HETEROGENEITY OF ANTEROGRADE FAST-PATHWAY AND RETROGRADE SLOW-PATHWAYCONDUCTION PATTERNS IN PATIENTS WITH THE FAST-SLOW FORM OF ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA - ELECTROPHYSIOLOGIC AND ELECTROCARDIOGRAPHIC CONSIDERATIONS

Objectives. This study sought to define the electrophysiologic and ele ctrocardiographic characteristics of fast-slow atrioventricular nodal reentrant tachycardia (AVNRT). Background. In fast-slow AVNRT the retr ograde slow pathway (SP) is located in the posterior septum, whereas t he anterograde fast pathway (FP) is located in the anterior septum; ho wever, exceptions may occur. Methods. Twelve patients with fast-slow A VNRT were studied. To determine the location of the retrograde SP, atr ial activation during AVNRT was examined while recording the electrogr ams from the low septal right atrium (LSRA) on the His bundle electrog ram and the orifice of the coronary sinus (CS). Further, to investigat e the location of the anterograde FP, single extrastimuli were deliver ed during AVNRT both from the high right atrium and the CS. Results. T he CS activation during AVNRT preceded the LSRA in six patients (poste rior type); LSRA activation preceded the CS in three patients (anterio r type), and in the remaining three both sites were activated simultan eously (middle type). In the anterior type, CS stimulation preexcited the His and the ventricle without capturing the LSRA electrogram (atri al dissociation between the CS and the LSRA), suggesting that the ante rograde FP was located posterior to the retrograde SP. In the posterio r and middle types, high right atrial stimulation demonstrated atrial dissociation, suggesting that the anterograde FP was located anterior to the SP. In the posterior and middle types, retrograde P waves in th e inferior leads were deeply negative, whereas they were shallow in th e anterior type. Conclusions. Fast-slow AVNRT was able to be categoriz ed into posterior, middle and anterior types according to the site of the retrograde SP. The anterior type AVNRT, where an anteriorly locate d SP is used in the retrograde direction and a posteriorly located FP in the anterograde direction, appears to represent an anatomical rever sal of the posterior type which uses a posterior SP for retrograde and an anterior FP for anterograde conduction. Anterior type AVNRT should be considered in the differential diagnosis of long RP (RP > PR inter vals) tachycardias with shallow negative P waves in the inferior leads . (J Am Cell Cardiol 1998;32:1731-40) 01998 by the American College of Cardiology.