Noninvasive assessment of fetal metabolic acidemia by automated analysis of cardiac function using color tissue Doppler imaging in a sheep model.

Reliable noninvasive methods for accurately diagnosing fetal metabolic acidemia are still lacking. Our aim was to evaluate an ultrasound-based noninvasive method for assessing metabolic acidemia by an automated analysis of cardiac motion using color tissue Doppler imaging (cTDI) of the fetal heart in an experimental sheep model. Ten pregnant sheep and their fetuses were instrumented at 119-120 days gestation under general anesthesia. After a four-day recovery period, fetal arterial blood pressure, blood gases and heart rate were measured invasively. Cine-loops of cTDI images of the fetal heart were recorded at baseline and every 15 min for 3 h after uterine artery occlusion followed by epidural anesthesia and maternal hypo-oxygenation aiming to achieve a fetal arterial pH ≤  7.2 or base excess ≤ - 12 mmol/L or lactate > 4.8 mmol/L. The cTDI images were analyzed using an automated algorithm to measure myocardial velocities, cardiac cycle time intervals and atrioventricular plane displacement (AVPD). A Bayesian multivariate multilevel model was fitted to quantify associations between fetal cardiac function parameters and blood gas values. Data from eight fetuses were available for analyses. Among 21 predictors, left AVPD showed credible associations with fetal arterial pH, base excess and lactate and was the strongest and most robust single predictor with the association driven by within-fetus change over time rather than differences between animals. Left ventricular systolic peak velocity and right ventricular pre-ejection period showed similar but weaker associations, consistent with a shared myocardial mechanism rather than independent predictors. No other parameter showed credible associations with all three outcomes. Decreased left AVPD measured by automated analysis of cTDI cine-loops of the heart was associated with fetal acid-base status and may represent a candidate noninvasive marker of metabolic acidemia, warranting further validation.