Heart beat but not respiration is the main driving force of the systemic venous return in the Fontan circulation

Figures

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  Figure 1. Real-time phase-contrast slice. Left: Coronal view showing the position of the real-time phase-contrast slice in axial orientation (green). Right: Image of the axial slice with the IVC contour (red).

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  Figure 2. Comparison of the physio-matrix in a healthy control subject (left) and a patient with Fontan circulation (right). The diagrams show how IVC flow depends on the respiratory and cardiac cycle. The color scheme emphasizes the changes of flow values: high flow values are indicated in red, whereas low values are indicated in blue.

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  Figure 3. Respiratory-to-cardiac amplitude ratio and retrograde flow. Left: Ratio of respiratory (Ar) and cardiac (Ac) systemic venous flow amplitudes was significantly different in normal controls (n = 11) versus Fontan patients (n = 14). Right: Retrograde flow fraction for patients in Fontan circulation as determined with three methods: simultaneous gating using the physio-matrix, ECG gating (C), and respiratory gating (R).

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  Figure 4. Correlation of the respiratory-to-cardiac-amplitude ratio with the fractional retrograde IVC flow (rho = 0.79, p < 0.01). Data is overlaid with a spline fit and a 95% confidence band.

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  Figure 5. Schematic drawing of the Fontan circulation as established in a patient with hypoplastic left heart syndrome. The right ventricle (RV) serves as the systemic ventricle that pumps blood through the aorta. The drawing shows the Fontan circulation in an anatomy where the IVC is guided through the right atrium by an intraatrial tunnel with fenestration. Systemic venous return from inferior (IVC) and superior (SVC) vena cava drains directly into the right (RPA) and left (LPA) pulmonary arteries without interconnection of a cardiac pump.

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  Figure 6. Illustration of the systematic error in measuring respiratory blood flow amplitudes when the respiratory cycle is divided into different numbers of respiratory phases. The determination was performed for a patient with Fontan circulation during 50 respiratory phases as repeated with gradually reduced numbers of phases. The error is indexed to a number of 50 phases. Using 40 phases underestimates respiratory amplitudes by ~one percent whereas the use of two phases introduces an error of ~60%.