Final answer:
ECG during orthodromic AVRT usually presents with a normal sinus rhythm and a narrowed QRS complex, without the presence of a delta wave.
Step-by-step explanation:
The ECG during orthodromic AVRT typically shows a normal sinus rhythm with a shortened PR interval and potentially a slurred upstroke in the QRS complex, known as a delta wave. However, during orthodromic AVRT, the delta wave is typically absent, and the QRS complex usually appears narrow unless there is underlying ventricular conduction delay. The condition involves reentrant tachycardia utilizing the atrioventricular (AV) node and an accessory pathway in a circuit for AV reentry. An important characteristic of orthodromic AVRT is the sequence of atrial and ventricular activation; because the ventricles are activated normally (via the AV node and His-Purkinje system), the QRS complex does not show the preexcitation pattern that is characteristic of antidromic AVRT, where the ventricles are activated first through the accessory pathway. Understanding these details is valuable in diagnosing and managing tachyarrhythmias.