An RSR' pattern in leads V5 or V6 on an electrocardiogram indicates which conduction abnormality?

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Multiple Choice

An RSR' pattern in leads V5 or V6 on an electrocardiogram indicates which conduction abnormality?

The main idea is intraventricular conduction delay—specifically a block of the left bundle branch. When the left ventricle’s activation is slowed, the depolarization that progresses through the left ventricle happens later than the initial activation, which produces a distinctive pattern in the leads that look at the left lateral wall (the chest leads toward the apex and left side). In these lateral leads, you can see an R wave, then a second positive deflection (an R′) as the left ventricle finally depolarizes. This results in an RS R′ pattern in those leads, and the overall QRS is widened (over 120 ms), both of which point toward left bundle branch block. This aligns with left bundle block rather than right bundle block, which typically shows the RSR′ pattern in the right precordial leads (V1–V3). Atrial fibrillation would give an irregular rhythm without a defined QRS morphology, and first-degree AV block shows a prolonged PR interval with a normal QRS morphology.

The main idea is intraventricular conduction delay—specifically a block of the left bundle branch. When the left ventricle’s activation is slowed, the depolarization that progresses through the left ventricle happens later than the initial activation, which produces a distinctive pattern in the leads that look at the left lateral wall (the chest leads toward the apex and left side). In these lateral leads, you can see an R wave, then a second positive deflection (an R′) as the left ventricle finally depolarizes. This results in an RS R′ pattern in those leads, and the overall QRS is widened (over 120 ms), both of which point toward left bundle branch block.

This aligns with left bundle block rather than right bundle block, which typically shows the RSR′ pattern in the right precordial leads (V1–V3). Atrial fibrillation would give an irregular rhythm without a defined QRS morphology, and first-degree AV block shows a prolonged PR interval with a normal QRS morphology.

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