The main findings of this study can be summarized as follows. First, CTO is found in about 29% of patients undergoing CABG. Among them, 80% of patients received complete bypass grafting for all CTOs. Second, ICR for CTO lesions was associated with increased 30-day and overall mortality. Also, ICR was related to increased MACCE after bypass grafting for CTOs. The rates of CR for CTOs were 86% in Fefer et al., nearly 85% in Banerjee et al., and 80% in our study, which was similar to those previous studies.9,10
In our study, ICR for CTOs was one of the independent risk factors for 30-day and overall mortality. Unlike our study, Fefer et al. showed that ICR for CTOs was not associated with increased long-term mortality.10 The following theories were supported by the conclusion of their study; the territory supplied by CTO can be non-viable, all non-revascularized territories were in the RCA and LCX territories, and the collateral flow often exists to CTO territory. However, their study lacked assessment of viability and had limited long-term follow-up data. In contrast, Kleisli et al. demonstrated that patients who underwent CABG with ICR had worse outcomes than did patients with CR.11 Data from SYNTAX also showed that patients with ICR had more adverse events than did patients with CR.12 Therefore, ICR for CTOs was associated with short- and long-term outcomes, as a negative factor.4 As a result, the overall survival in the ICR group for CTOs was significantly lower than that in the CR group.
Farooq et al. concluded that ICR for CTO lesions was associated with significantly higher frequencies of all-cause revascularization and MACCE than was CR.13 These findings are similar to the results shown in our study. Target vessel revascularization in the ICR group was significantly higher, as shown in Fig. 3. This event seemed to occur mostly within about 4 years after CABG.
In patients with CTO lesions, the possibility of CR was affected by many other factors, such as the revascularization for CTOs driven by the patient’s general condition and the angiographic findings. In this study, patients in the ICR group were older and had more comorbidities, such as diabetes and renal replacement, than did the CR group. According to other literature, patients with ICR were also significantly older and had higher prevalence of comorbidities, including diabetes, hypertension, and heart failure.9,10 Also, an anatomical coronary complexity with multiple long and diseased or small segments could have influenced the result of revascularization. Revascularization in patient with this sort of anatomical complexity and poor general condition may be a challenge, and longer surgical procedures are associated with higher postoperative morbidities, longer periods of hospitalization, and slower return to normal activities.4
There are several limitations in this study. First, it is a retrospective study in a singles institution with a small cohort. Given its observational nature and small sample size, potential confounders might have remained. However, incidence of CTOs was uncommon, so the number of patients with CTOs in our study was similar to that in previous studies for CTOs in CABG. Next, we did not evaluate the viability of the myocardium on CTO lesions routinely unless the myocardial thickness was maintained. Because assessment of viability in all patients undergoing CABG is not cost effective and has limited and uncertain accuracy, with uncertain false-positive and false-negative rates, uncertain prevalence of hibernating myocardium, and thus uncertain predictive values.12 Finally, we collected just hard endpoint follow-up data, like readmission due to heart failure and cardiac function on transthoracic echocardiography, so there is limited information on the relief of angina, history of repeated PCI, and MACCE during the follow-up period.