Post‐Myocardial Infarction Remodeling and Hyperkinetic Remote Myocardium in Sheep Measured by Cardiac MRI Feature Tracking

Abstract

BackgroundCardiac MRI feature tracking (FT) allows objective assessment of segmental left ventricular (LV) function following a myocardial infarction (MI), but its utilization in sheep, where interventions can be tested, is lacking.PurposeTo apply and validate FT in a sheep model of MI and describe post‐MI LV remodeling.Study TypeAnimal model, longitudinal.Animal ModelEighteen lambs (6 months, male, n = 14; female, n = 4; 25.2 ± 4.5 kg).Field Strength/SequenceTwo‐dimensional balanced steady‐state free precession (bSSFP) and 3D inversion recovery fast low angle shot (IR‐FLASH) sequences at 3 T.AssessmentSeven lambs underwent test–retest imaging to assess FT interstudy reproducibility. MI was induced in the remaining 11 by coronary ligation with MRI being undertaken before and 15 days post‐MI. Injury size was measured by late gadolinium enhancement (LGE) and LV volumes, LV mass, ejection fraction (LVEF), and wall thickness (LVWT) were measured, with FT measures of global and segmental radial, circumferential, and longitudinal strain.Statistical TestsSampling variability, inter‐study, intra and interobserver reproducibility were assessed using Pearson's correlation, Bland–Altman analyses, and intra‐class correlation coefficients (ICC). Diagnostic performance of segmental strain to predict LGE was assessed using receiver operating characteristic curve analysis. Significant differences were considered P < 0.05.ResultsInter‐study reproducibility of FT was overall good to excellent, with global strain being more reproducible than segmental strain (ICC = 0.89–0.98 vs. 0.77–0.96). MI (4.0 ± 3.7% LV mass) led to LV remodeling, as evident by significantly increased LV volumes and LV mass, and significantly decreased LVWT in injured regions, while LVEF was preserved (54.9 ± 6.9% vs. 55.6 ± 5.7%; P = 0.778). Segmental circumferential strain (CS) correlated most strongly with LGE. Basal and mid‐ CS increased significantly, while apical CS significantly decreased post‐MI.Data ConclusionFT is reproducible and compensation by hyperkinetic remote myocardium may manifest as overall preserved global LV function.Evidence LevelN/ATechnical EfficacyStage 2