Electric sign of the activity of the sinus node in the dog heart

The possibility of local recording of the electrical activity of the sinus node was investigated on 22 dogs. Using a small unipolar electrode positioned at the proximity of the sinus node and applying a 2-4-fold electric amplification, an early, slow and low-amplitude wave could be recorded 20-40 ms before the P wave. This early wave gradually decreased when the electrode was moved away from the sinus node and finally fused into the local P wave. Temporary arrest of sinus node activity by injection of adenosine into the sinus node artery, electrical stimulation of the vagal nerve by infiltration with phenol of the sinus node region made the local P wave to disappear. Similarly, no early action before the P wave could be seen if the sinus node was driven electrically. The early wave recorded in the proximity of the sinus node represents the depolarization of the sinus node, and it is suitable to study the pacemaker activity of the sinus node together with sinoauricular conduction.