Thin-Strut Drug-Eluting Stents are More Favorable for Severe Calcified Lesions After Rotational Atherectomy Than Thick-Strut Drug-Eluting Stents

Abstract: Aim. Percutaneous coronary intervention (PCI) for severe calcified lesions is still challenging, and there are few studies of drug-eluting stent (DES) implantation for severe calcified lesions, especially regarding long-term results and hemodialysis patients. The study purpose was to clarify the factors, including DES strut thickness, that affect the long-term outcome of severe calcified lesion treated with rotational atherectomy. Methods. We analyzed 79 consecutive patients (138 stents) with DES implantation for severe calcified lesions that required rotational atherectomy before stent implantation. Rotational atherectomy was performed for the lesions that showed over 270° severe calcification by intravascular ultrasound (IVUS) or where IVUS could not cross the lesion. We compared coronary risk factors, acute coronary syndrome and hemodialysis, the patients’ history of coronary bypass graft and myocardial infarction, medication, and procedure characteristics, including the thickness of the DES used (thin- or thick-strut [>100 µm] DES) between the patients with target vessel revascularization (TVR) versus those without TVR. Results. During the follow-up, TVR was performed in 30 patients (38.5%). A multivariate analysis revealed that age and thin-strut DES were independently related to TVR (P=.01 for both). A Kaplan-Meier curve showed a lower TVR rate in the thin-strut DES patients compared to the thick-strut DES patients. Conclusions. For severe calcified lesions that needed rotational atherectomy, thin-strut DESs resulted in lower rates of TVR compared to thick-strut DESs.  

J INVASIVE CARDIOL 2014;26(2):41-45

Key words: drug-eluting stent, interventional cardiology, stent design, rotational atherectomy, restenosis

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Percutaneous coronary intervention (PCI) using a drug-eluting stent (DES) has dramatically reduced target revascularization (TVR) and has shown good long-term clinical outcomes.^1,2 However, PCI for severe calcified lesions is still technically challenging, and the clinical outcome data for these lesions are limited. Incomplete stent expansion (ie, underexpansion), which may induce stent thrombosis and in-stent restenosis,^3,4 occurs frequently in cases of severe calcified lesions. One of the methods found to be effective for treating severe calcified lesions is mechanical rotational atherectomy with the Rotablator (Boston Scientific).⁵ A lesion modification strategy with a less aggressive Rotablator burr size was reported to be safe and effective for severe calcified lesions.⁶ In the DES era, rotational atherectomy in particular is considered useful to reduce the rate of underexpansion of stents deployed just after PCI for severe calcified lesions.

The uses of rotational atherectomy for severe calcified lesions have been reevaluated for the occurrence of stent underexpansion, but to the best of our knowledge, there are no published data on what type(s) of DES are most effective for implantation after rotational atherectomy for severe calcified lesions. It is known that the thickness of the struts of a bare-metal stent affects the clinical outcome after PCI.⁷ The aim of the present study was to identify the factors contributing to the most effective type of DES, including strut thickness, for the treatment of severe calcified lesions after rotational atherectomy.

Methods

Patients. We retrospectively assessed 79 consecutive patients (138 stents) who underwent PCI with rotational atherectomy and DES deployment between April 2007 and November 2011 in our hospital. All patients had a severe calcified lesion for which rotational atherectomy was performed because >270° severe calcification was observed by intravascular ultrasound (IVUS) or because the IVUS catheter could not cross the lesion even after adequate balloon angioplasty. Six types of DES were implanted after rotational atherectomy: a sirolimus-eluting stent (Cypher; Cordis Corporation), the paclitaxel-eluting Express stent (Taxus Express; Boston Scientific), the paclitaxel-eluting Liberte stent (Taxus Liberte; Boston Scientific), a zotarolimus-eluting stent (Endeavor; Medtronic Cardiovascular), an everolimus-eluting stent (Xience V; Abbott Vascular), and a biolimus A9-eluting stent (Nobori; Terumo Corporation). First-generation DESs included the sirolimus-eluting stent, paclitaxel-eluting Express stent, and paclitaxel-eluting Liberte stent; second-generation DESs included the zotarolimus-eluting stent, everolimus-eluting stent, and biolimus A9-eluting stent. During the study period, 6 different types of DES were not always available in our hospital. The latest 2 or 3 types of DES were chosen to be prepared. We selected stents among them using IVUS data of the reference lumen size and lesion length. The final decision of DES type was left to the treating operator’s discretion.

