Orthodromic atrioventricular reentrant tachycardia (AVRT) in the setting of an accessory AV pathway

The rhythm strip shows a sinus (S) beat that has a short PR interval and a wide QRS complex as a result of a delta wave (d). Panel A shows an atrial premature beat (APB,*) that is blocked in the accessory pathway (AP), which has a long refractory period but is conducted antegradely through the atrioventricular node (N) and the His-Purkinje system, resulting in a normal PR interval and a narrow and normal QRS complex, as seen on the rhythm strip. After normal myocardial activation, the impulse is conducted retrogradely along the AP, activating the atrium in a retrograde fashion (panel B), which results in a negative P wave. If this activation sequence repeats itself (panel C), an orthodromic atrioventricular reentrant (or reciprocating) tachycardia (AVRT) is established.