Direction of preoperative ventricular shunting affects ventricular mechanics after tetralogy of Fallot repair

Background - Tetralogy of Fallot (TOF) typically results in clinical cyanosis or volume overload of the left ventricle (LV), depending on the direction and magnitude of shunting across the ventricular septal defect (VSD). The present study examines the effects of surgical TOF repair on LV mechanics and compares these changes between patients with VSD shunts that are predominantly right-to-left (R-L; "blue TOF") and those with VSD shunts that are predominantly left-to-right (L-R; "pink TOF"). Methods and Results - Eleven patients (6 R-L and 5 L-R) 4.3 to 18.4 months old (median 7.1 months old) were studied. LV end-diastolic area (EDA) was calculated from transesophageal echocardiograms obtained during initiation and weaning of cardiopulmonary bypass. LV end-diastolic pressure was measured by micromanometer. Compliance was assessed by end-diastolic pressure-area curves. Contractility was assessed from preload recruitable stroke work by the stroke work-versus-LV EDA relation. VSD shunt direction was determined by preoperative Doppler echocardiography. Changes in LV function at the conclusion of cardiopulmonary bypass included decreased stroke area (from 6.6±0.9 to 4.1±0.4 cm²/m², P=0.012) and ejection fraction (from 55±2% to 41±3%, P<0.001). LV EDA at a common pressure in 8 patients decreased (from 10.4±1.4 to 7.6±1.2 cm ²/m², P=0.003), which suggests a decrease in ventricular compliance. Additionally, the end-diastolic pressure-area curves shifted to the left in all patients. Preload recruitable stroke work decreased (from 34.8±2.4 to 21.8±2.6 mm Hg, P=0.007), which demonstrates a decrease in ventricular contractility. When separated by preoperative shunt direction, LV EDA increased in R-L patients by 0.9±0.5 cm ²/m² postoperatively but decreased in L-R patients by 4.3±0.8 cm²/m² (P<0.001). Area ejection fraction decreased in all patients independent of shunting or change in LV EDA. Conclusions - LV diastolic and systolic function are depressed after TOF repair. Mechanical effects of the VSD patch and myocardial depressant effects of ischemia and reperfusion during surgery probably contribute to the observed changes in LV mechanics. Different effects of surgical repair on LV preload in pink and blue TOF also contribute to the spectrum of clinical results observed after surgery.