Complete Heart Block (Third Degree AV Block) ECG Example
Figure 1: Complete Heart Block (Third Degree AV Block) - Characteristic ECG Pattern
🔑 Key Points at a Glance
- Heart Rate: Atrial 60-100 bpm, Ventricular 20-60 bpm (escape rhythm dependent)
- Primary Significance: High-grade conduction block, high risk of asystole and sudden cardiac death, pacemaker indicated
- Key Management: Transcutaneous pacing immediately if symptomatic, atropine (if narrow QRS), emergent temporary pacemaker, permanent pacemaker indicated
- Clinical Category: Clinical
Overview and Clinical Significance
Complete Heart Block (Third Degree AV Block) represents a critical cardiac rhythm pattern that requires immediate recognition and intervention. High-grade conduction block, high risk of asystole and sudden cardiac death, pacemaker indicated
Understanding this ECG finding is essential for emergency physicians, cardiologists, intensivists, and all healthcare providers involved in acute cardiac care. Early recognition and appropriate management can significantly impact patient outcomes and prevent life-threatening complications.
ECG Characteristics and Recognition
📊 Diagnostic ECG Criteria
- Complete AV dissociation
- No relationship between P waves and QRS
- Regular P-P intervals
- Regular R-R intervals
- Wide QRS if ventricular escape
Systematic ECG Analysis Approach
When analyzing any ECG, including suspected Complete Heart Block (Third Degree AV Block), follow this systematic approach:
- Rate: Calculate ventricular rate using the 300-150-100-75-60-50 rule or count QRS complexes in 6 seconds × 10
- Rhythm: Assess regularity by measuring R-R intervals across the entire strip
- P Waves: Identify presence, morphology, and relationship to QRS complexes
- PR Interval: Measure from start of P wave to start of QRS (normal: 0.12-0.20 seconds or 3-5 small squares)
- QRS Complex: Assess duration (normal: Always assess hemodynamic stability FIRST - unstable patients require immediate intervention regardless of the specific ECG diagnosis
Evidence-Based Management
Acute Management Strategy
Primary Treatment Approach: Transcutaneous pacing immediately if symptomatic, atropine (if narrow QRS), emergent temporary pacemaker, permanent pacemaker indicated
🚨 Emergency Protocol - Time-Critical Actions
- Immediate ABC assessment (Airway, Breathing, Circulation)
- Attach continuous cardiac monitoring and obtain 12-lead ECG
- Establish large-bore IV access (×2) and check bedside glucose
- Administer supplemental oxygen if SpO₂ Recommendations for management of Complete Heart Block (Third Degree AV Block) are primarily supported by Level A evidence (multiple high-quality randomized controlled trials and meta-analyses).
Summary and Clinical Bottom Line
📋 Clinical Bottom Line
Complete Heart Block (Third Degree AV Block) is characterized by complete av dissociation on ECG. High-grade conduction block, high risk of asystole and sudden cardiac death, pacemaker indicated Primary management: Transcutaneous pacing immediately if symptomatic, atropine (if narrow QRS), emergent temporary pacemaker, permanent pacemaker indicated Key takeaway: This is a life-threatening emergency requiring immediate recognition and treatment - time-critical intervention saves lives
About the Author
Dr. Raj K
Emergency Medicine Physician Dr. Raj K is a board-certified Emergency Medicine physician with extensive experience in acute cardiac emergencies, advanced ECG interpretation, and critical care. He is passionate about medical education and bringing evidence-based emergency medicine knowledge to healthcare providers worldwide through E-PulsePoints. His clinical expertise includes STEMI management, complex arrhythmia recognition, and emergency cardiac procedures.
