Fontan physiology

Learning objectives

In a normal biventricular heart, the systemic and pulmonary circulations are in series and each circulation is supported by a ventricle
In patients with single-ventricle congenital heart disease, the two circulations are in parallel
These patients only survive because the systemic and pulmonary venous blood mix
The Fontan operation is a palliative procedure that places the two circulations in series
Selected patients should be in sinus rhythm, have a good ventricular function, and adequately sized pulmonary arteries

Contraindicated in the neonatal period due to high pulmonary vascular resistance
Staged approach to facilitate the progressive adaptation of the heart and lungs
- Stage 1: Systemic-pulmonary shunt
  - Placement of a restrictive synthetic conduit between a major systemic central vessel and a proximal pulmonary artery
  - Patients with hypoplastic left heart syndrome: Conduit placed between the right ventricle and the left pulmonary artery
- Stage 2: Superior cavopulmonary connection
  - Bidirectional Glenn shunt or hemi-Fontan procedure
  - Usually performed as soon as the pulmonary arteries have grown sufficiently to allow a low pulmonary vascular resistance (2-6 months)
  - Cardiopulmonary bypass and ligation of the previous systemic-pulmonary shunt
- Stage 3: Completion
  - Usually performed at 1-5 years of age
  - Blood in the inferior vena cava is directed into the pulmonary circuit via an extracardiac conduit or via an intra-atrial baffle

MAC, minimum alveolar concentration