Third-degree AV block typically presents with a ventricular rate of

Third-degree AV block typically presents with a ventricular rate of

• A. 60-100 bpm
• B. 30-40 bpm
• C. 40-60 bpm
• D. 80-120 bpm

Answer: (B)

In third-degree AV block the atria and ventricles beat independently because no atrial impulses get through to pace the ventricles. The ventricles then rely on an intrinsic escape rhythm from below the block to drive their rhythm. That escape rhythm is slow, since it comes from ventricular tissue rather than a normal conduction pathway. When the block is below the AV node (infranodal), the ventricular pacemaker typically fires at a sluggish rate around 30-40 beats per minute, which is why the typical ventricular rate in complete heart block is in that range. If the block were higher at the AV node and a junctional escape took over, you’d see a somewhat faster rate, roughly 40-60 bpm, but the classic presenting rate described in this context is 30-40 bpm. This slow rate explains why patients with complete heart block may experience dizziness or fatigue and often require pacing.

In third-degree AV block the atria and ventricles beat independently because no atrial impulses get through to pace the ventricles. The ventricles then rely on an intrinsic escape rhythm from below the block to drive their rhythm. That escape rhythm is slow, since it comes from ventricular tissue rather than a normal conduction pathway. When the block is below the AV node (infranodal), the ventricular pacemaker typically fires at a sluggish rate around 30-40 beats per minute, which is why the typical ventricular rate in complete heart block is in that range. If the block were higher at the AV node and a junctional escape took over, you’d see a somewhat faster rate, roughly 40-60 bpm, but the classic presenting rate described in this context is 30-40 bpm. This slow rate explains why patients with complete heart block may experience dizziness or fatigue and often require pacing.