Noninvasive quantification of systemic-to-pulmonary collateral flow: a major source of inefficiency in patients with superior cavopulmonary connections.

BACKGROUND Systemic-to-pulmonary collateral flow (SPCF) is common in single-ventricle patients with superior cavopulmonary connections (SCPC). Because no validated method to quantify that SPCF exists, neither its hemodynamic burden nor its clinical impact can be systematically evaluated. We hypothesize that (1) the difference in total ascending aortic (Ao) and caval flow (superior vena cava [SVC]+inferior vena cava [IVC]) and (2) the difference between pulmonary vein and pulmonary artery flow (PV-PA) provide 2 independent estimators of SPCF. METHODS AND RESULTS We measured Ao, SVC, IVC, right (RPA) and left (LPA) PA, and left (LPV) and right (RPV) PV flows in 17 patients with SCPC during routine cardiac MRI studies using through-plane phase-contrast velocity mapping. Two independent measures of SPCF were obtained: model 1, Ao-(SVC+IVC); and model 2, (LPV-LPA)+(RPV-RPA). Values were normalized to body surface area, Ao, and PV, and comparisons were made using linear regression and Bland-Altman analysis. SPCF ranged from 0.2 to 1.4 L/min for model 1 and 0.2 to 1.6 L/min for model 2, for an average indexed SPCF of 0.5 to 2.8 L/min/m(2): 11% to 53% (mean, 37%) of Ao and 19% to 77% (mean, 54%) of PV. The mean difference between model 1 and model 2 was 0.01 L/min (P=0.40; 2-SD range, -0.45 to 0.47 L/min). CONCLUSIONS We present a noninvasive method for SPCF quantification in patients with SCPC. It should provide an important clinical tool in treating these patients. Furthermore, we show that SPCF is a significant hemodynamic burden in many patients with bidirectional Glenn shunt physiology. Future investigations will allow objective study of the impact of collateral flow on outcome.