Ventricular Fibrillation (VF)

Ventricular fibrillation (VF) is a critical cardiac condition that requires immediate medical intervention. It is the most significant shockable cardiac arrest rhythm and is fatal without prompt advanced life support.

ECG Findings in Ventricular Fibrillation (VF)

• Chaotic irregular deflections with varying amplitude
• Lack of identifiable P waves, QRS complexes, or T waves
• Heart rate ranging from 150 to 500 beats per minute
• Amplitude decreases over time from coarse VF to fine VF

Clinical Significance of VF

• VF causes the ventricles to contract rapidly and irregularly, up to 500 bpm
• The heart loses its ability to pump effectively, resulting in cardiac arrest
• Requires immediate advanced life support to avoid a fatal outcome
• Prolonged VF transitions from coarse to fine waveform, leading to asystole

Mechanism

• VF can be preceded by various conditions in ischemic heart disease, including:
  • Premature ventricular contractions (PVCs)
  • ST segment changes
  • R on T phenomenon
  • Sinus pause
  • QT prolongation
  • Ventricular tachycardia
  • Supraventricular arrhythmias
  • Sinus tachycardia
• Hypotheses for VF mechanisms:
  • Multiple wavelet mechanism: Involves multiple small wavelets maintained by re-entry circuits
  • Mother rotor mechanism: A stable re-entry circuit gives rise to unstable wavefronts

Causes of Ventricular Fibrillation (VF)

Cardiac Causes

• Myocardial ischemia or infarction
• Various forms of cardiomyopathy: dilated, hypertrophic, restrictive
• Channelopathies (e.g., Long QT syndrome, Brugada syndrome)
• Aortic stenosis or dissection
• Myocarditis
• Cardiac tamponade
• Blunt trauma (e.g., Commotio Cordis)

Respiratory Causes

• Tension pneumothorax
• Pulmonary embolism
• Primary pulmonary hypertension
• Sleep apnea
• Bronchospasm
• Aspiration

Toxic and Metabolic Causes

• Drug effects (e.g., verapamil in AF+WPW)
• Drug-induced QT prolongation with torsades de pointes

Environmental Causes

• Electrical shocks
• Drowning
• Hypothermia
• Sepsis

Neurological Causes

• Seizures
• Cerebrovascular accidents (CVA)

ECG Examples of VF

• Multiple examples of ECG strips showing VF, ranging from coarse to fine VF
• R on T phenomenon leading to torsades de pointes and subsequent VF
• Importance of not diagnosing VF solely from a 12-lead ECG

References for Further Reading

• Various references including journal articles and textbooks on bradycardias, ventricular fibrillation mechanisms, and ECG interpretation
• Online courses and additional resources for advanced learning in ECG interpretation