Response to letter regarding article, "renal dysfunction as a predictor of stroke and systemic embolism in patients with nonvalvular atrial fibrillation: validation of the R2CHADS2 index in the ROCKET AF (Rivaroxaban Once-Daily, Oral, Direct Factor Xa Inhibition Compared With Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation) and ATRIA (Anticoagulation and Risk Factors in Atrial Fibrillation) study cohorts" - Piccini, Jonathan P.; Hacke, Werner (Circulation, 2013)