Improved cardiac tagging resolution at ultra-high magnetic field elucidates transmural differences in principal strain in the mouse heart and reduced stretch in dilated cardiomyopathy

Cardiac tagging resolution for regional principal strains El and E2 has been a limiting factor for the study of dilated mouse hearts, in which the left ventricle (LV) wall thickness can drop to below 1 mm. Therefore, high resolution tagging was performed at 14.1 T to enable transmural principal strain measurements across the LV wall of normal mouse hearts and average principal strains in thinned LV walls of a transgenic mouse (PKC epsilon TG) that develops dilated LV. A modified DANTE tagging and fast gradient imaging method produced a tagging grid dimension of 0.33 x 0.33 mm and line thickness under 0.1 mm. In normal mice, average El strain in the epicardium was significantly higher than the endocardial El (epi = 0.22 +/- 0.10; endo = 0.13 +/- 0.07, p < 0.05), while magnitude of average endocardial E2 was greater than in the epicardium (endo = -0.12 +/- 0.03, epi = -0.08 +/- 0.03; p < 0.001). El strain averaged over four segments was reduced in dilated hearts compared to controls (PKC epsilon TG = 0.14 +/- 0.02; control = 0.18 +/- 0.02, p < 0.01), with specific reductions in septal (33%) and lateral (31%, p < 0.01) segments. E2 strain was similar between dilated and control hearts at -0.11 +/- 0.01. Thus, improved tagging resolution demonstrates that stretch (El), but not compression strains (E2), are reduced as a result of significant LV wall thinning in a mouse model of dilated cardiomyopathy.