Ventricular Fibrillation

Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular fibrillation is most commonly caused by underlying ischemic heart disease. It leads to death within minutes unless advanced cardiac life support measures are started immediately.

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Epidemiology and Etiology

Epidemiology

Ventricular fibrillation (VF) secondary to myocardial infarction (MI) is the most common cause of sudden cardiac death (leading cause of death in developed countries).

  • Patients are monitored in the intensive care unit (ICU) after an acute MI due to the risk of VF.
  • Patients with a reduced left ventricular ejection fraction are at highest risk for VF following MI.
  • Half of all deaths due to coronary artery disease are caused by VF.
  • More common in men than in women

Etiology

  • Underlying cardiovascular disease:
    • Coronary artery disease (most common)
    • Congestive heart failure
    • MI
    • Cardiomyopathy
    • Myocarditis
    • Valvular stenosis or insufficiency
  • Cardiac conduction disorders:
    • Long QT syndrome
    • Wolff-Parkinson-White syndrome
    • Torsade de pointes
  • Electrolyte imbalance (e.g., hypokalemia)
  • Autonomic nervous system dysfunction (e.g., increased sympathetic activity from drugs such as dobutamine and albuterol)
  • Idiopathic (rare)

Pathophysiology

Ventricular tachyarrhythmias are caused by abnormal ectopic contractions in the ventricle.

  • Benign if the ectopic signal is regular and stationary and cardiac output is maintained
  • May lead to hemodynamic collapse and death if the ectopic signal has a variable location or rate

Detailed process

  • Myocardial scar formation (most commonly due to previous ischemic damage) causes slowing of the conduction of cardiac electrical impulses.
  • This unexcitable scar tissue is surrounded by hyperirritable myocardial cells.
  • Electrical impulse slows as it passes through the scar; the rest of the ventricle then has time to repolarize and it depolarizes again as the impulse exits the scar (known as re-entry).
  • Ventricular contractions are rapid and out of sync with the atria. 
  • Cardiac output decreases significantly → hemodynamic collapse occurs → loss of consciousness due to drop in cerebral oxygenation → cardiac arrest → sudden death
  • If the rapid ventricular contraction rate is tolerated, arrhythmia may cause cardiomyopathy over time.
  • Any medications and genetic disorders that result in a prolonged or delayed repolarization may result in early afterdepolarizations and torsade de pointes.

Mnemonic

Sustained VF after an MI results from: Myocardial ischemia → Necrosis → Reperfusion → Healing → Scar formation → Autonomic changes (mnemonic device: My Nephew Really Hates Scary Aliens!)

Clinical Manifestations

  • Chest pain
  • Hypotension and respective signs and symptoms (e.g., syncope, fatigue, pallor, cold extremities, heat intolerance, blurry vision) 
  • Confusion
  • Palpitations
  • Dizziness
  • Shortness of breath 
  • Loss of consciousness
  • Sudden death

Diagnosis

Electrocardiogram (ECG) confirms the diagnosis.

  • Disorganized/deranged electrical activity originating in the ventricles
  • Increased heart rate (> 300/min)
    • Ventricular flutter: heart rate of 240–300/min; frequently transitions to VF (300–400/min)
  • Loss of P waves
  • Indiscernible QRS complexes
    • Fibrillatory waves

Evaluation of underlying conditions:

  • Cardiac enzymes (elevated after MI)
  • Coronary angiography to evaluate myocardial ischemia
  • Electrolytes (abnormally high or low levels of potassium, calcium, or magnesium)
  • Urine drug screen for medications or stimulants that may affect the heart rate
  • Echocardiogram if structural cause is suspected

Treatment

  • Follow advanced cardiac life support algorithm.
  • Management:
    • Cardiopulmonary resuscitation to help maintain blood flow through the body
    • Defibrillation: delivery of electrical shock  to the heart (momentarily stops the electrical activity and chaotic beats); start at 200 joules
    • Epinephrine after 2 attempts at defibrillation; makes next attempt at defibrillation more likely to succeed
    • Consider antiarrhythmics: Amiodarone is superior to lidocaine in VF.
    • IV/IO access 
    • Advanced airway
  • Correct reversible causes (e.g., metabolic acidosis, electrolyte disturbances)
  • Implantable cardioverter-defibrillator should be used if no reversible cause is found and/or if there is recurrence of hemodynamically unstable ventricular fibrillation at a later time.
Ventricular fibrillation

Ventricular fibrillation/tachycardia management algorithm

Image by Lecturio.

Clinical Relevance

  • Ventricular tachycardia: a group of arrhythmias that can originate from anywhere in the ventricle and that result in a heartbeat > 100 bpm. There are 3 main types of ventricular tachyarrhythmias: ventricular fibrillation, monomorphic ventricular tachycardia, and polymorphic ventricular tachycardia (also known as torsades de pointes).
  • Coronary artery disease: the leading cause of death worldwide. It occurs as a result of atherosclerotic changes of the coronary arteries with subsequent narrowing of the vessels, preventing their dilation. 
  • Congestive heart failure: also called cardiac insufficiency; refers to the inability of the heart to supply the body with normal cardiac minute volume under normal end-diastolic pressure conditions
  • Myocardial infarction: refers to ischemia of the myocardial tissue due to a complete obstruction or drastic constriction of the coronary artery. This is usually accompanied by an increase in cardiac enzymes, typical ECG changes (ST elevations), and pain.
  • Cardiomyopathy: refers to a group of myocardial diseases associated with impaired systolic and diastolic function. The World Health Organization classifies 5 types based on cardiac changes:
    • Dilated cardiomyopathy
    • Hypertrophic nonobstructive or obstructive cardiomyopathy
    • Restrictive cardiomyopathy
    • Arrhythmogenic right ventricular cardiomyopathy
    • Unclassified cardiomyopathy
  • Myocarditis: an inflammatory disease of the heart muscle that mostly arises due to infections with cardiotropic viruses, especially infections with the coxsackievirus
  • Long QT syndrome: a condition that affects repolarization of the heart after a contraction. It results in an increased risk of an irregular heartbeat and ventricular tachyarrhythmias, which can result in sudden death.

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