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Three-dimensional electroanatomical mapping for non-pulmonary vein foci in a patient with complete situs inversus and dextrocardia

In patients with atrial fibrillation (AF) having congenital anatomical abnormalities, such as complete situs inversus and dextrocardia, pulmonary vein isolation (PVI) ablation can be performed safety using a three-dimensional electroanatomical mapping system. However, it is not clear whether a three-dimensional electroanatomical mapping system can be used to detect non-PV ectopic beats initiating AF in patients with complete situs inversus and dextrocardia. Here, we report a 21-year-old man with complete situs inversus and dextrocardia, who showed AF caused by non-PV ectopic beats. We successfully detected the origin of the triggered activity from the non-PV foci using three-dimensional electroanatomical mapping.


Introduction
Pulmonary vein isolation (PVI) is a cornerstone procedure in ablation treatment for atrial fibrillation (AF). In AF patients with anatomical abnormality, such as complete situs inversus and dextrocardia, a three-dimensional electroanatomical mapping system has been shown to be useful for performing the PVI procedure [1]. Recently, several studies have addressed the importance of non-PV ectopic beats initiating AF [2]. However, there have been no reports about the effectiveness of 12-lead electrocardiography (ECG) and a three-dimensional electroanatomical mapping system for detecting non-PV ectopic beats initiating AF in patients with complete situs inversus and dextrocardia. Here, we report a rare case of AF initiated by non-PV ectopic beats in a patient with complete situs inversus and dextrocardia and present the usefulness of threedimensional electroanatomical mapping for detecting the origin of the triggered activity from non-PV foci.

Case report
A 21-year-old man with complete situs inversus and dextrocardia, but without any disease linked to the disorder, was admitted to our institution for an ablation procedure to resolve persistent AF. Three-dimensional reconstruction of the right atrium (RA) and left atrium (LA) with computed tomography images was performed using an electroanatomical mapping system (Fig. 1). A 5-French deflectable multipolar catheter was positioned in the coronary sinus, and a mapping catheter and probe for intracardiac echocardiography were inserted via the left femoral vein. Transseptal catheterization was guided using fluoroscopy and intracardiac echocardiography (ViewFlex™ Xtra ICE Catheter, St. Jude Medical, Inc., St. Paul, MN, USA), and contrast medium was injected into the LA through the transseptal sheath (SL0 and Agilis™, St. Jude Medical) (Fig. 2). Even after performing bilateral PVI and electrocardioversion to terminate the AF, premature atrial contractions (PACs) emerged incessantly and initiated AF.
On 12-lead ECG (standard limb and left-sided precordial lead positions), the P-wave morphology during sinus rhythm was negative in leads I and aVL, positive in leads III, aVR, and V1, and isoelectric in leads II and aVF. The PACs triggering AF exhibited positive P waves in leads III and V1, negative waves in leads I and II, and isoelectric waves in leads aVL (Fig. 3A). On opposite 12-lead ECG (left-right reversal limb and right-sided precordial lead positions), the PACs exhibited positive P-waves in leads I, II, and V1, isoelectric waves in lead aVL, and negative waves in lead III. (Fig. 3B). A biatrial standard local activation time map of the PACs was created with an electroanatomical mapping system (EnSite Velocity™, St Jude Medical) that indicated a centrifugal activation pattern from the atrial septum (Fig. 4A). An irrigated ablation catheter, positioned at the mid-septum of the RA (left-sided), demonstrated the earliest electrical potentials of the PACs which proceeded the potentials observed on the surface electrocardiogram by 63 msec (Fig. 4B), and radiofrequency application at that point resulted in immediate disappearance of the PACs (Fig. 5). No atrial tachyarrhythmias recurred over 24 months of follow-up.

Discussion
Several cases of catheter ablation for paroxysmal AF in patients with complete situs inversus and dextrocardia have been reported [1,3]. However, to the best of our knowledge, this is the first report of AF initiated by non-PV ectopic beats in a patient with complete situs inversus and dextrocardia, who successfully underwent ablation using an electroanatomical mapping system. We identified two important clinical characteristics.
First, identification of the site of PAC origin using 12-lead ECG was challenging in patients with dextrocardia and situs inversus. Yamada et al. [4] reported that the P-wave morphology of PACs triggering AF might have limited information for predicting where the PACs originate in patients with dextrocardia. In the present case, on standard 12-lead ECG (standard limb and left-sided precordial lead positions), PACs triggering AF exhibited positive P waves in leads V1 and III, negative waves in leads I and II, and isoelectric waves in lead aVL. On opposite 12-lead ECG (left-right reversal limb and right-sided precordial lead positions), the PACs exhibited positive P waves in leads I, II, and V1, isoelectric waves in lead aVL, and negative waves in lead III. Kistler et al. [5] provided a detailed analysis of the utility of the P-wave configuration for localization of atrial tachycardia origins in patents with normal heart. They stated that either a negative or biphasic (positive, and then negative) P wave in lead V1 was associated with a specificity of 100% for right atrial tachycardia and a positive or biphasic (negative, and then positive) P-wave in lead V1 was associated with a sensitivity of 100% for atrial tachycardia originating in the LA. In this case, the P waves of PACs initiating AF were completely positive in both left and right-sided V1 leads, which raised suspicion of PAC origin in the LA. According to their P-wave morphology algorithm, the crista terminalis or right pulmonary vein was considered to be suspicious for PAC origin on standard 12-lead ECG, and the left pulmonary vein was considered to be suspicious on opposite 12lead ECG. Tang et al. [6] proposed an algorithm for predicting atrial tachycardia foci according to the P-wave configuration in lead aVL, distinguishing right from left atrial tachycardia. They stated that a negative or isoelectric P wave in lead aVL indicates left atrial      foci and a positive or biphasic P wave in lead aVL indicates either right atrial or right superior pulmonary vein foci. In this case, the PACs exhibited isoelectric P waves in lead aVL on standard and opposite 12-lead ECGs, suggesting left atrial foci according to their algorithm. Thus, although we recorded the PACs on standard and left-right reversal 12-lead ECGs in this case, the P-wave morphology of the PACs did not fit into any diagnostic algorithms for identifying PAC origin. This might be because the difference in three-dimensional excite activation sequences in patients with dextrocardia cannot be recorded on left-right reversal 12-lead ECG. Second, the three-dimensional electroanatomical mapping system was useful for detecting the source of non-PV ectopic beats initiating AF in patients with dextrocardia and situs inversus. Such mapping allows the determination of the precise location at which an ablation procedure should be performed either by isolating the PV or treating a non-PV arrhythmogenic site. The PV is a major site of ectopic foci that initiates paroxysmal AF, and isolation of the PV from the LA reportedly cures 70% of patients with paroxysmal AF [7]. Several studies have addressed the importance of non-PV ectopic beats initiating AF [8]. Such ectopy may arise from the superior vena cava, left atrial posterior free wall, crista terminalis, coronary sinus, ligament of Marshall, or interatrial septum. Non-PV ectopic beats from the interatrial septum are extremely rare, accounting for only 0.4% of cases of AF [9]. Thus, this case is exceptional because the patient had two very rare conditions, including complete situs inversus with dextrocardia and paroxysmal AF initiated from the interatrial septum. Three-dimensional electroanatomical mapping was a valid and feasible approach to detect the non-PV ectopic beats initiating AF in patients with complete situs inversus and dextrocardia.

Conclusion
The electroanatomical mapping system is useful for detecting the source of arrhythmogenic non-PV ectopic beats, particularly in patients with anatomical complexities associated with complete situs inversus anddextrocardia.

Conflicts of interest
None.