REGIONAL DEFORMATION AND CONTRACTILE FUNCTION IN CANINE RIGHT VENTRICULAR FREE WALL

We used biplane cinefluorography to study the regional deformation and local contractile function of the canine right ventricular free wall (RVFW) among the inflow, midventricular, and outflow regions. For a region delimited by three neighboring markers, under the assumption of homogeneous deformation, we identified the magnitudes and directions of principal shortening or elongation and changes in area every 16.7 ms. Furthermore, we extended this approach to study the alterations of these parameters during RV afterload increase by applying pulmonary artery (PA) occlusion. Results show that, at both control and PA occlusion states, the outflow region was subjected to maximal fractional area reduction (AR) and maximal time rate of fractional area reduction (ARR) during systole, with no differences between inflow and midventricular regions (P < 0.05). At the control state, the percent AR and the corresponding value for ARR were 27% and 179%/s at the outflow, 19% and 112%/s at the midventricular, and 15% and 107%/s at the inflow region, respectively. During PA occlusion, they became 21% and 115%/s at the outflow, 14% and 97%/s at the midventricular, and 15% and 102%/s at the inflow region, respectively. Statistically, only the outflow region deformation was affected by PA occlusion (P < 0.05). For the control state, we also compared the direction of regional principal shortening at end systole to the local transmural myocardial fiber orientations. The directions were found to correspond closely to the mean of all local transmural fiber orientations. This suggests that the regional RVFW deformation we measured is the combined deformation behavior from all the local participating myofibers.