Table 7.2.

In utero management of bradycardias

Diagnosis	Primary causes	In utero management	GOR/LOE	Comments
Sinus bradycardia	Ectopic atrial pacemaker	Rule out fetal distress as the cause of bradycardia	I/A	Can be seen in atrial isomerism
	Sinus node dysfunction (including immune mediated or infection)	Observation until bradycardia resolves	I/A	Test for anti-Ro/LA antibodies Maternal IgG/IgM for TORCH diseases and parvovirus
	Secondary causes: maternal medications, maternal hypothyroidism, fetal distress or fetal CNS abnormalities	Treat underlying cause of bradycardia	I/A
Blocked atrial bigeminy	Atrial extrasystoles	Observe / reduce maternal stimulants	I/A	10% risk of fetal SVT Weekly auscultation of fetal HR until arrhythmia resolves
AVB	Maternal anti-Ro/La antibodies	Observation	I/A	Structurally normal heart
		Dexamethasone for second-degree block or first-degree block with findings of cardiac inflammation	IIb/B	Endocardial fibroelastosis, associated valvular or myocardial dysfunctions
		For CAVB to prevent death or cardiomyopathy	IIb/B	4-8 mg/day
		IVIG (note: IVIG as prophylaxis is not recommended)	IIa/C
		Sympathomimetics for HR < 55 bpm or higher rates associated with fetal hydrops	Ib/C
	CAVB not related to antibodies	Observation	I/A	Associated with structural defects such as CTGA, left atrial isomerism
	CAVB related to channelopathies	Observation	I/A
		Avoid QT-prolonging drugs

AVB: atrioventricular block; CAVB: complete atrioventricular block; CNS: central nervous system; CTGA: corrected transposition of great arteries; GOR: grade of recommendation; HR: heart rate; IVIG: intravenous infusion of gammaglobulin; LOE: level of evidence; mg: milligrams; SVT: supraventricular tachycardia; TORCH: toxoplasma IgG, Rubella IgG, Cytomegalovirus IgG, and Herpes. Source: adapted from Donofrio et al.¹⁷