Alterations of the fetal ECG as an early indication of intra-uterine asphyxia

Abstract

During the study of the cerebral reactions of the fetal lamb to asphyxia the fetal ECG was found to react to asphyxia with elevation of the ST-segment and high and peaked T-waves. These alterations of the ECG occurred earlier than the typical changes in heart rate - bradycardia, dropped beats, A-V block. The ECG changes were well correlated to the cerebral reactions in terms of the somatosensory evoked EEG responses. To evaluate the relations between the ECG changes and hemodynamic variables ten experiments were conducted on mature lamb fetuses. In acutely exteriorized preparations ECG, arterial blood pressure, left ventricular pressure, myocardial contractility (dP/dt), heart rate and systemic blood flow (thermo-dilution) were measured and the fetus was subjected to varying degrees of hypoxia and hypercarbia. A close relation between the ECG changes and the total systemic blood flow and the myocardial contractility was obtained. Arterial blood pressure and heart rate deteriorated at a later stage and at more severe degrees of hypoxia than the ECG. It is concluded that the ECG pattern conveys information on hypoxia before typical effects of hypoxia on the heart rate appear in the fetal lamb.