Overview

Definition

Sudden cardiac arrest (SCA) is the abrupt cessation of cardiac activity.

Epidemiology

• Approximately 350,000 SCAs per year occur in the United States.
  • 60% occur out-of-hospital, with a 10% survival rate (up to 30% when witnessed by a bystander).
  • 40% occur in-hospital, with a 20% survival rate.
• Incidence of cardiac arrest increases linearly with age.
• 57% of patients are men.
• Survival rate is 10% for non-shockable rhythms and > 30% for shockable rhythms.

Risk factors

• Smoking 
• Family history of SCA
• Heavy alcohol intake (6 or more drinks/day) or binge drinking
• Elevated free fatty acids Fatty acids Fatty acids are integral building blocks of lipids, and can be classified as unsaturated or saturated based on the presence/absence of carbon-carbon double bonds within their nonpolar chains. Fatty Acids and Lipids (associated with sudden cardiac death ( SCD SCD Sickle cell disease (SCD) is a group of genetic disorders in which an abnormal Hb molecule (HbS) transforms RBCs into sickle-shaped cells, resulting in chronic anemia, vasoocclusive episodes, pain, and organ damage. Sickle Cell Disease) and ventricular arrhythmia after a 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)

Etiology and Clinical Presentation

Cardiac causes of cardiac arrest

• Structural heart disease: 
  • Coronary heart disease Coronary heart disease Coronary heart disease (CHD), or ischemic heart disease, describes a situation in which an inadequate supply of blood to the myocardium exists due to a stenosis of the coronary arteries, typically from atherosclerosis. Coronary Heart Disease (CHD): associated with up to 70% of SCAs
  • Congenital heart diseases
  • Cardiomyopathies
  • Valvular heart diseases
  • 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
  • Aortic dissection Aortic dissection Aortic dissection occurs due to shearing stress from pulsatile pressure causing a tear in the tunica intima of the aortic wall. This tear allows blood to flow into the media, creating a "false lumen." Aortic dissection is most commonly caused by uncontrolled hypertension. Aortic Dissection
  • Acute pericardial tamponade
• No structural heart disease:
  • Complete heart block
  • Brugada syndrome
  • Idiopathic ventricular fibrillation 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
  • 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
  • Preexcitation syndrome
  • Familial sudden cardiac death
  • Chest wall Chest wall The chest wall consists of skin, fat, muscles, bones, and cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. Chest Wall trauma (commotio cordis)

Non-cardiac causes of cardiac arrest

• Trauma
• Electrocution 
• Excessive hemorrhage
• Hypoglycemia Hypoglycemia Hypoglycemia is an emergency condition defined as a serum glucose level ≤ 70 mg/dL (≤ 3.9 mmol/L) in diabetic patients. In nondiabetic patients, there is no specific or defined limit for normal serum glucose levels, and hypoglycemia is defined mainly by its clinical features. Hypoglycemia
• Pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism
• Drowning Drowning Drowning occurs due to respiratory impairment from submersion or immersion in a liquid medium. Aspiration of water leads to hypoxemia, which affects all organ systems, resulting in respiratory insufficiency and acute respiratory distress syndrome (ARDS), cardiac arrhythmias, and neuronal damage. Drowning
• Sudden infant death syndrome Sudden Infant Death Syndrome Sudden infant death syndrome (SIDS) describes the sudden death of an otherwise healthy infant (< 1 year of age) with no identifiable cause. Sudden infant death syndrome is the leading cause of death in children between 1 and 12 months of age in the United States. Sudden Infant Death Syndrome (SIDS)
• Sudden unexplained death in epilepsy Epilepsy Epilepsy is a chronic brain disorder marked by recurrent and unprovoked seizures. These seizures can be classified as focal or generalized and idiopathic or secondary to another condition. Clinical presentation correlates to the classification of the epileptic disorder. Epilepsy (SUDEP)

Mnemonics

The 5 Hs and 5 Ts of the common reversible causes of SCA:

