Electrophysiologic spectrum of concealed intranodal conduction during atrial rate acceleration in a model of 2:1 atrioventricular block.
Concealed anterograde penetration of the atrioventricular (AV) node has been used to explain a wide variety of electrocardiographic findings. The effects of atrial rate acceleration on this phenomenon remain undefined. To examine the dynamic interrelations between conducted and nonconducted beats at different atrial rates, a unique atrial pacing protocol of functional 2:1 AV block was used in 10 patients. The pacing protocol involved abrupt transitions from 2:1 to 1:1 AV conduction and enabled quantification of conduction delay produced by nonpropagated impulses over extremes of atrial rate. Stable 2:1 AV conduction was maintained over a mean range of atrial paced cycle lengths of 289 +/- 29.6 to 223 +/- 33.0 msec, respectively. The mean AV conduction time during 2:1 and corresponding 1:1 drives at the longest atrial paced rates were 169 +/- 33.5 and 136.5 +/- 26.9 msec, respectively--revealing a significant effect of nonpropagated impulses on subsequent conduction. Surprisingly, at the shortest atrial paced rates, the mean AV conduction times were 191.5 +/- 31.8 and 161.0 +/- 23.3 msec, respectively. The lack of significant changes in conduction time between 2:1 and 1:1 drives at the extremes of atrial rate (32.5 vs. 30 msec, p = NS) suggests that the effect of concealed conduction is "fixed" and independent of rate. Clinical implications and postulated electrophysiologic mechanisms are discussed.
McKinnie
J
J
Electrophysiology Laboratory, University of Wisconsin, Sinai Samaritan Medical Center, Milwaukee 53201.
Avitall
B
B
Caceres
J
J
Jazayeri
M
M
Tchou
P
P
Akhtar
M
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001283:Atrioventricular Node / Q000503:physiopathology*; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006327:Heart Block / Q000503:physiopathology*; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged