Background: Coronary collateral flow in angiography has been linked with lower mortality rates in patients with coronary artery disease. However, evidence on the underlying mechanisms is sparse. Therefore, we tested the hypothesis that in patients with acute myocardial infarction (AMI) relevant coronary collateral flow is associated with more salvaged myocardium and lower risk for developing heart failure.

Methods: Patients with first acute myocardial infarction (AMI) who received a percutaneous coronary intervention within 24 hours after symptom onset were classified visually by assigning a Cohen-Rentrop Score (CRS) ranging between 0 (no collaterals) and 3 (complete retrograde filling of the occluded vessel). All patients underwent cardiac magnetic resonance (CMR) examination within 3 to 5 days after myocardial infarction and after 12 weeks to determine the area of risk, infarct size, and functional and volumetric parameters. Myocardial salvage index (MSI) was calculated as the difference between the area at risk baseline and infarct size at week 12 divided by the area at risk at baseline.

Results: A total of 36 patients (mean age 56 ± 9 years; 81% men) were included in the analysis. Patients with the relevant collateral flow (CRS 2-3) to the infarct-related artery had a significantly higher MSI compared to those without (78±14% vs. 57±19%, p=0.006). In multiple linear regression analysis, CRS 2-3 was significantly associated with a higher MSI after accounting for predictors of MSI such as antegrade flow, culprit vessel, time to revascularization after symptom onset, or age (B=0.179, CI (0.045 to 0.313), p=0.011). In addition, both groups showed improvement in left ventricular ejection fraction early after AMI, whereas the recovery was greater in CRS 2-3 compared to those with CRS 0-1 (+8±5% vs. +3±5%, p=0.015). NT-proBNP decreased in 12 weeks more in patients with CRS 2-3 (-616 pg/ml [213-1547] vs -384 pg/ml [231-709], p=0.060).

Conclusion: In patients with first AMI relevant collateral flow to the infarct-related artery was independently associated with more salvaged myocardium at 12 weeks, translating into greater improvement of systolic left ventricular function.