Epidemiology and Etiology

Epidemiology

Ventricular fibrillation (VF) secondary to myocardial infarction Myocardial infarction MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction ( MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction) 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 MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction due to the risk of VF.
• Patients with a reduced left ventricular ejection fraction are at highest risk for VF following MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction.
• 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 Congestive heart failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure
  • MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction
  • Cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Overview of Cardiomyopathies
  • Myocarditis Myocarditis Myocarditis is an inflammatory disease of the myocardium, which may occur alone or in association with a systemic process. There are numerous etiologies of myocarditis, but all lead to inflammation and myocyte injury, most often leading to signs and symptoms of heart failure. Myocarditis
  • Valvular stenosis or insufficiency
• Cardiac conduction disorders:
  • Long QT syndrome Long QT syndrome Long QT syndrome (LQTS) is a disorder of ventricular myocardial repolarization that produces QT prolongation on electrocardiogram (ECG). Long QT syndrome is associated with an increased risk of developing life-threatening cardiac arrhythmias, specifically torsades de pointes. Long QT Syndrome
  • Wolff-Parkinson-White syndrome
  • Torsade de pointes
• Electrolyte imbalance (e.g., hypokalemia Hypokalemia Hypokalemia is defined as plasma potassium (K+) concentration < 3.5 mEq/L. Homeostatic mechanisms maintain plasma concentration between 3.5-5.2 mEq/L despite marked variation in dietary intake. Hypokalemia can be due to renal losses, GI losses, transcellular shifts, or poor dietary intake. Hypokalemia)
• Autonomic nervous system Autonomic nervous system The ANS is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ANS consists of the sympathetic and parasympathetic nervous systems. 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 Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables 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 Cardiac arrest Cardiac arrest is the sudden, complete cessation of cardiac output with hemodynamic collapse. Patients present as pulseless, unresponsive, and apneic. Rhythms associated with cardiac arrest are ventricular fibrillation/tachycardia, asystole, or pulseless electrical activity. 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 MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction results from: Myocardial ischemia → Necrosis → Reperfusion → Healing → Scar formation → Autonomic changes (mnemonic device: My Nephew Really Hates Scary Aliens!)

Clinical Manifestations

• Chest pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
• Hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension and respective signs and symptoms (e.g., syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope, fatigue, pallor, cold extremities, heat intolerance, blurry vision) 
• Confusion
• Palpitations
• Dizziness
• Shortness of breath 
• Loss of consciousness
• Sudden death

Diagnosis

Electrocardiogram Electrocardiogram An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) ( ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal 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 Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes (elevated after MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction)
• Coronary angiography to evaluate myocardial ischemia
• Electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes (abnormally high or low levels of potassium, calcium, or magnesium)
• Urine drug screen for medications or stimulants Stimulants Stimulants are used by the general public to increase alertness and energy, decrease fatigue, and promote mental focus. Stimulants have medical uses for individuals with ADHD and sleep disorders, and are also used in combination with analgesics in pain management. 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 Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of 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 Metabolic acidosis The renal system is responsible for eliminating the daily load of non-volatile acids, which is approximately 70 millimoles per day. Metabolic acidosis occurs when there is an increase in the levels of new non-volatile acids (e.g., lactic acid), renal loss of HCO3-, or ingestion of toxic alcohols. 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.

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 Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. Ventricular Tachycardia, and polymorphic ventricular tachycardia Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. 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 Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries with subsequent narrowing of the vessels, preventing their dilation. 
• Congestive heart failure Congestive heart failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. 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 Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes, typical ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) changes (ST elevations), and pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain.
• Cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Overview of Cardiomyopathies: 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 Dilated Cardiomyopathy Dilated cardiomyopathy (DCM) is the most common type of non-ischemic cardiomyopathy and a common cause of heart failure (HF). The cause may be idiopathic, familial, or secondary to a variety of underlying conditions. The disease is characterized by the enlargement of 1 or both ventricles and reduced systolic function. Dilated Cardiomyopathy
  • Hypertrophic nonobstructive or obstructive cardiomyopathy
  • Restrictive cardiomyopathy Restrictive Cardiomyopathy Restrictive cardiomyopathy (RCM) is a fairly uncommon condition characterized by progressive stiffening of the cardiac muscle, which causes impaired relaxation and refilling of the heart during diastole, resulting in diastolic dysfunction and eventual heart failure. Restrictive Cardiomyopathy
  • Arrhythmogenic right ventricular cardiomyopathy Arrhythmogenic Right Ventricular Cardiomyopathy Arrhythmogenic right ventricular cardiomyopathy is an inherited disorder of the heart muscle that affects the right ventricle (RV); it can cause rhythm disturbances and sudden cardiac death (SCD). The disorder results from mutations in the genes that encode desmosomal proteins involved in cell-to-cell adhesion. Arrhythmogenic Right Ventricular Cardiomyopathy
  • Unclassified cardiomyopathy
• Myocarditis Myocarditis Myocarditis is an inflammatory disease of the myocardium, which may occur alone or in association with a systemic process. There are numerous etiologies of myocarditis, but all lead to inflammation and myocyte injury, most often leading to signs and symptoms of heart failure. Myocarditis: an inflammatory disease of the heart muscle that mostly arises due to infections with cardiotropic viruses, especially infections with the coxsackievirus Coxsackievirus Coxsackievirus is a member of a family of viruses called Picornaviridae and the genus Enterovirus. Coxsackieviruses are single-stranded, positive-sense RNA viruses, and are divided into coxsackie group A and B viruses. Both groups of viruses cause upper respiratory infections, rashes, aseptic meningitis, or encephalitis. Coxsackievirus
• Long QT syndrome Long QT syndrome Long QT syndrome (LQTS) is a disorder of ventricular myocardial repolarization that produces QT prolongation on electrocardiogram (ECG). Long QT syndrome is associated with an increased risk of developing life-threatening cardiac arrhythmias, specifically torsades de pointes. 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.