Variation of P-QRS relation during atrioventricular node reentry tachycardia

OBJECTIVES The main objective of this study was to characterize the phenome non of variation in the P-QRS relation during atrioventricular node reentry tachycardia. BACKGROUND Variation of P-QRS relation during tachycardia has been observed occasionally in atrioventricular node reentry tachycardia. However, the in cidence, the characteristics and the mechanisms of this phenomenon have not been investigated previously. METHODS Retrospective analysis was performed in 311 consecutive patients wi th slow-fast form and 108 patients with atypical or multiple form of atriov entricular node reentry tachycardia to examine whether variation of P-QRS r elation with changes in AH, HA and AH/HA (A = atria; H = His bundle) ratio occurred during tachycardia. RESULTS A total of 28 patients, 8 with slow-fast and 20 with atypical or mu ltiple tachycardias, were found to manifest this phenomenon. There were 6 m ales and 22 females, with an average age of 38 +/- 16 years. In 10 patients , this phenomenon occurred transiently following electrical induction of th e tachycardia. In 15 patients, changes in AH, HA and AH/HA ratio were assoc iated with the occurrence of Wenckebach or 2:1 block proximal to the His bu ndle (H) recording site without interruption of the tachycardia. In nine pa tients, three with nonsustained tachycardia and six after administration of adenosine triphosphate, this phenomenon was observed at the termination of the tachycardia. This phenomenon was usually accompanied by a mild lengthe ning of the tachycardia cycle length. CONCLUSIONS Variation of P-QRS relation with or without block may occur dur ing atrioventricular node reentry tachycardia, especially in atypical or mu ltiple-form tachycardias. It was postulated that decremental conduction in the distal common pathway, which exists between the distal link of the reen try circuit and the H, is primarily responsible for this phenomenon. (C) 19 99 by the American College of Cardiology.