svt in utero

What are the treatment guidelines for svt in utero?Heartrate 180 timess 45 minutes on monitor but 140 to 160 per auscultation at other times of day.34 weeks gestation.no cardiac structural anomalies-no edema.They will be monitoring the mother three times a week.What are they looking for?DO i assume that baby is handling high heartrate because there is no edema?Are the prenatal echocardiograms sophisticated enough to tell what type of svt?Should I be expecting them to give the mother medication to bring the heartrate down?Anything you can tell me about svt in utero would be appreciated.

[Jeffrey R Boris, M.D.]

Dear 8111953,

A heart rate of 180 may not necessarily be supraventricular tachycardia (SVT), actually.  Without seeing the baby's rhythm strips, I cannot say for sure if this is SVT or not.  However, a rate of 180 may be totally normal for your baby, especially since the normal heart rate range for a newborn is 80-200 beats per minute.  In the hands of experienced providers, fetal echocardiography can be quite accurate, and can even tell if the SVT is an atrioventricular re-entrant rhythm vs. atrial flutter.  At any rate, if a true diagnosis of SVT is given, then medications can be given to the mother which would then be passed on to the baby to prevent SVT from happening.  I do not know what kind of monitoring will be done, whether it will just be heart rate monitoring or ultrasound imaging.  The things that we see in untreated SVT in which the baby is not tolerating the arrhythmia can be decreased left ventricular function as well as hydrops, the findings of collections of edema around the heart, lungs, abdomen, or in the skin.