Sequential atrioventricular activation plays a critical role in the
physiology of Fontan circulation. Although bradycardia is usually well
tolerated, retroconducted junctional rhythm may acutely increase atrial
pressure impairing cardiac output. Echocardiographic evaluation can
reveal clues of this hemodynamic condition. The clinical impact of
arrhythmic disturbance on the follow up of patients who had undergone
total cavo-pulmonary connection is well recognized but the role of
transient periods of retroconducted junctional rhythm on the immediate
post-operative course is less defined. We describe two cases of acute
Fontan circulatory failure due to postoperative retroconducted escaping
junctional rhythm despite an adequate heart rate and circadian
variation. The patients rapidly improved after atrial pacing, allowing
discharge with a minimal dose of diuretic.