Third Degree Heart Block (Complete Heart Block) is typically characterized by which combination of features?

Third Degree Heart Block (Complete Heart Block) is typically characterized by which combination of features?

• A. Very slow rate and an abnormal pacemaker site
• B. Rapid rate with narrow QRS
• C. Normal rate and normal conduction
• D. Frequent PACs

Answer: (A)

In third-degree (complete) heart block, there is a total failure of conduction from the atria to the ventricles, so the atria and ventricles beat independently (AV dissociation). Because the ventricles must rely on an escape rhythm to drive the heart, this rhythm comes from a site below the block, which is inherently abnormal. That escape rhythm is typically slow, producing a very slow ventricular rate. So the hallmark combination is a very slow rate paired with an abnormal pacemaker site. The other patterns—rapid rates, normal conduction, or frequent premature beats—do not reflect the loss of AV conduction with an internecine escape rhythm driving the ventricles.