Recovery of retrograde fast pathway excitability in the atrioventricular node reentrant circuit after concealed anterograde impulse penetration

Abstract

The recovery of the retrograde fast pathway excitability in atrioventricular (AV) node reentry has been difficult to assess with ventricular extrastimulation because of difficulty in achieving sufficiently short intranodal coupling intervals and the potential interposition of “lower common pathway” nodal tissue. To circumvent these methodologic obstacles in 10 patients with inducible AV node reentrant tachycardia, a fixed atrial extrastimulus (A2) coupled to a basic atrial drive (A1) at a cycle length of 500 ms was utilized to reproducibly initiate AV node reentrant echoes. A ventricular extrastimulus (V3) was then introduced after A2at progressively shorter coupling intervals (A2V3) in an attempt to pre-excite the retrograde fast pathway after concealed anterograde penetration by A2.In six patients, retrograde fast pathway pre-excitation was achieved at critical A2V3intervals, as evidenced by the appearance of A3by up to 28 ± 6 ms in advance of the expected first AV node reentrant echo. In five of the six cases, the V3A3interval was virtually unaltered (≤5 ms decrease) when A2was omitted. In seven patients, at a critically short A2V3coupling interval (195 ± 27 ms), V3abruptly failed to elicit A3and concomitantly abolished all AV node echoes; yet when A2was omitted, an A3response returned, with V3A3identical to previous values.It is concluded that 1) anterograde concealment by A2in the retrograde fast pathway at onset of reentry car, be demonstrated in a significant proportion of patients with typical AV node reentrant tachycardia; 2) this concealment effect is most often manifested by retrograde block rather than decremental conduction; and (3) after concealed anterograde impulse penetration, the retrograde fast pathway in AV node reentrant tachycardia consists of tissue that, unlike the typical AV node, frequently exhibits an abrupt transition from full excitability to absolute refractoriness.