Angiography-derived index of microcirculatory resistance as a novel, pressure-wire-free tool to assess coronary microcirculation in ST elevation myocardial infarction

Abstract

Immediate assessment of coronary microcirculation during treatment of ST elevation myocardial infarction (STEMI) may facilitate patient stratification for targeted treatment algorithms. Use of pressure-wire to measure the index of microcirculatory resistance (IMR) is possible but has inevitable practical restrictions. We aimed to develop and validate angiography-derived index of microcirculatory resistance (IMRangio) as a novel and pressure-wire-free index to facilitate assessment of the coronary microcirculation. 45 STEMI patients treated with primary percutaneous coronary intervention (pPCI) were enrolled. Immediately before stenting and at completion of pPCI, IMR was measured within the infarct related artery (IRA). At the same time points, 2 angiographic views were acquired during hyperaemia to measure quantitative flow ratio (QFR) from which IMRangio was derived. In a subset of 15 patients both IMR and IMRangio were also measured in the non-IRA. Patients underwent cardiovascular magnetic resonance imaging (CMR) at 48 h for assessment of microvascular obstruction (MVO). IMRangio and IMR were significantly correlated (ρ: 0.85, p < 0.001). Both IMR and IMRangio were higher in the IRA rather than in the non-IRA (p = 0.01 and p = 0.006, respectively) and were higher in patients with evidence of clinically significant MVO (> 1.55% of left ventricular mass) (p = 0.03 and p = 0.005, respectively). Post-pPCI IMRangio presented and area under the curve (AUC) of 0.96 (CI95% 0.92-1.00, p < 0.001) for prediction of post-pPCI IMR > 40U and of 0.81 (CI95% 0.65-0.97, p < 0.001) for MVO > 1.55%. IMRangio is a promising tool for the assessment of coronary microcirculation. Assessment of IMR without the use of a pressure-wire may enable more rapid, convenient and cost-effective assessment of coronary microvascular function.

Keywords: Index of microcirculatory resistance; Microvascular dysfunction; Microvascular obstruction; Quantitative flow ratio; STEMI.

Conflict of interest statement

All authors declare that they have no conflict of interest to disclose.

Figures

Fig. 1

Study methods flow chart

Fig. 2

Patients flow chart

Fig. 3

IMRangio and IMR correlations in acute STEMI patients. Scatter plots summarise significant correlations between IMRangio and IMR in the overall cohort of 92 lesions assessed (a) and then split into IRA before stent implant (b), IRA after stent implant (c) and non-IRA (d). Dotted lines represent 95% Confidence interval. Panel E reports ROC curve analysis for IMRangio in predicting IMR ≥ 40U in the whole cohort of 92 lesions

Fig. 4

IMRangio and IMR concordance. Bland–Altman plots summarise concordance between IMRangio and IMR in the overall cohort of 92 lesions (a) and then split into IRA before stent implant (b), IRA after stent implant (c) and non-IRA (d)

Fig. 5

IMRangio and IMR variations before and after stent implant. IMRangio and IMR reduce after stent implantation (a). The change in IMRangio consistently mirrored the change in IMR; the relationships persist when patients were divided into ‘good’ (b) or ‘partial-poor’ (c) responders to stent implant

Fig. 6

IMRangio and MVO. The figure depicts two STEMI cases with IMR (a, d), IMRangio (b, e) assessment and corresponding short axis CMR images with presence (c) and absence (f) of MVO. The correlation between IMRangio and IMR with the occurrence of clinically relevant MVO (> 1.55% of left ventricle mass) is summarised by the box plots (g). Panel H depicts the ROC curve analysis of post-pPCI IMRangio in predicting MVO > 1.55

Fig. 7

Potential clinical implications of IMRangio in STEMI. IMR or IMRangio can be used to assess microvascular function in patients with STEMI undergoing pPCI before stenting (after flow restoration in the IRA) and at completion of pPCI