The Fontan operation is the most utilized surgical palliation for a univentricular congenital heart disease, encompassing 0.08–0.4 per 1000 births [1,2]. Since the 1980s surgical modifications have improved outcomes to a 30-year survival rate of 80–90% following a completed Fontan operation [3]. However, the passive blood flow to the pulmonary system causes cardiac remodeling resulting in ventricular dysfunction with peripheral stasis and lymphatic congestion [[4], [5], [6]]. This pathophysiology results in associated co-morbidities including protein losing enteropathy (PLE), plastic bronchitis (PB), serious thromboembolic events and tachyarrhythmias [[7], [8], [9]]. These comorbidities have an associated 36-fold increase in risk of Fontan takedown, heart transplant, or death [10]. Currently there are limited tools to assess the signs of Fontan circulation failure through noninvasive methods.

Vectorcardiography (VCG) applies a mathematical transformation to parameters in a 12 lead ECG to represent 3-dimensional vector loops at the vertical, transversal, and sagittal planes of the cardiac electrical forces [11]. This methodology assesses the P, QRS and T wave maximum deflection of vectors during depolarization and repolarization at the atrial and ventricular level as denoted by vector magnitude (Pvm, QRSvm, Tvm). The spatial peak QRST angle (SPQRS-T angle) is the maximum difference between the QRSvm and Tvm. Increased SPQRS-T angle have been associated with sudden cardiac death, ventricular arrythmias, cardiovascular mortality and all-cause mortality [[12], [13], [14]]. Similarly, QRSvm at lower values indicates a scattering and slowly propagating electrical wave causing dispersion of depolarization vectors. Studies have shown reduced QRS vector magnitude as a good predictor of ventricular tachyarrhythmias and reduced left ventricular ejection fraction [[15], [16], [17]]. As described in Cortez et al. [19] the right-precordial directed measures including RPD angle, RtQRS, RtTvm and RtPvm can be utilized to better assess right ventricular dominant physiologies such as subtypes of the Fontan.

Our study focuses on characterizing normal VCG parameters within the Fontan population and investigating the associations between VCG parameters/trends with Fontan failure as noted by PLE, PB, NYHA class III-IV, Fontan takedown, cardiac transplant, and death.