Successful flutter catheter ablation through the azygos continuation due to an interrupted inferior vena cava

Abstract

Inferior vena cava IVC is a crucial route for catheter access (both directly to the right heart and indirectly through a transeptal puncture to the left heart, used in most electrophysiological procedures). However, interrupted IVC is a real challenge to traditional arrythmia ablation approaches, compromising in certain cases the success of the procedure. A well-developed azygos continuation offers an alternative pathway, bypassing the interrupted segment of the IVC.

We report the case of a 60 years old female, who underwent catheter ablation of a counterclockwise flutter. During the procedure, she was discovered to have an uncommon anatomical venous pathway from femoral access to the right heart chambers. She was diagnosed to have an interruption of the supra-renal segment of the inferior vena cava with azygos continuation. Radiofrequency ablation of the cavotricuspid isthmus was successfully performed through the azygos continuation.

Introduction

IVC interruption is a rare congenital anomaly, its prevalence ranges from 0.15% to 2.1% [[1], [2], [3]] in the general population. Often asymptomatic and incidentally discovered [4], it requires no specific treatment. However, a good knowledge of this anomaly is key when performing percutaneous cardiac procedures through vein catheterization.

During embryogenesis, IVC development is a dynamic process, it results from regression and anastomosis of precursor veins [5]. Failure of this fusion results in an interruption of the IVC [6,7] affecting most commonly the suprarenal segment of it. The lower body blood is routed to the right atrium via an azygos continuation, and the suprahepatic veins are drained to the hepatic segment of the IVC or directly to the right atrium [[8], [9], [10], [11]].

The standard femoral venous access routinely used for electrophysiological procedures can be technically challenging with this uncommon venous anomaly. Catheters advancement through a well-developed azygos continuation can be attempted as a first approach to reach the right heart, in case of failure alternatives [12] using an upper approach through the superior vena cava should be considered.

This uncommon anatomical variant can occur in isolation or in combination with other malformations such as congenital heart disease [13]. It predisposes to deep vein thrombosis [14,15] due to blood stasis.

A multidisciplinary team including interventional cardiologists and radiologists, and a detailed preprocedural imaging are crucial to enhance the safety of electrophysiological procedures as well as the efficacy of catheter ablation in patients with IVC interruption [16].

Case report

We present the case of a 60-year-old female with cardiovascular risk factors including well-controlled type 2 diabetes and hypertension and no history of invasive procedures or abdominal surgery. She had presented an episode of pericarditis 1 year before, and was admitted to the emergency room with abrupt-onset palpitations and exertional shortness of breath for the past 5 days.

Upon admission, physical examination was unremarkable. Her ECG showed sawtooth pattern waves of the atrial activity typical of counterclockwise right atrial flutter. Biological assessment was normal, and transthoracic echocardiography showed preserved systolic function without structural heart disease. Transesophageal echocardiography showed no intracardiac thrombi.

Under local anesthesia, right sided femoral vein access was easily acquired, 3 femoral sheaths were placed in order to advance 2 decapolar catheters in the coronary sinus and right atrium, and an 8 mm catheter for ablation of the cavotricuspid isthmus CTI.

While advancing the catheters, an uncommon venous path to the right atrium was observed. A venogram using 15 mL of iodine contrast revealed that the IVC, instead of draining directly to the RA, continued to the azygos vein which drew a loop before reaching the superior vena cava. The procedure was halted and rescheduled pending further exploration of the venous anatomy.

Obstruction or compression of the IVC with collateral veins between the caval and azygos veins was suspected. A thoracoabdominal contrast enhanced CT scan with 3D reconstructions (Fig. 5) revealed a congenital interrupted IVC with agenesis of the suprarenal segment (Fig. 1), continuing into the azygos vein, and then joining the superior vena cava at the azygos arch (Fig. 2). The suprahepatic veins drained into a retrohepatic IVC (Fig. 3). The scan also showed polysplenia (Fig. 4) with a normal abdominal situs.

Fig. 5.

3D reconstruction of a thoraco-abdomino-pelvic CT angiography showing the infrarenal inferior vena cava (blue arrow) continuing as the azygos vein (yellow arrow) and then draining into the superior vena cava via the arch of the azygos vein (blue arrow). Interruption of the inferior vena cava with azygos continuation.

Fig. 1.

Axial slice (A) and coronal reconstruction (B) of a thoraco-abdomino-pelvic CT angiography showing the infrarenal inferior vena cava (green arrow) continuing as the azygos vein (yellow arrow).

Fig. 2.

Sagittal reconstruction of a thoraco-abdomino-pelvic CT angiography showing the drainage of the azygos vein (yellow arrow) into the superior vena cava via the arch of the azygos vein (green arrow).

Fig. 3.

Sagittal reconstruction of a thoraco-abdomino-pelvic CT angiography showing the drainage of the hepatic veins into the posthepatic inferior vena cava (red arrow).

