Patients were eligible for the study if they were aged 18 years or over and reported symptoms suggestive of ischemic heart disease in which a significant atherosclerotic vessel lesion was identified and CA and classified as CTO, i.e. a coronary lesion with Thrombolysis In Myocardial Infarction (TIMI) anterograde flow score of 0 with chronic characteristics thought to have been present for at least three months. Patients who only underwent a diagnostic study, despite having a CTO vessel, or had an unsuccessful procedure were excluded from the analysis. A previously published hybrid algorithm for CTO PCI was used for revascularization, and patients were divided into two groups according to the CTO vessel: left coronary artery (LCA)-CTO or RCA-CTO.7,14 Left ventricular ejection fraction (LVEF) was estimated by the modified Simpson's biplane method. Obesity was defined as a body mass index ≥30 kg/m2, and chronic renal failure was defined as creatinine clearance <60 ml/m2 (Cockcroft–Gault formula). The use of at least one antianginal drug, an angiotensin-converting enzyme inhibitor/angiotensin receptor blocker/angiotensin receptor-neprilysin inhibitor, aspirin (or anticoagulation in atrial fibrillation), dual antiplatelet therapy or dual antithrombotic therapy for at least six months, and a lipid-lowering drug (statin and/or ezetimibe) were defined as optimal medical therapy (OMT). Baseline patient demographic data, cardiovascular risk factors, and clinical, laboratory, echocardiographic and angiographic data were also recorded.

The study was conducted according to the ethical principles stated in the 1975 Helsinki Declaration and was approved by the local hospital ethics committee.

The primary outcome was recurrence of angina and/or heart failure (HF) symptoms (total symptom recurrence) in a two-year follow-up. HF symptoms were defined as dyspnea and/or fatigue presumed to be secondary to an underlying heart condition. Secondary outcomes were defined as myocardial infarction (MI) and all-cause mortality, as well the individual components of the primary outcome.

Comparisons between groups were performed using the chi-square test, Student's t test or Mann–Whitney test, as appropriate. Univariate and multivariate analysis were performed using Cox regression to identify predictors significantly associated with the outcomes. A p-value <0.05 was taken to indicate statistical significance. The statistical analysis was performed using IBM SPSS Statistics, version 21.0 (IBM SPSS, Chicago, IL, USA).

A total of 191 patients were recruited, with 14 patients being excluded from the study: 12 patients had an unsuccessful procedure (six with RCA-CTO and six with LCA-CTO) and two only underwent CA (LCA-CTO) (Figure 1).

Figure 1.

Study flowchart. CA: coronary angiography; CTO: chronic total occlusion; LCA: left coronary artery; PCI: percutaneous coronary intervention; RCA: right coronary artery.

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A total of 177 patients (82.5% male) were therefore included in the study, which took place in 2019 and 2020. The sample characteristics are summarized in Table 1. The two groups were composed of 98 patients (55.4%) with LCA-CTO and 79 (44.6%) with RCA-CTO, with an overall mean age of 64.5±11.4 years. Medical history was positive for hypertension in 74.6% of patients, dyslipidemia in 72.9%, obesity in 18.2% and HF in 15.3%. RCA-CTO patients were younger, with a mean age of 63.6±10.3 years (p=0.047). The most common clinical presentation was non-ST-elevation MI (32.2%), followed by stable angina (26%) and heart failure symptoms (22%), with no statistical differences between groups (p=0.072). The majority of patients were on OMT (83.1%, p=0.172) and antianginal drugs (98.3%, p=0.691), with no difference regarding the CTO vessel treated.

From a procedural point of view, RCA was the most frequent CTO artery (44.6%), followed by the left circumflex artery (29.4%). The procedures were mostly performed in a scheduled regime rather than a clinical emergent (ad-hoc) setting (32.2%, p=0.140). An anterograde approach was most commonly employed (88.7%, p=0.052), and contralateral access was preferred in RCA-CTO patients (62%, p<0.001). Multivessel disease was found in 152 (85.9%, p=0.217) patients, and complete revascularization at the time of CTO PCI was observed in 98 (55.4%), more frequently in the LCA-CTO group but without statistical significance (p=0.405). Mean SYNTAX and Multicenter CTO Registry of Japan (J-CTO) scores were 35.6±15.1 and 0.79±0.73, respectively. Ischemia or myocardial viability testing was performed in 43 (24.3%, p=0.322) patients, mainly stress echocardiography (10.7%, p=0.815). RCA-CTO patients presented with higher creatinine clearance levels (80.8±24.9 ml/min, p=0.038). There were no differences between groups with regards to radiation dose measured by air kerma (1784 mGy) or kerma area product (113 Gy cm2), contrast volume used (254±94.3 ml) or procedure time (132±56 min). The rate of periprocedural complications was 5.1%, of which vessel perforation was the most common (2.26%). Although LVEF was mildly reduced at baseline, ventricular function improved in both groups after intervention in a mean follow-up of 18 months (p<0.001) (Table 2).

The primary outcome occurred in 28 (16.6%) patients and was significantly more frequent in RCA-CTO patients (19, 24.7%, p=0.010) in two-year follow-up (mean follow-up of 18 months). This was mainly driven by recurrence of HF symptoms (12, 15.6%, p=0.013) (Table 3).

Rates of MI and all-cause mortality were similar between groups (RCA-CTO 1.3%, p=0.361 and 2.6%, p=0.673, respectively, on survival analysis) (Figures 2 and 3).

Figure 2.

Kaplan–Meier curve showing time until myocardial infarction (mean follow-up of 18 months) in chronic total occlusion patients undergoing percutaneous coronary intervention, compared by vessel treated. CTO: chronic total occlusion; LCA: left coronary artery; PCI: percutaneous coronary intervention; RCA: right coronary artery.

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Figure 3.

Kaplan–Meier curve showing time until death (mean follow-up of 18 months) in chronic total occlusion patients undergoing percutaneous coronary intervention, compared by vessel treated. CTO: chronic total occlusion; LCA: left coronary artery; PCI: percutaneous coronary intervention; RCA: right coronary artery.

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Revascularized RCA-CTO showed an association with and was an independent predictor of the primary outcome (p=0.016, hazard ratio [HR] 2.77, 95% confidence interval [CI] 1.21–6.32), although LVEF was not (p=0.482, HR 0.99, 95% CI 0.95–1.02). Multivessel disease was associated with the primary outcome but was not an independent predictor in multivariate analysis (p=0.968, HR 3.72, 95% CI 0.42–6.32). Complete revascularization was not associated with the primary outcome in univariate or multivariate analysis (Table 4).

LVEF was found to be an independent predictor of all-cause mortality (p=0.023, HR 0.92, 95% CI 0.85–0.98), although recanalized RCA-CTO was not (p=0.291, HR 0.40, 95% CI 0.07–2.17).

Some limitations should be acknowledged. This was an observational study, and so the data collected are limited to medical records. Patient symptoms were not assessed by scales or questionnaires, which could thus increase ambiguity. Our study included only successful CTO PCI; failed CTO PCI was not addressed, which may limit the validity of the conclusions. Finally, the data in our study are from only one CTO PCI center, so our conclusions may not be generalizable to other cardiac centers.