Left bundle branch block is characterized by which of the following QRS patterns in lateral leads?

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Multiple Choice

Left bundle branch block is characterized by which of the following QRS patterns in lateral leads?

Left bundle branch block changes how the ventricles activate, so the QRS becomes wide and the left ventricle shows late, abnormal activation. In the lateral leads (I, aVL, V5–V6) this produces broad, notched (or M-shaped) R waves with a slurred upstroke. Because normal septal activation is disrupted, the small initial Q waves that you’d expect in these leads are often absent. So a QRS that is wide (≥120 ms) with broad, notched, slurred R waves in the lateral leads and no initial q waves fits LBBB best. Patterns like rsR' in V1 point to RBBB, ST elevations in inferior leads suggest an MI, and a short PR interval points to pre-excitation; none of those describe LBBB in the lateral leads.

Left bundle branch block changes how the ventricles activate, so the QRS becomes wide and the left ventricle shows late, abnormal activation. In the lateral leads (I, aVL, V5–V6) this produces broad, notched (or M-shaped) R waves with a slurred upstroke. Because normal septal activation is disrupted, the small initial Q waves that you’d expect in these leads are often absent. So a QRS that is wide (≥120 ms) with broad, notched, slurred R waves in the lateral leads and no initial q waves fits LBBB best. Patterns like rsR' in V1 point to RBBB, ST elevations in inferior leads suggest an MI, and a short PR interval points to pre-excitation; none of those describe LBBB in the lateral leads.

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