Define Orthodromic and Antidromic AVRT.

• A. Orthodromic: down AP, up AVN
• B. Orthodromic: down AVN, up AP
• C. Antidromic: down AP and up AVN
• D. Antidromic: down AVN and up AP

Answer: (B)

In AVRT, the branch of the reentrant circuit that conducts toward the ventricles (anterograde) and the branch that conducts back toward the atria (retrograde) define the type. For orthodromic AVRT, the impulse travels antegrade through the AV node to activate the ventricles, then returns to the atria via the accessory pathway in a retrograde direction. So the circulating directions are down the AV node to the ventricles and up through the accessory pathway to the atria. That matches the description of orthodromic as down the AV node and up the accessory pathway. In antidromic AVRT, the order is reversed: down the accessory pathway to the ventricles and up through the AV node to the atria, which is the opposite pattern. Clinically, orthodromic AVRT usually presents with a narrow QRS because ventricular activation mostly follows the normal conduction system, whereas antidromic AVRT tends to produce a wide QRS.