What best describes a bystander pathway?

• A. An accessory pathway that is part of the tachycardia circuit
• B. An associate pathway that is passively activated but not in the tachycardia circuit
• C. A pathway that terminates tachycardia when ablated
• D. A normal conduction pathway in the ventricles

Answer: (B)

A bystander pathway is an accessory conduction pathway that is activated by the tachycardia impulse but is not part of the reentrant circuit sustaining the tachycardia. It is activated passively and does not participate in maintaining the arrhythmia, so ablating it typically does not terminate the tachycardia. This is why the description that fits best is a pathway that is passively activated but not in the tachycardia circuit.

Why the other ideas don’t fit: if the pathway were part of the tachycardia circuit, it would be a participating, not a bystander, pathway. If ablation of the pathway terminates the tachycardia, it implies the pathway is essential to the circuit, not merely a bystander. A normal conduction pathway in the ventricles is not an accessory pathway and does not describe a bystander phenomenon.