Electrophysiology of normal anterograde atrio-ventricular conduction with and without autonomic blockade.

The electrophysiological measures of atrio-ventricular (A-V) conduction were investigated in 20 normal subjects (mean age: 43.9 +/- 15.7 years) both during basal state and after pharmacological autonomic blockade. In the basal state A-H and H-V intervals and H wave duration ranged from 55-110 ms (mean 83 +/- 15.9), 35-45 ms (mean 39.5 +/- 3.9) and 10-20 ms (mean 17 +/- 4.1), respectively. The lowest atrial rate inducing Wenckebach periods ranged from 150-200 beats min-1 (mean 176.5 +/- 13.8). The effective refractory period (ERP) and the functional refractory period from FRP) of the atrium ranged from 160-260 ms (mean 211 +/- 26.7) and 210-280 ms (mean 252.5 +/- 21.2), respectively. The ERP and the FRP of the A-V node were in the ranges 230-310 ms (mean 269.3 +/- 27.2) and 330-450 ms (mean 395 +/- 41.2), respectively. After autonomic blockade the H-V interval and the H wave duration did not change in any subject. The A-H interval was in the range 55-105 ms (mean 82.5 +/- 15) and the lowest atrial rate inducing Wenckebach periods 150-220 beats min-1 (mean 179.5 +/- 13.5). The ERP and the FRP of the atrium ranged from 170-270 ms (mean 215.5 +/- 28.3) and 210-300 ms (mean 254 +/- 27.2), respectively. The ERP and the FRP of the A-V node were in the ranges 220-320 ms (mean 260.8 +/- 32) and 330-440 ms (mean 383.3 +/- 43.7), respectively. The A-V node variables did not change significantly following autonomic blockade. These data indicate that: the definition of normal values of A-V node measurements after autonomic blockade allow us to evaluate the role of the autonomic nervous system in the patients with A-V node conduction disturbances; in the basal state the normal values of A-V conduction variables we obtained, of refractory periods in particular, are shorter than those previously reported; this appears to be related to the strict criteria we used in subject selection.