Utility of Intracardiac Echocardiography During Ablation of Atrial Premature Depolarizations with a Prominent Chiari Network

A Chiari network is a fenestrated reticulum in the right atrium that is present in approximately 2% of the population. We present a case involving a 63-year-old-woman with symptomatic atrial premature depolarizations (APDs) who presented for a catheter ablation. Despite prior echocardiograms and during the initial electrophysiology study, her Chiari network was not appreciated. It was only after intracardiac echocardiography (ICE) was used that this structure was identified. We describe the value of using real-time ICE during mapping and catheter ablation in patients with rare anatomic variants.

A 63-year-old woman with palpitations and exertional dyspnea was found to have a 20% atrial premature depolarization burden (Figure 1). Her workup included a transthoracic echocardiogram and a stress echocardiogram that revealed normal biventricular systolic function, no evidence of valvular pathology or any anatomic variants along with a normal augmentation in systolic function with exercise. After metoprolol and flecainide incompletely suppressed her APDs, she presented for a catheter ablation. During the electrophysiology study frequent APDs were noted in the baseline state. A duodecapolar catheter was positioned along the lateral right atrium (RA) and into the coronary sinus (CS) along with a hexapolar catheter to record a His bundle electrogram. When the APDs occurred the CS activation was concentric and the earliest atrial electrogram (EGM) was on the His catheter. A RA electroanatomic map was created using a high-density mapping catheter (Pentaray^TM; Biosense Webster). No difficulties with catheter manipulation were encountered while positioning the diagnostic catheters or during mapping. The earliest activation when the APD occurred (28ms pre p-wave onset) was noted to be immediately adjacent to the bundle of His. Given the proximity to the conduction system, ablation was not performed, and a decision was made to map the non-coronary cusp. The activation in the aortic cusp was later than in the RA. The left atrium was subsequently mapped (Figure 2A). Use of ICE during transseptal puncture revealed a prominent Chiari network (Figure 2B, Supplemental Video). Real-time ICE guidance was used to navigate around the Chiari network during re-mapping of the RA septum with an irrigated 3.5mm, contact force-sensing ablation catheter (ThermoCool SMARTTOUCH® SF; Biosense Webster). A highly fractionated atrial electrogram (48ms pre-P wave onset) was noted on the RA septum, posterior to the CS ostium, near the Chiari network (Figure 2C, D, Supplemental Video). Following delivery of radiofrequency energy (20-35 Watts for up to 60-seconds with a target contact force range of 10-15 grams) there was complete suppression of the APD. There was no evidence of a junctional rhythm or atrioventricular block during ablation. After an adequate waiting period no further APDs were noted both with and without isoproterenol infusion. The patient was discharged the same day and has not had a recurrence of her APDs during a five-month follow-up period.

The Chiari network, which is present in approximately 2% of the population, is a fenestrated embryologic remnant that results from incomplete reabsorption of the right valve of the sinus venosus. This anatomic variant, which extends between the Eustachian valve, inferior vena cava, crista terminalis and superior aspect of the fossa ovalis has been implicated in cases of thromboembolic disease, catheter entrapment and atrial arrhythmias. In this case the prominent Chiari network impacted the ability to completely map the RA using the high-density mapping catheter. Use of real-time ICE, and mapping with the ablation catheter, both facilitated navigating around the Chiari network and identifying the successful ablation site. Without ICE, the Chiari network would not have been identified and lesions may have been delivered in the RA adjacent to the bundle of His at the site of earliest activation based on the original map. While ablation in this location may have resulted in suppression of the APD, it would have introduced an unnecessary risk as the successful ablation location was inferior and posterior to the bundle of His.

Although there was no evidence of catheter entanglement within the Chiari network during this case, ICE was a valuable tool when manipulating the ablation catheter near the network. Previous reports have described mapping and diagnostic catheters becoming entrapped within Chiari networks. Rotation and traction of impinged catheters can result in further entanglement. Prior publications have described use of endomyocardial biopsy forceps and lead extraction tools along with use of fluoroscopy and transesophageal echocardiography to successfully remove trapped catheters and prevent the need for surgical resections.^{,  ,}  In the event of catheter entanglement within a Chiari network, ICE could also be used to identify the problem and prevent further catheter manipulation, which can be deleterious. Furthermore, ICE could serve as an adjunctive imaging modality and can be used to assist during percutaneous removal attempts.

This case highlights that ICE is an invaluable tool, which can be used to assist with detailed mapping and successful ablation in patients with rare anatomic variants.