The T/QRS ratio of the electrocardiogram does not reliably reflect well-being in fetal lambs

OBJECTIVE: Our purpose was to determine the diagnostic power of the T/QRS ratio of the electrocardiogram to predict fetal well-being. STUDY DESIGN: In 47 fetal lambs (3 to 5 days after surgery, gestational age 123.5 ± 0.3 days) asphyxia was induced by restriction of uterine perfusion. Fetuses were either pretreated with an adenosine transport inhibitor (n = 16) or a calcium channel blocker (n = 12) or served as controls (n = 19). Arterial oxygen content ≥ 1.5 mmol/L or pH ≥ 7.15 were chosen as limits for fetal well-being. RESULTS: Arterial oxygen content was reduced from 3.3 (= 1.0) to 1.3 (± 0.5) mmol/L, and pH decreased to 7.03 (± 0.10). Mortality was 53%. Both drugs did not affect well-being, survival, or the T/QRS ratio. Maximum T/QRS ratios were reached at the peak of asphyxia. Sensitivity and specificity of the T/QRS ratio were 24.0% and 42.6% to predict hypoxemia and 25.1% and 45.3% to predict acidemia. Pearson correlation coefficients for T/QRS ratio versus oxygen content and pH were 0.169 and 0.192, respectively. CONCLUSIONS: (1) In fetal lambs the T/QRS ratio failed to predict hypoxemia or acidemia. (2) Fetal survival was not correlated with the height of the T/QRS ratio during or after asphyxia.