Microstructural characteristics of chronic infarct segments assessed using diffusion tensor imaging

Abstract

\n \n \n Type of funding sources: Foundation. Main funding source(s): British Heart Foundation\n \n \n \n The microstructural changes following myocardial infarction (MI) can be characterised in-vivo with cardiac diffusion tensor imaging (cDTI) imaging, using mean diffusivity (MD), fractional anisotropy (FA), secondary eigenvector angle (E2A) and helix angle (HA) maps. In this study, we use cDTI to explore the microstructural differences between subendocardial and transmural chronic infarct segments.\n \n \n \n Twenty STEMI patients (15 men, 5 women, mean age 59) underwent 3T CMR scan at 3 months following presentation (mean interval 107\u2009±\u200918 days). Scan protocol included: second order motion compensated (M012) free-breathing spin echo DTI (3 slices, 18 diffusion directions at b-values 100s/mm2[3], 200s/mm2[3] and 500s/mm2[12], acquired resolution was 2.20x2.27x8mm3; cine gradient echo and LGE imaging.\xa0Average MD, FA, E2A and HA parameters\xa0were calculated on a 16-AHA-segmental level.\xa0HA maps were described by dividing values into left-handed HA (LHM, -90° < HA < -30°), circumferential HA (CM, -30° < HA < 30°), and right-handed HA (RHM, 30° < HA < 90°) and reported as relative proportions.\xa0Infarct segments were identified using LGE; patients were categorised according to the maximal transmurality of their infarct segments, into subendocardial (<50% LGE) or transmural (>50% LGE) MI.\n \n \n \n DTI acquisition was successful in all patients (acquisition time 13\u2009±\u20095mins).\xa0Ten patients had transmural MI. The results are shown in table 1. Transmurally infarcted segments had significantly lower FA (FA\xa0subendocardial MI\xa0= 0.27\u2009±\u20090.04, FA\xa0transmural MI\xa0= 0.23\u2009±\u20090.02, p\u2009<\u20090.01), lower E2A (E2A\xa0subendocardial MI\xa0= 47\u2009±\u20097°, E2A\xa0transmural MI\xa0= 38\u2009±\u20096°, p\u2009<\u20090.01) and lower proportions of right-handed cardiomyocytes (RHM\xa0subendocardial MI\xa0= 21\u2009±\u20095%, RHM\xa0transmural MI\xa0= 14\u2009±\u20095%, p\u2009<\u20090.01) than subendocardial infarct segments.\xa0\n \n \n \n Compared to subendocardial MI segments, the diffusion of water molecules is more isotropic in transmurally infarcted myocardium as evidenced by lower FA values, signifying increased structural disarray. The significantly lower E2A values suggest that laminar sheetlets of transmural infarct segments remain fixed at shallower angles during systole and are unable to reach their usual contractile configuration. The lower proportions of RHM on HA maps highlight the significantly greater loss of subendocardial cardiomyocytes in transmural infarct segments. Further studies are required to assess if these segmental changes can be predictive of long-term LV remodelling.\n