Prevalence of left atrial thrombus and dense spontaneous echo contrast in patients with short-term atrial fibrillation < 48 hours undergoing cardioversion: value of transesophageal echocardiography to guide cardioversion - Kleemann, T; Becker, T; Strauss, M; Schneider, S; Seidl, K (J Am Soc Echocardiogr, 2009)