P2.024: Evaluating the Association of QRS Duration and Fragmentation on Cardiac Magnetic Resonance, Catheterization, and Exercise Capacity Measurements in Patients Post Fontan Palliation

Background: Patients who undergo Fontan palliation often exhibit exercise intolerance and face heightened risk of premature morbidity and mortality due to cardiovascular risk. Electrocardiographic (EKG) parameters, specifically QRS complex fragmentation (QRS-f) and prolongation, have been explored in numerous cardiac conditions but with limited relevance in Fontan patients. This study seeks to gain understanding of the predictive significance of QRS-f and prolongation in correlation with CMR measurements, catheterization findings, and exercise capacity.

Methods: We performed a retrospective analysis of Fontan patients with a 12-lead EKG and CMR in close date proximity. Analysis included exercise stress test and/or catheterization studies where available. QRS prolongation was defined by age groups as ≥90 ms for ≤5 years, ≥100 ms for 6-15 years and ≥120 ms for ≥16 years. QRS-f was defined as either (1) normal QRSd for age with an additional R wave or notch in the nadir of the S wave in ≥2 contiguous leads excluding age appropriate RSR’ in V1 and V2, (2) prolonged QRSd for age with ≥3 R-waves/notches in the R/S complex in ≥2 contiguous leads, or (3) paced QRS with ≥3 R-waves/notches in the R/S complex. An independent sample t-test was performed analyzing QRS fragmentation and prolongation against CMR, catheterization and exercise stress-test measurements. Chi squared analysis was performed in assessing clinical characteristics and outcomes.

Results: The study included 132 patients (QRS-f: 55, QRS prolongation: 44, both QRS-f and prolongation: 6). Those with QRS prolongation were younger in age (P = 0.020). Patients with QRS-f found to have a higher systemic ventricle mass index (P = 0.036) compared to those without QRS-f. Those with QRS-prolongation had a significantly higher systemic ventricle end diastolic volume index (P = 0.001) and a higher systemic ventricle end systolic volume index (P = 0.005) on CMR. There was no significant difference in ascending aorta flow or ejection fraction. Catheterization showed higher systemic ventricle end-diastolic pressure (P = 0.049) with QRS-f and exercise stress testing showed greater peak VO2 (P = 0.039) without QRS-f. There was no difference in catheterization and exercise stress testing with QRS prolongation. QRS-f and prolongation were more common in right ventricle dominant patients (P = 0.044 and P = 0.003 respectively). There was no significant difference in outcomes assessing death, arrythmias, protein-losing enteropathy, or heart transplant for QRS-f and QRS prolongation.

Conclusion: This study suggests that QRS prolongation is associated with ventricular dilation while fragmentation is associated with increased diastolic filling pressures in Fontan physiology. However, a larger sample size may further assess if EKG parameters using QRS-f and QRS prolongation could lead to improved patient management, with EKG serving as a non-invasive, cost-effective, accessible tool for predicting outcomes and tailoring therapy.