Since hypoxia inhibits conduction & automaticity predominantly in tissues dependent on the slow (Ca-channel) current, sinus node (SN) function should be selectively depressed. The effects of acute ...

however the P wave is not upright in lead II since it originates in the atrium at a different location than the sinus node.

This indicates that the pacemaker is coming from the sinus node and not elsewhere in the atria, with an atrial rate of greater than 100 beats per minute. The ventricular rate (indicated by the QRS ...