Delayed hypotension and subendocardial injury after repeated umbilical cord occlusion in near-term fetal lambs.

Objective: This study was undertaken to determine whether myocardial injury occurs after repeated intrauterine asphyxia.
Study Design: Near-term fetal sheep with implanted instrumentation underwent either sham occlusions (n = 8) or repeated brief umbilical cord occlusions (n = 12) continued until the onset of severe (<20 mm Hg) or sustained hypotension. After 3 days of recovery, the fetal hearts were perfusion fixed.
Results: Repeated umbilical cord occlusions led to a severe metabolic acidosis (pH, 6.84 +/- 0.09; lactate concentration, 14.1 +/- 1.5 mmol/L) with increasing hypotension during occlusions, which were terminated after 128 +/- 38 minutes. After the occlusions, the mean arterial pressure showed a delayed fall, which resolved after 12 hours. Ultrastructural examination showed evidence of subendocardial injury, with dilatation of sarcoplasmic reticulum, margination and clumping of nuclear chromatin, and mitochondrial swelling. The most severe morphologic changes, including electron-dense mitochondrial inclusions, were found in the fetuses with delayed recovery of the fetal heart rate after the final occlusion.
Conclusion: Subendocardial injury occurs after severe repeated intrauterine asphyxia in the late-gestation fetus, and this may contribute to cardiovascular compromise and the development of late decelerations.