Deliverability of Integrity Coronary Stents in Severely Tortuous Coronary Arteries: A Preliminary Experience

Abstract: Background. Stent delivery failure occurs in 4% of all percutaneous coronary interventions (PCIs) and >90% of these failures are due to vessel tortuosity and/or calcification. Stent performance of the newly launched Integrity coronary stent has markedly improved due to its novel manufacturing process utilizing continuous sinusoid technology. We sought to evaluate the deliverability of Integrity coronary stents in severely tortuous coronary lesions in real-world clinical practice. Methods. From January to August 2011, a total of 35 patients (25 males; mean age, 60.7 ± 11.4 years) with obstructive coronary artery disease involving severely tortuous coronary vessels underwent PCI with Integrity coronary stents. Results. The most common target vessel for PCI was left circumflex artery (54.3%) followed by right coronary artery (42.8%) and left anterior descending (2.9%), with 37.1% of lesions located distally. Mean stent diameter was 3.04 ± 0.51 mm and mean stent length was 20.5 ± 6.6 mm. Acute procedural success was achieved in 33 patients (94%) using conventional PCI techniques. Predilatation was performed in 31 patients (89%) and buddy wires were used in 12 patients (34.3%). For the 2 cases (6%) in which stent delivery failed, Heartrail catheters were used as a bail-out to facilitate stent delivery. There were no peri- or postprocedural adverse events. Conclusion. This early experience with Integrity coronary stent in severely tortuous coronary arteries yielded a promising result in terms of stent deliverability. It could potentially shorten PCI procedural time in this technically challenging subgroup of patients. 

J INVASIVE CARDIOL 2012(12);24:650-654

Key words: Integrity coronary stent

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Stent delivery failure¹ occurs in 4% of all percutaneous coronary interventions (PCIs) and >90% of these failures are due to vessel tortuosity and/or calcification. Various techniques^2-5 to facilitate stent delivery in these complex lesion subsets have been described by several operators. Most operators would emphasize choosing guiding catheters with good back-up, adequate lesion preparation with debulking techniques, and use of buddy wires/stiffer wires. The GuideLiner⁶ catheter (Vascular Solutions, Inc) is also a useful adjunctive tool to facilitate stent delivery across heavily calcified lesions in complex cases. One very important factor determining procedural success or failure is none other than flexibility of the coronary stent. At present, there is a variety of coronary stents available in the market and each has its own distinctive mechanical performance characteristics.^7,8 The deliverability of a coronary stent is usually assessed by how easy it is to navigate through tortuous/calcified vasculature to the target lesion and cross the lesion. By bench testing, stent performance of the newly launched Integrity coronary stent⁹ (Medtronic) has markedly improved when compared to the Driver/Micro-driver coronary stent system (Medtronic) due to its novel manufacturing process utilizing continuous sinusoid technology. We therefore sought to evaluate the deliverability of Integrity coronary stents in severely tortuous coronary lesions in real-world clinical practice.

Methods

Between January 2011 and August 2011, a total of 680 PCIs were performed at our institution. Of these, thirty-five patients (5.1%) with obstructive coronary artery disease (CAD) involving severely tortuous vessels underwent PCI with Integrity coronary stents. By SYNTAX score definition,¹⁰ a coronary lesion is defined as severely tortuous when it satisfies the following criteria: one or more bends of 90° or more, or three or more bends of 45-90° proximal to the diseased segment. All-comers who required PCI and who fulfilled the aforementioned SYNTAX score criteria were recruited into the study. Those who were unable to give consent for PCI and unable to tolerate the minimum length of dual antiplatelet therapy were excluded. Acute procedural success was defined as successful passage of the stent through the tortuous vasculature to the target lesion with successful stent deployment using conventional PCI techniques.

