Stent thrombosis Relation to drug eluting stents

# Overview
Overall lifetime incidence of stent thrombosis (ST) in patients with drug eluting stent(DES), from multiple trials is in the range of 0.5-2%. How ever there is wide variation of the incidence depending on the multiple variables which influence its occurrence.

# Relation to Drug Eluting Stents

## Incidence in Drug Eluting Stents
- In a study of 3548 registry patients who received a DES, the cumulative incidence of definite, probable or possible ST was 1.8%. The incidence for definite ST was 0.65% over a 15 month period.
- In a study of 1911 patients with DES and a follow up to a median 19.4 months , the overall incidence of ST was 0.8%.
- In a study of 1731 patients undergoing sirolimus eluting stent(SES) implantation the cumulative one year ST rate was 1.7%. This number was 3.2% for diabetics.
- In a real world observational study involving 15157 patients with SES acturial incidence of ST at 12 months was 0.87%.

## Incidence of Early Stent Thrombosis with Drug Eluting Stents
This group would include
- Intra-procedural ST
- Acute ST: up to 24 hrs
- Subacute ST: 24 hrs to 30 days
- Intra-procedural ST occurred in 0.7% of patients in a study of 670 patients with 1362 lesions who received a SES. The average stent length was 42.9  28.3 mm.
- A rate of 0.5% of acute ST was observed in a study of 1911 patients who were treated with aspirin, clopidogrel and on the discretion of the treating physician.
- A meta-analysis of 10 RCT involving 2602 patientes who received a DES, showed a ST rate of 0.34% by 30th day.
- In the real world setting a review of the e-cypher registry involving 15157 patients with SES, rate of sub-acute ST was 0.56%.
- An incidence subacute ST of 0.83 % was reported in a meta-analysis of 19 randomised controlled trails.
- In a large observational study of more than 8000 patients with DES, the cumulative incidence of subacute stent thrombosis was 1.1% at 30 days.  This accounted for 60% of total ST.

## Incidence of Late Stent Thrombosis with Drug Eluting Stent
This would include
- Late ST: 30 days to one year
- Very late ST: more than one year, but generally less than 3 years
- Later than 3 years
- In a study of more than 8146 patients in two academic centers, the cumulative incidence of late stent thrombosis was 1.7% at 1 year. The slope of the linear portion of the cumulative incidence curve between 30 days and 3 years indicated a steady rate of 0.6% per year. Late stent thrombosis was more frequent with PES (1.8%) than with SES (1.4%). 23% of patients who developed late ST were being treated with dual antiplatelet therapy. This study concluded that late stent thrombosis was encountered steadily with no evidence of diminution up to 3 years of follow-up. Cumulative incidence of very late stent thrombosis was 2.3% at 2 years, and 2.9% at 3 years
- In 1911 patients with DES with 100% follow-up, incidence of late ST was 0.6% which was similar to that for bare metal stents. The predictors of stent thrombosis were premature antiplatelet therapy interruption, primary stenting in acute myocardial infarction, and total stent length.
- A late angiographic ST rate of 0.35% (95% confidence limits 0.17% to 0.72%) was reported in a cohort of 2006 patients with 98% of the patients being followed up. The incidence of ST between 30 days to 1 year was 0.25% and incidence of very late ST was 0.15%. Also concluded that ST may occur even if the patients are stable on antiplatelet monotherapy.
- An incidence late ST of 0.7 % was reported in a meta-analysis of 19 RCT.
- The incidence of very late stent thrombosis more than 1 year after coronary revascularization is low, however drug-eluting stents appear to increase the risk for late thrombosis. In a meta-analysis of 14 trials analyzing 6675 patients, the incidence of very late thrombosis was 5.0 events per 1000 in drug-eluting stent patients and 5.9 events per 1000 incidence of very late thrombosis in paclitaxel stent patients. 
- A meta-analysis of 10 RCT involving 2602 patients with DES revealed a late ST rate of 0.23%.
- In the real world setting a review of the e-cypher registry involving 15157 patients with sirolimus, incidence of late ST was 0.19% at 12months follow-up.
- In a study of serial angioscopy study of 17 patients with sirolimus, 3 patients had visible thrombus at 21 months follow-up.

## Sirolimus Eluting Stent(SES) vs Paclitaxel Eluting Stent(PES)
It it not clear whether SES is better than PES as multiple studies demonstrate conflicting results.
- Study assessing 2 year outcomes in Western Denmark Heart Registry with patients implanted with SES and PES showed that the risk of developing ST with SES was lower. 2 year ST incidence with SES was 1.73% and 3.31% with PES.
- A meta-analysis of 878 patients treated with SES and 1400 treated with PES demonstrated that there was no difference in incidence rate(0.9%) of ST with SES compared to PES.
- SORT OUT II randomized clinical trial with 2098 patients, compared the outcomes in patients implanted with SES and PES. It inferred that there were no significant differences in ST incidence rates between the two.
- Incidence of ST in PES patients was observed to be significantly higher than that in SES patients in a meta-analysis involving 18,023 patients. This was re-emphasized by another meta-analysis involving 8,695 patients. However there were no significant differences in the mortality rate between the two.