Termination, Advancement, and Delaying Responses to His Synchronous Premature Ventricular Contractions During Narrow QRS Tachycardia: What Are the Possible Mechanisms?

The differential diagnosis of a regular, narrow QRS, long-R–P tachycardia includes atypical atrioventricular nodal reentry tachycardia, atrial tachycardia, and atrioventricular reentry tachycardia via a slowly conducting accessory pathway with decremental conduction properties. Almost all described diagnostic maneuvers in the electrophysiology laboratory have exceptions to their primary interpretation. The usual proviso is that the observation must be reproducible.