Biomechanics of the deconditioned left ventricle

To determine if strain and wall motion are enhanced in the left ventricle (LV) in a chronically afterload-reduced milieu, a magnetic resonance tagging technique was used to examine 19 subjects: 11 with transposition of the great arteries who have undergone an atrial inversion operation (TGA-LV, 11.6 +/- 4.3 yr postoperative) and eight normal adults. Finite strains (E1), regional twist, and radial motion were calculated at the atrioventricular valve and apical short axis levels in four anatomic wall regions. Strain was greatest in TGA-LV patients (-0.20 +/- 0.02 at the atrioventricular valve septal wall) and was significantly greater than controls in six out of eight regions. Marked differences were noted in the distribution of strain between TGA-LV and normal subjects as well as within the TGA-LV group. Ten of 11 LV of TGA-LV patients twisted clockwise in the lateral or inferior walls and counterclockwise in other walls (more counterclockwise than control subjects), whereas control LV twisted uniformly counterclockwise. The lateral wall of TGA-LV demonstrated the greatest radial inward motion, whereas controls demonstrated uniform radial inward motion. We conclude that the biomechanics of the LV faced with a chronic afterload reduction is enhanced; a marked increase in regional strain is observed in TGA-LV patients. Abnormalities in the distribution of strain were also observed. Markedly abnormal clockwise twist and increased lateral wall motion were demonstrated in TGA-LV patients.