You Never Know What You’re Going to Find: A Look at a Congenital Anomaly in the EP Lab

 Cor triatriatum sinister (CTS) is a rare congenital cardiac anomaly (incidence between 0.1–0.4%) whereby the left atrium is functionally and anatomically divided into two separate chambers by a thin membrane.¹ CTS is commonly thought to result from a failure of the common pulmonary vein to become fully incorporated into the left atrium during fetal development. This results in a fibromuscular, septum-like structure that divides the left atrium into a posterior-superior chamber receiving the pulmonary veins and an anterio-inferior chamber in direct continuity with the mitral valve. It usually presents in childhood, often associated with other cardiac abnormalities.¹ However, with improvements in diagnostic imaging, it is being diagnosed with increasing frequency in adults either incidentally or when they present with atrial and electrical remodeling in response to altered left atrial pressure and volume, which may also predispose them to atrial arrhythmias. Coupled with increasing frequency in diagnosis and the rapidly expanding availability of catheter ablation for the treatment of atrial fibrillation, this makes it inevitable that an increasing number of these patients will be seen. 

This congenital defect is recognized in infancy in most cases. The babies present with dsypnea ranging from mild forms to more severe presentations such as neonatal respiratory distress with an increased mortality.² If the child makes it into adulthood, the symptoms are not profound. Diagnosis is made by coincidence. CTS is not usually seen on electrocardiogram. In fact, there are essentially no changes found other than atrial arrhythmias such as atrial fibrillation (AF).³ Furthermore, there can be no inference made due to gender, as CTS affects males and females. However, the anomaly can be visualized during a cardiac catheterization procedure. Today, a three-dimensional echocardiogram is sufficient for diagnosis.² 

Although not previously diagnosed, our patient was found to have an anomalous congenital defect of the left atrium, similar to that of CTS. Research shows that this diagnosis can be made by CT scan, although MRI and echocardiogram are helpful as well.² Our patient is a 62-year-old male who lives a very active lifestyle, biking at least 75 miles per week. He has prior history of asthma, AF, hypercholesterolemia, sleep apnea, and multiple episodes of pneumonia. Interestingly, tachycardia and pneumonia are symptoms seen frequently in older patients with CTS. This patient presented to the electrophysiologist for consult for an AF ablation. The anomaly was discovered upon the CT scan during the preoperative workup. The anatomy was again confirmed when 3D mapping was performed during the ablation. The images obtained by the mapping were compared to the CT scan. (Figures 1-5)

Research suggests treating these patients according to symptoms. Nassar and Hamdan found that an incidental echographic finding of a left atrial extra membrane with no pressure gradient in an asymptomatic patient does not require medical management.² However, it is recommended that those with symptoms such as AF be treated aggressively, as tachycardias can lead to future deterioration. A routine AF ablation was performed, isolating all four pulmonary veins in the left atrium. Isolation was confirmed despite the large, anomalous atrium. Normal sinus rhythm was achieved, and the patient was sent to the Intensive Care Unit in stable condition. 

The incidence of CTS in the adult population is not common. In fact, the diagnosis is usually made in infancy or childhood, and the lack of treatment results in death in 75% of patients.³ Those that survive into adulthood will most likely be diagnosed by accident. In this example, the patient had no idea that he had a congenital defect, and had no family history of it. Of the many AF ablations we have performed, this was the first case of CTS we have ever seen. We found this case to be very interesting, and have learned that we never know what we will find until the procedure begins.

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

References

1. Gavin A, Singleton C, McGavigan AD. Successful Multi-chamber Catheter Ablation of Persistent Atrial Fibrillation in Cor Triatriatum Sinister. Indian Pacing Electrophysiol J. 2011;11(2):50-5. 

2. Nassar P, Hamdan R. Cor Triatriatum Sinistrum: Classification and Imaging Modalities. Eur J Cardiovasc Med. 2011;1(3):84-87.

3. Troxclair D, Ross KF, Newman WP 3rd. Cor triatriatum sinistrum: a rare congenital cardiac anomaly presenting in an adult with chronic atrial fibrillation. Am J Forensic Med Pathol. 2005;26(3):282-284.