Approach to Bradycardia
February 15th, 2021
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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