Electrophysiologic effects of atropine on human sinus node and atrium

Electrophysiologic studies were conducted in 17 patients without apparent sinus node disease before and after intravenous administration of 1 to 2 mg of atropine. Mean values in milliseconds (± standard error of the mean) before and after administration of atropine were as follows: sinus cycle length 846 ± 26.4 versus 647 ± 20.0 (P <0.001); sinus nodal recovery time 1,029 ± 37 versus 774 ± 36 (P <0.001); mean calculated sinoatrial (S-A) conduction time 103 ± 5.7 versus 58 ± 3.9 (P <0.001); mean P-A interval 34 ± 1.5 msec versus 31 ± 1.5 (P < 0.05); mean atrial effective and functional refractory periods during sinus rhythm 285 ±11.3 versus 238 ± 7.9 and 331 ± 11.6 versus 280 ± 8.6, respectively (P <0.001 for both); mean atrial effective and functional refractory periods measured at equivalent driven cycle length 239 ± 7.7 versus 213 ± 7.4 and 277 ±11.4 versus 245 ± 9.5, respectively (P <0.001 for both). In conclusion, atropine shortened sinus cycle length, sinus nodal recovery time and calculated S-A conduction time. The shortening of atrial refractory periods with atropine implies that vagotonia prolongs atrial refractoriness in man.