Cardiac conduction system activation pathway: which sequence is correct?

• A. SA node → cell-to-cell communication and specialized atrial fibers → AV node → Bundle of His → Left and Right bundle branches → Purkinje fibers → cell-to-cell communication throughout rest of cardiac tissue
• B. SA node → AV node → Bundle of His → Purkinje fibers → Left and Right bundle branches → cell-to-cell communication throughout rest of cardiac tissue
• C. SA node → Purkinje fibers → AV node → Bundle of His → Left and Right bundle branches → cell-to-cell communication throughout rest of cardiac tissue
• D. SA node → cell-to-cell communication throughout rest of cardiac tissue → AV node → Bundle of His → Purkinje fibers → Left and Right bundle branches

Answer: (A)

The main idea here is the normal order of electrical activation in the heart. The impulse starts in the sinoatrial (SA) node and spreads through the atrial myocardium via cell-to-cell connections (gap junctions). Then it reaches the atrioventricular (AV) node, which provides a brief delay to allow the atria to contract and fill the ventricles. From the AV node, the impulse travels down the His-Purkinje system: bundle of His, then left and right bundle branches, then Purkinje fibers, which rapidly distribute the impulse to the ventricular myocardium. After reaching the Purkinje network, activation spreads through the ventricles by cell-to-cell connections to produce coordinated contraction.

This sequence is correct because it preserves the AV nodal delay and follows the specialized conduction pathways (His-Purkinje) leading to rapid, uniform ventricular activation, ending with spread to ventricular muscle via gap junctions. Sequences that place Purkinje fibers before the AV node, or skip key steps, do not reflect the true pathway of normal cardiac conduction.