Which structure has the slowest conduction, delaying conduction into the ventricles?

Which structure has the slowest conduction, delaying conduction into the ventricles?

• A. AV Node
• B. Purkinje Fibers
• C. Atrial Myocardium
• D. Ventricular Myocardium

Answer: (A)

The important concept is that the AV node deliberately slows the electrical signal between the atria and the ventricles to allow adequate ventricular filling before contraction. The AV node has fewer gap junctions and relies on calcium-mediated conduction, so its upstroke is slower and the impulse moves through it more slowly than through atrial or ventricular myocardium or the Purkinje system. This slow conduction creates the essential delay that is seen as the PR interval on the ECG, ensuring the ventricles receive the atrial blood before they contract. In contrast, Purkinje fibers conduct quickly to rapidly depolarize the ventricles, while atrial and ventricular muscle conductors are faster than the AV node but slower than Purkinje tissue. So the structure that provides the slowest conduction is the AV node.

The important concept is that the AV node deliberately slows the electrical signal between the atria and the ventricles to allow adequate ventricular filling before contraction. The AV node has fewer gap junctions and relies on calcium-mediated conduction, so its upstroke is slower and the impulse moves through it more slowly than through atrial or ventricular myocardium or the Purkinje system. This slow conduction creates the essential delay that is seen as the PR interval on the ECG, ensuring the ventricles receive the atrial blood before they contract. In contrast, Purkinje fibers conduct quickly to rapidly depolarize the ventricles, while atrial and ventricular muscle conductors are faster than the AV node but slower than Purkinje tissue. So the structure that provides the slowest conduction is the AV node.