Methods

The IRIS-DES registry involves the prospective, multicenter recruitment of 6,066 consecutive patients who underwent PCI with DESs from 46 academic and community hospitals in Korea from April 1, 2008 to June 30, 2010 and for whom complete follow-up data were available for ≥1 year and ≤3 years after PCI. During the enrollment period, sirolimus-eluting or everolimus-eluting stents were used as the default device for PCI. The exclusion criteria were minimal. Patients with cardiogenic shock, malignant disease, or other co-morbid conditions with a life expectancy of <12 months; a known intolerance to the study drugs, antiplatelet drugs, metal alloys, or contrast media; those treated with a mixture of different DES types; and those with planned surgery necessitating interruption of antiplatelet drugs within 6 months after the procedure were excluded from the present study.

In addition, we also included study-specific exclusion criteria to avoid potential confounding effects on the relation between stent length and clinical outcomes. Patients who underwent stent implantation for multiple lesions and/or in multiple vessels (n = 2,074), patients who had previously undergone PCI (n = 760) or bypass surgery (n = 58), and patients who developed in-stent restenosis treated by stent implantation (n = 30) were excluded. Thus, the remaining 3,244 patients who underwent single or overlapping stent implantation in de novo coronary artery stenosis constituted the current study population.

The study cohort was divided by tertiles of implanted stent length (≤22, 23 to 32, and ≥33 mm) and by IVUS use. IVUS use was considered present when the IVUS examination was performed before the procedure (n = 100) or after the procedure (n = 192), or both (n = 1,324).

The ethics committee at each participating center approved the study protocol, and all patients provided written informed consent to participate.

All interventions were done according to the current practice guidelines for PCI. The operator was responsible for the decision to choose a specific treatment strategy, including the IVUS examination. In addition, the response to the IVUS findings was at the discretion of the treating physician.

Before or during the procedure, all patients received ≥200 mg of aspirin and a 300 to 600-mg loading dose of clopidogrel. Heparin was administered throughout the procedure to maintain an activated clotting time of ≥250 seconds. The administration of glycoprotein IIb/IIIa inhibitors was at the discretion of the operator. After the intervention, all patients were prescribed 100 to 200 mg/day aspirin indefinitely, clopidogrel 75 mg/day for ≥12 months, and other cardiac drugs, according to the judgment of the patient’s physician.

The baseline demographics, clinical and angiographic features, and procedural and outcome events were assessed. Clinical follow-up examinations were conducted during hospitalization and at 30 days, 6 months, and 12 months after surgery and every 6 months thereafter. At these visits, data pertaining to the patient’s clinical status, all interventions, and outcome events were recorded. The follow-up period extended to July 31, 2011 to ensure that all patients had an opportunity for ≥12 months of follow-up.

The primary end point of the study was major adverse cardiac events (MACE; composite of death, nonfatal myocardial infarction [MI], and target vessel revascularization). The secondary clinical end points were the individual component of the primary end point: a composite of death and MI, MI, target vessel revascularization, and stent thrombosis.

Death was defined as death from any cause. MI was defined as follows: (1) within the first 48 hours after the procedure: new Q waves and either an elevation in the creatinine kinase-MB fraction or troponin I concentration >3 times the upper limit, and (2) 48 hours after the procedure: any creatinine kinase-MB or troponin increase greater than the upper range limit with or without the development of Q waves on the electrocardiogram. Target vessel revascularization was defined as any percutaneous or surgical revascularization procedure associated with the target vessel. Stent thrombosis was defined according to the Academic Research Consortium definitions, and the definite and definite/probable occurrence of a thrombotic event were regarded as the secondary end points.

Differences between groups were evaluated using Student’s t test or 1-way analysis of variance for continuous variables and the chi-square test or Fisher’s exact test for categorical variables. Cumulative event curves were constructed using Kaplan-Meier estimates and compared with the log-rank test. To have the stent length effect adjusted for statistically or clinically meaningful factors, we used the multivariate Cox proportional regression model as follows. To select statistically significant variables, we used a backward variable selection approach, with the possible adjustment factors presented in Table 1 . In the multivariate regression analysis, we also considered the stent length as a continuous type variable and a 3-level categorical variable for analysis completeness. This adjusted stent length effect was re-evaluated according to the IVUS usage group. In contrast, the effectiveness of IVUS usage was tested using the log-rank test within the 3 stent length groups. Furthermore, to reduce the possible effect of potential confounding in the present observational study, we considered an inverse probability of treatment weighting method using a propensity score method. The weighted Cox models for testing the IVUS effects were fitted on the overall patient group and selected patient subgroups according to the implanted stent length. The proportional hazards assumption was confirmed by examination of log[−log(survival)] curves and the partial Schoenfeld residuals tests. We could not detect any significant violations. To obtain propensity scores for inverse probability weighting, we adopted an automated procedure using the twang package using generalized boosted regression in the R program (R Foundation, Vienna, Austria). Generalized boosted regression analysis included nonlinear effects and interactions in covariates so we could obtain statistically and numerically stable propensity scores. All reported p values are 2-sided, and p <0.05 was considered statistically significant. SAS software, version 9.1 (SAS Institute, Cary, North Carolina), and the R programming language (R Foundation) were used for the statistical analyses.

