electrocardiographic differential diagnosis of narrow qrs complex tachycardia an edoriented algorithmic approach the differentiation of narrow complex tachycardias is a common diagnostic conundrum encountered by emergency physicians although a number of published algorithms are available to assist the clinician in evaluating features of the 12lead electrocardiogram ecg many of these are too cumbersome requiring multiple decisions and introducing treatment suggestions within the diagnostic framework to optimize the diagnosis of the narrow complex tachycardia we propose 3 separate algorithms tailored to address varying levels of available clinical information the static algorithm depends only on the 12lead ecg without the benefit of historical data or diagnostic interventions the comparative algorithm requires a baseline ecg to which the presenting ecg is compared the dynamic algorithm encourages the clinician to take advantage of diagnostic maneuvers to further elucidate the tachycardia mechanism each of these algorithms requires the clinician to answer either yes or no for each criterion and does not include treatment recommendations