The mechanism of atrial tachycardia is typically enhanced automaticity, with or without some degree of block (not present in this case). The P wave rate is regular and can vary from 100-250 beats per minute; it is typically less than 200 beats per minute. The P wave in atrial tachycardia usually has a different morphology from the sinus P wave. The QRS is regular and usually narrow. Atrial tachycardia is usually episodic or particularly in children, incessant, and can be associated with heart or respiratory failure. The following animation illustrates what we have just described.