Non-invasive estimates of left atrial activation in a patient with dissociated left atrial tachycardia following ablation of atrial fibrillation

Introduction: Interatrial frequency gradient is used to guide catheter ablation of atrial fibrillation (AF) but reliable tools for its non-invasive estimation are lacking. We present a patient with dissociated left and right atrial rhythms that allows identification of surface ECG leads that closely reflect left atrial activity. Methods: 12-lead ECG was recorded simultaneously with electrograms from the right and left atrial appendages (RAA/LAA). AF frequency spectra have been calculated from all 12 leads using spatiotemporal QRST cancellation and Welch periodogram. The dominating atrial cycle length (ACL) in the surface ECG leads was subsequently compared with ACL_LAA. Results: RAA and LAA cycle lengths were 1276 ms and 252 ms respectively. Of all surface ECG leads, AF frequency spectra in leads VI and aVR demonstrated the best agreement with ACL_LAA showing prominent peaks corresponding to the LAA activation frequency. Conclusion: Leads VI and aVR contain a prominent left atrial component that has to be considered when interpreting fibrillatry activity from surface ECG.