The effects of intrapartum hypoxia on the fetal QT interval

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Abstract

Background

The morphology of the fetal ECG complex provides information on the fetal condition during labour, such as the ST segment and T-wave configuration. We hypothesised that the intrapartum fetal QT interval may provide additional information on the condition of the fetus, as it is known that the QT interval reacts to situations of stress and exercise.

Design

Retrospective study.

Setting

Data were substracted from a European community multicentre trial.

Methods

The intrapartum QT interval was measured in 68 fetuses who were acidemic at birth (pH <7.05 and BD ecf >12 mmol/L) and in a control group of similar size. All of these cases were monitored by STAN S21. Measurements were performed at the start of the recording at baseline heart rate, during variable decelerations and at the end of the recording. The QTc was calculated using Bazett's formula: QT/√RR. The intervals were compared using the Wilcoxon signed ranks test.

Main outcome measures

Fetal QT interval, and the corrected QT interval: QTc.

Results

In the acidemic fetuses, there was a significant shortening of the QTc interval at the end of the recording compared with the start of the recording (397 ms at the end vs 359.3 ms at start; P < 0.001), in association with a significantly lowered heart rate (136.3 vs 110.9 bpm, P < 0.001). Measurements of QT and QTc during variable decelerations at the start and end of the recording also showed a shortening of the QT interval (301.9 vs 273.3 ms, P≤ 0.001) and QTc interval (381.6 vs 340.3, P < 0.001), and this was not dependent on heart rate. In the control cases, no differences in FHR, QT and QTc intervals were present.

Conclusions

In intrapartum hypoxia, resulting in metabolic acidosis, a significant shortening of the fetal QT and QTc is present, irrespective of changes in heart rate. In control cases, this shortening does not occur. The intrapartum fetal QT interval may therefore provide additional information on the condition of the fetus.

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