Differential electrophysiologic properties of decremental retrograde pathways in long XXXX ' tachycardia.

@entity1 @entity859 @entity1855 @entity6391 @entity460 @entity972 @entity4710
Long @entity6391 ' @entity4710 ( @entity4710 ) often demonstrate both slow and decremental conduction properties in the retrograde pathway of the reentrant circuit. The electrophysiologic properties of these pathways are poorly understood. We studied 10 @entity1 with long @entity6391 ' @entity4710 ( @entity6391 '/RR, 0.52 to 0.71); five had the unusual form of atrioventricular nodal reentry (fast-slow) and five @entity1 had accessory AV pathways with slow, decremental retrograde conduction properties. During @entity4710 , the effects of intravenous @entity859 (37.5 to 150 micrograms/kg), which increases @entity972 current (iK) in supraventricular tissue and hyperpolarizes membrane potential toward Ek (-90 mV), and the response to slow-inward channel blockade with @entity1855 (0.10 to 0.20 mg/kg iv) were evaluated. @entity859 and @entity1855 has similar effects in the presence of fast-slow AV nodal reentry since both agents terminated @entity4710 by producing block in the retrograde slow AV nodal pathway. In contrast, @entity859 and @entity1855 had differential effects on retrograde conduction in decremental accessory pathways. @entity859 terminated all episodes of @entity4710 in the retrograde decremental pathway, whereas @entity1855 had a direct effect on this tissue in only two of five @entity1 . Decremental retrograde accessory pathways can therefore demonstrate at least two types of electrophysiologic responses. Pathways that respond only to @entity859 -induced hyperpolarizing K+ current likely comprise depressed fast-Na+ channel tissue, i.e., partially depolarized (greater than -60 to -70 mV) atrial tissue. In contrast, decremental accessory pathways that respond to both modulation of the slow-inward @entity460 current and K+ conductance have pharmacologic properties similar to those of the AV node and may represent more completely depolarized atrial fibers with resting membrane potentials of -60 mV or less.
