During pacing studies in a bypass tract, eccentric activation is a hallmark of which phenomenon?

During pacing studies in a bypass tract, eccentric activation is a hallmark of which phenomenon?

• A. Normal conduction
• B. Bypass tract presence
• C. Ventricular tachycardia
• D. Atrial tachycardia

Answer: (B)

Eccentric activation during pacing studies points to conduction through an accessory pathway rather than the normal His-Purkinje system. When a bypass tract is present, the impulse can reach parts of the ventricle or atrium via that pathway, so the earliest activation occurs at a site distant from the AV node. In mapping, this shows up as an activation sequence that is not the smooth, concentric spread you’d expect from normal conduction, but rather a nonuniform, distal-initiated pattern—hence “eccentric.” This characteristic pattern specifically indicates the existence of a bypass tract. Normal conduction would produce concentric activation, ventricular tachycardia and atrial tachycardia have distinct activation patterns tied to their circuits or foci, but the hallmark eccentric pattern during pacing is the telltale sign of an accessory pathway.

Eccentric activation during pacing studies points to conduction through an accessory pathway rather than the normal His-Purkinje system. When a bypass tract is present, the impulse can reach parts of the ventricle or atrium via that pathway, so the earliest activation occurs at a site distant from the AV node. In mapping, this shows up as an activation sequence that is not the smooth, concentric spread you’d expect from normal conduction, but rather a nonuniform, distal-initiated pattern—hence “eccentric.” This characteristic pattern specifically indicates the existence of a bypass tract. Normal conduction would produce concentric activation, ventricular tachycardia and atrial tachycardia have distinct activation patterns tied to their circuits or foci, but the hallmark eccentric pattern during pacing is the telltale sign of an accessory pathway.