Changes in the PR interval--fetal heart rate relationship of the electrocardiogram during fetal compromise in chronically instrumented sheep.

Objectives: The evaluation of the changes in the relationship of the PR interval and fetal heart rate during prolonged fetal compromise in sheep at levels of acidosis comparable to those seen during human fetal compromise and to see whether these changes are potentially of use in the detection of fetal distress.

Study Design: A retrospective analysis of continuous fetal electrocardiogram recordings during graded fetal hypoxemia in 20 chronically cannulated fetal sheep was performed. Baseline recordings during normoxemia were compared with recordings during hypoxemia by use of Fisher's exact test and the Student t test.

Results: Sixteen of the 20 cases could be used for final analysis. Twelve showed a statistically significant change from a predominantly negative relationship between the PR interval and the fetal heart rate during normoxemia to a predominantly positive relationship during hypoxemia. Two cases showed an obvious trend in the same direction, which was statistically not significant. In two other cases no change in the relationship was observed.

Conclusion: A changing relation between the PR interval and the fetal heart rate is of potential use in the detection of fetal compromise.