Overview
The heart rate is the ventricular rate, or the rate of ventricular depolarisation.
Normal Range
- 60 - 100bpm
How to Measure
- Count the number of large squares between consecutive R waves (the R-R interval), and divide 300 by that number.
Heart rate = 300 / no. of large squares between R waves
If the rhythm is irregular, the average R-R interval can be used to calculate the rate.
Tachycardia
A rapid ventricular rate of >100bpm may be in the context of a variety of rhythms that are clinically classified as narrow complex tachycardias (QRS duration <120ms) and wide complex tachycardias (QRS duration >120ms).
Tachyarrhythmias
Regular Narrow Complex Tachycardia
- Sinus tachycardia
- Focal atrial tachycardia
- Atrial flutter
- AV nodal reentrant tachycardia
- AV reentrant tachycardia
Irregular Narrow Complex Tachycardia
- Multifocal atrial tachycardia
- Atrial fibrillation
- Atrial flutter with variable block
Regular Wide Complex Tachycardia
- Monomorphic ventricular tachycardia
- SVT with aberrant conduction (bundle branch block)
- SVT with preexcitation (accessory pathway)
- Pacemaker-mediated tachycardia (atrial tracking or endless loop tachycardia)
Irregular Wide Complex Tachycardia
- Polymorphic ventricular tachycardia
- AF with aberrant conduction (bundle branch block)
- AF with preexcitation (accessory pathway)
Other
- Artefact - due to CPR, shivering, shaking or other movements
Bradycardia
A slowed ventricular rate of <60bpm (or <50bpm during sleep) 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
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