Based on previous reports of patients undergoing MRI before and after AF ablations, the % of patients with chronic cerebral lesions detected on MRI at baseline varies widely from 4 to 79 %, with 10 % being the most representative figure for patients with paroxysmal AF. Previous observations have reported varying frequencies of new silent cerebral lesions on MRI after AF ablation (4-38 %), coronary angiography (10 %) and retrograde aortic catheterisation of patients with aortic valve stenosis (22 %). New asymptomatic cerebral ischemic lesions in patients undergoing AF ablation have been reported after the use of irrigated radiofrequency (RF) catheters (7-11 %), the most common routine ablation procedure, and even a higher frequency of lesions (37 %) using a specialized circular RF ablation catheter. Based on these observations the investigators argued that a 20 % increase in incidence of new asymptomatic cerebral ischemic lesions in patients undergoing DC cardioversion would be clinically significant and warrant alternative routines for cardioversions.