12-lead electrocardiogram (ECG) showing orthodromic atrioventricular reentrant tachycardia (AVRT) in a patient with an accessory AV pathway

The 12-lead ECG from a patient with Wolff-Parkinson-White shows a regular tachycardia. However, in contrast to the QRS pattern during sinus rhythm, the QRS complexes are narrow, without evidence of a delta wave or pre-excitation; this is due to the fact that antegrade ventricular activation occurs via the normal atrioventricular node-His Purkinje pathway, while retrograde atrial activation is via the accessory pathway. Therefore, this is called an orthodromic atrioventricular reentrant tachycardia (OAVRT).

The 12-lead ECG shows the typical features of Wolff-Parkinson-White; the PR interval is short (*) and the QRS duration prolonged as a result of a delta wave (arrow), indicating ventricular preexcitation.