Correlation between thermodilution-based IMR and angio-IMR in the post-heart transplant population

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Abstract Background Coronary microvascular dysfunction (CMD), as defined by an elevated index of microcirculatory resistance (IMR), has been demonstrated to be an adverse prognostic indicator in patients early post-heart transplant (HT). Non-wire-based diagnostic methods, like angio-IMR, may improve access, as well as reduce risk and healthcare costs associated with invasive coronary physiology testing. However, angio-IMR has not been evaluated in HT patients. Purpose The objective of this study is to determine the diagnostic performance of angio-IMR in HT patients for identifying CMD using invasive wire-based IMR as a reference standard. Methods HT patients who underwent invasive coronary physiology study at our Institute as part of the ECAV and PET-CAV studies were included. QAngio Xa 2D was used to obtain angio-IMR measures. The relationship between angio-IMR and IMR was evaluated by Pearson correlation analysis and Bland-Altman plots. Receiver operating characteristic curve analysis was used to assess the diagnostic performance of angio-IMR in conjunction with Youden’s index to determine optimal cut points for detecting CMD (defined as an IMR >=25). Results 135 angio-IMR measures were obtained from 76 patients, from whom 95 (70.37%), 22 (16.30%) and 18 (13.33%) were obtained in the left anterior descending, left circumflex and right coronary artery, respectively. CMD was evident in 38 (38.15%) vessels. Mean IMR was 23.05 ± 18.66 and mean angio-IMR was 22.70 ± 13.11. There was a significant correlation between angio-IMR and IMR (r= 0.93; 95% CI 0.90-0.95; p<0.01) (Figure 1A). The mean difference between IMR and angio-IMR was 0.31 ± 9.27 (p=0.70) (Figure 1B), with increased differences observed with high IMR values. Angio-IMR displayed high diagnostic performance for detection coronary microvascular dysfunction (IMR >=25), with an area under the curve of 0.93 (95% CI 0.87-0.99) (Figure 2). The optimal angio-IMR cutoff for CMD was >=25. On the basis of this threshold, angio-IMR showed high accuracy (90.37%; 95% CI 84.10-94.77), sensitivity (84.21%; 95% CI 68.75- 93.98) and specificity (92.78%; 95% 85.70-97.05) Conclusion Angio-IMR has a high diagnostic performance for detection of microvascular dysfunction in HT patients. Angio-IMR enables additional coronary physiology assessment during routine invasive angiography that may improve HT patients risk stratification and enable tailored management.Figure 1 Figure 2

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