We excluded the patients treated with more than two types of DES. The patients treated electively were pretreated with ticlopidine (200 mg/day) or clopidogrel (75 mg/day) in addition to aspirin (100 mg/day). In the patients with acute coronary syndrome, a loading dose of aspirin (200 mg) and clopidogrel (300 mg) or 200 mg of ticlopidine was administered before the procedure if the patient was not pretreated. Written informed consent was obtained from each patient, and the study protocol was approved by the Ethics Committee of Osaka Rosai Hospital.

Thin-strut and thick-strut DESs. For the purposes of the present study, the Cypher stent (strut thickness, 140 µm), Taxus Express stent (132 µm), and Nobori stent (125 µm) were classified as thick-strut (>100 µm) DESs. The Taxus Liberte stent (97 µm), Endeavor stent (91 µm), and Xience V stent (81 µm) were classified as thin-strut DESs.

Rotational atherectomy and stent procedure. The rotablation (Rotablator; Boston Scientific) burr size was selected by angiogram or IVUS if the IVUS catheter crossed the target lesion according to a modification strategy.⁶ The rotational speed ranged between 175,000 and 210,000 rpm. Care was taken to prevent any 5000 rpm drop in rotational speed by using a to-and-fro pecking motion of the burr, avoiding long passes. Nicorandil, nitroglycerin, and heparin added in normal saline was continuously injected into the coronary artery to control any slow-flow occurring during or after the rotational atherectomy. During the procedures, patients received intravenous unfractionated heparin to maintain an activated clotting time >250 msec. All procedures were performed by IVUS (Atlantis Pro; Boston Scientific) guidance.

We decided the suitable stent type, size, and length based on the patient’s IVUS data. After the stent implantation, we used IVUS to determine whether malapposition or underexpansion of the stent persisted. If either of these findings was observed, additional dilatation was delivered. Procedure success was defined as a final residual stenosis <30% and grade-3 Thrombolysis in Myocardial Infarction (TIMI) flow.

Follow-up coronary angiography and clinical follow-up. Follow-up coronary angiography was performed at 8 months after the procedures in our hospital and was also performed before that date if clinically indicated. The clinical follow-up at 8 months after the procedures was conducted by office visit. A long-term clinical follow-up was conducted by office visit, and any evidence of cardiac ischemia was evaluated by symptom or stress test. The occurrence of major clinical events, including death (all-cause or cardiac), myocardial infarction (MI), and target vessel revascularization (TVR) were recorded. Stent thrombosis was classified according to the Academic Research Consortium (ARC) definition.⁸ The TVR group was defined as the patients who underwent TVR during the follow-up period. The non-TVR group was defined as the patients who did not undergo TVR during the follow-up period.

Target vessel revascularization. The coronary angiograms taken during the procedures and at follow-up were analyzed by two experienced observers after the administration of intracoronary nitroglycerin, with quantitative coronary angiographic analysis (QAngio XA, Version 7.1; MEDIS Medical Imaging Systems). If the patient showed angiographic stenosis (>50%), we evaluated ischemia of the lesion. If the patient showed typical chest pain with electrocardiographic changes or an ischemia finding by a stress thallium-201 scintigram, repeated PCI was performed and the patient was entered in the TVR group.

