More Is Better for Blood-Seeking Ischemic Myocardium

Coronary artery bypass grafting (CABG) has been the treatment of choice for patients who suffer from ischemic cardiomyopathy (ICMP) and have epicardial coronary arteries that are amenable for surgical myocardial revascularization.¹⁾ Several reasons that CABG results in favorable long-term clinical outcomes over other treatment options such as percutaneous coronary intervention (PCI) or optimal medical treatment in these patients are as following: (A) excellent long-term graft patency of the left internal thoracic artery (LITA), which is usually anastomosed to the left anterior descending coronary artery supplying a large myocardial territory, (B) ‘surgical collateralization’ of bypassed vessels that prevents future myocardial infarction, and (C) a high rate of complete revascularization (CR).¹⁾,²⁾,³⁾,⁴⁾ Achieving CR has long been a goal of CABG, and this is the reason why current guidelines recommend CABG as the preferred strategy over PCI for patients with ICMP.⁵⁾ In these patients, perfusion restoration of as much myocardium as possible might be the most important factor to improve myocardial function and clinical outcomes.

In addition to achieving CR, the number of inflow sources has been emphasized to improve myocardial perfusion and clinical outcomes after CABG. Previous studies have shown that a composite grafting strategy based on a single blood source, usually the in situ LITA, might be sufficient to supply whole ischemic myocardium even in multi-vessel disease patients.⁶⁾,⁷⁾ However, multiple inflow sources could be helpful for patients with ICMP in whom flow requirement of ischemic myocardium is greater than those with normal ventricular function.

In this recent study by Park and colleagues,⁸⁾ the authors evaluated 10-year clinical outcomes after CABG in ICMP patients, specifically focusing on the number of inflow sources. The authors retrospectively enrolled 447 patients with ICMP, and performed inverse probability of treatment weighting (IPTW)-adjusted analysis. The study results showed that long-term clinical outcomes such as all-cause mortality, cardiovascular death and major adverse cardiac events were significantly lower in 244 patients in the multiple inflow group compared to those in 203 patients in the single inflow group. In addition, there were no differences in early clinical outcomes despite complexity of surgical procedures in the multiple inflow group.

An early mortality rate of 1.8% in this high-risk population is commendable. Main strengths of this study include (A) a sufficient sample size of more than 400 patients during 11-year study period, (B) proper statistical methods such as IPTW-adjusted analysis to overcome retrospective nature of the study, and (C) a long-enough follow-up duration with a median follow-up of 5.3 years to clearly elucidate clinical outcomes.

There are nevertheless caveats in this study such as (A) selection bias in grafting strategy could not be perfectly overcome even with IPTW adjustment. Disease severity and other unadjusted confounders could affect this selection and the study results, (B) although not statistically significant, postoperative stroke rate of 2.0% in the multiple inflow group compared to 0% in the single inflow group should be paid attention, and (C) the finding that the number of inflow sources but not CR is a significant factor for long-term outcomes in patients with ICMP should be interpreted with caution when considering relatively low rate of CR in this patient population.

Despite these limitations, this study delivers a clear message. In the ICMP patients, CABG using multiple inflow sources are associated with favorable long-term clinical outcomes, particularly in those without recent or profound myocardial injury. I hope this study could intrigue and motivate scientists to elucidate this issue further based on a multi-institutional, large cohort study.