A, Biatrial endocardial electroanatomical reconstruction, left anterior oblique view. Note that the ablation catheter (yellow) is located inside the transverse sinus in the anatomical position of the Bachmann’s bundle. The transverse sinus is accessed from the left, passing between the left atrial appendage and the pulmonary veins. This access was feasible in 92% of the study cohort. B, low-amplitude fragmented potential (black arrow), typically recorded on the Bachmann’s bundle. C and D, left anterior oblique (C) and right anterior oblique (D) fluoroscopy projections, showing the ablation catheter inside the transverse sinus from the leftward approach. Abbreviations: BB, Bachmann’s bundle; CS, coronary sinus; LAA, left atrial appendage.