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, Ventricular 20-60 bpm
- Primary Significance: Medical emergency, high risk of sudden cardiac death, requires pacing
- Key Management: Transcutaneous pacing, atropine if narrow QRS escape, permanent pacemaker
- 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. Medical emergency, high risk of sudden cardiac death, requires pacing
Understanding this rhythm 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.
ECG Characteristics and Recognition
📊 Diagnostic ECG Criteria
- Complete AV dissociation
- No relationship between P and QRS
- Regular P-P and R-R intervals
- Escape rhythm determines QRS width
Systematic ECG Analysis Approach
When analyzing any ECG, including suspected Complete Heart Block (Third Degree AV Block), follow this systematic approach:
- Rate: Calculate the ventricular rate using the 300-150-100-75-60-50 rule or count complexes in 6 seconds × 10
- Rhythm: Assess regularity by measuring R-R intervals across the 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)
- QRS Complex: Assess duration (normal: 1mm is significant)
- T Waves: Check morphology, direction, and concordance with QRS
- QT Interval: Measure and correct for heart rate (QTc normal: Always assess hemodynamic stability before initiating treatment - unstable patients require immediate intervention regardless of the specific arrhythmia
Evidence-Based Management
Acute Management Strategy
Primary Treatment Approach: Transcutaneous pacing, atropine if narrow QRS escape, permanent pacemaker
🚨 Emergency Protocol
- Assess ABC (Airway, Breathing, Circulation) immediately
- Attach cardiac monitor and obtain 12-lead ECG
- Establish IV access and administer oxygen if SpO₂ Most recommendations for acute management of Complete Heart Block (Third Degree AV Block) are supported by Level A (multiple randomized trials) evidence.
Summary and Clinical Bottom Line
📋 Clinical Bottom Line
Complete Heart Block (Third Degree AV Block) is characterized by complete av dissociation and no relationship between p and qrs. Medical emergency, high risk of sudden cardiac death, requires pacing Management priority: Transcutaneous pacing, atropine if narrow QRS escape, permanent pacemaker Key takeaway: Immediate recognition and treatment are critical for patient survival
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 care and ECG interpretation. He is passionate about medical education and bringing evidence-based emergency medicine knowledge to healthcare providers worldwide through E-PulsePoints.
