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Overview of cardiac arrhythmias

Last updated: April 15, 2021

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Cardiac arrhythmias are accelerated, slowed, or irregular heart rates caused by abnormalities in the electrical impulses of the myocardium. Bradyarrhythmias include sinus node dysfunction and atrioventricular block, and are characterized by a resting heart rate < 60/minutes. Tachyarrhythmias (heart rates > 100/minute) are classified as supraventricular arrhythmias or ventricular arrhythmias. Supraventricular arrhythmias originate between the sinus node and the atrioventricular node. Ventricular arrhythmias originate below the atrioventricular node, on the ventricular level. This article provides an overview of cardiac arrhythmias based on the heart rate and site of origin of the arrhythmia. For details of the individual arrhythmias, see the corresponding articles. For the medical treatment of arrhythmias, see the article on antiarrhythmic drugs.



Supraventricular arrhythmias

Ventricular arrhythmias


Type of bradyarrhythmia Causes and mechanisms Main ECG findings
Atrial origin
Respiratory sinus arrhythmia
  • Physiological, particularly in youths
  • Minor changes in the R-R interval during respiration: reduction during inspiration and increase during expiration
Sinus bradycardia
Sinus pause or arrest
Tachycardia-bradycardia syndrome
  • Abnormal supraventricular impulse generation and conduction
  • See sick sinus syndrome for details
AV node origin
Atrioventricular block First-degree block
Second-degree block
Third-degree block
  • Complete block: no communication between the atria and ventricles


Supraventricular arrhythmias

Type of tachyarrhythmia Causes and mechanisms Main ECG findings
Atrial origin
Supraventricular premature beats
  • Physiological response in healthy individuals
  • Electrolyte imbalances
  • Underlying cardiovascular disease
Sinus tachycardia
  • Gradual onset
  • Regular rhythm
  • Rate: max. rate usually 180 bpm
  • P wave: normal morphology
  • Narrow QRS complex
Atrial flutter
  • Macroreentrant rhythms within the atria
Atrial fibrillation
  • Multiple mechanisms which are not completely understood
  • Rhythm: irregularly irregular
  • Rate: 350–450 bpm; < 200
  • P-waves are indiscernible
  • Narrow QRS complex

Atrial tachycardia (∼ 5%)

Focal atrial tachycardia
  • Discharge from a single ectopic focus in the atrium
Multifocal atrial tachycardia (MAT)
  • Very abrupt onset with rate variation
  • Rhythm: irregularly irregular
  • Rate: 150–250
  • Discernible P waves with ≥ 3 different P wave morphologies; no single morphology is predominant
  • Narrow QRS complex
AV node origin
Atrioventricular reentry tachycardia (AVRT)
AV nodal reentry tachycardia (AVNRT)

Junctional tachycardia

Ventricular arrhythmias

Type of arrhythmia Causes and mechanisms ECG findings
Premature ventricular beats
  • Premature, wide QRS complex that is not preceded by a P wave
  • Compensatory pause after the premature beat
Ventricular tachycardia
Torsade de pointes tachycardia

Ventricular fibrillation

  • Arrhythmic, fibrillatory baseline, usually > 300 bpm
  • Erratic undulations with indiscernible QRS complexes


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