Minimum and Average Heart Rates in Pediatric Fontan Patients with Favorable Postoperative Outcomes: A Holter Monitoring Study.

Fontan palliation is associated with an increased risk for arrhythmias and sinus node dysfunction. Although annual Holter monitoring is recommended for routine surveillance, there is no normative Holter data for this population, with only one study describing such data in healthy children. To describe Holter data for patients with Fontan physiology, compare this data to healthy children, and establish a normative data set for those undergoing routine ambulatory ECG screening. This retrospective, single-center study analyzed 642 Holter monitors from 133 Fontan patients aged 5-21 years, collected between 1970 and 2023. Patients with pacemakers, significant atrioventricular valve regurgitation, or severely depressed ventricular function were excluded. Demographic and clinical data were collected, and HR values were compared to a healthy control cohort. The Fontan cohort was predominantly male (69%), with right ventricular dominance (59%) and extracardiac Fontan palliation (80%). Compared to 502 healthy controls, Fontan patients had significantly higher minimum HRs in adolescents (14-16 years), lower average HRs in younger age groups (4-12 years), and universally lower maximum HRs. Within the Fontan group, males and those on digoxin had lower minimum HRs, while heterotaxy was associated with higher minimum and average HRs. This is the first study to establish normative Holter HR data in pediatric Fontan patients and compare it to healthy counterparts. These findings suggest Fontan patients do not have significantly lower minimum heart rates and provide a valuable reference for clinical evaluation, supporting the need for larger, multicenter studies.