Influence of expanded balloon diameter on Palmaz-Schatz stent recoil

On the Importance of Modeling Stent Procedure for Predicting Arterial Mechanics

The stent-artery interactions have been increasingly studied using the finite element method for better understanding of the biomechanical environment changes on the artery and its implications. However, the deployment of balloon-expandable stents was generally simplified without considering the balloon-stent interactions, the initial crimping process of the stent, its overexpansion routinely used in the clinical practice, or its recoil process. In this work, the stenting procedure was mimicked by incorporating all the above-mentioned simplifications. The impact of various simplifications on the stent-induced arterial stresses was systematically investigated. The plastic strain history of stent and its resulted geometrical variations, as well as arterial mechanics were quantified and compared. Results showed the model without considering the stent crimping process underestimating the minimum stent diameter by 17.2%, and overestimating the maximum radial recoil by 144%. It was also suggested that overexpansion resulted in a larger stent diameter, but a greater radial recoil ratio and larger intimal area with high stress were also obtained along with the increase in degree of overexpansion.

In vivo assessment of stent recoil of biodegradable polymer-coated cobalt-chromium sirolimus-eluting coronary stent system

INTRODUCTION

Immediate and acute stent recoil has been observed following balloon deflation in normal and diseased coronary arteries, and the degree varies by stent design.

METHODS

A total of 19 patients, who underwent elective stent implantation for single de novo native coronary artery lesions, were enrolled: all patients treated with the biodegradable polymer-coated sirolimus-eluting cobalt-chromium coronary stent system (Supralimus-Core(®)). The immediate, acute and cumulative stent recoil was assessed by quantitative coronary angiography. The cumulative stent recoil was measured at 24 h of stent implantation.

RESULTS

The absolute late loss due to recoil was found 0.08 ± 0.19 mm for Immediate Stent Recoil (ISR), 0.05 ± 0.21 mm for Acute Stent Recoil (ASR) and 0.11 ± 0.25 mm for Cumulative Stent Recoil (CSR) respectively.

CONCLUSIONS

In vivo acute stent recoil of the Supralimus-Core(®) has higher radial strength compared to other available standard drug-eluting stents.

Design criteria for the ideal drug-eluting stent

The deployment of drug-eluting stents (DESs) is an integral treatment option for patients with coronary artery disease. Although the development and testing of the first-generation DESs focused to a considerable degree on efficacy parameters, including restenosis, recent concerns over late clinical events have prompted a refinement of the design criteria for succeeding generations of these devices. This review assesses design criteria for the ideal DES from 3 complementary perspectives: deliverability, efficacy, and safety. Most new investigational balloon-expandable DES systems have lowered crossing profiles by thinning stent struts using a cobalt chromium alloy, while investigational self-expanding DESs often use nitinol as the platform material. Stents designed to be fully biodegradable are also being developed, with deliverability and performance to be determined in future clinical trials. Refinements in bifurcation-dedicated stents will secure branch accessibility to offer better deliverability in complex lesion morphologies. Experimentation in stent design is already realizing multiple-lesion stenting and the in situ customization of stent length. Rather than simply targeting further reductions in restenosis rates, efforts to improve efficacy are shifting toward a lesion-specific approach, including the design of stents dedicated to bifurcation lesions. Another future direction is a disease-specific approach, or an approach using DESs as local drug-delivery devices. The identification of long-term safety issues with the first-generation DESs has reignited clinical interest in the development of stents that are more biologically based, including fully biodegradable stents and stents using biomimetic and biodegradable polymers. Important performance criteria for future DES agents include more cell-type specificity, broader safety margins, and greater facility at promoting endothelialization and healing.

Comparison of in vivo acute stent recoil between the bioabsorbable everolimus-eluting coronary stent and the everolimus-eluting cobalt chromium coronary stent: Insights from the ABSORB and SPIRIT trials

OBJECTIVES

This study sought to evaluate and compare in vivo acute stent recoil of a novel bioabsorbable stent and a metallic stent.

BACKGROUND

The bioabsorbable everolimus-eluting coronary stent (BVS) is composed of a poly-L-lactic acid backbone, coated with a bioabsorbable polymer containing the antiproliferative drug, everolimus, and expected to be totally metabolized and absorbed in the human body. Because the BVS is made from polymer, it may have more acute recoil than metallic stents in vivo.

METHODS

A total of 54 patients, who underwent elective stent implantation for single de novo native coronary artery lesions, were enrolled: 27 patients treated with the BVS and 27 patients treated with the everolimus-eluting cobalt chromium stent (EES). Acute absolute recoil, assessed by quantitative coronary angiography, was defined as the difference between mean diameter of the last inflated balloon at the highest pressure (X) and mean lumen diameter of the stent immediately after the last balloon deflation (Y). Acute percent recoil was defined as (X - Y)/X and expressed as a percentage.

