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complete heart block third degree AV block ECG
Diagnosis: Complete (Third-Degree) AV Block
ECG Analysis
Clinical context: 82-year-old male, syncope, BP 70/35 mmHg (cardiogenic shock). All leads at half standard (5 mm/mV).
| Finding | Observation |
|---|---|
| P waves | Present, regular, marching independently through QRS and T waves |
| QRS complexes | Present, regular, but completely independent of P waves — no fixed PR interval |
| AV dissociation | Complete — atrial rate (~60–70 bpm) faster than ventricular rate |
| Ventricular rate | Slow (~30–35 bpm) — ventricular escape rhythm |
| QRS morphology | Wide/abnormal (best seen in V1–V3, leads II, III) — suggests infra-Hisian (ventricular) escape focus |
| Axis | Left axis deviation |
The hallmark finding is complete AV dissociation: P waves "march through" at their own rate with absolutely no relationship to QRS complexes.
Diagnosis
Complete (Third-Degree) AV Block with a ventricular escape rhythm
This represents total failure of conduction through the AV node/His-Purkinje system. The ventricles are driven by a slow, unreliable ventricular escape pacemaker (~30–35 bpm), explaining the syncope and hypotension (BP 70/35).
Pathophysiology
The block is most likely infra-Hisian (below the Bundle of His), given:
- Wide QRS escape complexes
- Very slow ventricular rate
- Left axis deviation
Common causes in an elderly man include:
- Idiopathic fibrosis of the conduction system (Lenègre-Lev disease) — most common
- Acute inferior/posterior MI (RCA occlusion)
- Drug toxicity (digoxin, beta-blockers, calcium channel blockers)
- Hyperkalemia
- Lyme carditis (less likely at this age)
Immediate Management
- Transcutaneous pacing — immediately for hemodynamic instability
- IV Atropine (0.5–1 mg) — partial temporizing measure (less effective for infra-Hisian block)
- Transvenous temporary pacemaker — urgent placement
- Permanent pacemaker implantation — definitive treatment (Class I indication per guidelines)
- Rule out reversible causes: check electrolytes, drug levels, troponin, inferior MI
Per Braunwald's Heart Disease: "Complete AV block can be accompanied by signs and symptoms of reduced cardiac output, syncope or presyncope, angina, or palpitations... Temporary or permanent pacemaker insertion is indicated for patients with symptomatic bradyarrhythmia."
This is a life-threatening emergency requiring immediate pacing.
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