VENTRICULAR FIBRILLATION

✓ Medically ReviewedDISEASEID: MDBT0166🚨 TRIAGE: EMERGENCYICD-10: I49.0

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Definition

CLINICAL DEFINITION

Ventricular fibrillation is a life-threatening cardiac arrhythmia characterised by chaotic, rapid, and uncoordinated electrical activation of the ventricular myocardium, resulting in the cessation of effective ventricular contraction and cardiac output. On an electrocardiogram (ECG), it manifests as irregular, undulating waves of varying amplitude and morphology without identifiable QRS complexes, ST segments, or T waves.

IN PLAIN ENGLISH

Ventricular fibrillation is a dangerous heart rhythm problem where the lower chambers of the heart quiver chaotically instead of pumping blood. This stops blood flow to the body and brain, causing sudden cardiac arrest and requiring immediate emergency treatment like CPR and a shock from a defibrillator.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Ventricular fibrillation is NOT ventricular tachycardia, which is a fast but organised ventricular rhythm that may still produce a pulse and identifiable QRS complexes. It is also NOT pulseless electrical activity (PEA) or asystole, which represent different mechanisms of cardiac arrest.

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Word Breakdown

ventriculo-

=pertaining to the ventricles of the heart (from Latin 'ventriculus', diminutive of 'venter' meaning belly)

fibrill-

=thread or fiber (from Latin 'fibrilla', diminutive of 'fibra')

-ation

=process, action, or condition (from Latin '-atio')

Literal Meaning: The condition of thread-like quivering of the ventricles

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Abbreviations

VF=Ventricular Fibrillation — life-threatening cardiac arrhythmia

VFib=Ventricular Fibrillation — common alternative abbreviation

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Synonyms & Variants

V-Fib›VFib›

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Category-Specific Context

As a Disease, ventricular fibrillation represents the most severe and immediately life-threatening end of the ventricular arrhythmia spectrum. It is classified functionally as a pulseless cardiac arrest rhythm and is the most common initial rhythm in out-of-hospital sudden cardiac arrest.

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Clinical Context & Usage

CLINICAL SETTINGS

Emergency DepartmentIntensive Care UnitCardiac Catheterisation LaboratoryOperating TheatrePre-hospital Emergency CareCoronary Care Unit

USAGE & DOCUMENTATION NOTES

In clinical documentation and emergency communication, VF is frequently referred to as 'V-fib' or 'VF'. During cardiac arrest resuscitation, it is documented as a 'shockable rhythm'. Defibrillation energy levels and the number of shocks delivered are explicitly recorded in the code event summary. Continuous ECG monitoring is required, and the rhythm is often described by its amplitude (e.g., 'coarse VF' vs 'fine VF'), though this does not alter the immediate need for defibrillation.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Ventricular fibrillation arises from multiple wandering re-entrant wavelets of electrical activity propagating chaotically through the ventricular myocardium. This disorganised depolarisation prevents the coordinated contraction of the ventricles necessary to generate stroke volume and cardiac output. The chaotic electrical activity is often initiated by a triggering event, such as premature ventricular complexes falling on the T wave (R-on-T phenomenon) in the setting of acute ischaemia, electrolyte derangements, or prolonged repolarisation. Without organised mechanical contraction, systemic perfusion ceases within seconds, leading to global ischaemia, loss of consciousness, and irreversible brain damage if not rapidly reversed. Over time, the metabolic depletion of myocardial ATP causes the ECG amplitude to decrease, transitioning from coarse to fine VF, and eventually to asystole if untreated.

PRIMARY CAUSES

Acute Myocardial Infarction / Ischaemia

Acute coronary occlusion causes regional ischaemia, altering resting membrane potentials and creating heterogeneous refractory periods that facilitate re-entrant circuits.

Severe Heart Failure / Cardiomyopathy

Structural remodelling, myocardial fibrosis, and ventricular dilation create anatomical substrates for macro-re-entrant circuits and abnormal automaticity.

Primary Electrical Disease (Channelopathies)

Genetic mutations affecting ion channels (e.g., Long QT syndrome, Brugada syndrome, CPVT) disrupt normal depolarisation and repolarisation, triggering polymorphic ventricular tachycardia that degenerates into VF.

Electrolyte Imbalances

Severe hypokalaemia, hyperkalaemia, hypomagnesaemia, or hypocalcaemia alter myocardial action potential duration and refractoriness, lowering the threshold for re-entry.

Drug Toxicity

Pro-arrhythmic effects from QT-prolonging drugs (e.g., antiarrhythmics, macrolides, antipsychotics) or sodium-channel blocker toxicity induce early or delayed afterdepolarisations leading to VF.

Electrocution or Lightning Strike

External electrical current passing through the myocardium during the vulnerable period of the cardiac cycle triggers chaotic, simultaneous depolarisation of ventricular myocytes.

