REGIONAL HETEROGENEITY OF OVINE MYOFIBER INCLINATION ANGLE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Quantification of myofiber inclination angle is necessary for calculating myofiber shortening strains and for modeling cardiac performance. This study offers insight into the regional differences in transmural myofiber inclination angle. Quantitative histologic techniques were used to characterize regional variations in myofiber orientation by examining the local helix angle in five healthy ovine hearts at an average of 9.4 (SD 2.2) transmural locations in eight circumferentially arranged blocks and within four slices across the left ventricle (LV). The mean midwall myofiber inclination angle was -7¿ (SD 9), but was better characterized by spatial heterogeneity (an average of 0¿ in the posterolateral and anterolateral wall near the papillary muscles, and -9¿ in all other regions). The transmural pitch (angular change per wall depth) averaged 93¿ (SD 21) and was lowest in the posterior wall (51¿ in the basal posterior sector) and highest in the anterolateral wall (130¿ in the mid-equatorial anterolateral sector). Transmural myofiber orientations were fit with cubic functions with a mean RMS error of 18¿ (SD 6¿). The lowest RMS fit error was in the lateral mid-equatorial sector (9¿) and highest RMS fit error was in the basal postero-septal sector (33¿) indicating that myofiber arrangement in the postero-septal wall may be less conserved than within the lateral wall. Our results corroborate previously published results, but importantly highlight regional differences in myofiber organization that may impact any results obtained from computational models.