Determinants and clinical significance of flow via the fenestration in the Fontan pathway: a multimodality study.

Background: The use of a fenestration in the Fontan pathway remains controversial, partly because its hemodynamic effects and clinical consequences are insufficiently understood. The objective of this study was to quantify the magnitude of fenestration flow and to characterize its hemodynamic consequences after an intermediate interval after surgery.

Methods: Twenty three patients with a fenestrated extracardiac conduit prospectively underwent investigation by cardiac magnetic resonance (CMR), echocardiography, and invasive manometry under the same general anesthetic 12 ± 4 months after Fontan surgery. Fenestration flow was determined using phase contrast CMR by subtracting flow in the Fontan pathway above the fenestration from Fontan flow below the fenestration.

Results: Fenestration flow constituted a mean of 31 ± 12% (range 8-50%) of ventricular preload. It was associated with a lower Qp/Qs (r = -0.64, p=0.001) and oxygen saturation (r = -0.74, p<0.0001). Fenestration flow volume was correlated with pulmonary vascular resistance (r = 0.45, p = 0.04) and markers of ventricular diastolic function (early diastolic strain rate r = 0.57, p = 0.008 and ventricular untwist rate r = 0.54, p = 0.02). In 14 patients (61%) all of the net inferior vena cava flow and part of the superior vena cava flow were diverted into the systemic atrium and did not reach the lungs.

Conclusions: Fenestration flow can be measured accurately with CMR. In two-thirds of the patients not only all of the inferior vena cava flow, but also some of the superior vena cava flow is diverted through the fenestration. Fenestration flow is driven by a balance between pulmonary vascular resistance and early diastolic ventricular function.