title: Beat-to-beat changes in atrioventricular nodal excitability and its modulation by concealed conduction during functional 2:1 block in man.
abstract: An atrial pacing model of functional 2:1 block was used in 10 patients to investigate for the first time the electrophysiologic properties of the human atrioventricular node during intermittent conduction. By varying the terminal portion of the 2:1 atrial train and using the extrastimulus technique, we characterized atrioventricular nodal (AVN) conduction and refractoriness after five different methods of AVN activation: a conducted beat (method I), a conducted beat with omission of the prior blocked beat (method II), a blocked beat (method III), a blocked beat "converted" to one that conducts by omission of the prior conducted beat (method IV), and finally, 1:1 conduction at twice the cycle length of the 2:1 train (control method V). Observed AVN conduction times obeyed the following relationship: method I greater than method II greater than method V, indicating a cumulative effect of concealed penetration by the blocked beats. During 2:1 block, the AVN effective refractory period (ERP) alternated with a mean beat-to-beat difference of at least 100 msec, due mostly to marked ERP abbreviation during AVN activation by method III (vs both 2:1 train cycle length and activation by method V). Concealed penetration by the blocked beat prolonged AVN ERP for the propagated beat (vs that with methods II and V), but to a lesser extent than conduction time was increased. Moreover, the AVN recovery curve with method I was displaced upward and to the right compared with that with methods II to V.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000328:Adult; D000368:Aged; D001283:Atrioventricular Node / Q000502:physiology* / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D005260:Female; D006327:Heart Block / Q000503:physiopathology*; D006329:Heart Conduction System / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012032:Refractory Period, Electrophysiological