3D radiofrequency ablation of atrio-ventricular nodal reentrant tachycardia and focal left atrial tachycardia in a patient with azygos continuation syndrome

Introduction:

Congenital absence of the hepatic segment of the inferior vena cava (IVC) is a well-known anatomical variant. In these cases, venous drainage of the lower extremities and some abdominal organs takes place via the azygos vein (azygos continuation syndrome). It is most commonly associated with other congenital structural heart defects (0.6-2% prevalence), but isolated incidental cases (<0.3% prevalence), are extremely rare and present access challenges to the investigator.

Case Report:

A 35-year-old woman was admitted because of recurrent tachycardia for 2 years with a maximum duration of 30 minutes. She was symptomatic with palpitations and anxiety. Her wearable 1-lead ECG (smartwatch) showed a regular narrow QRS complex tachycardia suspicious for AVNRT. 

During the electrophysiology study (EPS), a double venous access was placed in the right femoral vein. A quadripolar and a decapolar catheter were inserted, but access to the right atrium proved to be unusual. The catheters appeared to follow a structure that was fluoroscopically to the left of the suspected IVC. The catheters were advanced without resistance and the right atrium was finally reached from above like a shepherd's staff. The decapolar catheter was easily advanced into the coronary sinus (CS). Programmed atrial stimulation induced AVNRT. We terminated the EPS and planed a CT scan and a second staged EPS with 3D mapping. CT showed an azygos continuation syndrome with the IVC draining only venous blood from the liver (see Figure 1). There were no other signs of heterotaxy.

The second staged EPS with 3D guidance resulted in a successful complete non-irrigated radiofrequency ablation (50W, 55C°) of the slow pathway via the azygos vein (s. Figure 2A-D) despite limited maneuverability. Another programmed atrial pacing induced an atrial tachycardia with earliest activation in the high septum in the right atrium, but only 20ms before the earliest CS signal (proximal). Due to the unclear clinical significance of the suspected focal left atrial tachycardia (LAT) not yet detected by the smartwatch, we decided to stop the procedure and wait for the clinical outcome in daily life.

7 months later, the patient presented with an ECG that was suspicious for the previously detected LAT. A third EP study was performed under 3D guidance. In addition to the double femoral vein access, a short steerable sheath (8.5F) was inserted via the right jugular vein. Under transesophageal echocardiographic (TOE) guidance, transseptal access was performed with an RF wire through the short steerable sheath. High-density mapping localized the focal atrial tachycardia anterior to the left atrial appendage (Figure 3-4). No further tachycardia was inducible after cooled, pressure-controlled RF ablation. The patient remained arrhythmia free for a follow-up of 4 months.

Conclusion:

Congenital interruption of the IVC can be a significant obstacle to catheter ablation. Although there are case reports of AVNRT ablation in the azygos continuation using a superior approach via the left subclavian vein or a hypoplastic IVC, an ablation approach through the azygos vein is rather exceptional. Furthermore, to our knowledge, this is the first case of a transseptal approach using an RF wire and a short steerable sheath from the jugular vein. Here we demonstrate the successful ablation of a slow-pathway using the azygos approach and a focal LAT using a superior approach.

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