Diastolic Biomechanics in Normal Infants Utilizing MRI Tissue Tagging

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Abstract
Background —Most of what is known about diastolic function in normal infants is derived from flow and pressure measurements. Little is known about regional diastolic strain and wall motion. Methods and Results —Magnetic resonance tissue tagging was performed in 11 normal infants to determine regional diastolic strain and wall motion. Tracking diastolic motion of the intersection points and finite strain analysis yielded regional rotation, radial displacement, and E 1 and E 2 strains at 3 short-axis levels (significance was defined as P E 2 “circumferential lengthening” strains were significantly greater at the lateral wall, regardless of short-axis level, whereas E 1 “radial thinning” strains were similar in all wall regions at all short-axis levels. In general, no differences were noted in strain dispersion within a wall region or in endocardial/epicardial strain at all short-axis levels. At all short-axis levels, septal radial motion was significantly less than in other wall regions. No significant differences in radial wall motion between short-axis levels were noted. Rotation was significantly greater at the apical short-axis level in all wall regions than in other short-axis levels, and it was clockwise. At the atrioventricular valve, septal and anterior walls rotated slightly clockwise, whereas the lateral and inferior walls rotated counterclockwise. Conclusions —Diastolic biomechanics in infants are not homogeneous. The lateral walls are affected most by strain, and the septal walls undergo the least radial wall motion. Apical walls undergo the most rotation. These normal data may help in the understanding of diastolic dysfunction in infants with congenital heart disease.

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