CFM Cardiology Practice Test

Which of the following is a criterion for left bundle branch block?

QRS >120 ms Q waves in lateral leads Broad terminal R wave in V1-V3 Prolonged PR interval

Correct Answer:

QRS >120 ms

Explanation:

Left bundle branch block shows delayed activation of the left ventricle, which makes the QRS complex widen. The defining feature is a QRS duration of 120 milliseconds or more, indicating intraventricular conduction delay. Other patterns described aren’t used to define LBBB: Q waves in lateral leads aren’t a required criterion and are often absent in LBBB; a broad terminal R wave in V1–V3 is more typical of a right bundle branch block pattern; and a prolonged PR interval points to first-degree AV block, not LBBB.

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