Statistical analysis. Continuous variables with normal distribution are expressed as means ± standard deviation (SD). Dichotomous data are expressed as percentages. We used Mann-Whitney’s U-test to compare numerical data between the TVR and non-TVR groups, and we used a multiple logistic regression analysis to assess the predictors of TVR. The time-dependent outcome for TVR was examined by the Kaplan-Meier method. A P-value <.05 was considered significant. All calculations were performed using a commercially available statistical package (JMP 10; SAS Institute, Inc).

Results

Baseline and procedure characteristics. Among the 79 patients’ procedures, 1 procedure was defined as an unsuccessful PCI due to TIMI-2 final coronary flow. A total of 78 patients (98.7%) were identified as achieving a successful PCI. Among 70 patients who received the follow-up coronary angiography at 8 months, 22 patients had >50% angiographic restenosis. Five patients underwent coronary artery bypass graft (CABG) surgery for their multivessel stenosis including target vessel, 5 patients underwent re-PCI for typical symptom, and 5 patients underwent re-PCI without stress test due to severe restenosis (nearly occlusion). In addition, 7 patients received stress test and 2 patients showed significant myocardial ischemia to require re-PCI. Accordingly, in these 70 patients, TVR was performed in 17 patients. During the follow-up period (856 ± 500 days), TVR was performed in 30 patients (38.5%), MI occurred in 1 patient (1.3%), the number of all-cause deaths was 8 (10.2%), and 1 cardiac death (1.3%).

The patients’ baseline clinical characteristics are shown in Table 1. Fifty-two patients (66.7%) had diabetes mellitus and 27 patients (34.6%) were on hemodialysis. Ten patients (12.8%) were treated for acute coronary syndrome. Significant differences in age and history of CABG were observed between the TVR group and the non-TVR group. The patients’ lesion and procedure characteristics are shown in Table 2. All lesions were identified as American College of Cardiology/American Heart Association lesion classes B2/C. Multiple stenting was used in 52 patients (66.7%). The stent length per lesion was 40.3 ± 17.1 mm. Non-compliant balloon postdilatation was performed in 39 patients (50.0%). The number of patients who were treated with thick-strut DES was significantly higher in the TVR group than in the non-TVR group.

Follow-up coronary angiography. Follow-up coronary angiography at 8 months after the procedure was performed in 28 patients (93.3%) in the TVR group and in 42 patients (87.5%) in the non-TVR group. The results of the quantitative coronary angiographic analysis are shown in Table 3.

Univariate and multivariate analysis results. The univariate analysis revealed that age was significantly lower in the TVR group than in the non-TVR group, while the incidences of history of CABG and use of thick-strut DES were significantly higher in the TVR group than in the non-TVR group. The multivariate analysis showed that age and thick-strut DES independently predicted TVR during the follow-up period (Table 4).

TVR-free survival difference between the thick-strut and thin-strut DES groups. To identify the impact of stent strut thickness as the predictor of TVR, we compared the rate of TVR-free survival between the thick-strut DES group (n = 43) and the thin-strut DES group (n = 35). At 8 months after the procedures, 14 patients (32.6%) in the thick-strut DES group had undergone TVR, versus 7 patients (20.0%) in the thin-strut DES group; there was no significant difference in the TVR rate at 8 months after the procedures (P=.22). However, as shown in Figure 1, the thin-strut DES group (338.9 ± 268.6 days) showed significantly better TVR-free survival than the thick-strut DES group (736.6 ± 410.3 days) during the long-term follow-up.

TVR-free survival difference between first- and second-generation DESs. To identify the impact of the difference of DES generation as the predictor of TVR, TVR-free survival was compared between first-generation DES group (n = 46) and second-generation DES group (n = 32). Twenty-three patients (50.0%) in the first-generation DES group and 7 patients (21.9%) in the second-generation DES group underwent TVR. There was no significant difference in TVR rates between the two groups during long-term follow-up (Figure 2).

