QRS changes in direct fetal electrocardiogram during uterine overstimulation; report of four cases.

Four cases are presented in which increased QRS complex voltages or deviation of the mean electrical axis were observed in the fetus by direct fetal electrocardiogram (ECG) during delivery under anaesthesia. There was transformation of the initial QRS aspect before delivery. These changes were only observed when large doses of oxytocin (20 IU in 500 ml) were used after Pentothal administration in deliveries in which other fetal ECG alterations (bradycardia, ST changes, T inversion) and/or low pH values had been observed. In case 1 there were ST level changes, inversion of the T wave and transformation of the QRS complex from RS to Rs. Case 2 showed a change from RS to QR type complex associated with repolarization defects. In cases 3 and 4, ST level changes, inversion and increased QRS complex voltages were observed. We checked that the modifications observed were not due to changes in position of the fetus during recording. It is thought that the acute redistribution of the fetal blood volume due to oxytocin overstimulation in fetal hearts with hypoxic signs may lead to compensatory mechanisms such as tachycardia, increased contractile activity (higher QRS) and functional predominance of one side of the fetal heart (deviation of the electrical axis) subjected to sudden load.