Intra-coronary stents deployment reduces the rate of angiographic restenosis as compared to Balloon angioplasty. in-stent restenosis, usually defined as ≥50 percent diameter stenosis within previously deployed stent, is most often becoming clinically evident within the first 6 to 12 months after the stent was deployed. Several risk factors are predictors for the development of in-stent restenosis. These can be generally calcified as either clinical, angiographic or procedural related factors. However it is difficult to estimate to what extent In stent re-stenosis is influenced by these various components.

Drug eluting stent, as compared to bare metal stents, markedly reduced the incidence of angiographic in-stent restenosis. However this benefit must be weighed against a suggested increased risk of late and very late stent thrombosis, a catastrophic event often leading to myocardial infarction and death. Often in patients with existing risk factors for in-stent restenosis, drug eluting stents will be deployed even in cases where patency of a previously deployed bare metal stent have been demonstrated.

Therefore the researchers sought to investigate whether in patients with previously deployed bare metal stent and no evidence of in-stent re-stenosis there will be a significant difference in the rates of in-stent between drug eluting stents and bare metal stents deployed within de-novo stenotic lesions.

Intra-coronary stents deployment reduces the rate of angiographic restenosis and clinically-driven repeat target lesion revascularization (TLR) compared to percutaneous transluminal coronary angioplasty (PTCA) alone. Angiographic binary in-stent restenosis (ISR) is usually defined as ≥50 percent diameter stenosis within previously deployed intra-coronary stent. in-stent restenosis is most often becoming clinically evident within the first 6 to 12 months after the stent was deployed. Although there is an increase in neointimal tissue with subsequent reduction in the minimal luminal diameter (MLD) during the first six months after stent deployment, there may be no further reduction in luminal diameter, or even regression, at one year and a further increase in diameter at later time points. Hence, after one year recurrent ischemia is more likely to be due to new or progressive disease at another site rather than due to ISR.

Several risk factors are predictors for the development of ISR. These can be generally calcified as clinical related factors, angiographic related factors and procedural related factors:

clinical related factors- higher rates of ISR are seen in female patients, hypertensive or diabetic patients , patients suffering from multivessel disease or renal dysfunction and stenting performed in the setting of acute coronary syndrome (ACS).

angiographic related factors -higher rates of ISR are seen in some lesion types, such as smaller reference artery diameter, Smaller pretreatment MLD, longer lesion length, complex lesions, ostial lesions, ISR in a companion lesion or stenting of multiple lesions and bifurcation lesions and treatment of in-stent restenosis.

procedural related factors- lower rates of ISR are seen after high-pressure post-dilation while higher rates of ISR are seen with stent under-expansion, placement of multiple stents, longer stent length (>35 mm) and stented segment, Excessive stent length in relation to the lesion length, Overlapping stents, smaller post-treatment MLD (MLD after stenting <3 mm), post-procedural percent diameter residual stenosis, the use of coil stent and a shorter time interval, between prior angioplasty and current stent implantation. The configuration of the stent may also affect ISR rates. Stents with thinner strut thickness are less likely to demonstrate ISR. Contact allergy to metal compounds, particularly nickel, released from stainless steel stents have also been suggested to contribute to the development of ISR.

Drug eluting stents (DES) demonstrate the ability to suppress in-stent neointimal hyperplasia, a sustained effect that lasts even after two years from the time the DES was deployed. Multiple randomized trials, large registries and meta-analyses have demonstrated that drug DES, as compared to bare metal stents (BMS), markedly reduced the incidence of angiographic in-stent restenosis (ISR), rates of late lumen loss as well as the rates of target lesion revascularization (TLR).Likely scenarios, both "on-label" and "off label" use, for the preference of DES over BMS, owing to improved efficacy, include stenosis of the Left main coronary artery, left main equivalent disease, and stenosis of the ostial or proximal left anterior descending artery, large amount of viable myocardium at risk, need for multi-vessel revascularization, long lesions, stenosis of small diameter vessels, complex or bifurcation lesions, restenotic lesions, saphenous vein graft stenosis and chronic total occlusion (CTO). In most North America centers, DES have been utilized in preference to BMS whenever feasible.However the benefits of DES on ISR must be weighed against the concerns in regard to the suggested increased risk of late and very late stent thrombosis, especially if dual antiplatelet therapy with aspirin and a thienopyridine is prematurely discontinued, a catastrophic event often leading to myocardial infarction and death.Furthermore, the longer time period recommended with dual antiplatelet treatment, after deployment of DES as compared to BMS, poses an increased risk of major bleeding.

There is an increase in the use of DES. In patients suffering from ISR in other arteries or other segments of the artery, DES will often be deployed in de-novo stenotic lesions. However, it is difficult to estimate to what extent ISR is influenced by the various predictors for ISR. in patients with either clinical angiographic or procedural related risk factors, DES will often be deployed even in cases where patency of a previously deployed BMS have been demonstrated. Therefore the researchers sought to investigate whether in patients with previously deployed BMS and no evidence of ISR, so-called "non-restenosers", there will be a significant difference in the rates of ISR between DES and BMS deployed within de-novo stenotic lesions.

Inclusion Criteria:

• The patient underwent coronary angiography and subsequent angioplasty with deployment of a bare metal stent within de novo stenotic lesion.
• The patient underwent a second coronary procedure, more then six month from the first procedure, in which patency of the previously deployed bare metal stent was demonstrated, provided that no intervention was performed within this stent in the six month interim. In lieu, either bare metal stent or drug eluting stent were deployed within another stenotic lesion (another de novo lesion).
• The patient underwent a third coronary angiography procedure within the 12 month interim from the second coronary procedure, in which in-stent restenosis was demonstrated within the stent deployed in the second procedure
• If no in-stent restenosis was demonstrated within the stent, deployed in the second procedure within the 12 month interim from the second procedure, the patient underwent coronary angiography at least 12 month from the second procedure in which patency of the bare metal stent or drug eluting stent was determined

Exclusion Criteria:

• Patients in whom a stent, in either the first or second procedure was deployed within previously stent treated stenotic lesion.
• Patients in whom a stent, in either the first or second procedure, was deployed within a graft.
• Patient suffering from in-stent restenosis within the bare metal stent, during the six month interim between the first procedure and second procedure or at the time of the second coronary angiography
• Patients who underwent a coronary intervention within the bare metal stent in interim between the first and second procedures.

all patients who underwent percutaneous coronary intervention in Rambam Medical Center between 2000 -2010.