Assessment of pulmonary/systemic blood flow ratio after first-stage palliation for hypoplastic left heart syndrome: Development of a new index with the use of doppler echocardiography

Objective: Circulatory maldistribution is believed to be a major cause of early death after first-stage palliation for hypoplastic left heart syndrome. Flow reversal in the reconstructed aorta may reflect the pulmonary/systemic blood flow ratio. The purpose of our study was to investigate the utility of arterial Po₂, arterial oxygen saturation, and a newly developed Doppler-derived flow index in predicting the pulmonary/systemic flow ratio, after first-stage palliation for hypoplastic left heart syndrome. Methods: Twenty-four infants who underwent first-stage palliation for hypoplastic left heart syndrome or a variant were studied. Superior vena cava blood samples were drawn to estimate the mixed venous saturation and permit calculation of the pulmonary/systemic blood flow ratio. Fifty-four samples were evaluated within the first 24 hours after surgery. Simultaneous blood draw and Doppler echocardiography were performed with interrogation in the distal aspect of the arch reconstruction. The ratio of the Doppler velocity-time integral of retrograde flow to the velocity-time integral of forward flow was calculated and compared with the pulmonary/systemic blood flow ratio. Results: The median mixed venous saturation for the 54 samples was low (38.5%; range, 18%-64%). The median calculated pulmonary/systemic blood flow ratio was 1.4:1 (range, 0.3:1 to 4.2:1). Pulse pressure, mixed venous saturation, and arterial Po₂ were not statistically significant predictors of the measured pulmonary/systemic blood flow ratio. Although both aortic oxygen saturation (R² = 0.84, P < .01) and Doppler flow reversal ratio (R² = 0.94, P < .001) were significantly associated with the measured pulmonary/systemic blood flow ratio, the model coefficient of determination was greatest for Doppler flow reversal ratio. Conclusion: Measures of arterial oxygen saturation and arterial Po₂ may be misleading in assessing the circulatory status of infants after first-stage palliation for hypoplastic left heart syndrome. Doppler echocardiography, through use of the Doppler flow reversal ratio, provides a more useful measure of pulmonary/systemic blood flow ratio. Low mixed venous saturation after surgery may be due to factors other than pulmonary overcirculation, such as ventricular dysfunction and low cardiac output.