In 30 patients with a normal P R interval A H conduction time was analyzed by His bundle recordings during normal sinus rhythm (NSR) and atrial pacing (AP). AP was achieved at 100 and 120 stimuli/min for 2 and 5 min at each level. Continuous recordings were obtained before the onset of AP, during AP and on termination of AP. Two types of A H conduction patterns were observed. In 24 patients (group A), A H time gradually lengthened during the initial 10 paced beats; additional lengthening of a lesser magnitude occurred subsequently. In most cases the initial increase in A H time ranged from 15 to 30 msec. In the remaining six patients (group B) a wide range of beat to beat fluctuations in A H time was seen during the first 30 sec. The changes in A H time ranged from 150 to 225 msec and the prolongation of A H time was disproportionate to the increase in atrial rate unlike group A. Atropine administration in two of the group B patients abolished both the increment and wide swings in A H time. On termination of the AP the A H time immediately returned to control levels in all the 30 patients. These data are of significance during studies evaluating drug effect on A V nodal conduction. The initial gradual increase in A H time (group A) indicates that adaptive mechanisms in A V nodal conduction play a role during changes in atrial rate. These beat to beat wide fluctuations in A H time (group B) may be of significance in clinical interpretations of the standard ECG. Abolition of changes in A H time with Atropine suggests a role of vagal tone.
|Original language||English (US)|
|Number of pages||1|
|Issue number||3 (I)|
|State||Published - Jan 1 1973|
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