Left ventricular muscle volume in children and young adults.

A computer-assisted method of estimating left ventricular muscle volume and its clinical application in 193 children and young adults is described. Wall thickness was measured at the lower half of the left cardiac border in the angiographic posteroanterior projection of the left ventricle, where only three points are marked when the left ventricular contour is traced. The intra- and interobserver reproducibility of the wall thickness were both within 1 mm. The individual beat-to-beat variability was 0.6 mm, 10% of the mean thickness. In normal left ventricles, the ratio between ventricular muscle volume and end-diastolic volume, the muscle volume index (MVI), was independent of body surface area, being 1.01 + 0.14 (mean +/- SD, n = 28). MVI was normal in ventricles which were volume loaded secondary to a ventricular septal defect (n = 9) or ductus arteriosus (n = 11). It was significantly increased in aortic coarctation (1.66 +/- 0.44, n = 24, P less than 0.001) and in valvar aortic stenosis (1.34 +/- 0.31, n = 21, P less than 0.01). In tetralogy of Fallot (n = 34) MVI was normal. MVI was significantly reduced in the case of pressure and possibly volume-underloaded left ventricles of simple transposition of the great arteries (TGA) (0.53 +/- 0.15, n = 15) at the age of one year, compared to normal (P less than 0.001) and to the mean in TGA shortly after birth (P less than 0.05). However, it increased (P less than 0.001) to normal after banding of the pulmonary artery in TGA.