Inclusion criteria: All patients post-Acute Coronary Syndromewho have DM and underwent for coronary angiography with PTCA and stenting.

Acute coronary syndrome (ACS); Diabetes mellitus (DM);In-stent restenosis (ISR)

1. Diabetes mellitus: Both groups included diabetic patients as per inclusion criteria
2. Hypertension: In the BDP-DES group there were 31 patients with history of hypertension (62%) and 19 patients with no history of hypertension (38%). In the DP-DES group there were 27 patients with history of hypertension (54%) and 23 patients with no history of hypertension (46%). Chi-square test (p=0.417).
3. Smoking: In the BDP-DES group there were 31 smoker patients (62%) and 19 non-smoker patients (38%). In the DP-DES group there were 29 smoker patients (58%) and 21 non-smoker patients (42%). Chi-square test (p=0.683).
4. Body Mass Index (BMI): The Mean+/-SD BMI in the BDPDES group was 30.1 +/- 3.53. The Mean+/-SD BMI in the DP-DES group was 29.9 +/- 3.77. Independent t-test (p=0.813).
5. Dyslipidemia: In the BDP-DES group there were 23 patients with history of dyslipidemia (46%) and 27 patients with no history of dyslipidemia (54%). In the DP-DES group there were 24 patients with history of dyslipidemia (48%) and 26 patients with no history of dyslipidemia (52%). Chi-square test (p=0.841).
6. Family history of coronary artery disease:

1.  Diabetic patients who had PCI post ACS with deployment of BDP-DES and DP-DES in both groups had no statistical difference as regard baseline patient characteristics
   (age, gender, smoking, obesity, family history of IHD,hypertension and dyslipidemia). 
2. There was no statistically significant difference in the 12 months duration of follow up both clinically and angiographically between the patients who had Biodegradable polymer DES (BDP-DES) and the patients who had durable polymer DES (DP-DES) during their index and follow up PCI procedures (by comparing the percentages of patients who had symptoms ±ISR/ST) in diabetic patients admitted as ACS cases, despite slight numerical difference in favor of BDP-DES group.
3. Stented vessels, stent parameters and ejection fraction distribution in both BDP-DES and DP-DES patient groups, showed slight numerical difference although it was not statistically significant.
4. The number of patients having typical/atypical anginal symptoms and ISR with DP-DES patient group was slightly higher than BDP-DES patient group, although it was not statistically significant.
   

The results of our study were mainly concordant with the results of most of the clinical trials that compared the biodegradable polymer DES with the durable polymer DES as it showed non-inferiority of the biodegradable polymer DES regarding clinical outcome over a period of 12 months. The BIOFLOW-V trial was a prospective, multicenter, randomized, controlled trial by Kandzari DE et al. [9], that randomized 1,334 patients with 2:1 ratio to biodegradable polymer Orsiro Sirolimus Eluting Stent System with (treatment group) or durable polymer Xience Everolimus Eluting Stent System (control group). Follow-up in both arms was approximately 97% at 12 months, at which time the primary endpoint, target-lesion failure, had occurred in 6.2% of the Orsiro-treated patients and in 9.6% of the Xience-treated patients (P=0.04). There was no difference between groups as regard primary composite endpoints (cardiac death and clinically driven TLR).

Another trial by Pilgrim T et al. [10] who performed BIOSCIENCE randomized, all-comers multi-center trial, to compare biodegradable polymer Orsiro Sirolimus Eluting Stent and durable polymer Xience Everolimus Eluting Stent. Primary end point was TLF (cardiac death, target vessel MI and clinically indicated TLR) at 12 months and secondary end point (all cause death, Cardiac death, Myocardial Infarction (MI), Target Lesion Revascularization (TLR), Target Vessel Revascularization (TVR), Definite or Probable ST, Target Vessel Failure (TVF)) at 5 years, BDP-DES demonstrated non-inferiority to DP-DES for TLF at 12 months 6.7% and 7% respectively and at 5-years, TLF rates show no significant difference (20.2% and 18.8% respectively (p-value=0.49)

Scientific explanations of the finding in our study:

The non-significant difference between the incidences of instent restenosis (ISR) in both groups may be scientifically explained by the fact that the presence of the polymer in permanent polymer DES group did not affect the process of arterial healing or the process of neointimal proliferation over the duration of 12 months. The delayed hypersensitivity response caused by the polymer, that may be responsible for very late stent thrombosis (VLST) events, will not take place in the first 12 months after stent implantation. There was no record of any case of myocardial infarction or
stent thrombosis within the 100 patients included in our study. It may be explained that most of the theories regarding the role of polymer in the cascade of pathophysiological processes in the arterial wall emphasize the delayed hypersensitivity reactions that may be responsible for very late stent thrombosis events and usually do not take place in the first 12 months after stent implantation.

There was no record of any case of myocardial infarction or stent thrombosis within the 100 patients included in our study.

It may be explained that most of the theories regarding the role of polymer in the cascade of pathophysiological processes in the arterial wall emphasize the delayed hypersensitivity reactions that may be responsible for very late stent thrombosis events and usually do not take place in the first 12 months after stent implantation. Whereas a main cause of the clinical events caused by the DES in the first 12 months is the delayed arterial healing, represented by fibrin deposition and delayed re-reendothelialization which is mainly explained by the antiproliferative drug effect beside the role of the polymer [11,12].

Most of the clinical trials in the literature were undergone to compare the biodegradable polymer DES with the permanent polymer DES to prove non-inferiority of biodegradable polymer DES and their efficacy to be widely used in coronary intervention.

The results were from a single medical center with a rather small sample size.

The assessment of clinical outcome depends only on history taking and incidence of in-stent restenosis on angiographic assessment basis, without any intravascular imaging to assess late lumen loss or neointimal volume obstruction.

Relatively short duration of follow-up for the included patients, most of the trials showed difference regarding very late stent thrombosis (VLST) up to five years in favors of BDP-DES.

The comparison was between more than one type of durable polymer DES, which was Resolute™ zotarolimus-eluting stent (R-ZES; Medtronic Inc., Santa Rosa, CA, USA), and more than one type of stents with biodegradable polymer sirolimus-eluting DES.

The study selected only diabetic patients with exclusion of non-diabetics. The incidence of MACE, ST and all-cause death would have been detectable to compare between the 2 groups if non-diabetic patients were included.

In our comparative study, BDP-DES and DP-DES deployment in diabetic patients presenting to our facility as ACS, didn’t show any statistically significant difference as regard MACE, ISR and ST in both groups.

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