Fig. 4.

Coronal reconstruction of a thoraco-abdomino-pelvic CT angiography showing polysplenia (brown arrow).

The procedure was resumed 1 week later, catheters were successfully navigated through the azygos continuation to the right heart chambers (Fig. 6), otherwise, subclavian approach would be an alternative. The diagnosis of typical counterclockwise atrial flutter was confirmed. Despite difficulties in stabilizing the catheters, radiofrequency ablation of the cavotricuspid isthmus was successfully and safely performed. atrial flutter termination and Bidirectional block, were obtained with a total of 12 radio frequency applications.

Fig. 6.

Catheter projections for catheter ablation: the 3 leads positioned in the coronary sinus (A), the lateral wall of the right atrium (B), and the ablation lead in the cavotricuspid isthmus (C).

During follow-up, the patient had no recurrence of her arrythmia. She was prescribed long-term NOAC and was advised to seek urgent care if any symptoms of deep vein thrombosis or unexplained dyspnea occurred.

Discussion

Embryogenic development of the IVC is a complex process that occurs between the fourth and eighth weeks of gestation [17]. The IVC is formed from the fusion and regression of 3 paired primitive veins [18] (supracardinal, subcardinal, and posterior cardinal), resulting in a mature IVC composed of 4 segments [19] (iliac, subrenal, suprarenal, and intrahepatic). This dynamic process explains anatomical variations of the IVC.

IVC interruption with azygos continuation results from failure of anastomosis between the right subcardinal and vitelline veins leading to agenesis of the suprarenal IVC, the infrarenal IVC continues as the azygos vein.

The azygos vein [3,20] arises from the union of the right ascending lumbar vein and the right subcostal vein, with a possible contribution from a median root originating on the posterior side of the inferior vena cava (IVC). It follows a vertical course, passes through the diaphragm towards the posterior mediastinum, then curves forward to form the azygos arch and drains into the superior vena cava (SVC). It creates a connection between the 2 venae cava, providing an alternative drainage in case of IVC obstruction.

IVC interruption is typically associated with polysplenia, congenital heart disease, isomerism, or abnormal situs [21,22]. A retrospective study conducted in Taiwan [21], involving 34 patients diagnosed with IVC interruption, found that 35.7% had associated polysplenia, and 96.4% had left isomerism. Life expectancy was comparable to the general population, the severity of the associated congenital heart disease was the only risk factor.

Clinical presentation is not specific, often incidentally discovered in middle-aged adults [21,23] on imaging or during interventional or surgical procedures [24,25], especially if the azygos continuation is well developed. In case of a poorly developed collateral circulation, patients may present some symptoms such as abdominal pain, lower limb oedema and venous insufficiency [23,26] with an increased risk of deep venous thrombosis [27] but anticoagulation for primary prevention is not indicated.

The anomaly should be suspected in the presence of polysplenia or mediastinal widening on chest X-ray often appearing as a paratracheal mass [28] due to azygos vein dilation. Acquired IVC stenosis, can also lead to development of communications with the azygos and hemiazygos veins, mimicking congenital IVC interruption [11].

The prevalence of IVC interruption remains unknown in patients undergoing electrophysiological study procedures. Catheter ablation in patients with azygos continuation is technically challenging, and to the best of our knowledge, has been rarely reported.

In practical terms, the azygos continuation can be used to access the right heart chambers, as in our patient's case, if the IVC-azygos communication is well developed. The venous path from femoral access to the heart chambers is longer, which may require adapted sheath.

If the continuation is underdeveloped, alternative access routes such as, the internal jugular [29], or the subclavian veins [30] should be sought, especially for procedures requiring transseptal access to the left heart.

Difficulties during ablation include poor catheter maneuverability and stability. As flutter catheter ablation requires multiple linear radiofrequency energy applications between the tricuspid annulus and the IVC, achieving stable lead positioning, optimal orientation and consistent tip-tissue contact force is technically challenging with the superior approach compared to femoral vein and IVC access. Besides, the SVC approach must be undertaken with caution due to the risk of associated complications such as SVC stenosis, sinus node injury, phrenic nerve injury and radiation exposure with prolonged fluoroscopy time.

Our case illustrates the technical challenges of electrophysiology procedures in patients with abnormal venous anatomy, and highlights the importance of imaging for the precise diagnosis of these anomalies. Reconstructed images facilitate the selection of the optimal venous access for safe and successful ablation.

Conclusion

Electrophysiological procedures via femoral access in the presence of IVC interruption are feasible through the azygos continuation. Jugular or subclavian access should be considered if the IVC-azygos communication is absent or poorly developed. Ablation in these conditions is very challenging, underscoring the need for precise diagnosis of venous anatomy and associated congenital heart disease. Ablation with advanced mapping techniques would be highly beneficial for these patients.

Patient consent

As this is a case report, written informed consent for publication of the case has been obtained from the patient.