A 62-year-old woman with acute anterior wall myocardial infarction develops sudden-onset second-degree AV block (Mobitz type II) with a QRS duration of 140 ms on ECG. She is hemodynamically stable with a blood pressure of 110/70 mmHg and heart rate of 48 bpm. Which of the following is the most appropriate immediate next step in management?

Explanation

## Clinical Context This patient has **Mobitz type II AV block** (second-degree, infranodal) complicating acute **anterior wall MI**. The wide QRS (140 ms) confirms infranodal pathology involving the His-Purkinje system. Despite hemodynamic stability at presentation, this rhythm carries an extremely high risk of sudden progression to complete heart block or asystole. ## Why Immediate Temporary Transvenous Pacing Is Correct **Key Point:** Mobitz type II AV block in the setting of **acute anterior MI** is a **Class I indication for immediate temporary transvenous pacing**, regardless of hemodynamic status. This is because the block is infranodal, unpredictable, and can deteriorate abruptly to complete AV block with a slow or absent escape rhythm. **High-Yield (ACC/AHA Guidelines; Braunwald's Heart Disease):** Unlike inferior MI where AV block is usually nodal, transient, and atropine-responsive, anterior MI causes infranodal block due to ischemia of the bundle branches. The risk of progression to complete heart block is **30–50%**, and the escape rhythm, if any, is unreliable and slow. Waiting for hemodynamic deterioration before pacing is dangerous — collapse can be sudden and irreversible. **Clinical Pearl:** The distinction between "stable" and "unstable" as a trigger for pacing applies to **Mobitz I (Wenckebach)** and **sinus bradycardia**, not to Mobitz II in anterior MI. For Mobitz II in anterior MI, prophylactic transvenous pacing is the standard of care even in a currently stable patient. ## Decision Algorithm for AV Block in Anterior MI | Block Type | Setting | Action | |---|---|---| | Mobitz I (Wenckebach) | Inferior MI | Observe; atropine if symptomatic | | Mobitz II | Anterior MI | **Immediate temporary transvenous pacing** | | Complete (3rd degree) | Any MI | Immediate temporary transvenous pacing | ## Why Other Options Are Incorrect **Atropine (Option A):** Atropine acts at the AV node (muscarinic blockade) and is **ineffective** in infranodal Mobitz II block. The wide QRS (140 ms) confirms the block is below the AV node. Atropine may paradoxically worsen infranodal block by increasing sinus rate without improving AV conduction. It is contraindicated as primary therapy here. **Dopamine (Option B):** Dopamine is a temporizing catecholamine used for hemodynamic support in symptomatic bradycardia. It does not reliably improve infranodal conduction and is not a substitute for pacing. It is not indicated in a currently stable patient with a high-risk conduction abnormality. **Observe with standby pacing (Option D):** While this approach may seem reasonable given hemodynamic stability, it is **not appropriate** for Mobitz II in anterior MI. The risk of sudden complete heart block with asystole is too high to defer pacing. ACC/AHA guidelines (Braunwald's Heart Disease, 12th ed.) explicitly recommend immediate temporary pacing for new Mobitz II block complicating anterior MI. **Reference:** Braunwald's Heart Disease, 12th edition; ACC/AHA Guidelines for Management of ST-Elevation Myocardial Infarction.