Cover Story

A Case of Unexpected Bradycardia

Alexander S. Asser, MD, FHRS, FACC; Director, Arrhythmia Services; Adventist HealthCare Shady Grove Medical Center; Rockville, Maryland

Alexander S. Asser, MD, FHRS, FACC; Director, Arrhythmia Services; Adventist HealthCare Shady Grove Medical Center; Rockville, Maryland

An incidental finding of adult bradycardia is often overlooked in the hospital setting, as it may be attributed to increased vagal tone, medications, or electrolyte abnormalities. However, further workup may also lead to unexpected findings, as in this case of a rare initial diagnosis of congenital heart disease in a young adult.  

Case Presentation

A 22-year-old African American woman without known past medical history presented to our emergency room complaining of intermittent back and chest pain after being involved as a passenger in a motor vehicle accident 2 weeks prior. She was without other acute complaints. A routine EKG was performed (Figure 1). 

The EKG revealed a junctional bradycardia of unknown cause, and consultation was requested. The patient denied prior knowledge of the bradycardia, and did not remember ever having an EKG performed.

She reported poor exercise tolerance for most of her life. She related that her inability to exercise made it challenging to play sports even as a child. No recent illness, fevers, or rashes were noted. There was no prior syncope or dizziness. Her family history was unremarkable, without history of lung disease or cardiac disease. Her physical exam was unremarkable except for bradycardia and mild obesity. Leg lifts performed in her ER bed did not significantly increase heart rate. Lab tests, including TSH, Lyme panel, CRP, and ESR, were all within normal range. An exercise treadmill stress test was performed. Exercise performance was poor with the test terminating in Stage 2 of the Bruce protocol, only achieving 5.1 METS and a maximum heart rate of 119 bpm, and remaining in a junctional rhythm throughout (Figures 2 and 3). Echocardiogram revealed a mildly dilated left ventricle with an ejection fraction (EF) of 50-55%, trace aortic insufficiency, mild pulmonic insufficiency, and mild biatrial dilation. 

She was discharged and followed up 2 weeks later accompanied by her mother. Repeat EKG again revealed a junctional bradycardia at 40 bpm. Her mother recalled that there was difficulty identifying the fetal heartbeat during prenatal visits, but that no ultrasound was performed given normal fetal growth. The mother had no illnesses during pregnancy, and delivery was unremarkable. She recalled that her daughter always had difficulty keeping up with her brothers. A diagnosis of symptomatic sinus node dysfunction was made, but the etiology remained unclear. 

It was decided to perform a cardiac MRI to evaluate for a possible infiltrative process or other congenital abnormalities. The cardiac MRI revealed heterotaxy syndrome with left atrial isomerism and situs ambiguus. She was noted to have right-sided polysplenia, a right-sided stomach, a right-sided liver, and an interrupted inferior vena cava with a dilated azygous vein. The left ventricle was mildly dilated with an EF of 58%. The interatrial and interventricular septums were intact without evidence of shunting. There was biatrial dilation. There was no evidence for an infiltrative process (Figures 4-8).

After a lengthy discussion with the patient and her mother in follow-up, she underwent a routine dual-chamber permanent pacemaker implantation; the azygos vein was prominent, but the procedure was otherwise performed without difficulty. 

In subsequent follow-up appointments, she was noted to have a significant improvement in her functional capacity with the assistance of rate response mode. She is predominantly atrial paced with no evidence for AV block (Figure 9). Her pacemaker was initially set to DDDR 60 bpm. She did exhibit rare episodes of paroxysmal atrial fibrillation that have remained quiescent after her base rate was increased to 70 bpm. She has remained predominantly atrial paced 89% of the time (Figure 10).  


Left atrial isomerism is one of the heterotaxy syndromes characterized by failure of many right-left differentiations of the thoracic and abdominal organs. Situs solitus refers to the common arrangement of organs, while situs inversus refers to a mirror-image arrangement. Any arrangement other than those 2 are termed situs ambiguus. Historically, splenic descriptions were used to characterize these conditions, but as cardiac malformations are common, the terms right and left atrial isomerism have been become the preferred method for classification.1 

As this patient demonstrated, left atrial isomerism results in 2 morphologic left atriums and appendages. Patients frequently are without a sinoatrial node, resulting in significant bradycardia. Some patients may also have congenital heart block. In one study of congenital complete heart block, 34% of patients were discovered to have left atrial isomerism as the etiology.2 As a result, permanent pacing is frequently required in these patients. Other more complex cardiac defects may be present. These include a common atrium, single hypoplastic ventricle, septal defects, double-outlet right or left ventricle, pulmonary or aortic stenosis, and coarctation of the aorta. In a single-center study of 163 patients with left atrial isomerism, the median age of presentation was 2 days, ranging from <1 day to 16 years. Seventy-four percent of these patients had symptoms at presentation. Of the 13% in this cohort with a normal heart, there was an 18% overall mortality possibly secondary to extracardiac abnormalities.3 Fetal echocardiography can make the diagnosis when suspected early with improving accuracy. Polysplenia and systemic venous abnormalities are also common, as was also seen in our patient with her interrupted inferior vena cava. Other noncardiac features such as bronchial abnormalities, biliary atresia, and gut malrotation are common. Overall mortality, including in utero, is high; however, advancements in early detection and cardiac surgery have improved outcomes. 


This is a rare initial presentation of left atrial isomerism in an adult who incidentally was found to have junctional bradycardia while hospitalized. Adult electrophysiologists should be familiar with the heterotaxy syndromes and their implications. 

Disclosures: Dr. Asser has no conflicts of interest to report regarding the content herein.



Video 1: Video demonstrates the patient's interrupted IVC. 


  1. Jacobs JP, Anderson RH, Weinberg PM, et al. The nomenclature, definition and classification of cardiac structures in the setting of heterotaxy. Cardiol Young. 2007;17(Suppl 2):1-28. 
  2. Lopes LM, Tavares GM, Damiano AP, et al. Perinatal outcome of fetal atrioventricular block: one-hundred-sixteen cases from a single institution. Circulation. 2008;118(12):1268-1275. Epub 2008 Sep 2. 
  3. Gilljam T, McCrindle BW, Smallhorn JF, Williams WG, Freedom RM. Outcomes of left atrial isomerism over a 28-year period at a single institution. J Am Coll Cardiol. 2000;36(3):908-916.