AH interval prolongs with decreasing S1-S2 coupling intervals because decreased conduction down the AVN.

AH interval prolongs with decreasing S1-S2 coupling intervals because decreased conduction down the AVN.

• A. True
• B. False
• C. Because AVN conduction improves
• D. Not related

Answer: (A)

AH interval measures how long it takes for an impulse to travel through the AV node from the atrium to the His bundle. In a programmed atrial stimulation protocol that uses an S1 drive train with an extrastimulus S2, delivering S2 sooner after S1 (a shorter S1-S2 coupling interval) challenges the AV node. The AV node shows decremental conduction—its conduction velocity slows down as the impulse arrives earlier or at higher frequency. Because of this decremental property and the AV node’s relative refractoriness, the impulse takes longer to pass through the AV node, so the AH interval lengthens. Therefore, shortening the S1-S2 coupling interval causes prolongation of the AH interval due to decreased (slower) conduction in the AV node. The alternative explanations aren’t correct: AVN conduction does not improve with shorter coupling intervals, and the relationship is not “not related.”

AH interval measures how long it takes for an impulse to travel through the AV node from the atrium to the His bundle. In a programmed atrial stimulation protocol that uses an S1 drive train with an extrastimulus S2, delivering S2 sooner after S1 (a shorter S1-S2 coupling interval) challenges the AV node. The AV node shows decremental conduction—its conduction velocity slows down as the impulse arrives earlier or at higher frequency. Because of this decremental property and the AV node’s relative refractoriness, the impulse takes longer to pass through the AV node, so the AH interval lengthens.

Therefore, shortening the S1-S2 coupling interval causes prolongation of the AH interval due to decreased (slower) conduction in the AV node. The alternative explanations aren’t correct: AVN conduction does not improve with shorter coupling intervals, and the relationship is not “not related.”