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ECG Basics

Assessing Heart Rate

February 15th, 2021


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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