Popular Cardiologist in Vidyaranyapura, Bangalore • Atrial tachycardia The diagnosis of atrial tachycardia is based on the presence of P waves different from sinus P waves and from retrograde junctional ones; if the P waves are identical to sinus ones, it is called sinoatrial tachycardia. Most atrial tachycardias represent autonomous focal discharge rather than re-entry. The onset of AV block (as a result of drug treatment or carotid sinus massage) will reduce the ventricular rate without affecting the atrial rate Atrial tachycardia with block Atrial tachycardia with block (paroxysmal atrial tachycardia (PAT) with block) is also an autonomous (automatic, ectopic) atrial tachycardia but its P waves are usually smaller (often discernible only in lead V1) and faster. As a result of this high rate, AV block often variable—is usually present prior to any exposure to drugs or vagal manoeuvres . In the past this was one of the classic manifestations of digoxin toxicity. It can be difficult to distinguish from other atrial rhythms such as AF, flutter and even sinus rhythm