Chronotropic incompetence causes multiple organ complications in adults after the Fontan procedure

Abstract

Background: Although patients undergoing the Fontan procedure (FP) present a normal or close‑to‑‑normal function of the systemic ventricle, they cannot generate cardiac output or exhibit similar exercise capacity as their healthy peers. This can be attributed to chronotropic incompetence and multiple organ complications. Aims: We evaluated the prevalence of chronotropic incompetence in adults after FP and assessed the relationship between heart rate reserve (HRR) and multiple organ complications. Methods: Data were obtained from 50 post‑FP patients (mean [SD] age, 27 [6.6] years) and 30 healthy controls matched for age and sex. All patients were subjected to clinical examination, laboratory tests, echocardiography, cardiopulmonary exercise test, and chronotropic function evaluation. Results: Cardiopulmonary exercise test parameters were impaired in the post‑FP group. Chronotropic incompetence was identified in 46 patients (92%), who also had a lower median (interquartile range) chronotropic index (0.55 [0.47–0.62] vs 0.93 [0.88–0.99]; P < 0.001) and a greater median (interquartile range) HRR (32 [24–60] bpm vs 8 [1–14] bpm, P < 0.001). A negative correlation was observed between HRR and peak oxygen uptake, and a positive one between HRR and the peak ventilatory equivalent for CO2 and mean platelet volume. The study revealed the diagnostic utility of HRR in detecting an abnormal peak ventilatory equivalent for O2, alkaline phosphatase levels, the ratio of aspartate transaminase to alanine transaminase levels, and mean platelet volume. Conclusions: Chronotropic incompetence correlates with impaired exercise capacity, liver dysfunction, and platelet abnormalities in post‑FP patients. Heart rate reserve may be a promising indicator of organ complications as well as a sign of future bradyarrhythmia and the need for cardiac pacing.