Providing a framework of principles for conceptualising the Fontan circulation

Figures

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  Figure 1. Flow/pressure/saturation diagram of Fontan circulation: critical bottleneck. Schematic representation of a modern Fontan circuit: the caval veins are directly connected to the pulmonary arteries; systemic venous pressures are markedly elevated. The Fontan portal complex (see text) demonstrated by black rectangle. A fenestration is an efficient bypass as it relieves venous congestion and low flow. The critical bottleneck is therefore pinpointed: it has to be between the beginning and the end of the bypass. Ao, aorta; CV, caval veins; F, fenestration; LA, left atrium; PA, pulmonary artery; V, single ventricle. Line thickness reflects output, height reflects pressure and colour reflects oxygen saturation

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  Figure 2. Critical Bottleneck in circuit. Pathway where the flow has to go from left to right (black arrow). * Indicates the critical bottleneck. Bypass A will relieve flow obstruction, while B will have no effect on flow distal to the bottleneck. See the text for details

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  Figure 3. Flow/pressure/saturation diagram of a normal circulation: critical bottleneck in various disease conditions. Schematic representation of normal circulation: localisation of critical bottleneck in various diseases. A: Cardiomyopathy (CMP); B: Primary pulmonary hypertension PPHT; and C: Mitral stenosis (MS). See text for details. Ao, aorta; CV, caval veins; LA, left atrium; PA, pulmonary artery; LV, left ventricle; RA, right atrium; RV, right ventricle

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  Figure 4. Flow/pressure/saturation diagram of the Fontan circulation: changes over time. Fontan haemodynamics late (full colour) superimposed on Fontan early (transparent): with time the ventricular end‐diastolic pressure and pulmonary vascular resistance increase, resulting in overall decreased flow and increased caval vein pressure/congestion. A downward progressive spiral ensues. Ao, aorta; CV, caval veins; LA, left atrium; PA, pulmonary artery; V, single ventricle

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  Figure 5. Change of restriction by the bottlenecks in the Fontan circuit: circulatory failure with ‘preserved’ ventricular function. Normal flow at rest in normal human and minimal output to remain functional is indicated by the orange lines. The restriction of the two dominant bottlenecks in the Fontan circuit is depicted: (a) the Fontan portal complex FPC (blue) and (b) the ventricle (red). Height of the bottleneck reflects its restriction: the lower the more restrictive. Flow through the circuit will be determined by the most restrictive bottleneck. Early on, the ventricle is able to pump more flow than provided by venous return. Immediately after establishment of a Fontan circuit, the FPC is the most restrictive and thereby becomes the main controller of flow and congestion. Ventricular function is not restrictive (good cardiac reserve and extra‐cardiac operation) at the start, but may gradually decrease for various reasons. Over time, restriction related to FPC increases resulting in decreasing cardiac output; the FPC remains the most important determinant of cardiac output. Once flow reaches below a critical minimal, the circulation fails and demise ensues

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  Figure 6. Change of restriction by the bottlenecks in the Fontan circuit: acute ventricular dysfunction. Acute changes of the ventricle such as severe bradycardia or tachycardia, ventricular dysfunction or acute excessive afterload may shift the critical bottleneck towards the ventricle. Such an episode will severely compromise the patient and may kill him if the ensuing rise of ventricular filling pressure reaches the level of systemic venous pressure. Treating the underlying ventricular problem may re‐shift the bottleneck and restore the prior output

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  Figure 7. Change of restriction by the bottlenecks in the Fontan circuit: accelerated progressive ventricular dysfunction with interlocked bottlenecks (circulatory failure with poor ventricular function). Accelerated ventricular dysfunction may result in convergence of the two lines; the bottlenecks may become interlocked. Treatment of one and neglecting the other will inevitably lead to treatment failure. Once the two lines become interlocked, a vicious negative spiral ensues