Basic EPS: How to Differentiate the Mechanisms of Narrow and Wide Complex Tachycardias?

Abstract

A systematic approach to differentiate tachycardia of narrow and wide complex QRS morphology includes physical signs/symptoms, simple ECG criteria, pharmacologic and stimulation maneuvers in the EP lab. If narrow QRS duration ( 100 bpm in adults) is shown on 12 lead ECG, then additional ECG criteria such as RR regularity, RP/PR relation, onset/offset of tachycardia and response to vagal maneuvers or adenosine is examined to differentiate between AVNRT, pathway mediated tachycardia or atrial tachycardia. If wide complex tachycardia (WCT) is shown, then QRS morphology (compared with sinus), evidence of AV dissociation, QRS concordance pattern, fusion/capture beats are useful to differentiate if WCT is SVT with aberration, VT or preexcited tachycardia. Stimulation maneuvers include response of tachycardia to extrastimului, reset response to entrainment pacing. A His-refractory PVC delivered into SVT that is able to advance retrograde atrial activation timing with the same tachycardia sequence and resets or terminates tachycardia is diagnostic proof of a pathway mediated SVT and excludes AVNRT. A delta-VA of <85 ms or PPI-Tachy CL of <115 ms after ventricular entrainment pacing favors pathway mediated SVT over AVNRT. Post pacing VAAV response is more consistent with atrial tachycardia. Measurement of the HV interval during WCT helps to differentiate the mechanism, HV that is the same or longer than in sinus is consistent for SVT with aberration.