The influence of strut thickness and cell design on immediate apposition of drug-eluting stents assessed by optical coherence tomography

Abstract 

Background

Stent strut malapposition correlates with poor intimal coverage and this may increase the risk of late stent thrombosis. At present, there is limited data on whether stent strut thickness and stent design impact on acute apposition. We aimed to investigate the influence of stent strut thickness and design on acute stent strut apposition (SSA) immediately following drug-eluting stent (DES) implantation using optical coherence tomography (OCT), a technique with higher resolution and fewer artefacts than intravascular ultrasound.

Methods

Thirty-six DES in 23 patients (25 lesions) were studied by OCT. SSA was defined as embedded when a strut was buried in the intima for more than half its thickness, protruding when apposed to the intima but not embedded and malapposed when there was no intimal contact.

Results

Cypher Select stents were implanted in 52%, Taxus Liberte in 32%, Costar in 12% and Endeavour in 4%. A total of 6402 struts were evaluated. Despite stent optimisation using balloons with a final balloon/artery ratio of 1.26±0.19 at a maximum inflation pressure of 17.5±3.0 atm, only 57.1±20.7% of struts were embedded, whereas 33.8±18.4% were protruding and 9.1±7.4% were malapposed. Stent type was a strong predictor of malapposition on logistic multilevel analysis (OR 3.95, 95%CI: 1.27–12.23, p=0.017). At 12 months follow-up, there were no adverse clinical events.

Conclusion

Despite angiographic optimisation with high pressures and adequately sized balloons, malapposed stent struts are frequently found in complex coronary lesions and more often following the implantation of Cypher Select stents which have a thicker stent strut and closed cell design. With no adverse clinical events at 12 months follow-up, this likely represents a benign phenomenon at least as long as combined anti-platelet therapy is maintained.

Keywords: Angioplasty, Drug-eluting stents, Optical coherence tomography, Malapposition, Strut thickness