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Drug-Induced Causes

💊 QT-prolonging agents (Class IA and III antiarrhythmics, macrolides, fluoroquinolones, typical antipsychotics) ↗

Mechanism: Blockade of the hERG potassium channel delays ventricular repolarisation, prolonging the QT interval and predisposing to Torsades de Pointes which degenerates into VF.

→ Discontinue the offending agent immediately. Administer intravenous magnesium sulfate and consider overdrive pacing or isoprenaline if bradycardia-dependent.

💊 Sodium channel blockers (Tricyclic antidepressants, Class I antiarrhythmics, cocaine) ↗

Mechanism: Toxic doses block fast sodium channels, widening the QRS complex and slowing conduction velocity, which promotes re-entrant ventricular arrhythmias.

→ Administer intravenous sodium bicarbonate to overcome sodium channel blockade and narrow the QRS complex. Avoid Class IA and IC antiarrhythmics.

💊 Sympathomimetics (Epinephrine, cocaine, amphetamines) ↗

Mechanism: Excessive catecholaminergic stimulation increases intracellular calcium and myocardial oxygen demand, triggering delayed afterdepolarisations and ischaemia-induced VF.

→ Supportive care, benzodiazepines for sympathomimetic toxicity, and standard ACLS algorithms for cardiac arrest. Avoid beta-blockers in unopposed alpha-stimulation scenarios like cocaine toxicity until vasodilation is managed.

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Epidemiology

Prevalence:Ventricular fibrillation is the initial recorded rhythm in approximately 25–30% of out-of-hospital cardiac arrests (OHCA) and up to 60% of in-hospital cardiac arrests occurring in monitored settings like the intensive care unit. The incidence of sudden cardiac arrest due to VF is estimated at 0.5 to 1.0 per 1,000 person-years in Western populations.

Age Group:Risk increases significantly with age due to the rising prevalence of coronary artery disease and heart failure, peaking in adults aged 65 and older. However, it can occur at any age, including in infants and children with congenital long QT syndromes, structural heart anomalies, or myocarditis.

Sex Predilection:Male

Geographic Distribution:Incidence of VF secondary to ischaemic heart disease mirrors global patterns of coronary artery disease, with higher rates in regions with high prevalence of metabolic syndrome and smoking. Survival rates vary significantly based on geographic access to early defibrillation and emergency medical services.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 EMERGENCY

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Artifact mimicking VF — always assess the patient's clinical status and check for a pulse before delivering a high-energy shock to a conscious or perfusing patient.
Underlying reversible causes (the 'Hs and Ts') — failure to identify and treat conditions like acute coronary thrombosis, severe hypokalaemia, hypoxia, or cardiac tamponade will result in recurrent VF and failure to achieve sustained ROSC.

URGENT EVALUATION TRIGGERS

Witnessed sudden collapse with unresponsiveness and absent central pulse — immediate initiation of CPR and defibrillation.
Episodes of syncope or near-syncope in a patient with known structural heart disease or channelopathy — requires urgent cardiology evaluation for ICD consideration.
Documented non-sustained ventricular tachycardia or frequent premature ventricular complexes in the setting of acute chest pain — requires immediate evaluation for acute myocardial ischaemia.

Contraindications & Precautions

CONTRAINDICATIONS

Implantable cardioverter-defibrillator (ICD) placement is generally contraindicated in patients with a life expectancy of less than 1 year due to non-cardiac comorbidities or those with incessant VF refractory to all therapies where the device would continuously shock without clinical benefit.

SPECIAL PRECAUTIONS

When administering QT-prolonging medications to patients with structural heart disease or baseline QT prolongation
continuous telemetry monitoring is required to detect early repolarisation abnormalities.
Electrolyte repletion (potassium
magnesium) must be carefully monitored in patients with renal impairment to avoid iatrogenic hyperkalaemia or hypermagnesaemia
which can themselves precipitate cardiac arrest.
Following ROSC from a VF arrest
targeted temperature management and strict haemodynamic monitoring are required to mitigate reperfusion injury and prevent secondary neurological deterioration.

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Anoxic brain injury — global cerebral ischaemia during the arrest period leading to irreversible neurological damage or vegetative state
Post-cardiac arrest myocardial dysfunction — transient global myocardial stunning resulting in cardiogenic shock and low cardiac output syndrome after return of spontaneous circulation (ROSC)
Defibrillation-induced skin burns and skeletal muscle injury — thermal and electrical damage from high-energy transthoracic shocks
Rib fractures and sternal injuries — mechanical trauma resulting from high-quality chest compressions during CPR

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Atrial Fibrillation

Both are 'fibrillation' arrhythmias, but atrial fibrillation involves the upper chambers, is rarely immediately life-threatening, and usually presents with a pulse, whereas ventricular fibrillation involves the lower chambers and causes immediate cardiac arrest.

