Fractional flow reserve in acute coronary syndromes: A review

•Small studies support the use of FFR in non-culprit vessels during ACS.•FFR demonstrates diagnostic accuracy and reproducibility in AMI, particularly in intermediate lesions.•Microvascular dysfunction observed from earlier work does not appear to hinder FFR calculation, but further studies are required for validation.•Vasodilator independent assessment of coronary stenoses has some preliminary data supporting its use in non culprit arteries during ACS, but ongoing trial results are awaited regarding clinical outcomes.

Fractional flow reserve (FFR) assessment provides anatomical and physiological information that is often used to tailor treatment strategies in coronary artery disease. Whilst robust data validates FFR use in stable ischaemic heart disease, its use in acute coronary syndromes (ACS) is less well investigated. We critically review the current data surrounding FFR use across the spectrum of ACS including culprit and non-culprit artery analysis. With adenosine being conventionally used to induce maximal hyperaemia during FFR assessment, co-existent clinical conditions may preclude its use during acute myocardial infarction. Therefore, we include a current review of instantaneous wave free ratio as a novel vasodilator independent method of assessing lesion severity as an alternative strategy to guide revascularisation in ACS.