Syncope in Pregnancy: Case Report and Review of the Literature

Case Report

A 28-year-old pregnant woman (35 weeks pregnant; gravida four, para two, abortus two) was referred by a neurologist to rule out cardiac syncope. Initial neurologic examination and imaging were negative. Her past medical history is remarkable for a six-year history of recurrent syncope occurring up to ten times per day prior to pregnancy. Her history is also remarkable for a prior pregnancy complicated by fetal bradycardia and requiring a Cesarean section delivery. Since pregnancy, the patient has presented with more frequent syncopal episodes, occurring up to 15 times per day. Her symptoms occur while standing or sitting, and occasionally are preceded by lightheadedness, dizziness, and nausea. The patient had a normal electrocardiogram and echocardiogram.  

A passive tilt table test was performed at 70 degrees, and demonstrated a drop in blood pressure from a baseline of 119/84 mmHg with a heart rate of 106 beats per minute to a systolic blood pressure of 70 mmHg with a heart rate of 56 bpm while standing for 24 minutes (Figure 1). One week following the tilt table test, the patient presented with recurrent syncope and was sent to the emergency room for admission and monitoring on telemetry. No episodes of syncope or heart block were observed overnight, and an implantable loop recorder (ILR; Reveal LINQ^™ Insertable Cardiac Monitor, Medtronic, Inc.) was implanted prior to discharge. One week following the implant, she returned to the office with complaints of recurrent syncope, and the ILR demonstrated sinus tachycardia (Figure 2). 

Discussion

Syncope during pregnancy presents an inherent risk to both the mother and her unborn child. The most common causes of syncope are due to vasovagal syncope, orthostatic hypotension, neurologic causes, and cardiac arrhythmias. The last cause is the most serious, but is also easily treated. A thorough electrophysiological workup is not possible, since exposure to radiation is a typical component of the electrophysiology study and may expose the fetus to potentially dangerous radiation. That being said, it is possible to shield the fetus with radiation protective drapes and/or perform the procedure by nonfluoroscopic means (such as those employed by St. Jude Medical’s EnSite^™ Velocity^™ System or Biosense Webster’s Carto^® 3 System).¹ 

Arrhythmias of all types that present in pregnancy provide a challenge to the doctor and patient. Antiarrhythmic drugs such as propafenone and flecainide are classified by the U.S. Food and Drug Administration as category C.² This drug classification is normally a nonissue, the caveat being that category C medications cross the placental barrier. Thus, consumption of these drugs may potentially lead to negative consequences for the developing fetus.³ For pregnant patients with supraventricular tachycardias, avoiding most medications and invasive cardiologic procedures are a priority. Previously, one of our authors (TC) was part of a team that described an accessory pathway ablation during pregnancy in a patient who was refractory to other means.³ Ventricular tachycardias, with their more frequent hemodynamic consequences, can provide an even more challenging scenario during pregnancy. The authors (TC/AM) have also treated a number of patients during pregnancy with a history of ventricular tachycardia and an implantable defibrillator. The presence of a defibrillator does not preclude a successful delivery. 

Syncope occurring in an otherwise healthy pregnant patient may be related to the physiological changes that occur during pregnancy. The fetal mass itself and the changes in maternal circulation all may contribute to an exaggerated vasovagal response. The fetal mass can compress the inferior vena cava and prevent venous return into the central circulation.⁴ This postural collapse of the inferior vena cava has previously been described late in pregnancy and correlated with sinus arrest and neurocardiogenic syncope.⁴ Unlike this earlier case, our case exhibited no significant sinus node slowing, but instead exhibited second-degree atrioventricular block. The mechanism was presumably a heightened vagal response, which resulted from the myocardium’s detection of the absence of venous return and a compensatory increase in contractility with subsequent activation of mechanoreceptor C-fibers (located in the left ventricle). Hypotension and bradycardia correlated with 2:1 heart block (Figure 1). Typically, this type of heart block, when vagally mediated, is preceded by sinus node slowing and an increase in the PR interval. In this case, there was a slight increase in the PR interval prior to the heart block, but this finding, along with sinus node slowing, was not very evident. Table 1 lists the common causes of heart block during pregnancy. The presence of an abnormal cardiac substrate not only predisposes to heart block but to other arrhythmogenic causes of syncope (i.e., ventricular and supraventricular tachycardias). 

This patient experienced recurrent syncope even before her recent pregnancy. There is a probable association between the mechanism of syncope and the occurrence of heart block during the tilt table test. The additional data gathered from ILR monitoring, and the lack of heart block during syncopal episodes recorded by the ILR, demonstrates that heart block is not a prerequisite for syncope in this patient. The normal cardiac substrate, as defined by echocardiogram and electrocardiogram, effectively rules out the vast majority of cardiac abnormalities seen in Table 1. Therefore, in all likelihood, the mechanism of syncope in this patient was neurocardiogenic in nature and, more precisely, vagally mediated. 

Disclosures: The authors have no conflicts of interest to report regarding the content herein.   

References 

1. Bigelow AM, Crane SS, Khoury FR, Clark JM. Catheter ablation of supraventricular tachycardia without fluoroscopy during pregnancy. Obstet Gynecol. 2015 Mar 13. [Epub ahead of print]. 
2. Leiria TL, Martins Pires L, Lapa Kruse M, Glotz de Lima G. Supraventricular tachycardia and syncope during pregnancy: a case for catheter ablation without fluoroscopy. Rev Port Cardiol. 2014;33(12):805.e1-5.
3. Lesh MD, Van Hare GF, Schamp DJ, et al. Curative percutaneous catheter ablation using radiofrequency energy for accessory pathways in all locations: results in 100 consecutive patients. J Am Coll Cardiol. 1992;19(6):1303-1309.
4. Huang MH, Roeske WR, Hu H, Indik JH, Marcus FI. Postural position and neurocardiogenic syncope in late pregnancy. Am J Cardiol. 2003;92(10):1252-1253. PubMed PMID: 14609615. 
5. Tietge W, Daniëls M. A case of an acquired high-degree AV block in a pregnant woman. Neth Heart J. 2008;16:419-421.