TVR-free survival difference between paclitaxel-eluting Express stent and paclitaxel-eluting Liberte stent. To identify the impact of the difference of DES platform as the predictor of TVR, TVR-free survival was compared between paclitaxel-eluting Express stent (n = 15) and paclitaxel-eluting Liberte stent (n = 11). Eleven patients (73.3%) in the paclitaxel-eluting Express stent group and 1 patient (10.0%) in the paclitaxel-eluting Liberte stent group underwent TVR. As shown in Figure 3, the paclitaxel-eluting Liberte stent group (one of the thin-strut DESs) showed significantly better TVR-free survival than the paclitaxel-eluting Express stent group (one of the thick-strut DESs) during the long-term follow-up.

Stent thrombosis. Among the 78 patients, stent thromboses occurred in 2 cases (2.6%). One case was defined as subacute thrombosis and the other as possible very late thrombosis. Subacute thrombosis occurred in a hemodialysis patient who was on dual-antiplatelet therapy and was treated with everolimus-eluting stents in the right coronary artery. Very late stent thrombosis occurred in a hemodialysis patient who was on dual-antiplatelet therapy and died suddenly 637 days after the procedure. He had been treated with zotarolimus-eluting stents in the right coronary artery.

Discussion

We obtained the following findings: (1) the use of thin-strut DESs significantly reduced the TVR rate; (2) despite the use of DESs, the TVR rate was high (38.5%) in the patients with severe calcified lesions, including those with diabetes mellitus, those undergoing hemodialysis, and those who received multiple stents, even with the use of rotation atherectomy; (3) the thick-strut DESs showed the “late catch-up” phenomenon even on severe calcified lesions. To the best of our knowledge, this is the first report that has shown a difference in clinical outcome between the use of thin- and thick-strut DESs for severe calcified lesions for which rotation atherectomy was performed.

Severe calcified lesions have been one of the most difficult lesions subsets to treat.⁹ Rotational atherectomy had been reported to be a useful method to treat severe calcified lesions, but it has a high restenosis rate.⁵ Moussa et al reported a TVR rate of 18.0% and restenosis rate of 22.5% using bare-metal stents, although the mean lesion length was only 9.4 ± 6.8 mm.¹⁰ The innovation of the DES brought about less restenosis, but few data regarding the use of DESs for severe calcified lesions have been reported. Clavijo et al reported of the impressive TVR rate of 4.2% at 6 months after PCI with rotational atherectomy and sirolimus-eluting stents in 81 patients.¹¹ That study did not present the proportion of hemodialysis patients and had a smaller percentage of diabetes mellitus patients (44.4%) than the present study (66.7%). Their total stent length (24.4 ± 6.27 mm) was also shorter than ours (40.3 ± 17.1 mm).

Furuichi et al reported that the rate of TVR for these lesions with longer stent lengths (48.4 ± 24.9 mm) was 11.6%.¹² Although the Furuichi study showed more real-world aspects as compared to the former reports, their study included fewer patients with diabetes mellitus (30.5%) and chronic renal failure (7.4%) than our study. In addition, the follow-up period (14.7 months) was rather shorter than our study’s follow-up period (856 ± 500 days). The high proportion of diabetes mellitus (66.7%), hemodialysis (34.6%), multistenting (66.7%), and the long stent length (40.3 ± 17.1 mm) in the present study are considered to be “real-world” patient characteristics.

The higher age of the patients of the non-TVR group is explained as follows: in this study, the follow-up coronary angiography was scheduled only 8 months after PCI. Later follow-up was performed according to the patients’ symptoms. As the higher-aged patients often showed fewer ischemic symptoms due to their lower activity level, they occasionally refused additional coronary angiography or stress test.

