Cardiac conduction delay at AV node

Steps:

• Excitation begins at SA node and spreads rapidly across atria, causing atrial contraction.
• Impulse reaches AV node in interatrial septum, a narrow junction that slows conduction.
• Delay at AV node ensures atria empty blood into ventricles before ventricular contraction.
• Impulse then travels via AV bundle and Purkinje fibers to ventricles.

Why B is correct:

• AV node consists of small, specialized conducting fibers that inherently delay impulse transmission by 0.1 seconds, per cardiac physiology, allowing sequential contraction.

Why the others are wrong:

• A: AV bundle (not a "band of fibres") conducts quickly after AV node delay.
• C: Travel distance is not the primary factor; physiological delay at AV node is key.
• D: Purkinje tissue conducts rapidly, not slowly, to synchronize ventricular contraction.

Final answer: B