Sequential Changes in Right Ventricular Straein During the Development of Pulmonary Hypertension Assessed With Magnetic Resonance Feature Tracking: An Animal Study.

OBJECTIVE: To evaluate the sequential changes in right ventricular (RV) strain and histological vascular remodeling and their correlations during pulmonary hypertension (PH) development in a rat model by using cardiac magnetic resonance (CMR)-feature tracking (FT). MATERIALS AND METHODS: Separate cohorts of six-week-old male Wistar rats (10 per group) were allocated to a baseline group, PH induction groups assessed at 1, 2, 3, or 4 weeks after monocrotaline injection, and vehicle-injected control groups assessed at 2 and 4 weeks. Each rat underwent a single magnetic resonance imaging (MRI) examination and was subsequently euthanized for histological analysis. Cine images were acquired using a 9.4T MRI scanner, and strain was analyzed using the FT technique. Histological analysis was used to quantify pulmonary arterial wall thickness percentage (PA %WT) and RV collagen density. Overall group differences were analyzed using the Kruskal-Wallis test, which was followed by the Mann-Whitney U test with Bonferroni correction for pairwise comparisons with the baseline group. Correlations between the variables were assessed using Spearman's correlation coefficients. RESULTS: All CMR-derived RV parameters showed significant differences across the baseline and PH induction groups (all P < 0.001). RV free wall longitudinal strain (RVFWLS) showed the earliest impairment at 2 weeks, with a progressive decline thereafter. The RV free wall circumferential strain (RVFWCS) and RV ejection fraction were reduced beginning at 3 weeks, whereas the RV end-diastolic volume index increased significantly only at 4 weeks. The PA %WT increased progressively from week 2, whereas the RV collagen density did not change significantly. RVFWLS and RVFWCS showed strong positive correlations with PA %WT (r = 0.885 and r = 0.757, respectively; both P < 0.001), which were primarily driven by parallel changes across the post-induction time points. The control groups showed no significant temporal changes in the CMR or histological measurements. CONCLUSION: In this preclinical model of PH, staged CMR and histological assessments demonstrated sequential RV remodeling in parallel with PA remodeling, with RVFWLS impairment preceding overt RV dysfunction and enlargement.