Cryoablation for atrial tachycardia with cycle length variability originating from the vicinity of the sinus node

Abstract

This case is about atrial tachycardia with cycle length variability originating from the vicinity of the sinus node and diagnostic pacing maneuvers to assess the tachycardia circuit were not achieved. Activation mapping revealed that the origin of atrial tachycardia was 15 mm away from the sinus node and the phrenic nerve was captured by pacing at the posterior portion of atrial tachycardia. A multipolar catheter was placed in the right brachiocephalic vein to capture the right phrenic nerve by pacing. The absence of phrenic nerve palsy was confirmed by palpation of constant diaphragmatic movement. The cryoablation could be safely and efficiently performed without ablation-induced injury of sinus node and phrenic nerve palsy by confirming constant diaphragmatic movement. The efficacy of cryoablation in the vicinity of the conduction system and phrenic nerve will be increasingly confirmed in the future.

Learning Objective

Cryoablation for atrial tachycardia might be more safe and effective in terms of ablation-induced injury of conduction system and phrenic nerve palsy compared with conventional radiofrequency ablation when diagnostic pacing maneuvers are not able to estimate the circuit due to variability of tachycardia cycle length.

Introduction

Radiofrequency catheter ablation for supraventricular tachycardia is established therapy. However, there are several complications, including injury of conduction system and phrenic nerve palsy. In slow pathway ablation, treatment with cryocatheter is useful to avoid atrioventricular block compared with radiofrequency ablation [1]. Evaluation and monitoring of phrenic nerve palsy by electrical stimulation is routinely used in pulmonary vein isolation with cryoablation [2]. In this case, we successfully treated atrial tachycardia with cycle length variability originating from the vicinity of the sinus node by cryocatheter, which could avoid injury of conduction system and phrenic nerve palsy.

Case report

A 73-year-old woman presented with a sudden onset of palpitation and Holter monitoring demonstrated narrow QRS tachycardia (Fig. 1). The tachycardia had an irregular rhythm with occasionally overt P waves preceding QRS waves, which did not seem to be atrial fibrillation. On electrophysiological study, both burst atrial pacing and atrial extra-stimulation easily induced the tachycardia (Fig. 2A, B). Atrial activation was concentric with cranial to caudal activation (Fig. 2C). Overdrive pacing from the right ventricular apex revealed ventriculoatrial dissociation. In addition, the tachycardia cycle length constantly varied with the preceding P waves (Fig. 2D). Therefore, diagnostic pacing maneuvers were not achieved. Activation mapping with a multipolar catheter (PENTRAY, Biosense Webster Inc., Diamond Bar, CA, USA) using the CARTO 3 mapping system (Biosense Webster Inc.) revealed that the origin of atrial tachycardia was 15 mm away from the sinus node, based on the earliest activation site (Fig. 3A, B). The earliest area was relatively broad because the tachycardia cycle length was not constant. The phrenic nerve was captured by pacing at the posterior portion of origin of atrial tachycardia. The risk of phrenic nerve palsy and sinus node injury during radiofrequency catheter ablation was expected. Therefore, a 7F Freezor® Xtra 6 mm tip catheter (Medtronic, Minneapolis, MN, USA) was advanced via the right femoral vein and placed at the anterior portion of the earliest activation (Fig. 3C-E). Next, a multipolar catheter (EPSTAR, Japan Lifeline, Tokyo, Japan) was placed in the right brachiocephalic vein to capture the right phrenic nerve by pacing (Fig. 3F). The absence of phrenic nerve palsy was confirmed by palpation of constant diaphragmatic movement. Atrial tachycardia could not be induced by extra atrial pacing during cryoablation mapping mode (Fig. 2E). Subsequently, two 4-min cryoablations were performed during sinus rhythm and atrial tachycardia was no longer inducible, even with isoproterenol infusion.

Fig. 1.

Holter monitoring. The QRS rhythm was irregular and occasionally overt P waves (red arrow) preceded the QRS waves.