Interventional procedure and clinical endpoints. All PCIs were performed using standard techniques and according to current practice guidelines. All patients were front-loaded with oral aspirin 300 mg and clopidogrel 600 mg before the procedure. They all received dual antiplatelet therapy after the procedure; aspirin 100 mg daily indefinitely and clopidogrel 75 mg daily for at least 1 month to 1 year depending on type of stent implanted and clinical decision of the attending physician. Procedural success rate was examined, as well as procedural variables and complications. Fluoroscopic time and amount of contrast used were also recorded. In-hospital major adverse cardiac events (MACEs) like all-cause mortality, myocardial infarction (MI), re-infarction, target lesion revascularization (TLR), and stent thrombosis were also analyzed. For patients undergoing non-emergency PCI, MI was defined as the presence of new Q-waves in at least 2 contiguous leads with elevated creatine kinase above the upper limit of the normal range; in the absence of pathologic Q-waves, MI was diagnosed in the presence of an elevation in creatine kinase >2 times the upper limit of normal range. For patients undergoing PCI for ST-elevation MI (STEMI)/non-ST elevation MI (non-STEMI), the diagnosis of re-infarction was made when there were new electrocardiographic changes indicative of transmural ischemia with an increase in the total creatine kinase and MB isoenzyme activity of at least 3 times the upper limit of normal. Target lesion revascularization (TLR) was defined as any repeat revascularization (percutaneous or surgical) secondary to a stenosis >50% within the stent or within 5 mm proximal or distal to the stented segment. Stent thrombosis was defined according to the Academic Research Consortium criteria.¹¹ 

Statistical analysis. Continuous data are presented as mean ± standard deviation while categorical variables are presented as numbers and percentages.

Results

Baseline clinical, angiographic and procedural characteristics are presented in Tables 1 and 2. The mean age at presentation was 60.7 ± 11.4 years with male preponderance (>70%). 

Diabetes mellitus was present in 19 patients (54.3%). The mean left ventricular function was 46.0 ± 13%. Acute coronary syndrome (STEMI, non-STEMI/unstable angina) was the most common indication for PCI (82.9%).

Based on the SYNTAX score criteria of severely tortuous lesions, 14 patients (40%) were found to have ≥1 bend of ≥90° on coronary angiography, with the remaining 21 patients (60%) having ≥3 bends of 45-90° proximal to the diseased segment. The majority of patients (80%) had multivessel disease on coronary angiography. The most common target vessel for PCI was left circumflex artery (LCX; 54.3%), followed by right coronary artery (RCA; 42.8%) and left anterior descending artery (LAD; 2.9%), with 37.1% of lesions located at the distal end of arteries. Moderate to heavy calcification was observed in 6 tortuous coronary vessels (17.1%). Transradial PCI was performed in 29 patients (83%) with a 6 Fr system the most commonly used (94.3%). Resolute Integrity drug-eluting stents (DESs) were implanted in 17 patients (49%). Mean stent diameter was 3.04 ± 0.51 mm and mean stent length was 20.5 + 6.6 mm. Glycoprotein IIb/IIIa inhibitors were used in 23 patients (65.7%).

Acute procedural success was achieved in 33 patients (94%) using conventional PCI techniques. Predilatation was performed in 31 patients (89%) and buddy wires were used in 12 patients (34.3%). For the 2 cases (6%) in which stent delivery failed, Heartrail catheters (the so-called “five-in-six” system; Terumo) were used as a bail-out to facilitate stent delivery. For the first Heartrail patient, the lesion was located in the distal RCA and the major impediment to stent delivery (besides the underlying tortuosity) was the presence of  3 long overlapping stents that were previously implanted in the proximal to mid RCA. The second Heartrail patient had lesions in the mid and distal RCA, but the stent passage was largely impeded by extreme tortuosity in the proximal RCA, which had moderate calcification. 

For the overall study group, there were no peri- or postprocedural MACEs. Mean fluoroscopic time was 25.3 ± 17.2 minutes and mean contrast volume was 203.1 ± 80.1 mL. Figures 1 through 8 illustrate our experiences with Integrity coronary stents in some of the “classical” tortuous coronary vessels. 

