Resolution of fetal second-degree atrioventricular block

Abstract

Fetal atrioventricular (AV) block is a rare and potentially devastating condition. Most commonly fetal AV block is mediated by maternal lupus antibodies which cause irreversible damage to the AV node. For many fetuses, the only potential intervention is premature delivery and highly invasive pacemaker implantation. However, there exists a small subset of fetuses with non-immune mediated AV block who appear to have far better outcomes, with potential for spontaneous resolution and a return to sinus rhythm. Despite this, it is not clear that prenatal counseling takes this fact into account. We describe a series of three patients with non-immune fetal second-degree AV block with spontaneous resolution prior to delivery, underscoring the need for appropriate prenatal counseling in this scenario.

Introduction

Atrioventricular (AV) heart block is the interruption of electrical impulses from the atria to the ventricles due to an anatomical or functional defect in the conduction system, leading to an uncoordinated contraction between the atria and ventricles [1]. In neonates, congenital heart block occurs in 1:20,000 births and is commonly associated (90–95%) with the transplacental passage of maternal lupus anti-Ro/SSA and/or anti-La/SSB antibodies [2,3]. Mechanistically, the deposition of immune complexes on the developing fetal heart leads to the disruption of normal cardiac electrical conduction, resulting in bradycardia and the possibility of severe cardiovascular compromise including hydrops and fetal demise [2].

However, in 1–5% of congenital AV block cases, fetuses present with similar ultrasound findings but no associated maternal lupus antibodies. In this small patient population, the treatment options are limited to pacemaker implantation to regulate heart rate, an option that an estimated 89% of patients eventually undergo if they survive to a viable gestational age [3]. The prenatal counseling of these families is complicated, as the perceived necessity of pacemaker implantation may suggest the necessity of premature delivery for this high-risk procedure. While most of these fetuses eventually undergo pacemaker implantation, there have been several reports of spontaneous resolution of congenital AV block, suggesting that pharmacological or surgical intervention might not always be necessary [4,5]. However, to our knowledge prenatal counseling regarding the potential spontaneous resolution of non-immune congenital AV block is not described in the literature. Here, we report three cases of spontaneous reversal of second degree AV block without medical intervention, which underscores the importance of such prenatal counseling.