International Circulation: A number of researchs have suggested that new anticoagulation agents， rivaroxaban， apixaban， dabigatran， can prevent stroke in atrial fibrillation patients. Can you compare and contrast those new anticoagulation agents?
　　《国际循环》：一些研究表示，在心房颤动患者中，新型抗凝药物利伐沙班、apixaban 和达比加群可预防卒中。请您谈谈这些新型抗凝剂的差异？
　　Dr. Ezekowitz: First of all， it is very difficult and probably hazardous to compare one drug with another. The only way that you can make a legitimate comparison is to do a head-to-head comparison between these various agents in a single clinical trial. When you compare these trials without a head-to-head comparison， it lends itself to criticism. Hav