Transient Fetal Atrioventricular Block: A Series of Four Cases and Approach to Management
Sandra D. Kikano, MD and Stacy A. S. Killen, MD, MSCI
Thomas P. Graham Division of Pediatric Cardiology Monroe Carell Jr Children’s Hospital at Vanderbilt University, Nashville, TN, USA.
Funding: none
Disclosures: none
Correspondence:
Stacy A. S. Killen, MD, MSCI
2220 Children’s Way, Suite 5230
Nashville, TN 37232-9119
Phone (615) 322-7447
Fax (615) 322-2210
E-mail: stacy.statemann@vumc.org
Abstract :
Fetal atrioventricular block (AVB) is a failure of conduction from atria to ventricles. Immune- and non-immune-mediated forms occur, especially in association with congenital heart disease. Second-degree (2°) AVB may be reversible with dexamethasone and IVIG in immune-mediated disease. However, once third-degree AVB develops, it is deemed irreversible with need for a pacemaker and risk for cardiomyopathy. Rarely, 2° AVB is a transient, benign phenomenon in the immature conduction system. Few case series of transient AVB have been reported, but a management approach has not been defined. We report four patients with self-resolving, non-immune fetal AVB and outline a management strategy.
Key Words: Fetal atrioventricular block, Fetal heart block, Fetal second-degree atrioventricular block, Long QT syndrome
Introduction :
Fetal atrioventricular block (AVB) is estimated to occur in ~ 1: 20,000 live births[1]. It occurs in immune- and non-immune-mediated forms[1-6]. Immune-mediated block develops from transplacental passage of maternal anti-Ro/SSA autoantibodies that, beginning in the second trimester, damage the fetal AV node[1]. Complete (third-degree) immune-mediated AVB is considered irreversible and has significant associated mortality (15-30%) and morbidity, with about two-thirds of infants requiring permanent pacing postnatally[2-4]. Non-immune AVB most often occurs in the setting of complex structural heart disease, such as left atrial isomerism (LAI) and congenitally-corrected transposition of the great arteries (ccTGA), in which discontinuity of the AV node and ventricular tissue causes complete heart block[5, 6].
There are a few case reports of non-immune-mediated fetal AVB without structural heart disease, with variable outcomes. Some reports describe hydrops or permanent pacing in most patients[7]. Other reports describe transient AVB without significant long-term complications[8-11]. We describe four patients, evaluated in the Vanderbilt University Medical Center fetal cardiology clinic from 2016-2020, with benign, self-resolving, non-immune-mediated, second-degree (2°) fetal AVB and outline a management approach.