Impact of Atrioventricular Conduction Time and Heart Rate on Fetal Left Ventricular Function Quantification—The Role of 2D Speckle‐Tracking Echocardiography

BACKGROUND: Each myocardial function parameter has limitations. The myocardial performance index (MPI) relies solely on cardiac time intervals and appears optimal. However, its accuracy may be compromised in fetuses with prolonged atrioventricular (AV) conduction time and variable fetal heart rate (FHR). We evaluated whether ejection fraction (EF) and fractional area change (FAC), assessed by two-dimensional speckle-tracking echocardiography (2D-STE), are less influenced by AV conduction time and FHR than MPI. METHODS: We studied 468 fetuses without structural, hemodynamic, or major vessel abnormalities. Fetuses with AV time >90th percentile for the corresponding trimester comprised the study group. MPI and its components, AV time, and FHR were measured using simultaneous left ventricular (LV) inflow and outflow pulsed-wave Doppler (PWD) recordings. LV EF and FAC were assessed via 2D-STE. RESULTS: AV time correlated strongly with isovolumic contraction time (ICT) in both the second (r = 0.73, p < 0.001, after Bonferroni correction) and third trimesters (r = 0.63, p < 0.001). AV time showed moderate correlation with MPI in both trimesters (second: r = 0.41; third: r = 0.34; p < 0.001). MPI increased significantly with prolonged AV time. EF and FAC remained robust and independent regardless of AV time or FHR changes. A significant negative correlation between FHR and ejection time (ET) was observed in both trimesters (second: r = -0.56; third: r = -0.60; both p < 0.001). Logistic regression identified MPI as the sole parameter discriminating between groups (AUC >0.7), whereas EF and FAC showed no discrimination (AUC ≈0.5). CONCLUSIONS: This study demonstrated that the LV MPI showed a significant dependence on AV conduction time. In contrast, LV EF and FAC, calculated using 2D-STE, remained robust and independent of variations in AV conduction time and FHR in healthy fetuses.