Approach to Bradycardia
Overview
Bradycardia may generally be caused by sinus node dysfunction, atrioventricular block or escape rhythms in the setting of either of the above.
Bradyarrhythmias
Regular
- Sinus bradycardia
- Sinus arrest with escape rhythm
- Complete heart block with escape rhythm
Irregular
- Sinus arrhythmia
- Sinus arrest
- Second or third degree sinoatrial exit block
- Atrial fibrillation with slow ventricular rate
- Atrial flutter with variable block
- Second or third degree AV block
Causes of Bradycardia
Intrinsic (SA or AV Nodal)
- Idiopathic degeneration
- Myocardial infarction
- Congenital - congenital heart disease, neonatal lupus
- Infiltrative disease - sarcoidosis, amyloidosis, haemochromatosis
- Connective tissue disease - SLE, scleroderma, RA
- Cardiac procedures - valvular surgery, correction of congenital heart disease, catheter ablation
- Infections - Lyme disease, endocarditis, viral myocarditis
Extrinsic
- Physiologic - sleep, athletes
- Autonomic - neurocardiogenic syncope, carotid sinus massage, carotid sinus hypersensitivity
- Drugs - beta blockers, calcium channel blockers, digoxin, adenosine, amiodarone, ivabradine, clonidine, acetylcholinesterase inhibitors
- Hypothyroidism
- Hypothermia
- Hyperkalaemia
- Obstructive sleep apnoea
- Raised intracranial pressure
Pearls
- Sinoatrial exit block and sinus arrest present as pauses without P waves or QRS complexes.
- Escape rhythms are likle to be present if there are pauses or non-conducted P waves followed by bradycardia with junctional or ventricular complexes.
- Atrial fibrillation with slow ventricular rate produces fibrillation waves without P waves and with irregular QRS complexes.
- Atrial flutter with variable block manifests as a sawtooth wave at ~300bpm with irregular QRS complexes.
- Second degree heart block presents with intermittently non-conducted P waves (without a subsequent QRS complex); the pattern of PR interval prolongation determines the type.
- Complete AV block produces complete dissociation between P waves and QRS complexes.
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