A study of the relationship between the electrocardiogram and hemodynamics in the fetal lamb during asphyxia.

Progressive changes in the S-T interval of the fetal ECG were studied in 22 lamb fetuses, acutely exteriorized and submitted to graded hypoxia. The ECG changes were studied in order to correlate them with cardiovascular function, as measured by heart rate, mean arterial pressure, end diastolic pressure and combined cardiac output, estimated by the thermodilution method, as well as with blood gases and acid-base status. Close correlations were obtained between PaO2, pH and base deficit and the severity of ECG changes, graded according to a scoring system. Alterations in the ECG pattern consistently preceeded signs of failing cardiovascular function. Our previous findings indicated that the hypoxic ECG changes could be regarded as a sign of myocardial glycolysis. Accordingly, similar progressive ECG changes could be induced by isoprenaline injections. It is concluded that progressive changes of the S-T interval of the fetal ECG contains information about fetal hypoxic stress before signs of failing cardiovascular function are seen.