Ventricular Fibrillation (VF)

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Diagnosis | Management

Definition

Ventricular fibrillation (VF) is a type of cardiac arrhythmia in which the ventricles of the heart quiver chaotically instead of contracting in a coordinated manner. This disorganised electrical activity prevents the heart from effectively pumping blood, leading to cardiac arrest and loss of consciousness. VF is a medical emergency requiring immediate treatment, typically with a defibrillator to shock the heart back into a normal rhythm.

Aetiology

Ventricular fibrillation can be classified into two main categories: ischaemic and non-ischaemic.

Ischaemic causes:

• Coronary artery disease
• Myocardial infarction (heart attack)
• Cardiomyopathy

Non-ischaemic causes:

• Hypertrophic cardiomyopathy
• Idiopathic dilated cardiomyopathy
• Structural heart disease
• Electrolyte imbalances (such as low potassium or magnesium levels)
• Certain medications
• Genetic disorders
• Trauma or injury to the heart
• Overheating or heat stroke
• Complications from cardiac surgery or medical procedures such as ablation for atrial fibrillation

Pathophysiology

VF is characterised by rapid, chaotic contractions of the ventricular muscle. The electrical activity of the heart becomes disorganised, preventing the ventricles from pumping blood effectively. This lack of coordinated contraction can lead to cardiac arrest, where blood flow to the brain and other vital organs is interrupted (see Image 1).

Image 1: This image illustrates the disorganised electrical activity in ventricular fibrillation. The chaotic impulses prevent the ventricles from contracting properly, leading to the heart's inability to pump blood.

Risk Factors

Several factors increase the risk of developing ventricular fibrillation:

• Coronary artery disease
• Heart attack
• Heart failure
• Cardiomyopathies (diseases of the heart muscle)
• Hypertrophic cardiomyopathy (a genetic condition where the heart muscle thickens)
• Valvular heart disease
• Cardiac trauma or injury
• Electrocution
• Drug abuse, particularly cocaine use
• Excessive alcohol consumption
• Inherited arrhythmia syndromes
• Long QT syndrome
• Wolff-Parkinson-White syndrome
• Pulmonary embolism
• Hyperthyroidism
• Anaemia
• Dehydration
• Hypoxia
• Electrolyte imbalances
• Certain medications, such as those used to treat heart disease, high blood pressure, and asthma

Signs and Symptoms

Ventricular fibrillation often presents with sudden and severe symptoms, including:

• Sudden collapse or loss of consciousness
• No pulse or weak pulse
• No breathing or shallow breathing
• Chest pain or discomfort
• Palpitations (irregular, rapid, or fluttering heartbeat)
• Dizziness or light-headedness
• Shortness of breath
• Fatigue

Investigations

To diagnose and assess ventricular fibrillation, the following investigations are typically performed:

• Electrocardiogram (ECG): This is the primary tool used to measure the electrical activity of the heart and detect abnormal rhythms, such as VF (see Image 2).
• Blood Tests: To check for underlying medical conditions or causes of VF, such as electrolyte imbalances or heart disease.
• Imaging Tests: Echocardiography or computed tomography (CT) scans are used to assess the structure and function of the heart.
• Specialised Tests: An electrophysiology study or cardiac catheterisation may be performed to further evaluate the cause of VF.

Image 2: This ECG displays the chaotic, irregular pattern characteristic of ventricular fibrillation, with no discernible QRS complex or P waves. The heart rate is typically very fast and irregular, often between 100 and 160 beats per minute.

Diagnosis

Ventricular fibrillation is typically diagnosed in an emergency situation. A pulse examination will show no pulse if sudden cardiac death has occurred. ECG is the definitive diagnostic tool, revealing the characteristic chaotic electrical activity of VF.

Management

Treatment for ventricular fibrillation (VF) focuses on restoring a normal heart rhythm as quickly as possible to prevent cardiac arrest and death:

• Defibrillation: The primary treatment for VF involves delivering an electrical shock to the heart using a defibrillator (either automated external defibrillator (AED) or manual) to stop the chaotic contractions and restore a normal rhythm.
• Cardiopulmonary Resuscitation (CPR): Performed to support circulation and oxygenation until a normal rhythm can be restored.
• Anti-Arrhythmic Drugs: Medications such as amiodarone may be used to control the heart rate and rhythm after defibrillation.
• Procedures: Coronary artery bypass surgery or angioplasty may be required to treat underlying heart disease contributing to VF.
• Implantable Devices: A pacemaker or an implantable cardioverter-defibrillator (ICD) may be implanted to prevent future episodes of VF or other abnormal heart rhythms.

References

1. National Institute for Health and Care Excellence (NICE) (2024) Guidelines for the Management of Ventricular Fibrillation. Available at: https://www.nice.org.uk/guidance/ng196 (Accessed: 26 August 2024).
2. British Heart Foundation (2024) Understanding Ventricular Fibrillation. Available at: https://www.bhf.org.uk (Accessed: 26 August 2024).
3. American Heart Association (2024) Ventricular Fibrillation and Cardiac Arrest. Available at: https://www.heart.org (Accessed: 26 August 2024).

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