A completely negative LBBB appearance on lead V1 indicates VT origin from which chamber?

A completely negative LBBB appearance on lead V1 indicates VT origin from which chamber?

• A. Right ventricle
• B. Left ventricle
• C. Atrioventricular node
• D. His-Purkinje system

Answer: (A)

The main idea is that the direction of the initial depolarization in VT shows where the impulse starts. Lead V1 sits over the right ventricle, so if the QRS in V1 is a completely negative QS complex, the earliest activation is moving away from V1. In a VT that has a left-bundle-branch–block–like pattern (wide QRS with LV activation characteristics) this away-from-V1 vector points from the right ventricle into the left ventricle. That makes the QRS in V1 entirely negative, signaling a right-ventricle origin. If the focus were in the left ventricle, the initial activation would tend to move toward V1, producing at least some positive deflection in V1, not a fully negative complex. The options involving the AV node or His-Purkinje system describe nonchamber origins or different activation patterns and don’t fit the characteristic V1 negativity seen with RV-origin VT.

The main idea is that the direction of the initial depolarization in VT shows where the impulse starts. Lead V1 sits over the right ventricle, so if the QRS in V1 is a completely negative QS complex, the earliest activation is moving away from V1. In a VT that has a left-bundle-branch–block–like pattern (wide QRS with LV activation characteristics) this away-from-V1 vector points from the right ventricle into the left ventricle. That makes the QRS in V1 entirely negative, signaling a right-ventricle origin.

If the focus were in the left ventricle, the initial activation would tend to move toward V1, producing at least some positive deflection in V1, not a fully negative complex. The options involving the AV node or His-Purkinje system describe nonchamber origins or different activation patterns and don’t fit the characteristic V1 negativity seen with RV-origin VT.