Concealed conduction

Abstract: Extracellular action potentials of the A-V node (N), His bundle (H), and right bundle branch (RB) were recorded in subjects with an electrode cardiac catheter which was fluoroscopically positioned across the tricuspid valve. The N potential is a slow diphasic wave occurring between the atrial electrogram (P) and the H potential. It is characterized by slurring or notching on the upstroke. The H potential, as previously described, is a biphasic or triphasic wave of 15 to 20-msec duration. The RB potential is a fast biphasic wave of 10 to 20-msec duration occurring between the H potential and the Q wave. During single atrial pacing and premature atrial stimulation, the A-V conduction delay could be localized to the N-H interval. Evidence suggests that during aberrant ventricular conduction of the right bundle-branch block type the impulse was blocked proximally in the right bundle. During concealed conduction the nonconducted impulse was completely blocked within the A-V node or the N-H interval.

Abstract: Serial autocorrelation functions and histograms of R-R intervals in patients with atrial fibrillation, with and without digitalis, at rest and during exercise, were produced by a computer. At rest with and without digitalis the first and higher order coefficients did not differ from zero. During exercise (also with and without digitalis) only the first autocorrelation coefficient became slightly positive (in the order of 0.07) whereas the form of the histograms was profoundly altered by both exercise and digitalis. The change in form of the histograms reveals the change in electrophysiologic properties of the A-V conduction system. Since the serial autocorrelation functions were not influenced by digitalis and only slightly by exercise, the conclusion seems justified that the refractory period of, and the concealed conduction in, the A-V system cannot be (solely) responsible for the random nature of the ventricular rhythm in patients with atrial fibrillation. The effect of randomly spaced atrial impulses of random strength reaching the A-V node from random directions can explain these results.

Abstract: His and right bundle electrograms were recorded in a patient with unexplained P-R prolongations and periods suggestive of both type I and II second degree A-V block. The mechanism of these conduction disturbances was shown to be due to multiple nonpropagated premature His bundle depolarizations (H') which produced their effects on the subsequent cycle by virtue of concealed conduction into the A-V junction. The effects on A-V conduction were related to the time of occurrence of H' in relation to the subsequent P wave: If H'-P was short, a more profound conduction defect occurred. H' was generally undetectable on the ECG because of both antegrade and retrograde block, but a few propagated H' produced typical junctional premature contractions. Propagation of H' depended on a short preceding cycle length and a late occurrence of H'. The site of origin of H' appeared to be in the bundle of His. The mechanism of production of H' did not appear to be either reentry or parasystole. The term pseudo A-V block is u...

Abstract: Recognition of concealed conduction of the cardiac impulse is shown to be indispensable for the understanding of many cardiac arrhythmias. After a historical review of the concept of concealed conduction, records are presented to demonstrate established, as well as hitherto undescribed, aspects of concealed A-V conduction. Then, the manifestations of concealed intraventricular conduction are pointed out and, finally, the relationship of the phase of concealed conduction to the supernormal phase is discussed.