Differentiation of atypical atrioventricular node re-entrant tachycardia from orthodromic reciprocating tachycardia using a septal accessory, pathwayby the response to ventricular pacing

OBJECTIVES The purpose of this study was to determine whether the response to ventricular pacing during tachycardia is useful for differentiating atyp ical atrioventricular node re-entrant tachycardia (AVNRT) from orthodromic reciprocating tachycardia (ORT) using a septal accessory pathway. BACKGROUND Although it is usually possible to differentiate atypical AVNRT from CRT using a septal accessory pathway, a definitive diagnosis is occasi onally elusive. METHODS In 30 patients with atypical AVNRT and 44 patients with ORT using a septal accessory pathway, the right ventricle was paced at a cycle length 10 to 40 ms shorter than the tachycardia cycle length (TCL). The ventriculo -atrial (VA) interval and TCL were measured just before pacing. The interva l between the last pacing stimulus and the last entrained atrial depolariza tion (stimulus-atrial [S-A] interval) and the post-pacing inter-Val (PPI) a t the right ventricular apex were measured on cessation of ventricular paci ng. RESULTS All 30 patients with atypical AVNRT and none of the 44 patients wit h ORT using a septal accessory pathway had an S-A-VA interval > 85 ms and P PI-TCL > 115 ms. CONCLUSIONS The S-A-VA interval and PPI-TCL are useful in distinguishing at ypical AVNRT from CRT using a septal accessory pathway. (C) 2001 by the Ame rican College of Cardiology.