Left Atrial Stiffness Identifies Children with Magnetic-Resonance-Imaging-Proven Acute Myocarditis Despite Preserved Left Ventricular Systolic Function

BackgroundLeft atrium (LA) may be labeled as a "forgotten" chamber in echocardiographic evaluation of pediatric myocarditis. Recently, LA stiffness has gained attention in identifying both diastolic dysfunction and myocardial injury in children. MethodsWe retrospectively analyzed 51 pediatric patients with acute myocarditis diagnosed by cardiac MRI based on updated Lake-Louise-Criteria, along with 40 age-matched healthy controls. Only patients with preserved LVEF (>55%) were included, given their increased risk of adverse outcomes due to diastolic impairment. Follow-up imaging was available for 41 of the 51 patients. LV systolic and diastolic function, and LA strain were evaluated by conventional 2D and speckle-tracking echocardiography. LA stiffness was calculated as the ratio of E/e to peak LA strain as depicted in following equation: O_FD O_INLINEFIG[Formula]C_INLINEFIGC_FD ResultsLA stiffness was significantly increased in myocarditis patients (0.27 {+/-} 0.09 vs. 0.15 {+/-} 0.04 %-1, p<0.001) and remained impaired at early follow-up. LA stiffness showed the best correlation with peak BNP (r = 0.66, p<0.001). Moreover, LA stiffness had the highest diagnostic performance among all echocardiographic indices, with an AUC of 0.94, and remained an independent diagnostic power in multivariable regression model (OR 1.58 [95% CI: 1.32 - 1.89], p<0.001). When it was incorporated into a composite score with LV peak longitudinal strain, the AUC yielded the highest with 98% sensitivity. ConclusionAn optimal LA stiffness cutoff of 0.2%-1 may provide incremental value as a new diagnostic marker for the diagnosis of acute myocarditis with preserved LVEF in children, when this value is exceeded. Clinical PerspectiveO_ST_ABSWhat Is New?C_ST_ABSO_LIWe evaluated the diagnostic utility of left atrial (LA) stiffness in pediatric patients with acute myocarditis and preserved left ventricular ejection fraction (LVEF), using both conventional and two-dimensional speckle-tracking echocardiography. C_LIO_LILA stiffness was significantly elevated alongside reduced peak LA strain in pediatric myocarditis patients confirmed by cardiac magnetic resonance imaging (CMR), even during early follow-up, reflecting persistent left ventricular diastolic dysfunction. C_LIO_LILA stiffness demonstrated the highest diagnostic accuracy in distinguishing patients with acute myocarditis from normal control, with an AUC of 0.94 (cutoff of 0.2%-1), and incorporating it with LV longitudinal strain enhanced the diagnostic performance. C_LI What Are The Clinical Implications?O_LILA strain analysis may play a pivotal role in helping clinicians identify diastolic dysfunction and detect pediatric patients with CMR-proven acute myocarditis, even with preserved LVEF, facilitating early diagnosis and support tailored management during follow-up. C_LI