Selective Inhibition of Epicardial Function Reduces Left Ventricular Endocardial Torsion and Principal Strain: Magnetic Resonance Imaging Study Using Tissue Tagging

Cardiac motion results from the complex interaction of individual muscle fibers organized into layers. Epicardial (epi) fibers are aligned with the direction of endocardial (endo) torsion and principal strain (PS) angle, suggesting an influence on endo function. Therefore, we hypothesized that selective inhibition of epi function will alter endo deformation. Twelve open chest dogs underwent continuous pericardial lavage at baseline (BL) and with heating of the lavage fluid (HT), while the blood temperature was held constant. Heating decreases contractile function. Imaging was performed at BL and at HT and included 4 short axis images with 4 radially prescribed tags and 4 long axis images with 4 parallel transverse tags. Gradient echo images were obtained at end-diastole and end-systole. The tag-endo and tag-epi intersections were located and reconstructed into 24 3-D myocardial cuboids for 3-D finite strain analysis. Torsion was measured as the apex to base difference in rotation about the cavity centroid at end-systole. Results compare the free wall (exposed to heated lavage) at BL and at HT. Results: Lavage temperature increased from 35.7° ± 1.2 at BL to 40.0° ± 0.7 at HT (p < 0.001). As direct result of the heating, epi torsion and PS magnitude decreased from −4.1° ± 3.0 to −1.4° ± 2.4 (p < 0.02) and from −0.10 ± 0.03 to −0.08 ± 0.03 (p < 0.001), respectively. Although blood and therefore, endo temperature was constant (34.7°) at both BL and HT, endo torsion and PS magnitude decreased from −9.1° ± 6.8 to −2.5 ± 4.9 (p = 0.002) and from −0.29 ± 0.06 to −0.23 ± 0.10 (p < 0.05), respectively. Wall thickening decreased from 30.8% ± 14.3 to 18.5% ± 17.6 (p = 0.004). In the septum (unexposed to heated lavage) torsion, PS and thickening were unchanged. In conclusion, selective inhibition of epicardial function by augmented temperature caused significant decline in endocardial torsion and PS magnitude, local measures of endocardial function, demonstrating the important contribution of epicardial function to endocardial deformation.