] outlines the basic demographic details of patients. The study population included higher proportion of male (n=317; 75.7%) and average age was 54.1±10.2 years. The rate of hypertension was high in the enrolled patients (n=243; 58.0%). There were 134 (32.0%) diabetic patients in the study. Majority of the patients presented with stable angina (n=153; 36.5%) and non ST-elevation myocardial infarction (n=120; 28.6%). Total 491 lesions were intervened successfully with 525 stents (1.1±0.3 per lesion). The average stent length and diameter were 23.1±8.7 mm and 2.9±0.3 mm, respectively. Type B2 and C lesions accounted for 55 (11.2%) and 200 (40.7%) lesions and there were 88 (17.9%) totally occluded lesions. The lesion and procedural characteristics are detailed in [Table/Fig-2].

Follow up was completed in 396 (94.5%) patients at the end of 12 months. The occurrence of MACE during in-hospital stay, at 30 days, and 6 months was 5 (1.2%), 5 (1.2%), and 9 (2.2%), respectively. The MACE at 12 months was found to be 14 (3.5%). These included 9 (2.3%) cardiac deaths, 1 (0.3%) MI, 3 (0.8%) TLRs and 1 (0.3%) TVR. There was one incidence of definite ST at 12 months follow-up. [Table/Fig-3] details clinical outcomes of the study. The cumulative event free survival was found to be 96.5% by Kaplan-Meier method [Table/Fig-4].

[Table/Fig-4]:

Cumulative event-free survival rate upto 12 months.

The Flexinnium stent has shown excellent procedural and post-procedural clinical outcomes upto 12 months follow up. The diabetic patients included in the study were 134 (32.0%). More than half (58.0%) of patients were hypertensive. Overall 266 (63.5%) patients presented with acute coronary syndromes. The type of patients included in the study are veracious representative of routine clinical practice for treatment of CAD in India. Type C lesions accounted for 200 (40.7%) lesions. Moreover, the average stent length and diameter were 23.1±8.7 mm and 2.9±0.3 mm, respectively. The primary endpoint, MACE at 12 months was found to be 3.5%. The study included real-world patients with relatively complex lesions and characteristics; still it demonstrated low MACE rates. Thus, it can be postulated that the remarkable ultrathin stent struts (60 μm); the exceptional ‘S-link’ design and the illustrious Co–Cr alloy have contributed to the splendid clinical performance.

Thinner struts have been associated with lower rates of restenosis, which has been depicted by the ISAR STEREO and ISAR STEREO II trials [16,17]. Thin struts have manifested improved stent crossing, superior trackability, and reduced periprocedural MI [18]. Additionally, the Co-Cr stents can be designed with thinner struts when compared to Stainless Steel (SS) stents owing to its high tensile properties leading to thinner struts without compromising radial strength. Previously a study had reported higher cumulative survival at six months for patients treated with Co-Cr stents than those with SS stents (log-rank p=0.03) [19]. Literature suggests that stent designs have also been responsible for the clinical outcomes. The rigid stents have resulted into development of thicker neointima at follow up when compared to flexible stents [20]. Thicker neointima consecutively results into augmented in-stent restenosis. Thus, the flexible ‘S-link’ design also contributes towards the lower MACE rates after the implantation of Flexinnium stents.

[Table/Fig-5] represents comparison of patient characteristics and clinical outcome data of some previously published studies and the present study. This study includes greater number of diabetic patients (32.0%) and longer stent length (23.1±8.7 mm) than most studies. Despite the definition of MACE was not uniform in all these studies, our comparison demonstrated favourable MACE rate in the Flexinnium study when compared to most other studies. The MACE in other studies with 12 months follow-up [7, 21-24] was higher than the present study; OMEGA study (12.8%), Polish NexGen Registry (25.2%), KARE study (8.2%), Arthos Pico Austrian Multicenter Registry (15.0%), MULTIBENE (14.5%). Moreover, Flexinnium has the lowest strut thickness among all the compared stents; this represents role of strut thickness towards the clinical outcomes after stent implantation. Based on this comparative data, it could be reasonable to infer that Flexinnium stent had depicted propitious clinical performance at 12 months follow up. In addition, recently a study had also depicted favourable outcomes after implantation of Flexinnium in unselected real-life patients with simple and complex coronary lesions [25].

Currently, the DESs have been extensively used with favourable outcomes in terms of lower rates of restenosis when compared with BMS. Nevertheless, DESs suffer a major drawback of late stent thrombosis which has been associated with a mortality rate of around 45% [26]. Moreover, the BASKET-LATE study emphasizes that DES have been allied with augmented rate of late, apparently thrombosis-related, death or non fatal MI when compared to BMS [8]. There was low rate of restenosis-related TVR after DES (4.5%) when compared to BMS (6.7%), on the other hand the rates of cardiac death (1.2% vs. 0%) and non fatal MI (4.1% vs. 1.3%) were higher after DES implantation than BMS at 7 to 18 months follow up. Likewise, the DEDICATION trial determined that long term cardiac death, presumably due to stent thrombosis, was higher in DES than in BMS (7.7% vs. 3.2%; p =0.02) [27]. Similarly, Vogt A et al., had reported that on multivariate analysis at long term follow-up in STEMI patients after the implantation of DES and BMS, DES was not found to be superior to BMS [26]. The differences in clinical outcomes of DES and BMS are now being diminished through versatile mechanical characteristics and improved deliverability of BMS. Thus, it can be proposed that as the BMS are being improved with better designs and breakthrough engineering, they have been used in parallel with DES under myriad situations.

The present study is limited by the fact that it was an observational, non-randomized, retrospective, single-arm study without any direct concurrent comparator. In this era of drug eluting stents, the extraction of sizeable clinical data of BMS becomes difficult and takes longer time. Nevertheless, these unselected consecutive patients represent real-world practice; whereas, patients enrolled in clinical trials are carefully selected. We did not have any information on bleeding complications or antiplatelet therapy during follow-up. Despite these limitations, this study demonstrates favourable clinical outcomes that are representative of the real-world situation.

Our results demonstrate that the Flexinnium stent is associated with a low 12 months incidence of MACE in a wide range of real-world population. The remarkable ultrathin stent struts (60 μm); the exceptional ‘S-link’ design and the illustrious Co-Cr alloy have also contributed to the favourable clinical performance of Flexinnium. Long-term follow up would further confirm its clinical performance profile.