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1Mouse Imaging Centre and 2Cardiovascular Research Program, Hospital for Sick Children, 3Heart and Stroke/Richard Lewer Centre of Excellence, 4Sunnybrook and Women's College Health Sciences Centre, 5Department of Medical Biophysics, and 6Department of Molecular and Medical Genetics, University of Toronto, Toronto, Ontario, Canada
Submitted 11 January 2005 ; accepted in final form 21 April 2005
Tbx5del/+ mice provide a model of human Holt-Oram syndrome. In this study, the cardiac functional phenotypes of this mouse model were investigated with 30-MHz ultrasound by comparing 12 Tbx5del/+ mice with 12 wild-type littermates at 1, 2, 4, and 8 wk of age. Cardiac dimensions were measured with two-dimensional and M-mode imaging. The flow patterns in the left and right ventricular inflow channels were evaluated with Doppler flow sampling. Compared with wild-type littermates, Tbx5del/+ mice showed significant changes in the mitral flow pattern, including decreased peak velocity of the left ventricular (LV) early filling wave (E wave), increased peak velocity of the late filling wave (A wave), and decreased or even reversed peak E-to-A ratio. The prolongation of LV isovolumic relaxation time was detected in Tbx5del/+ neonates as early as 1 wk of age. In Tbx5del/+ mice, LV wall thickness appeared normal but LV chamber dimension was significantly reduced. LV systolic function did not differ from that in wild-type littermates. In contrast, the Doppler flow spectrum in the enlarged tricuspid orifice of Tbx5del/+ mice demonstrated increased peak velocities of both E and A waves and increased total time-velocity integral but unchanged peak E/A. In another 13 mice (7 Tbx5del/+, 6 wild-type) at 2 wk of age, significant correlation was found between Tbx5 gene expression level in ventricular myocardium and LV filling parameters. In conclusion, the LV diastolic function of Tbx5del/+ mice is significantly deteriorated, whereas the systolic function remains normal.
Tbx5 mutation; atrial septal defect; left ventricular diastolic function; right ventricular dilatation; Doppler flow sampling
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