Abstract Background Despite growing evidence of its clinical implications, assessment of coronary microvascular dysfunction (CMD) remains limited in routine clinical practice. Hence, there is an increasing interest in angiography-derived indices to encourage assessment of CMD in the cardiac catheterisation laboratory. We investigate here a novel approach, IMRhybrid, using a combination of pressure-wire-based assessment of distal coronary pressure (Pd) and an angiography-derived surrogate of coronary flow. Methods Patients were enrolled to the OxAMI-Hybrid study. The accuracy of IMRhybrid was assessed in diagnosing CMD using fully pressure wire and bolus thermodilution Index of Microcirculatory Resistance (IMR) as a reference. The accuracy of IMRhybrid was then compared against a fully angiography-derived index of microvascular resistance (IMRangio). Based on previous work, angiography-derived IMR, IMRangio, was calculated as IMRangio = Quantitative Flow Ratio (QFR) ado x Pahyperaemia x TIMI Frame Count (TFC) hyperaemia / Frame Rate. Conversely, IMRhybrid was expressed as IMRhybrid = Pdhyperaemia x TFChyperaemia / Frame Rate, where frame rate was fixed at 15 frame per second for both indices. In both cases, TFC/frame rate represented angiography-derived mean transit time, mTt in hyperaemia. Results 60 patients were enrolled prospectively, of which 28 with acute coronary syndrome and 32 with stable coronary artery disease. A total of 66 vessel analyses were performed. Both IMRhybrid and IMRangio correlated with IMR (rho=0.51, p <0.001 and rho=0.51, p <0.001 respectively) and showed good and comparable overall diagnostic accuracy in predicting IMR ≥ 25 (83.3% and 75.4% respectively) with a receiver operator curve (ROC) analyses showing an AUC of 0.82 and 0.81 respectively (p for comparison= 0.97). Conclusion Both approaches, IMRhybrid and IMRangio provide viable and comparable methods of assessing CMD which correlate with bolus thermodilution-based IMR, retaining good diagnostic accuracy. IMRhybrid is a simple alternative to conventional bolus thermodilution-based IMR, offering the advantage of being suitable with any pressure wire system.A: IMR, B: QFR, C: TFCA+C: IMRhybrid, B+D: IMRangio