A 72-year-old woman with chronic kidney disease and diabetes mellitus presents with syncope. Her ECG shows a PR interval of 320 ms, and on continuous monitoring, every third atrial impulse is conducted to the ventricles (2:1 AV block pattern). Her heart rate is 38 bpm, blood pressure is 88/54 mmHg, and she is diaphoretic. What is the most appropriate immediate next step in management?

Explanation

## Clinical Presentation This patient has **second-degree AV block (Mobitz II pattern)** with haemodynamic compromise: - Syncope (symptom of cerebral hypoperfusion) - Hypotension (88/54 mmHg) - Bradycardia (38 bpm) - Diaphoresis (sign of sympathetic activation / shock) ## Distinguishing Mobitz II from Mobitz I | Feature | Mobitz I (Wenckebach) | Mobitz II | |---------|----------------------|----------| | PR interval | Progressive lengthening | Fixed, then sudden drop | | Block location | AV node (usually) | His bundle or below | | Prognosis | Benign, often transient | Serious; risk of complete block | | QRS | Normal | Often widened | | Haemodynamics | Usually stable | Often unstable | | Treatment | Observation ± atropine | Pacemaker | **Key Point:** The 2:1 AV block pattern with fixed PR intervals and haemodynamic instability indicates **Mobitz II**, not Mobitz I. ## Why Temporary Pacemaker Is Mandatory ### Indications for Pacing in Mobitz II 1. **Haemodynamic instability** — present here (syncope, hypotension, altered perfusion) 2. **Risk of progression** — Mobitz II can abruptly degenerate to complete (third-degree) AV block 3. **Symptomatic bradycardia** — syncope is a cardinal symptom **High-Yield:** Mobitz II is a **medical emergency**. Unlike Mobitz I (which is benign and often self-limiting), Mobitz II requires pacemaker support because the block is infranodal and unpredictable. ### Why Atropine Fails in Mobitz II **Clinical Pearl:** Atropine works only if the block is at the AV node (Mobitz I). In Mobitz II, the block is at or below the His bundle — atropine has no effect and may delay critical pacemaker insertion. **Warning:** Do not waste time with atropine in a haemodynamically unstable patient with Mobitz II. Pacemaker insertion is the definitive treatment. ### Pacemaker Approach ```mermaid flowchart TD A[Mobitz II AV Block]:::outcome --> B{Haemodynamically Stable?}:::decision B -->|Yes| C[Temporary pacemaker at bedside<br/>Prepare for permanent pacing]:::action B -->|No| D[Immediate transvenous<br/>temporary pacemaker]:::urgent D --> E[Assess for reversible causes<br/>Prepare for permanent pacing]:::action ``` **Tip:** In an unstable patient, pacemaker insertion should not be delayed. Transcutaneous pacing (external) can be initiated while preparing for transvenous access.