• Clinical science

Overview of cardiac arrhythmias

Abstract

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 learning card 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 learning cards. For the medical treatment of arrhythmias, see the learning card on antiarrhythmic drugs.

Classification

Bradyarrhythmias

Tachyarrhythmias

Supraventricular arrhythmias

Ventricular arrhythmias

References:[1][2]

Bradyarrhythmias

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
Sinoatrial pause or arrest
  • Transient absence of the P wave
SA nodal exit block
  • Impaired impulse conduction from the SA node to atrial tissue
  • First-degree block: cannot be recorded with a regular surface ECG
  • Second-degree block: see SA nodal exit block for details
  • Third-degree: absent P wave
Tachycardia-bradycardia syndrome
  • Abnormal supraventricular impulse generation and conduction
  • See sick sinus syndrome for details
Non-respiratory sinus arrhythmia
  • A variation in heart rate that is not related to respiration
  • May occur in healthy individuals, underlying cardiovascular disease or digitalis intoxication
  • Minor changes in the R-R interval during respiration
Atrial fibrillation (AF) with bradycardia
AV node origin
Atrioventricular block First-degree block
Second-degree block
Third-degree block
  • Complete block: no communication between the atria and ventricles
Intraventricular block
  • Conduction of the electrical impulse is blocked on the ventricular level
  • Myocarditis

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References:[3][4][5][6]

Tachyarrhythmias

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; positive P waves in II, III, aVF, biphasic with initial positive deflection in V1, negative P wave in aVR; P waves may be taller in the inferior limbs
  • Narrow QRS complex
Atrial flutter
  • Macroreentrant rhythms within the atria
  • Very abrupt onset without rate variation
  • Regular rhythm
  • Rate: atrial 250–350; ventricular < 200
  • P waves
    • Occur before every QRS complex
    • Sawtooth appearance of regular P waves (flutter waves) especially in leads II, III, and aVF
  • Narrow QRS complex
Atrial fibrillation
  • Multiple mechanisms which are not completely understood
  • Very abrupt onset with rate variation
  • 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
  • Very abrupt onset without rate variation
  • Regular rhythm
  • Rate: atrial 150–250; ventricular < 200
  • P wave: morphology varies depending on the site of the ectopic focus
  • Narrow QRS complex
Multifocal atrial tachycardia (MAT)
  • Very abrupt onset with rate variation
  • Rhythm: irregularly irregular
  • Rate: 150–250; ventricular: < 200
  • Variable PR intervals
  • Discernible P waves with ≥ 3 different P wave morphologies; no single morphology is predominant (P wave occurs before the QRS complex)
  • Narrow QRS complex
AV node origin
Atrioventricular reentry tachycardia (AVRT; 30%)
AV nodal reentry tachycardia (AVNRT; 65%)
  • Very abrupt onset without rate variation
  • Regular rhythm
  • Rate: 150–250
  • P waves occur during (i.e. are not visible) or after the QRS complex
  • RP interval is shorter than PR interval (except in atypical AVNRT)
  • Narrow QRS complex

Junctional tachycardia

  • Gradual onset
  • Regular rhythm
  • Rate: 100–130
  • P waves occur before, during, or after the QRS complex
  • RP interval longer than PR interval
  • P waves are inverted (downgoing in II, III and aVF and/or upright in aVR)
  • Retrograde 1:1 ventriculoatrial conduction: ventricular rate and atrial rate are equal (100–130)
  • AV dissociation may occur
  • Narrow QRS complex
Permanent junctional reciprocating tachycardia
  • Rare condition mostly observed in childhood
  • Incessant reentrant tachycardia
  • A form of orthodromic AVRT

Ventricular arrhythmias

Type of arrhythmia Causes and mechanisms ECG findings
Premature ventricular beats
  • Ectopic beat that originates from a ventricular focus
  • Due to hypoxia, hyperthyroidism, electrolyte abnormalities
  • Premature, wide QRS complex that is not preceded by a P wave
  • Compensatory pause after the premature beat
Ventricular tachycardia
Torsade de pointes tachycardia
  • Associated with Long QT syndrome
  • Proarrhythmic drugs
  • Electrolyte abnormalities (hypokalemia)

Ventricular fibrillation

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

References:[3][7][8][9][10][11][12]

Pathophysiology