A 72-year-old woman with chronic kidney disease and a history of Lyme disease presents with complete heart block (third-degree AV block) and a wide QRS escape rhythm (rate 35 bpm). She is hypotensive and symptomatic. Temporary pacemaker placement is being arranged. Which drug should be initiated immediately while awaiting the procedure?

Explanation

## Management of Symptomatic Complete Heart Block with Infranodal Escape Rhythm ### Why Dopamine, Not Atropine? **Key Point:** Third-degree AV block with a wide QRS escape rhythm indicates an **infranodal block** (below the AV node). Atropine is ineffective for infranodal blocks because the problem is not vagal hyperactivity but structural/ischemic damage to the His bundle or bundle branches. ### Mechanism of the Block - Wide QRS (> 120 ms) escape rhythm indicates the pacemaker is in the ventricular myocardium or distal His bundle - Infranodal blocks are unresponsive to vagolytic agents - The escape rate (35 bpm) is inadequate to maintain perfusion ### Why Dopamine Is First-Line Here 1. **Chronotropic effect:** Increases heart rate via beta-1 adrenergic stimulation 2. **Inotropic effect:** Increases contractility to improve cardiac output 3. **Vasopressor effect:** Maintains blood pressure (critical in this hypotensive patient) 4. **Dose:** 5–20 mcg/kg/min IV infusion, titrated to heart rate and BP **Clinical Pearl:** Dopamine is a bridge therapy while awaiting temporary pacemaker placement. Permanent pacemaker is the definitive treatment for complete heart block with infranodal escape rhythm. ### Temporary vs. Permanent Pacing | Feature | Temporary | Permanent | |---------|-----------|----------| | Indication | Symptomatic bradycardia, acute MI, drug toxicity | Chronic complete block, recurrent syncope | | Placement | Transvenous, bedside | Surgical, subcutaneous | | Duration | Hours to days | Years | **High-Yield:** **Infranodal block = Dopamine (or pacemaker). Nodal block = Atropine.** The QRS width tells you the level of block. [cite:Harrison 21e Ch 297]