Atrial Fibrillation (AF) poses a significant burden to patients as well as the healthcare system. It can be a complex diagnosis and requires a holistic approach to treatment. Every patient with AF should be evaluated for the need for anticoagulation therapy to prevent systemic embolization. In those that require long-term anticoagulation, a novel oral anticoagulation agent (NOAC) has become the drug of choice. In recent years there have been huge developments in the field of anticoagulation in AF with the presence of the various NOACs on the market. However, there remains uncertainty around prescribing in obese patients.

A 30-year-old male with electrocardiographic (ECG) evidence of manifest pre-excitation (figure 1) was referred for an electrophysiology study (EPS). Quadripolar catheters were placed in the His position (His) and right ventricular apex (RVA) and a decapolar catheter was placed in the coronary sinus (CS). Ventricular pacing (VP) with and without isoproterenol infusion revealed poor retrograde ventriculoatrial (VA) conduction in both the atrioventricular node (AVN) and the accessory pathway (AP). Single atrial extra-stimuli (AES) were introduced after a drive train at 400ms from poles CS 9,10. The following reproducible phenomenon was observed (figure 2A, 2B). What has been unveiled, and how is it explained?