Changes in the ST waveform of the fetal lamb electrocardiogram with hypoxemia

Am J Obstet Gynecol. 1982 Dec 15;144(8):950-8. doi: 10.1016/0002-9378(82)90190-9.

Abstract

The ST waveform of the fetal electrocardiogram (ECG) was examined in 10 chronically instrumented fetal lambs from 115 days to term. Averaged ST waveforms were plotted at 5-minute intervals in six fetuses for 2 to 22 days. No diurnal or other rhythms were seen. To correct for changes in signal gain the amplitude of the T wave was measured relative to the amplitude of the QRS complex. The T/QRS ratio was normally less than 0.30. Persistently elevated ST waveforms with a T/QRS range 0.32 to 0.65 preceded fetal death by some days in three fetuses and were associated with anemia and/or hypotension in a further three. In these animals hypoxia produced a further rise in the ST waveform (mean T/QRS, from 0.48 to 0.81) and all died during labor. In lambs with a normal ST waveform there were differences in the response to hypoxia over 1 hour for a similar fall in PO2. In eight experiments the ST segment and T wave increased (mean T/QRS, from 0.17 to 0.59) and promptly reverted to normal with normoxia. There was a significant rise in mean arterial blood pressure, plasma lactate, and glucose and a fall in pH. In four experiments there was little change (mean T/QRS, from 0.19 to 0.25), with a small rise in plasma lactate suggesting that these lambs were able to maintain aerobic myocardial metabolism. Overall there was a strong correlation of the T/QRS ratio to the rate of rise of lactate. These findings complement previous results in the acute fetal lamb preparation and suggest that ST waveform elevation expressed as the T/QRS ratio identifies a change to anerobic myocardial metabolism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Glucose / analysis
  • Blood Pressure
  • Electrocardiography*
  • Female
  • Fetal Heart / physiopathology*
  • Fetal Hypoxia / physiopathology*
  • Hydrogen-Ion Concentration
  • Hypotension / physiopathology
  • Lactates / blood
  • Pregnancy

Substances

  • Blood Glucose
  • Lactates