Here, the thin-strut DES group showed better clinical outcomes than the thick-strut DES group. There was a significant difference in the follow-up period for primary endpoint (all-cause death) between the thick- and thin-strut DES groups (1022.9 ± 569.9 days vs 752.5 ± 425.1 days; P=.02). However, the follow-up period for TVR in the thick-strut DES group was significantly shorter than in the thin-strut DES group (338.9 ± 268.6 days vs 736.6 ± 410.3 days; P<.001). Accordingly, we concluded that TVR was performed in the thick-strut DES group not because this group was followed longer, but because the patency in this group was poor. During the long-term follow-up period, 7 patients (20%) underwent a revascularization procedure. Rathore et al reported a binary restenosis rate of 33.7% following the use of DES in a chronic renal failure population.¹³ Compared to the Rathore study, the thin-strut DES group in the present investigation showed adequate clinical outcomes. We suspect that the reason why our thin-strut DES group showed better outcomes is that thin-strut DESs would show better crossability in severe lesions. The thick-strut DESs needed more “pushing” to cross the lesion, and the polymer from the drug-eluting thick-strut DESs may have come off of the stent metal.¹⁴ 

The patients who received a thick-strut DES in our study showed the “late catch-up” phenomenon. This phenomenon was also reported in another study,¹⁵ but it had not been reported previously in patients with severe calcified lesions.^5,10-13

Multiple factors, including stent thrombogenicity, patient and lesion factors, and procedure-related factors are apparently involved in the development of stent thrombosis.¹⁶ Several eluting drugs have been found to be very useful and to have similar ability to reduce TVR. A number of studies have demonstrated that sirolimus-eluting stents and paclitaxel-eluting Express stents (both thick-strut DESs) showed similar safety and efficacy,¹⁷ and that zotarolimus-eluting stents and everolimus-eluting stents (both thin-strut DESs) have similar good clinical outcomes after stent implantation.¹⁸

However, it was reported that use of the paclitaxel-eluting Express stent (a thick-strut DES) and the paclitaxel-eluting Liberte stent (a thin-strut DES) resulted in different grades of neointimal coverage even though the eluting drug used was the same.¹⁹ Thus, in the present study, we focused on stent design, especially the thickness of the stent struts. The present study revealed that the difference of stent strut thickness showed the difference of clinical outcome, although there was no significant difference of clinical outcome between first- and second-generation DESs. For the treatment of severe calcified lesions in the DES era, we think the selection of the stent design may be more important than the selection of the eluting drug.

We observed definite subacute stent thrombosis in 1 patient (1.3%), which is relatively high compared to other simple lesions.¹⁵ However, Furuichi et al reported a higher rate (2.1%) of definite stent thrombosis in severe calcified lesions.¹² Both stent underexpansion and stent malapposition, which tend to occur in severe calcified lesions even with IVUS guidance and rotational atherectomy, might cause DES thrombosis.²⁰ Optical coherence tomography may be helpful to detect small malapposition, which cannot be detected with IVUS,²¹ and may reduce DES thrombosis in these lesions.

Study limitations. This study was a retrospective and non-randomized analysis. However, we systematically enrolled all patients who underwent PCI with rotational atherectomy and received a single type of DES during the study period in our hospital. Thus, we believe the selection bias has been reduced.

