Tachycardia
| Baseline FHR greater than 160 beats per min
(NICHD)
|
There are several causes of fetal tachycardia that
must be considered, including:
- Maternal fever
- Chorioamnionitis
- Fetal sepsis
- Drugs (Atropine, Vistaril, Phenothiazines, Beta-sympathomimetics)
- Fetal hypoxemia
- Tachyarrhythmias
- Fetal heart failure
- Severe fetal anemia, fetal hydrops
- Maternal hyperthyroidism
In general, tachycardia from any cause is related
to an increase in sympathetic tone and/or a diminishment of
parasympathetic tone. This means that one would normally expect an
overall decrease in variability in association with tachycardia.
Fetal tachycardia is occasionally seen
after a deceleration of the FHR, and in this instance is likely
indicative of hypoxemia. This may be due to an attempt by the fetus to
increase perfusion by increasing cardiac output or it may be due to
increased catecholamine activity from the adrenal medulla in response
to the stress of hypoxemia, when associated with a deceleration, and
the loss of vagal tone.
Because the mechanisms for tachycardia related to
hypoxemia are predisposed by some other signal hypoxic event, such as a
prolonged deceleration, then isolated tachycardia, without evidence of
periodic changes and in the presence of normal, though slightly
diminished variability, is almost always due to a cause other than
hypoxemia. Fever and/or chorioamnionitis are very common causes and
fetal tachycardia may persist up two hours after correction of maternal
fever.
See illustration below for an example of
tachycardia. Please click to enlarge.
 Tachycardia Video 1
Tachycardia Video 2
<< Late Deceleration
| Prolonged
Deceleration >>
|