RESULTS

Acute absolute recoil of the BVS and EES was 0.20 +/- 0.21 mm and 0.13 +/- 0.21 mm, respectively (P = 0.32). Acute percent recoil was 6.9% +/- 7.0% in the BVS group and 4.3% +/- 7.1% in the EES group (P = 0.25).

CONCLUSIONS

In vivo acute stent recoil of the BVS is slightly larger but insignificantly different from that of the EES, implying that the BVS may have good radial strength similar to the metallic stent.

Mechanisms of residual lumen stenosis after high-pressure stent implantation: a quantitative coronary angiography and intravascular ultrasound study

BACKGROUND

Intravascular ultrasound (IVUS) studies have demonstrated that stents are frequently suboptimally expanded despite the use of high pressures for deployment. The purpose of this study was to identify the mechanisms responsible for such residual lumen stenosis.

METHODS AND RESULTS

Fifty-seven lesions from 50 patients treated with high-pressure (median+/-interquartile range, 14+/-2 atm) elective (44 de novo, 13 restenotic lesions) stenting were prospectively studied (29 Wiktor, Medtronic; 28 Palmaz-Schatz, Cordis Corp). Balloon subexpansion was calculated as the difference between maximal and minimal balloon cross-sectional areas at peak pressure measured by automatic edge detection; elastic recoil was calculated as the difference between minimal measured balloon size and IVUS-derived minimal lumen area within the stent. Angiographic residual diameter stenosis was 10+/-13% (reference diameter, 3.1+/-0.7 mm; balloon to artery ratio, 1.12+/-0.23) and IVUS-derived stent expansion was 80+/-28%. However, although balloon nominal size was 9.6+/-1.3 mm2 and maximal balloon size measured inside the coronary lumen was 12.5+/-3.2 mm2, final stent minimal lumen area was only 7.1+/-2.2 mm2. Balloon subexpansion of 4.0+/-1.8 mm2 (33%) and elastic recoil of 1.6+/-2.3 mm2 (20%) (both P<0.0001) were the two mechanisms responsible for residual luminal stenosis. Wiktor stent and peak inflation pressure correlated with balloon subexpansion, whereas Wiktor stent, de novo lesion, and minimal lumen area at baseline correlated with elastic recoil.

CONCLUSIONS

Despite high-pressure deployment, lumen dimensions after stenting are only 57% of maximal achievable. Inadequate balloon expansion and elastic recoil are responsible for residual lumen stenosis, suggesting that plaque characteristics and stent resistance deserve further investigation.

Three-year clinical follow-up after Palmaz-Schatz stenting

OBJECTIVES

Our goals were to examine late clinical outcome in a cohort of patients who electively received Palmaz-Schatz intracoronary stents, to identify specific predictors of outcome and to determine the time course of the development of ischemic cardiac events after stenting.

BACKGROUND

Short-term results of Palmaz-Schatz intracoronary stenting have been promising, with a reduction in both angiographic restenosis and clinical cardiac events up to 1 year after stenting.

METHODS

We analyzed the clinical outcomes in 65 consecutive patients who underwent stenting at least 3 years before analysis. Demographic, clinical and procedural predictors of survival and event-free survival, defined as freedom from myocardial infarction, stent-site percutaneous transluminal coronary angioplasty, coronary artery bypass graft surgery or death, were analyzed at a mean follow-up of 39 +/- 17 months.

RESULTS

Absolute survival and event-free survival at 3 years were 88% and 56%, respectively. Three-year freedom from stent-site revascularization was 66%. Predictors of decreased long-term survival (p < 0.05) included diabetes and a high angina score (Canadian Cardiovascular Society class III/IV) at 6 and 12 months after stenting. Predictors of decreased event-free survival (p < 0.05) included a high angina score at 3, 6 and 12 months after stenting, smaller stent deployment balloon size and greater number of stents implanted. Freedom from adverse events by 6 months after stenting also correlated with long-term event-free survival. Eighty-five percent of stent-site revascularizations occurred within 1 year. During late follow-up (>24 months), no patients had stent-site stenoses requiring revascularization, whereas 11% of patients required revascularization in nonstented coronary segments.

CONCLUSIONS

Clinical predictors of worse long-term outcome included diabetes mellitus, higher angina score at follow-up, smaller stent deployment balloon size and greater number of stents at implantation. During follow-up, the majority of adverse events and stent-site revascularizations occurred early after stenting, and disease progression in nonstented vessels accounted for the majority of late revascularization events.