Summary of fetal arrhythmias

Fetal heart rate (beats/minute)	Fetal heart rate pattern	Echocardiography findings	Likely diagnosis(es)
<80	Fixed	AV dissociation Atrial rate normal (110 to 160 beats/minute)	Complete heart block
100 to 160	Variable	1:1 conduction, normal AV interval	Sinus rhythm
50 to 180	Irregular Possibly abrupt drops in heart rate	1:1 conduction with early atrial signals Blocked atrial signals	Atrial or ventricular premature beats Blocked atrial beats Blocked atrial bigeminy Possibly "low grade" ectopic atrial tachycardia
180 to 220	Essentially normal Abrupt drops to normal	1:1 conduction Normal AV intervals	Persistent or permanent junctional reciprocating tachycardia (PJRT) type supraventricular tachycardia
180 to 200	Minimal variability Smooth increases	1:1 conduction Normal AV intervals	Sinus tachycardia
200 to 220	Fixed	2:1 atrial to ventricular conduction	Atrial flutter
>240	Fixed Episodic break to 100 to 160 beats/minute	1:1 conduction	Supraventricular tachycardia

AV: atrioventricular.

Courtesy of Mark Alexander, MD, and Jami Levine, MD.

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