Background The Index of Microcirculatory Resistance (IMR) can identify Coronary Microcirculatory Dysfunction (CMD), but its pathophysiological effects are uncertain. We characterised relations between IMR and downstream myocardial perfusion and LV function.

Methods 60 patients with stable coronary disease (67±8 years, 72% male) had adenosine stress Cardiac MRI to assess myocardial perfusion reserve (MPR), systolic and diastolic function (LV strain). All patients had invasive angiography and Fractional Flow Reserve (FFR) and IMR assessment in all possible vessels (135/180).

Results In 96 vessels FFR>0.8, IMR was inversely related to MPR (rho −0.65), systolic (rho −0.57) and diastolic strain (rho −0.50), all p<0.001. An IMR cut-off of 25 detected ischaemia (AUC 0.93, p<0.001) (figure 1). In patients with all vessels FFR>0.80, as the number of high IMR (≥25) vessels increased, global myocardial perfusion, systolic and diastolic strain reduced in a step-wise fashion, reflecting increasing severity of CMD (all p<0.01). In vessels FFR≤0.8, IMR was not related to MPR (rho −0.23; p=0.15), systolic (rho −0.14; p=0.45) or diastolic strain (rho −0.12; p=0.49).

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Abstract 10 Figure 1 Relations of IMR with myocardial perfusion, systolic and diastolic strain on CMR

Conclusions An IMR of ≥25 is associated with impaired myocardial perfusion, systolic and diastolic dysfunction. The implications of these novel findings deserve further study.