Fig. 2.

Intracardiac electrograms and 12‑lead electrogram of tachycardia.

A. Atrial tachycardia was induced by burst pacing from high right atrium.

B. Atrial tachycardia was induced by single extra pacing from high right atrium.

C. Atrial activation was concentric with cranial to caudal activation, and tachycardia cycle length was not constant.

D. Twelve‑lead electrogram demonstrated P waves preceding QRS waves.

E. Intracardiac electrogram of success site with a corresponding bipolar and unipolar signal on the ablation catheter. Atrial tachycardia was not induced by extra pacing during mapping mode.

HRA, high right atrium; HBE, his bundle electrogram; CS, coronary sinus; RVA, right ventricular apex; prox, proximal; dist, distal.

Fig. 3.

Activation map and fluoroscopy images.

A. During atrial tachycardia, focal activation of the right atrium was viewed from a posterorlateral projection.

B. The activation map of sinus rhythm revealed that the earliest activation site was located 15 mm anterior to the earliest activation site of atrial tachycardia.

C. The activation map of atrial tachycardia with the catheter shadow indicating the site of cryocatheter. The phrenic nerve was captured by pacing (white arrow).

D. Corresponding fluorescence image of ablation site from right anterior oblique.

E. Corresponding fluorescence image of ablation site from left anterior oblique.

F. Multipolar catheter was placed in the right brachiocephalic vein for phrenic nerve pacing.

HRA, high right atrium; CS, coronary sinus; RVA, right ventricle apex; ABL, ablation catheter.

Discussion

The first problem with catheter ablation for arrhythmia originating from the vicinity of the sinus node is injury to the conduction system. Currently, the development of a 3D mapping system can precisely evaluate the earliest activation site in sinus rhythm before ablation. In a previous report, radiofrequency ablation of the earliest activation site was successful in all cases of sinoatrial node reentrant tachycardia (SANRT) and the earliest activation sites were shifted in 3 of 11 patients [3]. The optimal distance from the sinus node for ablation attempt so as to avoid injury is unclear. Yamabe et al. revealed the reentrant circuit of SANRT by the entrainment pacing method and the efficacy of radiofrequency ablation for the entrance of intranodal sinoatrial node conduction [4]. Therefore, assessment of the tachycardia circuit is important to avoid ablation-induced injury. In the current case, the variability of tachycardia cycle length made it difficult to estimate the circuit using diagnostic pacing maneuvers, and ablation for the earliest site was necessary. We estimated the approximate earliest site using the CARTO system, because a constant tachycardia circuit might exist in this case. The atrioventricular block is fully reversible in slow pathway ablation using a cryocatheter. In contrast, this complication has been reported in up to 1 % of patients treated with radiofrequency ablation [2]. Although it is still speculative whether injury is reversible in the sinus node as well, it may be possible to attempt adequate ablation using a cryocatheter with careful monitoring.

The second problem is palsy of the right phrenic nerve, which travels from the lateral superior vena cava and the right atrial wall. In the present case, the phrenic nerve was captured by pacing at some areas of the earliest activation site. During pulmonary vein isolation with cryoballoon, diaphragmatic compound monitor action potential (CMAP) monitoring was applied to avoid phrenic nerve palsy [1]. A case of atrial tachycardia along the crista terminalis, where phrenic nerve injury is a potential complication, was treated using cryoablation with CMAP monitoring [5]. In our case, the cryoablation could be safely and efficiently performed by confirming the palpation of diaphragmatic movement, instead of CMAP monitoring.

Conclusion

Our case demonstrated the efficacy of cryoablation in the vicinity of the conduction system and phrenic nerve. Although there are some problems with the current 3D mapping system and application of cryocatheter is still limited for atrioventricular nodal reentrant tachycardia in some institutions, the usefulness of cryoablation will be increasingly reconfirmed in the future.

Conflict of interest

The authors declare that there is no conflict of interest.