EDAN F6 User Manual page 192

F Series Fetal & Maternal Monitor User Manual Limitations of Ultrasonic Monitoring
(3) Halving:
When the FHR increases to 180 bpm or higher, it is possible for the monitor to mistake the two
separate hearbeats for the diastole and systole of a single heartbeat. As a result, a heart rate trace
that is half the actual heart rate is produced. This often happens during tachycardia, representing
an abrupt switch of the trace to half the actual heart rate. The clinicians may interpret it as a
"deceleration".
However, the heart beat sound from the monitor speaker is still reliable even when doubling or
halving is occurring.
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