www.chestpubs.org CHEST / 141 / 2 / FEBRUARY, 2012 SUPPLEMENT e537S tic plaque in the descending aorta seen on transesophageal echo- cardiography [TEE] or a history of peripheral arterial disease) independently predicts stroke risk among patients with AF.21-23 1.4.3 Stroke Risk Strati cation Schema: Many risk strati - cation schema, which use various combinations of the risk fac- tors discussed previously, have been developed to aid clinicians in the assessment of stroke risk in patients with nonrheumatic AF (Table S13).12 Despite substantial efforts in this eld over the past several decades, all available schema have only modest ability to predict stroke in patients with AF, with C statistics typi- cally between 0.55 and 0.70.4,24-43 (A C statistic of 0.50 indicates a model that does not discriminate better than chance alone, and a C statistic of 1.00 indicates perfect discrimination.) The CHADS2 score is the most validated risk scheme, having been independently tested in at least 10 separate cohorts after its original derivation.24,32,35-46 The CHADS2 score gives a single point for each of congestive heart failure (originally de ned as a recent exacerbation of congestive heart failure), hypertension (de ned as a history of hypertension, rather than a presence of elevated BP), age 75 years, and diabetes mellitus and two points for prior stroke or TIA (Table 2).30 Despite its widespread adoption and ease of use, the CHADS2 score has limitations. First, congestive heart failure is not a consis- tently demonstrated independent predictor of stroke. 