Brady-arrhythmias
Bradycardias
Differential Diagnosis
All of the following may lead to junctional / ventricular 'escape' rhythms:
- sinus bradycardia
- AV heart block 1o, 2o, 3o
- agonal rhythm (slow irreg. rhythm, wide QRS (varying morphology), seen in unsuccessful resusc. attempts)
- asystole
Sinus bradycardia
- physiological (sleep, athletes)
- cardiac (sick sinus syndrome*, MI (esp. inferior)
- neural (carotid sinus hypersensitivity**, vasovagal syndrome, raised ICP)
- metabolic (hypothermia, hypothyroidism, jaundice, drugs (beta-blockers, digoxin)
* SSS (sick sinus syndrome)
- Idiopathic degeneration of SA nodal cells (?? in RCA disease)
- ECG: SA block (periods of prolonged P-P) or alternating block + SVT (tachy-brady syndrome)
**Carotid sinus hypersensitivity
- Affects both SA and AV nodes
- ECG: sinus pause / AV block > 3s in response to 5s carotid massage
AV heart block
1oHB
Often normal.
Causes
- acute MI
- acute rheumatic fever
- digitalis toxicity
- electrolyte disturbances
Management
- observation
2oHB
Usually indicates myocardial disease.
Causes
- acute MI
Types
- Möbitz I (Wenckebach) - classically low risk
- Möbitz II (Mobitz) - classically high risk
Management
- pacing if 2:1 (esp. if ventricular rate is slow)
3oHB
Indicates conducting system disease.
Causes
- congenital
- idiopathic fibrosis around bundle of His
- acute in MI
- AS
- LBBB + RBBB
Management
- atropine if symptomatic
- urgent pacing
