QUANTITATIVE-ANALYSIS OF CONCEALED CONDUCTION INTO ACCESSORY ATRIOVENTRICULAR PATHWAYS IN WOLFF-PARKINSON-WHITE-SYNDROME

Concealed conduction is demonstrated to occur in an accessory AV pathw ay (AP). To test the hypothesis that anterograde and retrograde concea led conduction in the AP would have different characteristics, 35 cons ecutive patients with single APs were studied. The anterograde or retr ograde ERP of the AP could be determined in 23 of those patients. Ante rograde concealed conduction in the AP was assessed in the first 23 pa tients with retrograde AP conduction (8 APs with retrograde conduction only and 5 with both directions) (group A). Retrograde concealed cond uction in the AP was evaluated in the remaining 10 patients with anter ograde AP conduction (6 APs with anterograde conduction only and 4 wit h both directions) (group B). The concealed conduction in the AP Mras quantified by determining the ERP of the AP using a ''probe'' extrasti mulus (S-p) introduced in the opposite chamber. The ERP was determined both during conventional extrastimulus (S1S2 method; ERPc) and during that with an S-p (S1SpS2 method; ERPp). The S-p was delivered before or after the last S-1 with various S1Sp, intervals. The ERP, was deter mined at each SIS, interval. Three distinct patterns in concealed cond uction in the AP were noted. In the first pattern, the ERPp was always shorter than the ERPc, whereas the reverse relation was noted in the second pattern. The third pattern showed a combination of the two. In group A, only the first pattern was noted. In group B, the first, seco nd, and third patterns M ere noted in 4, 2, and 4 patients, respective ly. The first pattern was noted only in septal APs and the second and third were seen only in left free-wall APs. The second pattern was see n in patients with retrograde AP conduction, whereas the third one was mainly noted in patients without retrograde AP conduction. These obse rvations indicate that anterograde and retrograde concealed conduction in the AP have different characteristics. Shortening of the ERP, migh t be due to the ''peeling back'' phenomenon.