Maternal conduction disorders and bradycardia during pregnancy

INTRODUCTION — Arrhythmias and conduction disorders are the most common cardiac complications encountered during pregnancy in women with and without structural heart disease [1-3]. They may manifest for the first time during pregnancy, and in other cases, pregnancy can trigger exacerbations in women with pre-existing arrhythmias [1,4-6]. Women with established arrhythmias or structural heart disease are at highest risk of developing arrhythmias during pregnancy. Due to surgical advances, there has been an increase in the number of women of childbearing age with congenital heart disease and this group of women is at particularly high risk for arrhythmias (figure 1) [1,2,7-11]. Because of these associations, any woman who presents with an arrhythmia should have a clinical work up (including an electrocardiogram and a transthoracic echocardiogram) for evidence of structural heart disease.

In general, the approach to the treatment of conduction disturbances and bradycardia in pregnant women is similar to that in the nonpregnant patient. Treatment strategies during pregnancy are hampered by the lack of randomized trials in this cohort of women. Choice of therapy, for the most part, is based on limited data from case reports, observational studies, and clinical experience.

The prevalence, clinical presentation, and management of conduction disorders and bradycardia during pregnancy will be reviewed here. Electrocardiographic characteristics of sinus bradycardia and conduction disorders are discussed in detail elsewhere. (See "ECG tutorial: Rhythms and arrhythmias of the sinus node" and "ECG tutorial: Atrioventricular block".)  

Issues relating to supraventricular and ventricular arrhythmias, as well as cardiac arrest during pregnancy, are discussed separately. (See "Sudden cardiac arrest and death in pregnancy" and "Supraventricular arrhythmias during pregnancy" and "Ventricular arrhythmias during pregnancy".)

PALPITATIONS — Palpitations occur frequently during pregnancy and are a common indication for cardiac evaluation during pregnancy. The differential diagnosis of palpitations is extensive and the diagnostic evaluation of pregnant women with palpitations does not differ from nonpregnant women. (See "Evaluation of palpitations in adults".)

In one study of 110 pregnant women with arrhythmia-related symptoms (palpitations: 87 percent; dizziness: 13 percent; syncope/presyncope: 6 percent) who were evaluated with 24-hour Holter ambulatory monitoring, bradycardia was identified as a cause only 1 percent of the time [12].

SINUS BRADYCARDIA — Sinus bradycardia is a rhythm in which fewer than the normal number of impulses arises from the sinoatrial (SA) node. The normal heart rate has been considered historically to range from 60 to 100 beats/min, with sinus bradycardia being defined as a sinus rhythm with a rate below 60 beats/min. Sinus bradycardia is not common during the antepartum period. Normally, there is a pregnancy-related physiologic increase in heart rate of 10 to 20 beats/min above baseline [13]. Mild sinus bradycardia may occur transiently after normal delivery and may persist for a few days in the postpartum period [13]. In the absence of structural heart disease, sinus bradycardia is seldom associated with symptoms and requires no intervention. (See "Sinus bradycardia".)

FIRST DEGREE AV BLOCK — First-degree atrioventricular (AV) block may be seen in women with structural heart disease such as rheumatic or congenital heart disease [13]. Transient first degree AV block may be seen in settings of increased vagal tone. It is not uncommon for sinus bradycardia with first degree AV block to occur in healthy individuals while sleeping. This is a physiologic rather than a pathologic condition. Transient AV block resulting from increased vagal tone would be expected to occur less frequently in pregnant women than nonpregnant women. The exact prevalence of first-degree AV block is unknown [13]. The site of AV delay is usually located in the atrioventricular node, above the bundle of His, and it rarely progresses to advanced heart block. (See "First-degree atrioventricular block".)

SECOND DEGREE AV BLOCK — Second-degree AV block is sometimes seen in pregnancy. Mobitz type I (Wenckebach) AV block is more commonly encountered and generally has a benign outcome [14-16]. Typical Mobitz Type I (Wenckebach) block occurs at the level of the atrioventricular node, and, like first degree AV block, it rarely progresses to more advanced heart block. Accordingly, a conservative clinical strategy of monitoring is appropriate.

Mobitz type II block (usually below the AV node) may precede the development of complete infra His AV block. It is uncommon during pregnancy. It is more likely to occur in women with structural heart disease. AV block at a level below the His bundle is usually associated with a very slow or absent ventricular escape rhythm, and therefore commonly results in hemodynamic compromise and/or syncope. Because of the risk of progression of Mobitz II block to complete infra His block, a permanent pacemaker is usually recommended even in an asymptomatic patient. (See "Second-degree atrioventricular block: Mobitz type I (Wenckebach block)" and "Second-degree atrioventricular block: Mobitz type II".)

