Epidemiology and Etiology
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
- Underlying cardiovascular disease:
- Coronary artery disease (most common)
- Congestive heart failure
- 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)
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
- 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.
Sustained VF after an MI results from: Myocardial ischemia → Necrosis → Reperfusion → Healing → Scar formation → Autonomic changes (mnemonic device: My Nephew Really Hates Scary Aliens!)
- Chest pain
- Hypotension and respective signs and symptoms (e.g., syncope, fatigue, pallor, cold extremities, heat intolerance, blurry vision)
- Shortness of breath
- Loss of consciousness
- Sudden death
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
- Follow advanced cardiac life support algorithm.
- 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 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.