Editorial note: The following quiz is related to the article Mahaim-mediated tachycardia using at times the atrioventricular node and other times a left lateral accessory pathway, by Jabri and colleagues from the October 2021 issue of Heart Rhythm Case Reports.

Question 1: The baseline 12-lead ECG during sinus rhythm in a patient with Mahaim (atriofascicular) accessory pathway usually shows the following:

Question 2: Which unique electrophysiological features of Mahaim fibers allow its differentiation from other accessory pathways?

Question 3: What is the mechanism of tachycardia utilizing a Mahaim atriofascicular pathway?

Question 4: Which of the following congenital abnormalities are Mahaim fibers most commonly associated with?