Discussion

With advances^12,13 in PCI procedural tools, refinement of procedural techniques, and improvement in adjunctive antithrombotic therapy, the success rate of PCI has increased dramatically over the years. Nevertheless, specific lesion characteristics, such as tortuous lesions, calcified lesions, etc., are still regarded as technically challenging subsets (American College of Cardiology/American Heart Association type B-C lesions) that are associated with lower procedural success rates and higher complication rates. The flexibility of the coronary stent may play a pivotal role in the procedural success or failure of these complex lesions. There are limited data¹⁴ in the literature on the evaluation of new-generation coronary stents in PCI of severely tortuous coronary vessels in real-world clinical practice. Our initial experiences demonstrated the clinical efficacy of Integrity coronary stents in this subgroup of patients.

The Integrity coronary stent system⁹ is a low-profile, open-cell, cobalt-chromium-alloy metallic stent made with a process called continuous sinusoid technology. This novel manufacturing process (Figure 9) allows stent construction via wrapping a single thin strand of wire around a mandrel in a sinusoid configuration with laser fusion of adjacent crowns. The wire-forming process and fusion pattern provide the stent with a continuous preferential bending plane, allowing easier access and smoother tracking within distal and tortuous vessels while radial strength is maintained. As mentioned before, bench testing shows that stent performance of the Integrity coronary stent is markedly improved when compared to the Driver/Micro-driver coronary stent system, which is considered to be one of the most deliverable stents in the market. 

Although we did not perform a head-to-head comparison between the two stents, our in vivo experiences with the Integrity coronary stent were favorable, with acute procedural success achieved in 33 patients (94%). There were no in-hospital MACEs. The majority of patients (66%) in our study underwent successful PCI with Integrity coronary stents by conventional PCI techniques on the first try with a single guidewire. About one-third of patients required buddy-wire technique to facilitate stent delivery. Extreme difficulty was encountered with 2 patients and stent delivery was successful only with the assistance of Heartrail catheters. The major obstacle for both patients (besides the underlying tortuosity) was the presence of previously implanted stents and moderate calcification, underlining the impact of friction between the stent system and coronary vasculature on stent deliverability. 

One striking feature we observed about the Integrity coronary stent was that it conformed very well to the vessel wall (Figures 1-8). This is important, since it means the stent has sufficient radial strength to resist the elastic recoil of the media and can mold its shape along the contour of a curved segment with minimal vessel straightening and provide a large desired lumen. When the DES is implanted, excellent apposition of the struts on the vessel wall will ensure uniform delivery of the cytostatic drug to prevent neointimal hyperplasia. An in vitro conformability test¹⁵ has shown the Integrity DES to have better strut apposition and lower vessel wall stress when compared to other market-leading DESs. This has important implications, as one study¹⁶ has suggested a possible link between incomplete stent apposition or poor conformability with increased risk of restenosis and late stent thrombosis.

Study limitations. There were several limitations to our study. We did not perform head-to-head comparisons between different coronary stent platforms in vivo for severely tortuous vessels; hence, we are not able to conclude definitively that one stent is more deliverable/flexible than the other. Realistically, it is difficult to perform such studies in human beings with suitable coronary anatomy because of ethical and cost considerations. One possible option to answer this question is to review cases (with severely tortuous lesions) in which it was not possible to deliver another stent, but delivery of the Integrity stent was successful. Furthermore, our study was a single-center registry, subject to selection and operator bias. We also had a small number of patients with moderate-to-heavily calcified lesions; hence, we are not able to draw any firm conclusions on the deliverability of Integrity stents in this lesion subset. 

Conclusion

Continuous sinusoid technology represents an innovation in the design of the coronary stent platform, thus resulting in a more flexible and deliverable stent. Our preliminary experiences with Integrity coronary stents in severely tortuous coronary arteries yielded a promising result in terms of stent deliverability. It could potentially shorten PCI procedural time in this technically challenging subgroup of patients. Further studies in a larger patient population are needed to confirm our observation.

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From the Department of Cardiology, Tan Tock Seng Hospital, Singapore.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted May 4, 2012, provisional acceptance given May 30, 2012, final version accepted June 11, 2012.

Address for correspondence: Hee Hwa Ho, MD, Department of Cardiology, Tan Tock Seng Hospital, 11, Jalan Tan Tock Seng, Singapore 308433. Email: hokai_wah@yahoo.com