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1 Division of Cardiology, Johns Hopkins Hospital, Baltimore, MD, USA
2 Department of Radiology, Johns Hopkins Hospital, Baltimore, MD, USA
3 Center for Imaging Science, Department of Electrical and Computer Engineering, Johns Hopkins Hospital, Baltimore, MD, USA
* To whom correspondence should be addressed. E-mail: jlima{at}jhmi.edu.
Objectives and background- Left ventricular relaxation entails myocardial deformation that induces left ventricular filling. Yet, the precise mechanisms of the
earliest changes in tissue properties that characterize myocardial relaxation remain incompletely understood.
Methods- Ten healthy volunteers (seven males), 25-43 yrs, underwent tagged and cine MRI with high temporal resolution (25-35 ms). Normal strains including radial
(Err), circumferential (Ecc), and longitudinal (Ell) strains, shear strains, including Ecl (circumferential -longitudinal), Ecr (circumferential-radial), and Erl (radiallongitudinal) and principal strains (E1, E2 and E3) were calculated using a displacement field-fitting method. Temporal changes in angular strains indicative of shear and torsion release, and normal strains were studied during late systole and early relaxation.
Results- The onset of individual relaxation strains was heterogeneous relative to LV filling. Shear strains (Ecr, Erl and Ecl) and radial thinning were first to develop. Times of onset of Ecr, Erl, Ecl and Err occurred 108, 93, 67 and 73 ms prior to aortic valve closure, respectively. Ell, Ecc and LV volume change commenced
significantly later after the onset of diastolic shear strains and radial thinning. The onset of Ecc, Ell and LV volume change was noted 38 ms prior to aortic valve
closure, (p
0.05 relative to the onset of shear strains and Err).
Conclusions- Myocardial relaxation is characterized by a three-dimensional unfolding deformation that includes release of torsion, shear, and radial thinning beginning prior to aortic valve closure. This unfolding pattern precedes longitudinal and circumferential elongation and may facilitate early diastolic filling.
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