Comparison of fully angiography-derived versus a hybrid of angiography and pressure-wire-derived approach to assess coronary microvascular resistance: the OxAMI-Hybrid study

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