Abstract 1791: Early Postoperative Blunting of Rapid Diastolic Subepicardial Fiber Lengthening and Left Ventricular Circumferential Expansion
Introduction: We have recently shown, in hearts 8 weeks after surgery, that circumferential expansion of the subepicardium, unlike that of the subendocardium, is virtually complete by the time one-third of LV filling has been achieved. We tested the hypothesis that this behavior, reflecting a mechanism likely enhancing postoperative diastolic compliance during early diastolic LV filling, would also be observed during the early postoperative period (1 week after surgery).
Methods: Thirteen radiopaque markers were surgically implanted to silhouette the LV chamber and three columns of four transmural markers each were implanted in the lateral equatorial wall in seven sheep. 4-D marker dynamics were studied one and eight weeks thereafter with biplane videofluoroscopy of closed-chest anesthetized animals. LV volume (LVV) was calculated every 16.7 ms by summing the volumes of multiple space-filling tetrahedrons. LV transmural circumferential strain (Ecc) was studied from filling onset (10% LVPmax during IVR; reference configuration) to deformed configurations at end of early filling (EOEF; 100 msec after filling onset) and end diastole (ED; maximum LVV). Fiber strain (Eff) was computed from strain transformations employing transmural fiber angles obtained from quantitative histology. Strains are reported at 20% (EPI) and 80% (ENDO) wall depths.
Conclusions: Unlike the transmural mechanics in the late postoperative period (8 weeks after surgery), in the early postoperative period (1 week after surgery) subepicardial circumferential re-lengthening during rapid diastolic filling is greatly blunted, and subepicardial fiber re-lengthening over this interval is zero. This provides a possible mechanistic basis for diastolic dysfunction in the early postoperative period. Such subepicardial malfunction could serve as a target for the development of future protective therapies to improve early postoperative LV function.