Author + information
- Received August 21, 2008
- Revision received October 20, 2008
- Accepted November 11, 2008
- Published online February 1, 2009.
- Hiroshi Ashikaga, MD, PhD⁎,⁎ (, )
- Tycho I.G. van der Spoel, MD†,
- Benjamin A. Coppola, PhD⁎ and
- Jeffrey H. Omens, PhD⁎
- ↵⁎Reprint requests and correspondence:
Dr. Hiroshi Ashikaga, Division of Cardiology, Johns Hopkins University School of Medicine, 600 North Wolfe Street, Carnegie 568, Baltimore, Maryland 21205
Objectives We sought to resolve the 3-dimensional transmural heterogeneity in myocardial mechanics observed during the isovolumic contraction (IC) phase.
Background Although myocardial deformation during IC is expected to be little, recent tissue Doppler imaging studies suggest dynamic myocardial motions during this phase with biphasic longitudinal tissue velocities in left ventricular (LV) long-axis views. A unifying understanding of myocardial mechanics that would account for these dynamic aspects of IC is lacking.
Methods We determined the time course of 3-dimensional finite strains in the anterior LV of 14 adult mongrel dogs in vivo during IC and ejection with biplane cineradiography of implanted transmural markers. Transmural fiber orientations were histologically measured in the heart tissue postmortem. The strain time course was determined in the subepicardial, midwall, and subendocardial layers referenced to the end-diastolic configuration.
Results During IC, there was circumferential stretch in the subepicardial layer, whereas circumferential shortening was observed in the midwall and the subendocardial layer. There was significant longitudinal shortening and wall thickening across the wall. Although longitudinal tissue velocity showed a biphasic profile; tissue deformation in the longitudinal as well as other directions was almost linear during IC. Subendocardial fibers shortened, whereas subepicardial fibers lengthened. During ejection, all strain components showed a significant change over time that was greater in magnitude than that of IC. Significant transmural gradient was observed in all normal strains.
Conclusions IC is a dynamic phase characterized by deformation in circumferential, longitudinal, and radial directions. Tissue mechanics during IC, including fiber shortening, appear uninterrupted by rapid longitudinal motion created by mitral valve closure. This study is the first to report layer-dependent deformation of circumferential strain, which results from layer-dependent deformation of myofibers during IC. Complex myofiber mechanics provide the mechanism of brief clockwise LV rotation (untwisting) and significant wall thickening during IC within the isovolumic constraint.
Supported by the American Heart Association 0225001Y (to Dr. Ashikaga, Western States Affiliate) and R01-HL32583 (to Dr. Omens).
- Received August 21, 2008.
- Revision received October 20, 2008.
- Accepted November 11, 2008.
- American College of Cardiology Foundation