Joffe SW, Chalian A, Tighe DA, Aurigemma GP, Yarzebski J, Gore JM, Lessard D, Goldberg RJ. Trends in the use of echocardiography and left ventriculography to assess left ventricular ejection fraction in patients hospitalized with acute myocardial infarction. Am Heart J. 2009 Aug; 158(2):185-92.