Diagnosis
- by echocardiography: function and morphology of the systemic ventricle, AV valves and semilunar valves. Connection of the pulmonary and systemic veins, PFO, pulmonary arteries and aortic arch.
- by heart catheterization: UCLA criteria and evaluation of the surgical risk
Variable: surgical risk: slight/moderate/high:
= MPAP ? <12 / 13 – 15 / >15mmHg
= Transpulmonary gradient <7 / <15 / >15mmHg
= PVR <2 / 2-3 /> 3 Wood/m²
= EF > 45% / EF < 45%
= EDP <10 / 10- 15 / >15 mmHg
Evaluation:
- Pulmonary artery vessel bed developed? Desirable parameters are a total lower lobe index >120±30mm²/m², transpulmonary gradient [TPG] = PA pressure diastolic – LA mean < 12mmHg, with EDP <12mmHg; PVR < 4 Wood units.
- Hemodynamics: patients with low enddiastolic chamber pressures who have good oxygen saturation (75-85%) will tolerate the Fontan circulation well, even with borderline PA size.
- Aortic arch: morphology/pressure gradients across the aortic arch --> if necessary intervention with or without stent implantation.
Operation
In the bidirectional Glenn operation the heart-lung machine is used in normothermia and with the heart beating. The inferior caval vein with the hepatic veins is detached from the right atrium. The stump on the atrial side is closed with sutures and then by means of a GORE-TEX® patch a connection is created between the inferior caval vein and the lower aspect of the central pulmonary arteries. So that the change in circulation is better tolerated, a small window is often created between the prosthesis and the atrium. Extracardiac or intracardiac conduit: if the Fontan operation is preceded by a Glenn operation the next step can only be an extracardiac Fontan operation. This means that all the venous blood from the body circulation reaches the lung, bypassing the heart, which in effect means a division of the circulation. The single ventricle must now only accomplish the transport of the oxygenated blood from the lung to the body. If a hemi-Fontan operation (see Glenn operation) was performed, the only possible next step is an intracardiac Fontan operation. Here a dividing wall (GORE-TEX®) is created in the right atrium to take the blood from the inferior caval vein to the right pulmonary artery. The dividing wall left between the atrium and the superior caval vein during the hemi-Fontan operation must be removed at this stage.
At the DHZB the extracardiac conduit is favored. Comparative studies have not yet produced conclusive results but we consider the extracardiac conduit to have the theoretical advantage of reducing the incidence of rhythm disturbances by avoiding sutures and scarring in the atrium.