Ventricular Tachycardia

Both are life-threatening ventricular arrhythmias; however, VT is a fast but organised rhythm that may produce a pulse and has identifiable QRS complexes, while VF is chaotic and pulseless.

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Ventricular Tachycardia (Pulseless)

Key Distinguishing Feature: Shows organised, wide QRS complexes at a rapid rate, whereas VF shows chaotic, undulating waves without identifiable QRS complexes.

Torsades de Pointes

Key Distinguishing Feature: A specific form of polymorphic VT characterised by QRS complexes that twist around the isoelectric line, typically occurring in the setting of a prolonged QT interval; it may degenerate into VF.

Artefact / ECG Interference

Key Distinguishing Feature: Patient has a palpable pulse and is conscious; the chaotic waveform is caused by patient movement, loose leads, or electrical interference rather than true myocardial depolarisation.

Coarse Atrial Fibrillation with Bundle Branch Block

Key Distinguishing Feature: Irregularly irregular rhythm with wide QRS complexes and fibrillatory baseline, but the patient has a pulse and organised ventricular response.

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Clinical Pearls

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Coarse VF (higher amplitude) generally indicates a more recent onset of cardiac arrest and is more responsive to initial defibrillation than fine VF, which suggests prolonged arrest and severe myocardial metabolic depletion.

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If VF is refractory to standard shocks and epinephrine, consider double sequential external defibrillation (DSED) or vector-change defibrillation, alongside aggressive correction of hypoxia, acidosis, and electrolyte abnormalities.

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Amiodarone or lidocaine are recommended by ACLS guidelines for shock-refractory VF, but they improve survival to hospital admission rather than long-term neurological survival; high-quality CPR and early defibrillation remain the only interventions proven to improve long-term outcomes.

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In a patient with an implantable cardioverter-defibrillator (ICD) who receives multiple shocks, treat the patient, not the device. Assess for a pulse and clinical status, as the device may be firing inappropriately due to lead fracture, SVT with rapid ventricular response, or oversensing.

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Example Usage & SOAP

CLINICAL SENTENCE

"The patient suffered a witnessed out-of-hospital cardiac arrest with an initial rhythm of ventricular fibrillation, achieving return of spontaneous circulation after three defibrillation shocks and administration of intravenous amiodarone."

IN A SOAP NOTE

S: Bystander reports the 58-year-old male suddenly collapsed while mowing the lawn; unresponsive with agonal breathing. O: Pulseless, apnoeic. Monitor shows coarse ventricular fibrillation. High-quality CPR in progress. A: Out-of-hospital cardiac arrest secondary to ventricular fibrillation, likely secondary to acute myocardial ischaemia. P: Immediate defibrillation at 200J biphasic. Resume CPR. Administer epinephrine 1mg IV per ACLS algorithm. Prepare for advanced airway and consider amiodarone 300mg IV if VF persists. Activate cardiac catheterisation lab for emergent coronary angiography post-ROSC.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for a chaotic, wide-complex rhythm on monitor: (1) Ventricular Fibrillation — patient is pulseless, requires immediate shock; (2) Pulseless Ventricular Tachycardia — organised wide QRS complexes, also requires immediate shock; (3) ECG Artefact — patient is conscious and has a palpable pulse, caused by loose leads or patient movement; (4) Torsades de Pointes — polymorphic twisting QRS complexes, often associated with prolonged QT interval.

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Prognosis

SHORT-TERM OUTCOME

Survival to hospital discharge for out-of-hospital VF cardiac arrest is approximately 20–30% overall, but can exceed 50% if witnessed, bystander CPR is initiated immediately, and early defibrillation is achieved within 3–5 minutes. In-hospital VF arrests in monitored settings have higher initial ROSC rates but discharge survival remains dependent on the underlying aetiology and post-arrest care.

LONG-TERM PROGNOSIS

Survivors of VF cardiac arrest who achieve good neurological recovery have a long-term prognosis heavily dictated by their underlying cardiac pathology (e.g., left ventricular ejection fraction). Without secondary prevention such as an implantable cardioverter-defibrillator (ICD), the recurrence rate of lethal ventricular arrhythmias is extremely high.

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References & Coding

ICD-10 DIAGNOSTIC CODE

I49.0

LITERATURE CITATIONS & GUIDELINES

[1]Priori SG, Blomström-Lundqvist C, Mazzanti A, et al. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J. 2015;36(41):2793-2867.

[2]Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death. J Am Coll Cardiol. 2018;72(14):e91-e220.

[3]Merchant RM, Topjian AA, Panchal AR, et al. Part 1: Executive Summary: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2020;142(16_suppl_2):S337-S357.

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.