Regional endocardial strains in the left ventricle enable more accurate assessment of acutely-evolving and chronic heart failure post-myocardial infarction

Introduction Left ventricular (LV) global strains have been shown to be useful metrics in assessing the condition and progression of heart failure (HF) following myocardial infarction (MI) [1]. Regional strains can be more laborious to calculate, however it has been suggested they can play useful roles in determination of infarct location and regional differences in tissue constitutive properties [2]. The aim of this study was to investigate the relative merits of calculating regional and global circumferential endocardial strains using unique experimental data. Methods MI was induced via inflation of a balloon catheter in three porcine specimens (A, B, & C) in the left anterior descending artery to produce an apical infarct. The occlusion lasted 60 minutes, after which it was deflated allowing for reperfusion. Short and long axis cine-CMR images were taken before surgery, four hours post-MI, and four weeks later, marking the healthy heart, acute and chronic HF. Endocardial borders were manually traced (OsiriX, Pixmeo, Geneva, Switzerland), as in Figure 1a. Strains for each MRI slice were calculated according to standard clinical practice, and from these, regional strains for the base, equator and apex of the left ventricle were found, as well as global metrics including LV ejection fraction (LVEF) and global circumferential strain. Results No data was available for specimens B at the acute stage, or C at the chronic stage. Regional apical strains decreased significantly from healthy to acute and chronic stages (15% & 20% average reduction respectively), whilst basal strains remained unchanged, as seen in Figure 1c for specimen A. Equatorial slices experienced moderate decreases. Global circumferential strains decreased across specimens A and C during acute HF (~10%), and decreased further in the chronic HF phase for specimens A and B (~13%). LVEF decreased significantly in the acute timeframe (~15%) for specimens A and C, with specimen A experiencing a further decrease in LVEF at the chronic stage. Discussion The global metrics suggested the presence of remodelling and HF, however did not indicate the particular regions affected. Regional strains provided this localisation in an uncomplicated way, whereas slice-by-slice analysis was harder to visually interpret due to the large number of slices and noise in the data sets. Local changes shown by regional analysis corresponded to the known location of the infarct. Further work on additional porcine specimens is ongoing, including investigation of other metrics such as strain rate, and both longitudinal and epicardial strains. The results suggest that localised clinical measurement could prove to be useful for patient management, with quantitative strain analysis in the acute setting possibly indicating the severity of infarct. References [1] Ersbøll et al. (2013) J. Am. Coll. Cadiol. 61(23)