References

1. Weisz G, Leon MB, Holmes DR Jr, et al. Five-year follow-up after sirolimus-eluting stent implantation results of the SIRIUS (Sirolimus-Eluting Stent in De-Novo Native Coronary Lesions) trial. J Am Coll Cardiol. 2009;53(17):1488-1497.
2. Stone GW, Midei M, Newman W, et al. Randomized comparison of everolimus-eluting and paclitaxel-eluting stents: two-year clinical follow-up from the Clinical Evaluation of the Xience V Everolimus Eluting Coronary Stent System in the Treatment of Patients with de novo Native Coronary Artery Lesions (SPIRIT) III trial. Circulation. 2009;119(5):680-686.
3. Camnitz WM, Keeley EC. Heavily calcified coronary arteries: the bane of an interventionalist’s existence. J Interv Cardiol. 2010;23(3):254-255.
4. Kuntz RE, Safian RD, Carrozza JP, et al. The importance of acute luminal diameter in determining restenosis after coronary atherectomy or stenting. Circulation. 1992;86(6):1827-1835.
5. Warth DC, Leon MB, O’Neill W, et al. Rotational atherectomy multicenter registry: acute results, complications and 6-month angiographic follow-up in 709 patients. J Am Coll Cardiol. 1994;24(3):641-648.
6. Safian RD, Feldman T, Muller DW, et al. Coronary angioplasty and Rotablator atherectomy trial (CARAT): immediate and late results of a prospective multicenter randomized trial. Catheter Cardiovasc Interv. 2001;53(2):213-220.
7. Kastrati A, Mehilli J, Dirschinger J, et al. Intracoronary stenting and angiographic results: strut thickness effect on restenosis outcome (ISAR-STEREO) trial. Circulation. 2001;103(23):2816-2821.
8. Cutlip DE, Windecker S, Mehran R, et al. Clinical end points in coronary stent trials: a case for standardized definitions. Circulation. 2007;115(17):2344-2351.
9. Tan K, Sulke N, Taub N, et al. Clinical and lesion morphologic determinants of coronary angioplasty success and complications: current experience. J Am Coll Cardiol. 1995;25(4):855-865.
10. Moussa I, Di Mario C, Moses J, et al. Coronary stenting after rotational atherectomy in calcified and complex lesions. Angiographic and clinical follow-up results. Circulation. 1997;96(1):128-136.
11. Clavijo LC, Steinberg DH, Torguson R, et al. Sirolimus-eluting stents and calcified coronary lesions: clinical outcomes of patients treated with and without rotational atherectomy. Catheter Cardiovasc Interv. 2006;68(6):873-878.
12. Furuichi S, Sangiorgi GM, Godino C, et al. Rotational atherectomy followed by drug-eluting stent implantation in calcified coronary lesions. EuroIntervention. 2009;5(3):370-374.
13. Rathore S, Matsuo H, Terashima M, et al. Rotational atherectomy for fibro-calcific coronary artery disease in drug eluting stent era: procedural outcomes and angiographic follow-up results. Catheter Cardiovasc Interv. 2010;75(6):919-927.
14. Wiemer M, Butz T, Schmidt W, et al. Scanning electron microscopic analysis of different drug eluting stents after failed implantation: from nearly undamaged to major damaged polymers. Catheter Cardiovasc Interv. 2010;75(6):905-911.
15. Stone GW, Moses JW, Ellis SG, et al. Safety and efficacy of sirolimus- and paclitaxel-eluting coronary stents. N Engl J Med. 2007;356(10):998-1008.
16. Honda Y, Fitzgerald PJ. Stent thrombosis: an issue revisited in a changing world. Circulation. 2003;108(1):2-5.
17. Raber L, Wohlwend L, Wigger M, et al. Five-year clinical and angiographic outcomes of a randomized comparison of sirolimus-eluting and paclitaxel-eluting stents: results of the Sirolimus-Eluting Versus Paclitaxel-Eluting Stents for Coronary Revascularization LATE trial. Circulation. 2011;123(24):2819-2828.
18. von Birgelen C, Basalus MW, Tandjung K, et al. A randomized controlled trial in second-generation zotarolimus-eluting Resolute stents versus everolimus-eluting Xience V stents in real-world patients: the TWENTE trial. J Am Coll Cardiol. 2012;59(15):1350-1361.
19. Otake H, Shite J, Shinke T, et al. Impact of stent platform of paclitaxel-eluting stents: assessment of neointimal distribution on optical coherence tomography. Circ J. 2012;76(8):1880-1888.
20. Fujii K, Carlier SG, Mintz GS, et al. Stent underexpansion and residual reference segment stenosis are related to stent thrombosis after sirolimus-eluting stent implantation: an intravascular ultrasound study. J Am Coll Cardiol. 2005;45(7):995-998.
21. Prati F, Regar E, Mintz GS, et al. Expert review document on methodology, terminology, and clinical applications of optical coherence tomography: physical principles, methodology of image acquisition, and clinical application for assessment of coronary arteries and atherosclerosis. Eur Heart J. 2010;31(4):401-415.