COMPARISON OF ATRIAL-HIS INTERVALS DURING TACHYCARDIA AND ATRIAL-PACING IN PATIENTS WITH LONG RP TACHYCARDIA

Long RP Tachycardia, Introduction: The purpose of this study is to des cribe a simple and reliable diagnostic maneuver that allows for the ra pid differentiation of atypical AV nodal reentrant tachycardia (AVNRT) from other causes of long RP tachycardia. Long RP tachycardias may be caused by atypical AVNRT, orthodromic reciprocating tachycardia (ORT) involving a slowly conducting retrograde accessory pathway, or atrial tachycardia. The differentiation of atypical AVNRT from ORT or atrial tachycardia may be difficult, especially when the differential diagno sis includes a posteroseptal accessory pathway or an atrial tachycardi a arising in the posteroseptal right atrium. Methods and Results: Twel ve patients with atypical AVNRT, 21 with ORT, and 12 with an atrial ta chycardia diagnosed using conventional criteria were enrolled in this study. The atrial-His (AH) interval was measured at the His-bundle pos ition during the tachycardia and during atrial pacing from the high ri ght atrium at the tachycardia cycle length in the setting of sinus rhy thm. In patients,vith atypical. AVNRT, the mean AH interval was 69 mse c +/- 50 msec (+/- SD) longer during high right atrial pacing than dur ing the tachycardia (P < 0.001). In 10 of 12 patients with atypical AV NRT, the AH interval during atrial pacing was more than 40 msec longer than the AH interval measured during the tachycardia. In contrast, in patients with ORT or atrial tachycardia, the differences in AH interv al between atrial pacing and tachycardia were never more than 20 and 1 0 msec, respectively. Conclusion: The difference in the AH interval be tween atrial pacing and the tachycardia allows a simple and rapid mean s of differentiating atypical AVNRT from other types of long RP tachyc ardias.