Methods

From January 2007 to December 2009, a total of 2,568 patients in whom CTO intervention was attempted were enrolled in the Korean-CTO registry. The Korean-CTO registry is an observational online registry that has 26 participating centers in Korea. Patients with CTO diagnosed as stable angina or unstable angina while having a large area of reversible ischemia assessed using imaging modalities were registered. CTO was defined as an obstruction of a native coronary artery with Thrombolysis In Myocardial Infarction flow grade 0 and an estimated duration of at least 3 months based on the clinical history or previous coronary angiography. The duration of CTO was determined based on the interval from the last episode of acute coronary syndrome or from the first episode of effort angina consistent with the location of the occlusion in patients without histories of acute coronary syndrome. All patients had typical symptomatic angina or a positive test result in various functional studies evaluating ischemia. Exclusion criteria were presentation with acute MI or cardiogenic shock; those undergoing only bare-metal stent implantation or balloon angioplasty without DES implantation; CTO lesions with DES restenosis, graft vessel occlusion, or culprit lesion of acute coronary syndrome within 4 weeks; severe hepatic dysfunction (≥3 times of the normal reference values); life expectancy <3 years; or contraindication to antiplatelet agents. In the present study, patients who failed revascularization of CTO lesions, those with first-generation DESs, both first- and second-generation DES implantations, and those without any information regarding IVUS usage were excluded. Thus, a total of 534 patients with second-generation DESs, including everolimus- and zotarolimus-eluting stents, were finally analyzed for the present study. Of the 534 patients, IVUS guidance during CTO PCI was performed on 206 patients (39%). IVUS guidance was considered when IVUS examination was undertaken while performing the procedure on CTO lesions before or after stenting. The institutional review board or ethics committee at each participating institution approved this study protocol, and the patients gave their written informed consent before study entry.

PCI was performed using standard techniques. Treatment strategy, stenting techniques, and selection of DES type were determined according to the operator’s discretion. The use of IVUS was also determined at the discretion of the operator, and IVUS was performed before stenting, after stenting, or both with a standard technique. One of 2 commercially available systems was used after intracoronary administration of 200 μg of nitroglycerin (Atlantis S or I-Lab [Boston Scientific Corp/SCIMED, Minneapolis, Minnesota] or Eagle Eye [Volcano Therapeutics, Rancho Cordova, California]). All patients were administered loading doses of aspirin (300 mg) and clopidogrel (300 to 600 mg) unless they had previously received these antiplatelet medications. Anticoagulation during PCI was performed according to routine practices of each hospital. After the procedure, aspirin (100 to 200 mg/day) was prescribed indefinitely, and use of clopidogrel was recommended for at least 12 months. Clinical follow-up, by telephone contact or office visits, was performed at 1, 6, 12, and 24 months after the index PCI. At follow-up, patients were specifically questioned regarding the occurrence of any adverse events or the presence of angina symptoms.

The primary end point was definite or probable stent thrombosis, defined according to the Academic Research Consortium. Secondary end points were MI, target lesion revascularization (TLR), target vessel revascularization (TVR), cardiac death, all-cause death, and major adverse cardiovascular event (MACE). Clinical events were also defined according to the Academic Research Consortium. All deaths were considered cardiac deaths unless a definite noncardiac cause could be established. MI was defined as the presence of clinical symptoms, electrocardiographic change, or abnormal imaging findings of MI combined with an increase in creatine kinase-MB fraction or troponin T or I greater than the ninety-ninth percentile of the upper normal limit and unrelated to an interventional procedure. The MACE included cardiac death, MI, stent thrombosis, and/or TLR. All events were reported by the participating centers and reviewed by an independent clinical event adjudicated committee.

Continuous variables are expressed as mean ± SD. Categorical variables are presented as a number (percentage). Continuous variables were analyzed using the independent-samples t test or the Wilcoxon signed-rank test, and categorical variables were analyzed with the chi-square test or Fisher’s exact test. Occurrence of adverse events during the follow-up period was analyzed using the Kaplan-Meier method. Differences between event-free survival curves were compared using the log-rank test. Subgroup analyses stratified based on selected clinical characteristics (age; gender; clinical presentation; presence of hypertension, diabetes, or heart failure; and lesion length) were performed for TLR events to assess for interactions between IVUS usage and clinical characteristics.

To reduce treatment selection bias and potential confounding factors and to adjust for significant differences in characteristics of patients or lesions, propensity score matching was performed. Propensity scores were estimated using a nonparsimonious multiple logistic regression model for treatment with IVUS guidance versus angiography guidance. The following variables were selected to calculate the propensity score: age, gender, diabetes, hypertension, heart failure, dyslipidemia, smoking, clinical presentation (stable angina and unstable angina), and number of diseased vessels. New propensity scores were incorporated to assess the efficacy of the IVUS guidance. For development of propensity score–matched pairs without replacement (a 1:1 match), a local optimal algorithm with the caliper method was used. The Hosmer and Lemeshow goodness-of-fit test was used to assess the model fit to the data (p = 0.946). The C statistic for the model was 0.62. After propensity score matching, covariates were compared with the paired t test for continuous variables and the McNemar test for categorical variables. All statistical analyses were performed using SAS (version 9.2; SAS Inc, Cary, North Carolina). A p value <0.05 was considered significant.

