These studies of diagnostic evaluation of syncope, therefore, clearly indicate that there is a subgroup of patients with syncope who have arrhythmias as a cause of their syncope which were not apparent from initial history, physical examination, and EKG. Therefore, prolonged electrocardiographic monitoring has assumed a central role in the diagnostic evaluation of this group of patients for detection of arrhythmias. Because of the prognostic and therapeutic importance of arrhythmias causing syncope, it is important to identify patients who are likely to have arrhythmias from the data available at presentation. There were no studies prior to 1987 attempting to identify such patients at presentation. The predictors of diagnostic arrhythmias at presentation may be helpful for four reasons. First, the variables suggesting high likelihood of arrhythmias may provide a basis for decisions regarding the need for hospital admission. Secondly, predictors of diagnostic arrhythmias may identify patients who may need to be monitored immediately as opposed to electively. Thirdly, patients who have predictors of diagnostic arrhythmias may be more appropriate candidates for invasive diagnostic testing such as intracardiac electrophysiologic studies. Fourthly, since patients with arrhythmias are at high risk of sudden death, these predictors may identify an appropriate subset of patients for further studies involving therapeutic interventions. Since many patients with syncope have multiple risk factors for sudden death, the development of a multifactorial model to more effectively and expeditiously predict the degree of risk of sudden death may be important in the management of patients with syncope after initial presentation.