The relationship between signal-averaged electrocardiography parameters and late gadolinium enhancement in acute myocarditis: a pilot study

Background/Introduction Signal-Averaged Electrocardiography (SAECG) is a well-established non-invasive tool for detecting late potentials (LPs) and predicting arrhythmogenic risk in ischemic heart disease. However, its diagnostic and prognostic utility in the acute inflammatory phase of non-ischemic conditions, such as acute myocarditis, remains unclear. Cardiac Magnetic Resonance (CMR) is the gold standard for characterizing myocardial tissue, including the detection of necrotic and fibrotic scars via Late Gadolinium Enhancement (LGE). Understanding the electrophysiological correlates of these CMR findings in the acute setting could provide a widely accessible method for risk stratification. Purpose To investigate the relationship between late potentials detected by 40-250 Hz filtered SAECG and myocardial scar visualized by LGE on CMR in patients with acute myocarditis. Methods This prospective observational pilot study included 36 consecutive patients diagnosed with acute myocarditis. All patients underwent a high-resolution SAECG recording and a 1.5-T CMR examination. The cohort was divided into two groups based on the presence (n=23) or absence (n=13) of LGE on CMR. Standard time-domain SAECG parameters (fQRS, LAS40, and RMS40) were acquired using a 40-250 Hz high-pass filter. Following normality assessment, comparisons between the LGE-positive and LGE-negative groups were performed using the Student's t-test or Mann-Whitney U test as appropriate. Correlation analyses were performed to evaluate the relationship between continuous SAECG variables and LGE presence. Results The mean age of the cohort was 33.3 ± 10.5 years, and 26 patients (72.2%) were male. LGE was present in 23 patients (63.8%). Time-domain SAECG analysis revealed no statistically significant differences between the LGE-negative and LGE-positive groups regarding the fQRS duration (99.9 ± 12.4 ms vs. 98.8 ± 12.8 ms, p=0.80) and LAS40 (30.5 ± 9.0 ms vs. 28.7 ± 9.5 ms, p=0.59). Similarly, the RMS40 values did not show a significant difference between the cohorts (mean 55.7 µV vs. 49.0 µV, p>0.05). Overall SAECG positivity for late potentials was relatively low in the acute phase and did not significantly differ between the LGE-negative and LGE-positive groups (15.4% vs. 13.0%, p=1.00). Correlation analyses indicated no significant linear relationship between the quantitative SAECG parameters and the presence of LGE (p>0.05 for all). Conclusions In this pilot cohort of patients with acute myocarditis, the presence of LGE on CMR did not significantly correlate with abnormal SAECG parameters. While SAECG is an established tool for assessing dense fibrotic scar in ischemic heart disease, its utility in detecting the diffuse and edematous scar of acute myocarditis appears limited. Further large-scale studies are warranted to validate these preliminary findings.