Objective: To evaluate the relationship of the PR interval and fetal heart rate during repetitive umbilical cord occlusions in immature sheep fetuses.
Study design: In seven chronically cannulated immature sheep fetuses [gestational age 90.6 days (mean)], we analyzed continuous fetal electrocardiogram recordings during repetitive cord occlusions for 2 out of every 5 min until fetal mean arterial pressure dropped to 50% of baseline value. PR interval-fetal heart rate correlation coefficients (Pearson) was measured on consecutive blocks of 2.5 min. R-values of the baseline and the repetitive occlusion period were compared by Fisher's exact test.
Results: Repetitive cord occlusions resulted in acidosis and hypotension. Two fetuses died at the end of the repetitive occlusion period. Four out of seven fetuses showed a significant change from a negative relationship between the PR interval and fetal heart rate during baseline to a predominantly positive relationship during the repetitive occlusion period.
Conclusion: In immature fetal sheep, a change from a negative relationship between the PR interval and fetal heart rate to a predominantly positive relationship between the PR interval and fetal heart rate was observed in four out of seven fetuses following the initiation of repetitive umbilical cord occlusions.