Sequence of Cardiac Impulse Conduction Steps:

• Impulse originates at sinoatrial (SA) node, initiating the cycle (statement 4).
• Impulse spreads rapidly through atrial myocardium via internodal pathways.
• Impulse arrives at atrioventricular (AV) node.
• AV node delays impulse briefly to allow atrial contraction to complete (statement 3). Why B is correct:
• The AV node delay is the fourth event, as defined in cardiac conduction physiology, ensuring atria empty before ventricular depolarization begins. Why the others are wrong:
• A: Purkinje tissue conduction occurs after AV delay, during ventricular depolarization.
• C: SA node activation is the first event, starting the impulse.

Final answer: B