THE EFFECT OF VARIABLE RETROGRADE PENETRATION ON DUAL AV NODAL PATHWAYS - OBSERVATIONS BEFORE AND AFTER SLOW PATHWAY ABLATION LDD

Retrograde VA conduction is usually or er the fast pathway and rarely over the slow pathway in patients with dual AV nodal pathways. It is u nknown whether this apparent unidirectional conduction of the slow pat hway is due to the lack of its retrograde conducting ability or the re sult of concealment. The effect of variable retrograde AV nodal penetr ation on antegrade AV nodal conduction was determined in patients with typical AV nodal reentrant tachycardia before and after the slow path way ablation. Variable retrograde penetration was produced by deliveri ng a ventricular extrastimulus simultaneously with (VE-0), 50 ms after (VE-50), or 100 ms after (VE-100) the last basic atrial stimulus, whi le atrial extrastimuli were used to determine changes of anterograde A V nodal effective refractory period (ERP) and A-H interval. The AV nod al functions measured without the ventricular extrastimuli sen ed as t he baseline. Although the mean slow pathway ERP rr as not significantl y different among the different stimulation protocols, a significant s hortening of the slow pathway conduction time (A-H from 348 +/- 60 to 324 +/- 119 ms, P < 0.05) was observed with upper level retrograde pen etration of the Air node (VE-0). This facilitating effect became a pro longing effect when the retrograde penetration level moved to the lowe r level (VE-100, A-H from 324 +/- 119 to 366 +/- 122 ms P < 0.05). The fast path rr av ERP shortened with an upper level penetration (VE-0) but tended to prolong with a lower level retrograde penetration (VE-10 0) both before and after the slow pathway ablation (preablation, from 348 +/- 143 of the baseline to 302 +/- 114 to 360 +/- 143 ms, P < 0.05 ; postablation, from 314 +/- 101 of the baseline to 274 +/- 118 to 361 +/- 143 ms, P < 0.05). The mean A(2)-H-2 interval of the slow pathway was significantly shorter than the baseline (350 +/- 44 ms) with VE-0 (249 +/- 48 ms, P < 0.05) and VE-50 stimulation (285 +/- 82 ms, P < 0 .05) but not with VE-100 stimulation (330 +/- 83 ms, P = NS). Before s low pathway ablation, the A(2)-H-2 interval of the fast pathway at equ al coupling intervals was shorter than the baseline (165 +/- 53 ms) wi th VE-0 (144 +/- 47 ms, P < 0.01) and VE-50 stimulation (152 +/- 43 ms , P < 0.05) but tended to be longer with VE-100 stimulation (175 +/- 4 7 ms, P = NS). After slow pathway ablation, the mean A(2)-H-2 interval at the same coupling interval rr as shorter than the baseline (173 +/ - 39 ms) with VE-0 (139 +/- 35 ms, P < 0.05), VE-50 (153 +/- 32 ms, P = 0.05) but tended to be longer with VE-100 stimulation (178 +/- 49 ms , P = NS). We conclude that: (I) concealed retrograde conduction can b e demonstrated in both the slow and rhs fast ii Ir nodal pathways; and (2) concealed retrograde conduction may either shorten or prolong ant erograde refractoriness and conduction time, depending on the level of retrograde penetration.