Coronary Microcirculation Downstream Non-Infarct-Related Arteries in the Subacute Phase of Myocardial Infarction: Implications for Physiology-Guided Revascularization

Abstract

Background: Concerns exist about reliability of pressure-wire-guided coronary revascularization of non-infarct-related arteries (non-IRA). We investigated whether physiological assessment of non-IRA during the subacute phase of myocardial infarction might be flawed by microcirculatory dysfunction. Methods and Results: We analyzed non-IRA that underwent fractional flow reserve, coronary flow reserve, and the index of microcirculatory resistance assessment. Microcirculation and hyperemic response were evaluated in 49 acute myocardial infarction patients (59 non-IRA) and compared with a matched control group of 46 stable angina (SA) patients (59 vessels). Time between acute myocardial infarction to physiological interrogation was 5.9±2.4 days. Fractional flow reserve was similar in both groups (0.79±0.11 in non-IRA versus 0.80±0.13 in SA vessels, P=0.527). Lower coronary flow reserve values were found in non-IRA compared with SA vessels (1.77 [1.25–2.76] versus 2.44 [1.63–4.00], P=0.018), primarily driven by an increased baseline flow in non-IRA (rest mean transit time 0.58 [0.32–0.83] versus 0.65 s [0.39–1.20], P=0.045), whereas the hyperemic flow was similar (hyperemic mean transit time 0.26 [0.20–0.42] versus 0.26 s [0.18–0.35], P=0.873). No differences were found regarding index of microcirculatory resistance (15.6 [10.4–21.8] in non-IRA versus 16.7 [11.6–23.6] U in SA vessels, P=0.559). During adenosine infusion, the hyperemic response was similar in both groups (non-IRA versus SA vessels) in terms of the resistive reserve ratio (3.1±2.1 versus 3.7±2.2, P=0.118). Conclusions: In the subacute phase of myocardial infarction, non-IRA show an increased baseline flow that may cause abnormal coronary flow reserve despite preserved hyperemic flow. In non-IRA, microcirculatory resistance and adenosine-induced hyperemic response are similar to those found in SA patients. From a physiological perspective, these findings support the use of fractional flow reserve to interrogate non-IRA during the subacute phase of myocardial infarction.