title: In vivo validation of longitudinal-circumferential area change ratio to estimate myofiber shortening in the heart.
abstract: The aim of this paper was to validate area change ratio (%AC) against myofiber shortening (%λ(f)) in the heart in vivo. %AC is emerging as a mechanical index that may approximate %λ(f) by incorporating both circumferential and longitudinal shortening. However, the physiological significance of % AC remains unclear. We studied the time course of %AC in the anterior midleft ventricular wall of normal canine heart in vivo (n = 14) during atrial pacing over the entire cardiac cycle using transmurally implanted markers and biplane cineradiography (8 ms/frame). %AC was calculated as the myocardial area change relative to the elemental material area on the circumferential-longitudinal plane at the reference configuration (=end diastole). %AC was compared with %λ(f) that was determined from the transmural fiber orientation directly measured in the heart tissue. The time course of both %AC and %λ(f) was determined in the subepicardial, midwall, and subendocardial layers. The time course of %AC and %λ(f) was significantly different, and the difference was more pronounced towards the endocardium. %AC consistently overestimated %λ(f). The timing of the peak %AC was significantly delayed compared to that of the peak %λ(f). We conclude that %AC is significantly different from %λ(f) both in magnitude and timing in vivo. %AC overestimates %λ(f), and the overestimation is worse toward the endocardial layers. This may be a potentially important limitation when applying %AC to optimization and responder identification for cardiac resynchronization therapy.
authors.affiliation: Division of Cardiology, The Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA. hashika1@jhmi.edu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ashikaga
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Omens
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology*; D002933:Cineradiography; D003952:Diagnostic Imaging / Q000379:methods*; D004285:Dogs; D004562:Electrocardiography; D057918:Fiducial Markers; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology*; D009206:Myocardium / Q000166:cytology*; D009210:Myofibrils / Q000502:physiology* / Q000648:ultrastructure; D015203:Reproducibility of Results