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ECG Basics

Assessing Heart Rate



  • 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.


  • 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


  • 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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