Which conduction disturbance represents a complete heart block that requires pacing for safety?

Which conduction disturbance represents a complete heart block that requires pacing for safety?

• A. First-degree AV block.
• B. Third-degree AV block without pacing.
• C. Second-degree AV block Type I.
• D. Left bundle branch block.

Answer: (B)

A complete heart block means no atrial impulses reach the ventricles. The atria and ventricles beat independently—P waves occur at one rate while the QRS complexes appear at their own slower, separate rate. Because the ventricles rely on a slow escape rhythm, the heart rate is usually inadequate to maintain perfusion, which can lead to dizziness, syncope, or arrest. To keep a safe, reliable heart rate, pacing is required. This differs from first-degree AV block, where every atrial impulse still conducts to the ventricles, just with a longer PR interval, so pacing isn’t typically needed. Second-degree AV block type I shows progressive PR prolongation with occasional dropped beats and is often observed rather than immediately requiring pacing. Left bundle branch block is a ventricular conduction delay, not a complete AV block, and does not by itself necessitate pacing for safety.

A complete heart block means no atrial impulses reach the ventricles. The atria and ventricles beat independently—P waves occur at one rate while the QRS complexes appear at their own slower, separate rate. Because the ventricles rely on a slow escape rhythm, the heart rate is usually inadequate to maintain perfusion, which can lead to dizziness, syncope, or arrest. To keep a safe, reliable heart rate, pacing is required.

This differs from first-degree AV block, where every atrial impulse still conducts to the ventricles, just with a longer PR interval, so pacing isn’t typically needed. Second-degree AV block type I shows progressive PR prolongation with occasional dropped beats and is often observed rather than immediately requiring pacing. Left bundle branch block is a ventricular conduction delay, not a complete AV block, and does not by itself necessitate pacing for safety.