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

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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.

Section snippets

Patient enrolment and pharmacological treatment

From January 2005, OCT became the mainstay intravascular imaging modality used at our institution to assess results of stent implantation. For this particular study, we only enrolled patients undergoing percutaneous coronary intervention for complex coronary lesions defined as long (> 20 mm), heavily calcified or at a bifurcation. Clinical exclusion criteria were: poor renal function (serum creatinine > 1.5 mg/dL), left ventricular ejection fraction < 30% and haemodynamic instability. Angiographic

Baseline clinical characteristics

Between February 2006 and August 2006, 36 stents implanted in 25 complex lesions from 23 patients were assessed using OCT. Baseline clinical characteristics are shown in Table 2. Mean age of patients was 64.5 ± 10.3 years with 91.3% male. Diabetes mellitus was a risk factor in 17.4% of patients with nearly half of the patients presenting with an acute coronary syndrome.

Angiographic and procedural characteristics

Angiographic and procedural characteristics are shown in Table 3. All lesions were complex (ACC/AHA classification type B or C),

Discussion

This is the first study using OCT to assess stent strut apposition systematically following implantation. Our study has shown that in complex coronary lesions, stent strut malapposition persists despite angiographic optimisation. Further, the thinner struts of the Taxus Liberte stent with its open cell design were more likely to be embedded to the vessel wall compared to the thicker Cypher stent struts employing a closed-cell system. Nevertheless, using high pressure stent expansion with

Conclusions

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 compared to other DES. 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.

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