Validity of angiography-derived microvascular resistance in hypertrophic cardiomyopathy: a head-to-head comparison with pressure-wire IMR

Angiography-derived indices of microvascular resistance offer wire-free assessment from routine angiograms, but their validity in hypertrophic cardiomyopathy (HCM) remains uncertain. We evaluated correlation, agreement, diagnostic performance, and reproducibility of angiography-derived IMR versus invasive pressure-wire IMR in HCM. Consecutive HCM patients without obstructive coronary artery disease underwent invasive left anterior descending artery IMR during adenosine hyperaemia. Angiography-derived IMR was computed offline using three-dimensional reconstruction, QFR, TIMI frame count, and pressure assumptions. Analyses included Spearman correlation, Bland-Altman agreement, ROC analysis, and intraclass correlation coefficients. Thirty patients were included. Invasive IMR was ≥ 25 mmHg × s in 20 patients (67%). Angiography-derived IMR correlated moderately with invasive IMR (Spearman r = 0.53, 95% CI 0.21-0.75; P = 0.003). Bland-Altman analysis showed a mean bias of 4.1 mmHg × s, with 95% limits of agreement from - 28.4 to 36.6 mmHg × s. Angiography-derived IMR identified invasive IMR ≥ 25 mmHg × s with an AUC of 0.83 (95% CI 0.65-0.96). The optimal cutoff was 26, yielding 80% sensitivity (95% CI 56-94%) and 80% specificity (95% CI 44-97%). Intra-observer reproducibility was high and inter-observer reproducibility moderate. In HCM, angiography-derived IMR showed moderate correlation and acceptable cohort-level discrimination but wide agreement limits, indicating limited individual-level interchangeability. HCM-specific refinement is required before replacing invasive microvascular assessment.Clinical trial registration: ClinicalTrials.gov identifier: NCT03479580.