COMPLETE HEART BLOCK — Complete heart block may be congenital or acquired. The prevalence of new onset of complete heart block during pregnancy is unknown, but is likely quite rare. There is no obvious association between pregnancy and new onset complete heart block [17], although some experts have suggested that the atrial stretch associated with pregnancy may provoke conduction disorders [18,19]. Newly acquired complete heart block is rarely first detected during pregnancy [13,18]. The development of complete heart block may be associated with prior cardiac surgery, congenital heart disease, acute myocardial infarction, cardiomyopathy, drug intoxication, metabolic disturbances, systemic lupus erythematosus, or acute infection [20-22]. Progressive conduction disturbances during pregnancy that resolve in the postpartum period have been reported [18].

Because placement of a pacemaker during pregnancy usually requires radiation exposure, women with complete heart block contemplating pregnancy should be evaluated by a cardiologist prior to becoming pregnant so a decision can be made regarding pacemaker implantation.

Clinical presentation — Many women with congenital complete heart block present before pregnancy, often in childhood [23]. Congenital heart block is sometimes identified in adulthood or, rarely, during pregnancy. Women may present with presyncope, syncope, or the heart block may be an incidental finding on an ECG. Typically, there is an escape rhythm with a narrow QRS complex. Many women with symptomatic congenital complete heart block will have a permanent pacemaker implanted before pregnancy. The role of prophylactic pacemaker implantation in asymptomatic women with congenital complete heart block to prevent sudden death is not known. There is an emerging body of evidence to suggest that pacemaker implantation should be carefully considered in the asymptomatic adult with congenital complete heart block, as it may prevent development of cardiomyopathy, mitral regurgitation, and lower the risk of ventricular arrhythmias.

In one study of pregnancy outcomes in women with congenital complete heart block (n = 32), 24 women without a pacemaker gave birth to 45 children [24]. Thirteen percent (3 of 24) of the pregnancies were complicated by syncope, and a pacemaker was implanted in two women. The eight women with a pacemaker before pregnancy had 14 uneventful pregnancies.

MANAGEMENT DURING PREGNANCY — There are no guidelines that address monitoring during pregnancy in women with conduction disorders.

Approach to monitoring — Women with first degree AV block should have an electrocardiogram (ECG) at the time of clinic visits. They do not require ambulatory ECG monitoring during pregnancy or telemetry at the time of labor and delivery.

In the asymptomatic patient, we perform an ambulatory ECG monitor to examine the extent of heart block and an exercise stress test to confirm robust AV nodal conduction with exercise.

Management of Mobitz type II and complete heart block with narrow QRS must be individualized. Management is dependent on the presence of structural heart disease and the symptom status of the patient. All women should have ECG at the time of clinic visits to assess any changes in conduction. Serial ambulatory ECG monitoring is useful to assess the burden of conduction disease. The frequency of ambulatory ECG monitoring is dependent on the symptom status of the women and the underlying cardiac condition. Women with syncope and high degree AV block should be admitted to hospital for monitoring and assessment for pacemaker implantation.

At the time of labor and delivery, women with Mobitz type II block or complete heart block should have continuous telemetry monitoring. Some women may develop postpartum bradycardia and therefore monitoring should continue in the immediate postpartum period while in hospital.

After hospital discharge, ambulatory ECG monitoring is recommended as some women with newly identified conduction block in pregnancy may have resolution of conduction block postpartum.

Pacemaker therapy — Pacemaker implantation is recommended for almost all patients with complete heart block who are symptomatic. For women with complete heart block first detected during pregnancy who have a stable narrow complex junctional escape rhythm, pacemaker implantation can be deferred until after delivery [24-28]. However, women with complete heart block who exhibit a slow wide QRS complex escape rhythm (suggestive of block below the His bundle) should undergo pacemaker implantation during pregnancy [28,29].

In women with a pacemaker who undergo cesarean delivery, the interference generated by monopolar surgical diathermy/electrocautery can be sufficient to temporarily inhibit pacemaker output, or may give rise to a temporary increase in pacing rate. Therefore, the pacemaker should be programmed to avoid inappropriate inhibition or high-rate pacing. All patients with permanent pacemakers should be on continuous cardiac monitoring during labor and following delivery.

