An electron microscopic study of left ventricular regression in children with transposition of great arteries.

Over the years the age limit for the arterial switch operation (ASO) is being redefined with increasing expertise and adoption of extra-corporeal membrane oxygenator (ECMO) in the surgical program. We conducted a study to see the differences in ultrastructural features in eight children with transposition of the great arteries, four with prepared and the remaining four with regressed left ventricle (LV) during the ASO. Children with prepared LV had prominent Z bands with uniform and round mitochondria, few fat vacuoles and minimal collagen in the background, whereas children with regressed LV had Z band disruption with non-uniform elliptical mitochondria and myofibrillary disarray and an abundance of fat vacuoles and collagen in the background. Children with regressed LV and abundance of collagen had a prolonged postoperative course. Collagen deposition in the LV may point to the situation where the postoperative course following ASO may be prolonged due to the increased time required for the regressed LV to increase its mass and to sustain the systemic circulation.