Results

Clinical baseline characteristics of 328 patients in the angiography-guidance group and 206 patients in the IVUS-guidance group are listed in Table 1 . Patients in the IVUS-guidance group had a lesser prevalence of hypertension and diabetes mellitus for total population. Other characteristics were similar between the 2 groups. Lesion characteristics, including length, were not different between the 2 groups for both total and matched population ( Table 2 ). However, the total stented length was longer and the mean stent diameter was larger in the IVUS-guidance group compared with the angiography-guidance group for the total population and matched population. In addition, the numbers of stents per lesion were greater in the IVUS-guidance group.

The median follow-up duration was 727 days (interquartile range 602 to 751), and there were no differences in follow-up duration between the 2 groups (p = 0.998). Clinical event rates at 1 month, 1 year, and 2 years are listed in Table 3 . Four patients (2.0%) in the angiography-guidance group had stent thrombosis at 1 month, whereas none had stent thrombosis in the IVUS-guidance group (p = 0.046) for matched population. At 2 years, 6 patients (3.0%) in the angiography-guidance group had stent thrombosis, but none had stent thrombosis in the IVUS-guidance group (p = 0.014) for matched population. Of 7 patients who had stent thrombosis in total population, 3 patients had definite and 4 patients had probable stent thrombosis. Three patients with definite stent thrombosis presented with acute MI. Of the 4 patients who had probable stent thrombosis, unexplained death occurred in 3 patients, and the other patient presented with acute MI with worsening wall motion abnormality at recanalized territory of CTO lesion. All 4 patients with probable stent thrombosis were stented at only CTO lesions. Kaplan-Meier curves showed higher stent thrombosis rates in the angiography-guidance group than in the IVUS-guidance group (p = 0.015; Figure 1 ). At 2 years, the rate of MI was lower in the IVUS-guidance group with borderline significance (p = 0.061). The rate of cardiac death and all-cause death at 1 month and 2 years did not differ between the 2 groups. The TLR rates at 1 month and 2 years were not different. Additionally, the TVR rates at 1 month and 2 years were not different. The rates of MACE did not differ between the 2 groups.

Table 3

Analysis of clinical outcomes at 1 month, 1 year, and 2 years

Variable	Total Population			Matched Population
	IVUS Guidance (N = 206)	Angiography Guidance (N = 328)	p-Value	IVUS Guidance (N = 201)	Angiography Guidance (N = 201)	p-Value
1-Month outcomes
Stent thrombosis	0	4 (1.2%)	0.304	0	4 (2.0%)	0.046
Myocardial infarction	1 (0.5%)	4 (1.2%)	0.653	1 (0.5%)	4 (2.0%)	0.180
Target lesion revascularization	0	0	1.000	0	0	1.000
Target vessel revascularization	0	3 (0.9%)	0.288	0	3 (1.5%)	0.083
Cardiac death	1 (0.5%)	3 (0.9%)	1.000	1 (0.5%)	3 (1.5%)	0.317
All cause of death	2 (1.0%)	2 (0.6%)	1.000	2 (1.0%)	3 (1.5%)	0.655
Major adverse cardiovascular event	1 (0.5%)	4 (1.2%)	0.653	1 (0.5%)	4 (2.0%)	0.180
1-Year outcomes
Stent thrombosis	0	5 (1.5%)	0.162	0	5 (2.5%)	0.025
Myocardial infarction	2 (1.0%)	9 (2.7%)	0.217	2 (1.0%)	6 (3.0%)	0.157
Target lesion revascularization	12 (5.8%)	18 (5.5%)	0.869	12 (6.0%)	8 (4.0%)	0.371
Target vessel revascularization	15 (7.3%)	27 (8.2%)	0.691	15 (7.5%)	18 (9.0%)	0.578
Cardiac death	2 (1.0%)	7 (2.1%)	0.493	2 (1.0%)	4 (2.0%)	0.414
All cause of death	3 (1.5%)	8 (2.4%)	0.436	3 (1.5%)	4 (2.0%)	0.705
Major adverse cardiovascular event	12 (5.8%)	24 (7.3%)	0.503	12 (6.0%)	15 (7.5%)	0.549
2-Year outcomes
Stent thrombosis	0	7 (2.1%)	0.047	0	6 (3.0%)	0.015
Myocardial infarction	17 (8.3%)	25 (7.6%)	0.869	17 (8.5%)	17 (8.5%)	0.896
Target lesion revascularization	21 (10.2%)	34 (10.4%)	0.949	21 (10.4%)	24 (11.9%)	0.631
Target vessel revascularization	2 (1.0%)	12 (3.7%)	0.058	2 (1.0%)	8 (4.0%)	0.061
Cardiac death	2 (1.0%)	8 (2.4%)	0.223	2 (1.0%)	5 (2.5%)	0.257
All cause of death	4 (1.9%)	11 (3.4%)	0.336	4 (2.0%)	6 (3.0%)	0.527
Major adverse cardiovascular event	18 (8.7%)	31 (9.5%)	0.781	18 (9.0%)	22 (10.9%)	0.610

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