Which AV block is Second Degree Heart Block Type 1 (Wenckebach), with causes including anoxia, edema after open‑heart surgery, digoxin toxicity, hyperkalemia, and anterior MI?

• A. First Degree Heart Block
• B. Second Degree Heart Block Type I (Wenckebach)
• C. Second Degree Heart Block Type II
• D. Third Degree Heart Block

Answer: (B)

Wenckebach is an AV nodal second-degree block in which conduction through the AV node progressively slows until a beat is dropped, then the cycle restarts. On the ECG, you see a PR interval that lengthens with each beat and eventually a QRS complex is missing, followed by a new, shorter PR interval. This pattern reflects the AV node’s transient delay rather than a fixed block below the AV node.

The causes listed—anoxia, edema after open-heart surgery, digoxin toxicity, hyperkalemia, and even ischemic events involving the AV nodal region—can impair AV nodal conduction and produce this Wenckebach pattern. Because the problem is at the AV node, it’s often more reversible with treatment of the underlying condition or toxic effect.

This differs from other second-degree blocks and from third-degree block. In a Mobitz II pattern, dropped beats occur with a constant PR interval, indicating a below-nodal (infra-nodal) issue and is usually less reversible. Third-degree heart block shows complete dissociation between atrial and ventricular activity with no consistent relationship at all.

So the description matches Second Degree Heart Block Type I (Wenckebach).