Results

From April 2008 to June 2010, 3,244 patients underwent single or overlapping stent implantation in a de novo coronary artery stenosis, and these patients were enrolled in the present study. The average number and length of the implanted stents was 1.30 ± 0.61 and 31.1 ± 17.8 mm, respectively. We used IVUS guidance in 1,616 patients (49.8%) during the PCI procedure.

The patient characteristics according to the tertiles of implanted stent length (≤22, 23 to 32, and ≥33 mm) are listed in Table 1 . A longer implanted stent length was associated with a greater incidence of diabetes, hyperlipidemia, stable angina at presentation, a greater risk angiographic profile, and a lower left ventricular ejection fraction. IVUS guidance was used more often in those with a longer implanted stent length than in patients with shorter stents (395 [39.5%], 487 [43.9%], and 734 [64.6%] for the first, second, and third tertiles, respectively, p <0.001).

The patient characteristics stratified by IVUS use are listed in Table 2 . IVUS use was associated with younger age, male gender, hyperlipidemia, stable angina at presentation, a greater risk angiographic profile, and a lower incidence of hypertension. In addition, IVUS use was associated with an increased number of implanted stents (1.44 ± 0.71 vs 1.16 ± 0.43, p <0.001), longer stenting (35.5 ± 20.4 mm vs 26.9 ± 13.3 mm, p <0.001), and larger stents (3.28 ± 0.38 vs 3.10 ± 0.39 mm, p <0.001).

Complete follow-up data for major clinical events were obtained for all patients. During the 1 to 3 years of follow-up (mean 1.4 ± 0.4 years), 145 events (4.5%) of the primary end point occurred, including 69 deaths (2.1%), 16 MIs (0.5%), and 76 target vessel revascularizations (2.3%). Ten patients (0.3%) had definite or probable stent thrombosis.

The observed 2-year clinical outcomes according to implanted stent length in the IVUS and no-IVUS groups are listed in Table 3 and Figures 1 and 2 . Among the patients in the IVUS group, no significant differences were found according to the tertile of implanted stent length in the risk of MACE. However, among the patients in the no-IVUS group, the incidence of MACE and the composite of death and MI increased significantly with increasing implanted stent length. In the subgroup analysis stratified by implanted stent length, in the short stent length group, no statistically significant difference in the rate of MACE was found. However, in the longer stent length group, the IVUS group had a lower rate of MACE than did the no-IVUS group.

Table 3

Two-year clinical outcomes according to implanted stent length and intravascular ultrasound (IVUS) use

Stent Length (mm)	All Patients (n = 3,244)	IVUS (n = 1,616)	No IVUS (n = 1,628)	p Value
Death, myocardial infarction, or target vessel revascularization
≤22 (n = 998)	3.9 ∗	3.4	4.2	0.57
23–32 (n = 1,109)	5.1	2.9	7.0	0.009
≥33 (n = 1,137)	6.0	4.7	8.2	0.006
p Value	0.13	0.46	0.025
Death or myocardial infarction
≤22 (n = 998)	2.0	1.3	2.5	0.26
23–32 (n = 1,109)	3.0	1.4	4.4	0.018
≥33 (n = 1,137)	3.5	2.2	5.7	<0.001
p Value	0.081	0.56	0.010
Target vessel revascularization
≤22 (n = 998)	2.1	2.1	2.1	0.98
23–32 (n = 1,109)	2.4	1.6	3.1	0.12
≥33 (n = 1,137)	3.2	2.8	4.3	0.33
p Value	0.50	0.48	0.42
Stent thrombosis, definite or probable
≤22 (n = 998)	0.4	0	0.7	0.22
23–32 (n = 1,109)	0.3	0	0.5	0.12
≥33 (n = 1,137)	0.4	0.1	1.0	0.036
p Value	0.59	0.55	0.35

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