Atrioventricular Block in Pregnancy: 15.8 Seconds of Asystole

Abstract

Atrioventricular (AV) block in pregnancy is infrequently encountered and there is little management guidance available. We present a case of a 24-year-old G3P1011 at 24 weeks' gestation who presented to the obstetrics and gynecology clinic complaining of palpitations, fatigue, and dyspnea on exertion. Cardiology workup including an electrocardiogram (ECG) and Holter monitor detected second-degree type II (Mobitz) AV block with the longest asystole event lasting 15.8 seconds. A St. Jude's dual-chamber pacemaker (Abbott Laboratories, Abbott Park, IL) was implanted immediately. Standard radiation precautions were taken with additional shielding for the fetus. The patient experienced significant improvement in her symptoms. The patient went into labor at 37 3/7 weeks. Due to non-reassuring fetal heart tones, a cesarean section was performed, and a healthy baby girl was born. The management of heart block in pregnancy can be divided into involving those who are symptomatic and those who are asymptomatic. Symptoms of heart block can include palpitations, fatigue, dyspnea, and/or syncope; the presence of these symptoms warrants the placement of a pacemaker, preferably during pre-pregnancy or during the first two trimesters, as high-grade heart block is associated with significant mortality. Those who are in their last trimester or postpartum should consider the use of a temporary pacemaker as heart block could be due to pregnancy-related cardiovascular changes. For women with heart block, labor and delivery could result in worsening of bradycardia due to uterine contractions displacing blood into the central circulation. Most women with heart block do well in labor and delivery and having a pacemaker is not necessarily an indication for a cesarean section.

Keywords: atrio-ventricular block; high degree av block; permanent pacemaker implantation (ppm); pregnancy and heart disease; second degree heart block.

Figure 1. In-office ECG showing premature ventricular complexes

ECG: electrocardiogram

Figure 2. Holter monitor detection of high-grade AV block type II (Mobitz). The lowest heart rate recorded was 22 bpm

AV: atrioventricular

Figure 3. Electrical conduction of the heart

Atrioventricular (AV) conduction provides the communication point between atria and ventricles, which eventually allows for myocardial ventricular contraction. AV block refers to a delay in the transmission of the electrical signal between the atria and ventricles. The location of the delay, which can include the AV node, bundle of His, and bundle branches, helps dictate the type of block and the outcomes of the delay. While first and second-degree type I Wenckebach tend to cause delay at the AV node, second-degree type II Mobitz and third-degree tend to be associated with delay below the AV node. The blue marker at the bundle of His along with the inferior Purkinje fibers denotes the possible locations of the AV block in our patient SA: sinoatrial