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 underwen t either sham occlusions (n = 8) or repeated brief umbilical cord occlusion s (n = 12) continued until the onset of severe (<20 mm Hg) or sustained hyp otension. After 3 days of recovery, the fetal hearts were perfusion fixed. RESULTS: Repeated umbilical cord occlusions led to a severe metabolic acido sis (pH, 6.84 +/- 0.09; lactate concentration, 14.1 +/- 1.5 mmol/L) with in creasing hypotension during occlusions, which were terminated after 128 +/- 38 minutes. After the occlusions, the mean arterial pressure showed a dela yed fall, which resolved after 12 hours. Ultrastructural examination showed evidence of subendocardial injury, with dilatation of sarcoplasmic reticul um, margination and clumping of nuclear chromatin, and mitochondrial swelli ng. The most Severe morphologic changes, including electron-dense mitochond rial inclusions, were found in the fetuses with delayed recovery of the fet al 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 cardiovas cular compromise and the development of late decelerations.