Heart Block Disrupts Impulse Conduction to Ventricles

Steps:

• Normal heart rhythm starts at sinoatrial node (SAN), which generates impulses.
• Impulses travel to atrioventricular node (AVN) for conduction to ventricles.
• From AVN, impulses reach bundle of His, then Purkinje fibers for ventricular contraction.
• In heart block, normal initiation but poor ventricular conduction implicates AVN and Purkinje system.

Why A is correct:

• Heart block impairs AVN delay or block and Purkinje fiber spread, slowing ventricular rate per cardiac conduction physiology.

Why the others are wrong:

• B includes SAN, but impulses initiate normally there.
• C includes SAN, which functions correctly, and omits key AVN role.
• D targets only SAN, ignoring conduction pathway issues.

Final answer: A