Atrioventricular block (AVB) is caused by the dysfunction of the cardiac electroconductive pathways and characterized by a prolongation of the PR interval on the electrocardiogram (ECG) [10]. According to the pattern and feature of the disruption of electrical activity, the blocks are classified in three categories: first degree, second degree (Mobitz type 1 or 2), and third-degree [10, 11]. The pathogenesis underlying the block could be an anatomical defect or functional impairment in the heart’s conduction system [11].
The high-grade heart block can cause palpitations, fatigue, dyspnea, and/or syncope, and associated with significant mortality [4]. Importantly, during the laboring process, bradycardia may get worse when uterine contractions displace blood into the central circulation. The serious cardiac and obstetric complications may occur and impact both mother and fetus. In the literature, only some case reports for pregnancy with AVB have been found, and there is no an established consensus guiding peripartum management for pregnant women with AVB [3,4,5,6,7,8]. It will be beneficial to study and share our experiences with these pregnant women.
Maternal cardiac complications
In general, with the increase in the degree of AVB, the complications and mortality of patients increased. Most pregnant patients with I° AVB were asymptomatic and did not have significant complications. While the treatment was not necessary for these patients, regular evaluation is essential because the risk of atrial fibrillation and development of higher degree AVB increases with the growth of gestational age [1]. In our study, no patient in this group needs the placement of a pacemaker.
Regarding II° AVB, the block may be temporary or permanent depending on the impairment of the conduction system and divided into two types (Mobitz type I and Mobitz type II). Patients with II° AVB may be asymptomatic or have symptoms like syncope and lightheadedness [1]. Of note, Mobitz type II block has the potential for progressing to a complete heart block, which may result in death if unrecognized. Previous study reported that a patient with type II of II° AVB identified at 24 gestational weeks. She had symptoms of palpitations and fatigue and experienced episodes of asystole, and the longest episode lasted for 15.8 s [12]. In our study, other mild arrhythmias were also frequently present in the patient with II° AVB type I AV block. But the severe arrhythmias including PVC and PVC + APB were observed in second-degree type II AV block. Therefore, patients with II° AVB type II have high risk for more unexpected complications, which may change and progress rapidly during pregnancy and lead to adverse maternal and neonatal outcomes.
The III° AVB indicates a complete loss of communication between the atria and the ventricles, so it’s also called complete heart block. Without appropriate conduction through the AV node, the SA node cannot control the heart rate, and cardiac output can diminish secondary to the loss of coordination between the atria and the ventricles. The condition can be fatal if not promptly treated. Most patients usually receive a temporary pacemaker and later replaced by a permanent one. Pacemaker can improve the survival rate of patients with III° AVB during pregnancy [1, 8]. In this study, except one patient who did not have a pacemaker because of emergency surgery, the remaining 32 patients with III° AVB received pacemaker implantation before delivery and did not have cardiac/obstetric complications or maternal death.
In the literature, several studies demonstrated that pregnancy in women with high-grade AVB was associated with high maternal and fetal mortalities, if pacemaker placement could not be achieved before delivery [8, 13, 14]. However, it has also been proposed that temporary or permanent pacemakers in asymptomatic women should be assessed on a case-by-case basis [6, 9]. One recent study found that stress tests to assess the change between the PR interval and heart rate could help to identify those higher-risk individuals and could be used as possible indication for the placement of a permanent pacemaker [15]. In our center, the patients complicated with heart disease have been managed conservatively by a multidisciplinary team. In the current study, permanent pacemakers have been placed in 6 patients with severe symptoms before pregnancy, and all of them maintained good cardiac function during pregnancy. The remaining patients have been closely monitored during pregnancy and received temporary pacemakers (except the above mentioned one) before delivery and removed after delivery. The good NYHA classification and the pacemaker placement may be relevant factors for maternal and neonatal outcomes. In addition, these extensive care and intervention might help the patients with high-grade AVB to achieve the similar overall outcome as in the patients with I° AVB.
Congenital atrioventricular block and fetal cardiac abnormalities
Atrioventricular block could be congenital or acquired post birth. Congenital AVB may be caused by cardiac malformations or damaged by maternal antibodies (autoimmune AVB). Family history of AVB is one of the risk factor for congenital AVB [16, 17]. During pregnancy of patients with autoimmune conditions, maternal autoantibodies can across the placenta and attack the atrioventricular (AV) node in susceptible fetuses. For example, anti-Ro/SS-A is one specific type of antinuclear auto antibodies, which have been found to be associated with fetal congenital heart disease (CHB) [16,17,18]. It has been reported that one woman with congenital heart disease and III° AVB gave birth to one child with CHB [19]. In our study, cardiac abnormalities were identified in 3 out of 76 fetuses (3.95%), which was slightly higher than among fetuses (3.23%) born by pregnant women with tetralogy of Fallot who our research group have studied previously [19]. Based on the close relationship between anti-Ro/SS-A antibodies and AVB and the family history, we were interested in studying the autoimmune antibodies in pregnant women with AVB. Unfortunately, auto antibodies are not routinely tested for pregnant women in our hospital, we could not retrieve the data to study anti-Ro/SS-A antibodies in pregnant women with AVB in the current study. It will be studied in our future research to test this assumption.
Obstetric complication
In our study, 28.4% patients showed obstetric complications, including premature labor, premature rupture of membranes (PROM), gestational diabetes mellitus (GDM), preeclampsia, placental adhesion, velamentous placenta, thrombocytopenia in pregnancy, proteinuria. The most common fetal complications were prematurity, oligohydramnios, SGA and fetal distress. No neonatal and maternal death was observed in the current study.
For pregnant women with AVB, in addition to obstetric conditions, the baseline cardiac function and the risk for exacerbation of cardiac function during delivery were also taken into the consideration. In the current study, while most patients (81.08%) with high NYHA-FC and/or high-grade AVB received caesarean section, 14 women (18.92%, including 2 patients with III° AVB) had successful vaginal delivery. Of note, all patients with II° AVB type II received cesarean section. Two of our patients with III° AVB who have received pacemaker showed good outcome for the vaginal delivery. Accordingly, the presence of a pacemaker in a patient may not necessarily be an indication for cesarean section [3]. The determination of delivery mode is not straightforward for pregnant women with AVB, evaluation from multidisciplinary team may be necessary to achieve the best benefit for both mother and neonate.
In summary, most women with AVB could achieve successful pregnancy and delivery. Patients with II° AVB type II and III° AVB should be monitored vigilantly during pregnancy and post-partum. Temporary pacing before delivery appeared to be beneficial for women with III° AVB. In the patients without pacing, especially those with II° AVB type II should be closely monitored with precautious plan for unexpected complications.