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Bradycardia

Bradycardia is an abnormally slow heart rate, defined as under 60 beats per minute (BPM) in adults. Pathological bradycardia in pregnant women is rare. Some women who have physiological bradycardia may, in the second trimester, feel symptomatic as their blood pressure drops due to a reduction in systemic resistance; however, treatment is rarely required. Rarely, symptomatic bradycardia has been attributed to supine hypotensive syndrome of pregnancy, which is a result of compression of the inferior vena cava by the gravid uterus and responds to maternal changing of position. (Adamson, Nelson-Piercy, 2007) Bradycardia may also be caused by opioids (e.g. morphine, diamorphine, pethidine) administered during labour. Opioids reduce the heart rate by direct action on the cardiovascular centres in the medulla, by decreasing the activity of the sympathetic nervous system and by reducing anxiety. In labour this may contribute to a fall in blood pressure and reduction in placental perfusion. The subsequent depression of the fetal heart rate may be interpreted as fetal distress, prompting medical intervention. Some fetal bradycardia on administration of opioid analgesia by any route is normal, but a significant change in fetal heart rate is an indication of fetal compromise.

Resources

Dawn Adamson and Catherine Nelson-Piercy. (2007) Managing palpitations and arrhythmias during pregnancy. Heart 2007;93:1630-1636 http://heartrhythmuk.org.uk/files/file/Docs/Guidelines/Palpitations%20and%20Pregnancy%20EiH.pdf

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