[[Image:DVA0237.jpg|thumb| In this narrow complex tachycardia with a normal morphology of the QRS-complexes (thus no ventricular tachycardia) you can see that there is AV-association (i.e. every QRS complex is preceded by a P-wave) but the P-waves are inverted (negative in aVF), therefore this is an atrial tachycardia ]]
In ill patients the atrial tachycardia may originate from multiple atrial sites and therefore may have varying P-wave morphologies, PR-intervals (AV block may occur) and subsequent variable ventricular frequencies. Vagal stimulation (carotid sinus massage) should lower AV conduction and will then clearly show the fast atrial rhythm dissociating from the ventricular rhythm (AV dissociation). Atrial tachycardias may be treated with antiarrhythmic drugs or ablation.