The role of surface electrocardiogram after complex left atrial arrhythmias' ablation: behind electrical mechanisms.

We report of an interatrial dissociation after two relatively limited left atrial ablations for paroxysmal atrial fibrillation (PAF), with sinus rhythm in the right atrium and ongoing atrial tachycardia (AT) in the left atrium (LA). Patients suffering from PAF are supposed to have less electrical and anatomical remodelling; however, the role of low-voltage and scar areas with functional conduction block in these patients is still ongoing discussion. A 64-year-old woman was referred to our centre for PAF on therapy with beta-blockers, occurring since 1 year. Echocardiography revealed a moderate dilatation of the LA with preserved left ventricular systolic function. She underwent successful pulmonary vein isolation (PVI) and no antiarrhythmic drugs were prescribed following the procedure. During a 3-month follow-up, the patient developed highly symptomatic episodesof persistent AF requiring a secondablation.The patientunderwent a re-PVI and, thereafter, limited additional ablation of complex fractionated atrial electrograms (CFAEs) wasperformed in LA (roof and anterior wall, no additional linear lesions were created), including the coronary sinus (CS) region (ablation was commenced endocardially by dragging along the inferior perimitral left atrium and was continued epicardially fromwithin the vessel). Atrial fibrillation converted into an organized AT. Entrainment and activation mapping revealed one localized re-entry at the cranial posterior LA and a second one anteriorly located, both related to a slow conduction zone within spontaneous low voltage area. After a total of 30 min of RF ablation, we observed an inter-atrial (left to right atrium) dissociation of atrial activation (Figure 1A): surface electrocardiogram (ECG) showed a conversion into sinus rhythm, whereas intracardiac electrograms revealed complete electric dissociation of the right atrium (RA) from the LA. Sinus rhythm in the RAwas recorded at the proximal electrodes of CS catheter placed at CS ostium, while ongoing AT was recorded from the circular mapping catheter placed in the left atrial appendage and from the distal electrodes of the CS catheter placed along the inferior perimitral LA (Figure 1B). We performed an electrical cardioversion with the restoration of sinus rhythm in both atria. During a follow-up of 5 months, the patient had no clinical recurrence of supraventricular arrhythmias on Holter ECG monitoring, off antiarrhythmic medications. She was in good performance status and further