Pacemaker implantation is recommended for all patients with complete heart block who are symptomatic, and also in patients with asymptomatic complete heart block below the bundle of His. Perhaps the only exception to these indications for pacemaker implantation is patients with congenital complete heart block who are completely asymptomatic and have a stable junctional escape rhythm. Because placement of a pacemaker during pregnancy requires radiation exposure, women with complete heart block contemplating pregnancy should be evaluated by a cardiologist prior to becoming pregnant so a decision can be made regarding pacemaker implantation.

Although rare, women with complete heart block who develop symptomatic bradycardia, including syncope and presyncope, may need to have a pacemaker implantation during pregnancy [18,30-33], but there is no consensus among experts on the best location for a pacemaker placement [29]. Radiation exposure due to the use of fluoroscopy during pacemaker implantation is the most frequent concern for pregnant women and clinicians. (See "Diagnostic imaging in pregnant and lactating patients".)

Fetal risks of anomalies, growth restriction, or abortions are not increased with radiation exposure of less than 50 mGy (5 rads) [34]. One study estimated that the average radiation dose to the fetus was <1 mGy during catheter ablation of supraventricular tachycardia (much longer fluoroscopy times compared with pacemaker implantation) [35].

Other precautions can be used to minimize radiation exposure. During fluoroscopy for pacemaker implantation, the uterus is positioned outside the field of view and therefore, the fetus is exposed to internal and external scattered radiation only. It may be possible to use a lead shield to protect the uterus from external scattered radiation; however, because the dose from external scattered radiation is minimal, the use of lead shielding is left to the discretion of the operator. Modifying the exposure time, number of films obtained, beam size, and imaging area can further reduce the amount of radiation exposure. If necessary, pacemaker implantation can be safely performed with minimal radiation exposure by a skilled operator in a cath lab with pulse fluoroscopy. Although some have advocated echocardiographic guidance during the first trimester, the amount of fluoroscopy received is sufficiently low, that it is our opinion that an echocardiographic guided approach should not be advised [30,31,33]. Three-dimensional (3D) electro-anatomic mapping systems can be used to implant permanent pacemakers without using fluoroscopy [36]. With an experienced implanting clinician and appropriate fluoroscopy equipment and shielding of the fetus, temporary and permanent pacemaker leads can be safely placed during all stages of pregnancy [37-39]. (See "Diagnostic imaging in pregnant and lactating patients".)

Prophylactic temporary pacing for labor — The Valsalva maneuver during labor can be associated with a vasovagal reaction, resulting in slowing of the heart rate and potentially syncope. Thus, some centers advocate prophylactic temporary transvenous pacing for labor and delivery in asymptomatic women [23,40,41]. Other centers do not prophylactically insert pacemakers in all women with complete heart block [18,42-44]. In one small case series of six asymptomatic, non-paced women with complete heart block, there was no significant change in heart rate before, during, or after labor and delivery [42]. Only one woman developed hypotension secondary to postpartum hemorrhage.

In general, the indications for temporary pacing during labor are identical to those for nonpregnant adults. In emergency situations, temporary transcutaneous pacing can be used. However, this is painful and generally poorly tolerated by patients. Transcutaneous pacing generally is used for a short period of time while a transvenous pacing is placed or the bradycardia resolves. (See "Temporary cardiac pacing".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)

●Basics topics (see "Patient education: Bradycardia (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Sinus bradycardia – This can occur transiently after normal delivery and may persist for a few days in the postpartum period. (See 'Sinus bradycardia' above.)

●Conduction disorders – These can be associated with structural heart disease such as rheumatic heart disease or ischemia heart disease. (See 'First degree AV block' above.)

●Complete heart block during pregnancy – This may be acquired or congenital.

Because placement of a pacemaker during pregnancy usually requires radiation exposure, women with complete heart block contemplating pregnancy should be evaluated by a cardiologist prior to becoming pregnant so a decision can be made regarding pacemaker implantation. (See 'Complete heart block' above.)

●Indications for pacing – In general, the indications for temporary and permanent pacing during pregnancy are similar to those in the general population. (See 'Complete heart block' above.)

●Safety of undergoing pregnancy in women with pacemakers – Pregnancies in women with pacemakers are safe. Women with pacemakers who undergo cesarean delivery may require pacemaker reprogramming to avoid interference caused by electrocautery. (See 'Pacemaker therapy' above.)

●Prophylactic temporary pacing for labor – There is no consensus with regard to prophylactic temporary pacing for labor in asymptomatic women with congenital complete heart block. (See 'Prophylactic temporary pacing for labor' above.)