Junctional rhythm produces retrograde flow in the whole Fontan system: cardiac magnetic resonance–derived flow documentation—a case report

BACKGROUND: Arrhythmias after palliation of congenital malformations with functional monoventricle by different Fontan modifications are very common. Sinus node dysfunction and junctional rhythm are known to have a high prevalence and a detrimental impact on the optimal functioning of Fontan circulations. Maintaining sinus node function has high prognostic significance, and some cases have even been described where atrial pacing with restoring of atrioventricular synchrony was able to reverse protein-losing enteropathy with overt failure of the Fontan. CASE SUMMARY: A 12-year-old boy with a complex congenital malformation (double outlet right ventricle, transposition of the great arteries, pulmonary stenosis, and straddling atrioventricular valve) palliated through a modified Fontan (total cavopulmonary connection with a fenestrated extracardiac 18 mm Gore-Tex conduit) presented for cardiac magnetic resonance evaluation for mild asthenia and worsening of exercise tolerance. Flow profiles in all the regions of the Fontan (both caval veins and right and left pulmonary arteries) showed a small amount of retrograde flow; a four-chamber cine sequence clearly showed contraction of the atria against closed atrioventricular valve; this haemodynamic condition can be caused either by retro-conducted junctional rhythm (previously demonstrated in our patient) or by isorhythmic dissociation of sinus rhythm. DISCUSSION: Our finding directly demonstrates the profound impact of retro-conducted junctional rhythm on the haemodynamic of a Fontan circulation in which, with each cardiac beat, the pressure rise in the atria and pulmonary veins due to atrial contraction with closed atrioventricular valves is able to stop and invert the passive flow of the systemic venous return towards the lungs.