Myocardial transit time mapping by CMR: A novel potential parameter of microcirculatory dysfunction in hypertrophic cardiomyopathy with and without atrial fibrillation

Purpose: This study aimed to explore myocardial transit time (MyoTT) by cardiovascular magnetic resonance (CMR) as a potential parameter of coronary microvascular dysfunction (CMD) in hypertrophic cardiomyopathy (HCM) with and without atrial fibrillation (AF). Materials and Methods: This study enrolled 50 patients with HCM and 50 healthy control subjects to assess cardiac function, native T1, extracellular volume (ECV), myocardial strain, and MyoTT. Factors associated with HCM status were estimated by logistic regression analyses, adjusting for potential confounders. Meanwhile, we evaluated the discriminative performance of the aforementioned parameters for HCM (vs control) and for AF status among HCM patients. Results: In the HCM and control groups, the HCM group exhibited significant reductions in LV-GLS, RV-EDVI, and RV-ESVI (all P < 0.05) and significant increases in LVMI, LVGPWT, native T1 values, ECV values, absolute MyoTT values and presence of LGE (all P < 0.05). Logistic regression analysis revealed HCM was significantly associated with MyoTT, native T1, ECV and LV-GLS. In HCM with and without AF, the HCM with AF group showed nominally higher native T1 values and absolute MyoTT values before correction. Logistic regression analysis revealed HCM with AF was significantly associated with MyoTT and native T1. The AUCs for ECV, MyoTT, LV-GLS, and native T1 were 0.828, 0.848, 0.708, and 0.862, respectively (P < 0.05). The AUCs for discriminating HCM with AF from HCM without AF for MyoTT and native T1 were 0.740 and 0.681, respectively (P < 0.05). Conclusion: MyoTT levels are elevated in patients with HCM, particularly when AF is present. This suggests that MyoTT may reflect CMD-related alterations in HCM, especially in those with AF.