3rd Degree (Complete) AV Block
criticalLead II
25 mm/s10 mm/mV
Heart rate
72bpm
RR
833ms
QT
358ms
RR
833ms
PR
162ms
QRS
105ms
QT
358ms
QTc
380ms
3rd Degree (Complete) AV Block
Complete dissociation between atria and ventricles. No atrial impulses reach the ventricles. The atria and ventricles beat independently — the atria driven by the SA node, the ventricles by an escape pacemaker (junctional or ventricular).
Recognition· 4
- P waves and QRS complexes both present
- Completely independent (no relationship)
- Regular P-P intervals, regular R-R intervals
- More P waves than QRS complexes
Mechanism
Complete block at AV node — atria and ventricles beat independently
No atrial impulses reach the ventricles. The SA node continues firing normally, producing P waves. A lower escape pacemaker (junctional 40-60 bpm or ventricular 20-40 bpm) independently drives the ventricles. The two rhythms are completely dissociated.
Findings· 3
- P waves and QRS complexes present but completely independent (AV dissociation).
- Regular P-P intervals and regular R-R intervals, but no relationship between them.
- Escape rate depends on the level of the escape focus.
Clinical Impact
Bradycardia with poor cardiac output
↓Syncope (Stokes-Adams attacks)
↓Sudden cardiac arrest if escape failsRISK
Medical emergency — risk of cardiac arrest
Management· 3
1
Primary Treatment
Temporary pacing immediately if symptomatic.
2
Additional Options
Atropine or dopamine for temporary rate support.
3
Long-term Management
Permanent pacemaker required in most cases.
Differential· 2