RAPID 2-STAGE ARTERIAL SWITCH OPERATION ACQUISITION OF LEFT-VENTRICULAR MASS AFTER PULMONARY-ARTERY BANDING IN INFANTS WITH TRANSPOSITION OF THE GREAT-ARTERIES

Background Banding of the pulmonary artery (PAB) in preparation for ar terial switch operation (ASO) in patients with transposition of the gr eat arteries (TGA) represents a unique model of acute left ventricular pressure overload in humans. Methods and Results To establish the rat e, magnitude, and determinants of left ventricular hypertrophy and the acute effect on ventricular function, serial bidimensional echocardio graphic evaluations were performed on 26 patients with TGA after PAB. Mass, volume, and ejection fraction of the left ventricle were measure d. Cardiac catheterization data before PAB and again before ASO were r eviewed. The mean interval between the PAB and ASO was 9+/-4 days. The left ventricular to right ventricular pressure ratio before PAB was 0 .5 and increased to 1.0 before ASO. The mean percentage increase in le ft ventricular mass from PAB to ASO was 96%, 95% of which was achieved in the first 7 days. The average rate of left ventricular hypertrophy for the entire period was 0.06 g/h and was 0.19 g/h during the interv al from PAB to attainment of maximum left ventricular mass. The most r apid rate of hypertrophy was seen by day 2, with an exponential fall i n the growth rate thereafter approaching zero by day 7. Ejection fract ion was significantly reduced at 12 hours after PAB, but mean values r eturned to pre-PAB levels by 3.5 days after banding. The absolute rate of left ventricular hypertrophy correlated directly with body surface area but not to other hemodynamic variables. Conclusions Doubling of left ventricular mass can be achieved in 1 week after PAB. Function fa lls acutely due to afterload excess and/or depressed contractility but recovers rapidly as compensatory hypertrophy occurs.