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True atrial tachycardia.

True atrial tachycardia.
True atrial tachycardia.

This narrow QRS tachycardia arises from an abnormal automatic focus or intra-atrial reentry. P waves precede the QRS complexes; it is often a long RP tachycardia (PR RP) but may be a short RP tachycardia (PR > RP) if atrioventricular nodal conduction is slow.