Role of physiology in the management of multivessel disease among patients with acute coronary syndrome.

Multivessel coronary artery disease (CAD), defined as ≥50% stenosis in 2 or more epicardial arteries, is associated with a high burden of morbidity and mortality in acute coronary syndrome (ACS) patients. A salient challenge for managing this cohort is selecting the optimal revascularisation strategy, for which the use of coronary physiology has been increasingly recognised. Fractional flow reserve (FFR) is an invasive, pressure wire-based, physiological index measuring the functional significance of coronary lesions. Understanding this can help practitioners evaluate which lesions could induce myocardial ischaemia and, thus, decide which vessels require urgent revascularisation. Non-hyperaemic physiology-based indices, such as instantaneous wave-free ratio (iFR), provide valid alternatives to FFR. While FFR and iFR are recommended by international guidelines in stable CAD, there is ongoing discussion regarding the role of physiology in patients with ACS and multivessel disease (MVD); growing evidence supports FFR use in the latter. Compelling findings show FFR-guided complete percutaneous coronary intervention (PCI) can reduce adverse cardiovascular events, mortality, and repeat revascularisations in ACS and MVD patients compared to angiography-based PCI. However, FFR is limited in identifying non-flow-limiting vulnerable plaques, which can disadvantage high-risk patients. Here, integrating coronary physiology assessment with intracoronary imaging in decision-making can improve outcomes and quality of life. Further research into novel physiology-based tools in ACS and MVD is needed. This review aims to highlight the key evidence surrounding the role of FFR and other functional indices in guiding PCI strategy in ACS and MVD patients.