Correct answer: 3. Mahaim fiber tachycardia is always orthodromic
Mahaim fibers do not conduct retrogradely. So Mahaim fiber tachycardia is always with wide QRS complexes, antidromic with LBBB pattern.
It may be noted that in WPW syndrome both narrow QRS (orthodromic) and wide QRS (antidromic) tachycardia are possible as the pathway can conduct both anterogradely and retrogradely. Kent bundle responsible for WPW syndrome does not have decremental conduction, which is a usual property of the atrioventricular (AV) node. Read more on Mahaim fiber tachycardia.