The effects of atropine on sinoatrial conduction time directly measured from sinus node electrogram. A comparison with results furnished by indirect methods.

The effects of atropine on sinoatrial conduction time (SACT) measured directly (SACTD) from the sinus node electrogram (SNE) were investigated in 15 patients with normal sinus node function. A comparison was undertaken with the results furnished by indirect methods which employ premature (SACTS) and asynchronous atrial stimulation (SACTN) to calculate SACT. In the control state SACTD was 92.5 +/- 16.4 ms, SACTS 78.2 +/- 22 ms, and SACTN 97.9 +/- 32.2 ms. After atropine SACTD was 70.6 +/- 15.6 ms (P less than 0.0005), SACTS 46.7 +/- 14.3 ms (P less than 0.0005) and SACTN 43.1 +/- 12.7 ms (P less than 0.0005). Mean percent decreases of SACTN (51.6 +/- 21) and SACTS (37.4 +/- 18) were statistically greater than that of SACTD (23.5 +/- 13.3) (P less than 0.0005 and P less than 0.01 respectively). While the reduction of SACTS and SACTN was greater than that of sinus cycle length (SCL) (29.2%), SACTD showed a reduction significantly less than that of SCL (P less than 0.005). Thus, SNE recording confirms that atropine induces a shortening of SACT in normal patients, but significantly less than that indicated by indirect methods.