OPTIMIZATION OF LEFT-VENTRICULAR FIBER ORIENTATION OF THE NORMAL HEART FOR HOMOGENEOUS SARCOMERE-LENGTH DURING EJECTION

During the ejection phase of the cardiac cycle, left ventricular muscl e fibres shorten while generating force. It was hypothesized that fibr es are oriented in the wall such that the amount of shortening is the same for all fibres. We evaluated this hypothesis for the equatorial r egion of the left ventricle. In a finite element model of left ventric ular wall mechanics fibre orientation was quantified by a helix angle which varied linearly from the inner to the outer wall. Fibre length w as characterized by sarcomere length, set at 1.95 mu m everywhere in t he passive state of 0 transmural pressure. For a cavity pressure of 15 kPa, considered representative for ejection, inhomogeneity in mechani cal loading was expressed by the variance of the sarcomere length. The variance was minimized by adapting the transmural course of fibre ang le. First, only the slope was optimized and in a second optimization t his was done for both slope and intercept. Optimal helix fibre angles were 69.6 degrees endocardially, 0 degrees at the middle of the wall a nd -69.6 degrees epicardially for the first optimization and 78.2 degr ees, 20.7 degrees and, -36.7 degrees respectively for the second. Sarc omere length changed from 1.95 to 1.975+/-0.012 and 1.981+/-0.004 mu m (mean+/-SD) respectively. Conclusion: After optimization calculated h elix fibre angles were in the physiological range. Describing the tran smural course of fibre angle with slope and intercept significantly im proved homogeneity in mechanical load.