Overview of cardiac arrhythmias

Last updated: December 19, 2022

Summary

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.

Classification

Bradyarrhythmias

Definition: heart rates of < 60/min
Types: see bradyarrhythmias below

Tachyarrhythmias

Definition: heart rate of > 100/min

Supraventricular arrhythmias

Definition: arrhythmias that originate in the sinoatrial node, atrial myocardium, or atrioventricular node (regular QRS complex)
Types: see supraventricular tachyarrhythmias below

Ventricular arrhythmias

Definition: arrhythmias that originate below the atrioventricular node (wide QRS complex)
Types: see ventricular tachyarrhythmias below

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		Physiological, particularly in athletes Sinus node dysfunction (see sick sinus syndrome) Drugs: beta blockers, calcium channel blockers	Rate < 60 bpm Normal P wave before every QRS complex
Sinus pause or arrest		May occur in healthy individuals Underlying cardiovascular disease (see sick sinus syndrome)	Transient (sinus pause) or complete (sinus arrest) absence of the P wave Often with an escape rhythm (with variable origin)
Tachycardia-bradycardia syndrome		Abnormal supraventricular impulse generation and conduction See sick sinus syndrome for details	Intermittent tachyarrhythmias and bradyarrhythmias
AV node origin
Atrioventricular block	First-degree block	Physiological response Increased vagal tone Drugs: beta blocker or calcium channel blocker	PR interval > 200 ms
	Second-degree block	Drugs: digoxin, beta blocker, calcium channel blocker Increased vagal tone Sinoatrial conduction disease Right coronary infarction	Mobitz type I/Wenckebach: progressive lengthening of the PR interval until a beat is dropped Mobitz type II: irregular dropped beats
	Third-degree block	Complete block: no communication between the atria and ventricles	AV dissociation: no relationship between P waves and QRS complexes

Sinus bradycardia Tachycardia-bradycardia syndrome First-degree atrioventricular block Second-degree atrioventricular block Third-degree atrioventricular block (complete heart block) Respiratory sinus arrhythmia and right bundle branch block

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	P wave abnormalities or absent P waves
Sinus tachycardia		Sympathetic activation or vagal withdrawal on the SA node	Gradual onset Regular rhythm Rate: max. rate usually 180 bpm P wave: normal morphology Narrow QRS complex
Atrial flutter		Macroreentrant rhythms within the atria	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	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 Regular rhythm Rate: 150–250 P wave: morphology varies depending on the site of the ectopic focus Occurs before the QRS complex Narrow QRS complex
Atrial tachycardia (∼ 5%)	Multifocal atrial tachycardia (MAT)	Discharge from multiple ectopic foci in the atrium Associated with pulmonary disorders (e.g., COPD exacerbation, pulmonary embolism), cardiac conditions (CHF exacerbation), and treatment with theophylline	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)		A form of paroxysmal supraventricular tachycardia Tachycardia caused by an accessory pathway between the atria and ventricles	Very abrupt onset Regular rhythm Rate: 150–250 P wave Inverted (downgoing in II, III and aVF and/or upright in aVR) Occur after the QRS complex RP interval is shorter than PR interval QRS complex Orthodromic AVRT: narrow QRS complex Antidromic AVRT: wide QRS complex with delta waves
AV nodal reentry tachycardia (AVNRT)		A form of paroxysmal supraventricular tachycardia A dysfunctional AV node that contains two electrical pathways	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 Narrow QRS complex
Junctional tachycardia		The AV node takes over the pacemaker function Digitalis toxicity Myocarditis Myocardial infarction	Regular rhythm Rate: 100–130 P waves occur before, during, or after the QRS complex P waves are inverted AV dissociation may occur Narrow QRS complex

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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	Coronary artery disease Myocardial infarction Structural heart diseases	Regular, rapid rhythm Wide QRS complexes (≥ 3 consecutive premature ventricular beats) Monomorphic VT (most common): single QRS morphology Polymorphic VT: multiple QRS morphologies AV dissociation (P waves may or may not be discernible)
Torsade de pointes tachycardia	Associated with Long QT syndrome Proarrhythmic drugs Electrolyte abnormalities (hypokalemia)	Polymorphic ventricular tachycardia with QRS complexes that appear to twist around the isoelectric line
Ventricular fibrillation	Myocardial infarction Structural heart diseases	Arrhythmic, fibrillatory baseline, usually > 300 bpm Erratic undulations with indiscernible QRS complexes

Atrial fibrillation Atrial fibrillation with rapid ventricular response Atrial fibrillation and trigeminy in ECG Supraventricular premature beats Sinus tachycardia Multifocal atrial tachycardia Ventricular and supraventricular tachyarrhythmia Junctional tachycardia ECG rhythm strip with frequent premature ventricular contractions Monomorphic ventricular tachycardia Polymorphic ventricular tachycardia Torsades de pointes Ventricular bigeminy and ventricular tachycardia ECG with bigeminy Ventricular fibrillation

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

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References

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