CARDIAC DYSFUNCTION MARIA SERRANO, KERSTI LINASK, GANESH ACHARYA, JIZHEN CHEN, MINGDA HAN, JAMES HUHTA, University of South Florida, Pediatrics, St. Petersburg, Florida OBJECTIVE: Lithium exposure in early gestation is known to affect human cardiac development and cause structural cardiac malformations. Our aim was to evaluate the effect of early, one-time lithium exposure on mouse embryonic cardiovascular function using Doppler (echo). STUDY DESIGN: Thirteen time-dated pregnant mice (C57BL/6J) received an intraperitoneal injection of 100 ml of 6.5 mg/mL lithium chloride (Li) or 0.9% sodium chloride (C) on ED 6.75. On ED15.5 the mice were anesthetized with isoflurane and embryo echo was performed using color directed pulsed Doppler and the pulsatility index (PI) was calculated from blood velocity waveforms of the uterine artery (UtA), descending aorta (DAo), umbilical artery (UA), and ductus venosus (DV). From the inflow-outflow velocity waveforms the outflow velocity (OFV) and the cardiac cycle time intervals including isovolemic relaxation time (IRT) were measured and myocardial performance index (MPI) computed. Semilunar (SL) or atrioventricular (AV) valve regurgitation (VR) was noted. RESULTS: Thirty-six (36) Li and 29 C embryos were studied. Maternal HR was higher (499 vs 449 beats/min; p!0.0001) and the UtA PI (1.55 vs 2.33; p = 0.003) was lower in the Li vs. C. DAo PI (1.76 vs 1.39; p = 0.001) and UA PI (1.35 vs 1.14; p = 0.004) were higher in Li embryos. Cardiac velocities and DV PI were not significantly different between groups. None in the C group had VR, but 21/36 (58%) of the Li group had VR: semilunar VR in 17 (47%) and both AV and SL VR in 4 (11%). Four embryos that had SLVR also had an abnormal monophasic ventricular inflow. Subgroup analysis showed that Li with VR had higher UAPI vs C (1.36 vs 1.14; p = 0.041) and increased IRT% (18.4 vs 12.4; p = 0.021) and MPI (0.66 vs 0.49; p=0.020): without VR, OFV and IRT% were similar. CONCLUSION: Pulse Li exposure in early gestation raised placental resistance and increased afterload. SLVR occurred with Li exposure and embryos with VR showed evidence of impaired diastolic and preserved systolic function. Li affects the outflow and inflow valve function. *Supported by HL67306 to KKL.