Influence of Natural Variability and Anatomical Misalignment on the Correlation Between Segmental Myocardial Edema and Strain in Acute Myocarditis

Background: Acute myocarditis (AM) affects myocardial structure and function, assessed by cardiac magnetic resonance late gadolinium enhancement (CMR-LGE) and speckle tracking echocardiography (STE), respectively; however, the correlation between the two techniques at the segmental level is inconsistent. We studied natural heterogeneity and anatomical orientation mismatch as potential causes of correlation discrepancy. Methods: A total of 30 AM patients underwent left ventricle LGE-CMR and STE measurement, acquiring 18 segmental values depicting edema extent and peak longitudinal strain, respectively. Baseline segmental correlation was compared to average patient segmental correlation and to segmental correlation after spatial resolution reduction achieved by averaging adjacent segments in four successive iterations, where the degree of spatial resolution reduction was evaluated based on the relative decrease in segmental standard deviation. Results: Baseline segmental correlation was weak, i.e., r = 0.24 (p < 0.05) but improved in fitted SLGE and SpLS baseline correlation (r₀ = 0.44, p < 0.05) and in average patient correlation (r = 0.55, p < 0.05). Iterative spatial resolution reduction increased the correlation to r₁ = 0.49 and r₂ = 0.51 and then decreased it to r₃ = 0.11 (p < 0.05) and r₄ = 0.07 (p > 0.05), with corresponding decreases in segmental standard deviation relative to baseline from σ₀ = 12.87 to σ/σ₀ = 0.68, 0.51, 0.38, and 0.29 in SLGE values and σ₀ = 4.77 to σ/σ₀ = 0.57, 0.41, 0.31, and 0.23 in SpLS. Conclusions: Improved correlation in average patients is associated with natural heterogeneity, which indicates a need to develop more robust indicators of ventricular function. The improved correlation in moderate spatial resolution reduction indicates a potential solution for anatomic orientation mismatch between CMR-LGE and STE techniques.