Past studies have not detected consistent improvement in ventricular function (VFxn) following initiation of cardiac resynchronization therapy (CRT) in Fontan patients. However, these studies used qualitative assessments of VFxn and/or quantitative assessments of VFxn that rely upon anatomic and/or geometric assumptions that may not be valid in patients with single ventricles. To address this, we used quantitative indices of global VFxn (dP/dt_ic and the Tei index) that are not encumbered by the limitations associated with the indices used in previous studies of CRT in Fontan patients.

Patients with Fontan physiology who had received CRT therapy from 2004 to 2019 were included in the study. They were compared to a concurrent group of Fontan patients who had received standard dual-chamber pacemakers (DCPMs).

VFxn was assessed at 3 time points: prior to, shortly after, and late after initiation of pacemaker therapy. Prior to initiation of pacemaker therapy, VFxn of the CRT patients tended to be worse than that of the DCPM patients. For both groups, VFxn appeared to be stable or slightly improved shortly after initiation of pacemaker therapy. In the CRT group, VFxn improved significantly between early and late follow-up. In contrast, VFxn in DCPM patients tended to decline during this period. Changes in VFxn correlated with concurrent changes in New York Heart Association classification.

Quantitative assessments of VFxn using indices not confounded by complex cardiac anatomy, segmental wall motions abnormalities, or inappropriate geometric assumptions revealed that CRT in Fontan patients is associated with preservation or improvement VFxn compared to standard DCPM. Changes in VFxn correlate with concurrent changes in New York Heart Association classification.