• 5 Hs:
  1. Hypoxia
  2. Hypovolemia
  3. 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 or hyperkalemia Hyperkalemia Hyperkalemia is defined as a serum potassium (K+) concentration >5.2 mEq/L. Homeostatic mechanisms maintain the serum K+ concentration between 3.5 and 5.2 mEq/L, despite marked variation in dietary intake. Hyperkalemia can be due to a variety of causes, which include transcellular shifts, tissue breakdown, inadequate renal excretion, and drugs. Hyperkalemia
  4. Hypothermia Hypothermia Hypothermia can be defined as a drop in the core body temperature below 35°C (95°F) and is classified into mild, moderate, severe, and profound forms based on the degree of temperature decrease. Hypothermia
  5. Hydrogen ion (acidosis)
• 5 Ts:
  1. Toxins
  2. Tamponade
  3. Tension pneumothorax Pneumothorax A pneumothorax is a life-threatening condition in which air collects in the pleural space, causing partial or full collapse of the lung. A pneumothorax can be traumatic or spontaneous. Patients present with a sudden onset of sharp chest pain, dyspnea, and diminished breath sounds on exam. Pneumothorax
  4. Thrombosis ( 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)
  5. Thrombosis (pulmonary embolism)

Clinical presentation

• Unresponsive (loss of consciousness)
• Pulseless
• Apneic (may have agonal respirations)
• Some have warning symptoms
  • Most common symptoms:
    • 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
    • Dyspnea
  • Up to 80% of patients have symptoms 1 hour before and 50% have symptoms 1 month before the SCA.

Management with Basic Life Support (BLS)

Chain of survival

1. Recognize an arrest and confirm scene safety. 
   • Attempt to rouse the patient verbally and physically.
   • Observe for signs of breathing (patients may have agonal breathing in cardiac arrest).
   • Check the patient’s pulse within 10 seconds:
     • Use the carotid artery in adults.
     • Use the brachial or femoral artery in children.
2. Activate the emergency response system.
   • Call for help/call other people for assistance.
   • Call 911.
   • Have someone get an automated external defibrillator (AED), if available.
3. Start cardiopulmonary resuscitation (CPR) immediately.
   • Ideally done simultaneously with calling for help
   • Important addition: If opioid overdose is suspected, give naloxone if available.
4. Check the cardiac rhythm with an AED once it arrives.
5. When 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 is indicated, continue chest compressions until just before 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 is ready to be given.
6. Resume chest compressions immediately after delivery of 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, continuing until emergency responders are available.

High-quality CPR

• Single most important intervention for cardiac arrest; should be provided promptly!
• No serious harm from CPR found in patients determined not to be in cardiac arrest
• 30 chest compressions followed by 2 rescue breaths (30:2) in adults
• 15:2 in child/infant victim if with 2 rescuers
• Principal components: 
  • Rate: 100–120 compressions/min
  • Compression depth: 5–7.6 cm (2–3 in) (child: 5 cm (2 in), infant: 3.8 cm (1.5 in))
  • Continuity: Limit pauses during CPR.
  • Allow full chest recoil.
  • Avoid excessive ventilation (1 breath every 5–6 seconds).
• Airway access:
  • Head tilt/chin lift to establish an airway.
  • For cervical injury: jaw Jaw The jaw is made up of the mandible, which comprises the lower jaw, and the maxilla, which comprises the upper jaw. The mandible articulates with the temporal bone via the temporomandibular joint (TMJ). The 4 muscles of mastication produce the movements of the TMJ to ensure the efficient chewing of food. Jaw and Temporomandibular Joint thrust without head extension
  • Deliver breath mouth-to-mouth or via bag-mask ventilation.

Post-resuscitation Care

Goals

• Brain injury mitigation
• Manage ischemia-reperfusion injury and support multi-organ systems.
• Determine and treat cause of SCA.
• Involve a multidisciplinary medical team given complexity of post-arrest patient care.

Critical care

• Hemodynamic support:
  • Use of crystalloid and/or vasopressor or inotropic support
  • Maintain systolic blood pressure > 90 mm Hg or mean arterial pressure Mean Arterial Pressure Mean arterial pressure (MAP) is the average systemic arterial pressure and is directly related to cardiac output (CO) and systemic vascular resistance (SVR). The SVR and MAP are affected by the vascular anatomy as well as a number of local and neurohumoral factors. Vascular Resistance, Flow, and Mean Arterial Pressure > 65 mm Hg.
  • Emergent cardiac intervention in cases of ST-segment elevation 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 and/or cardiogenic 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
• Mechanical ventilation:
  • Titrate fraction of inspired oxygen (FiO₂) for oxygen saturation (SPO₂) > 94%.
  • Titrate to partial pressure Partial pressure The pressure that would be exerted by one component of a mixture of gases if it were present alone in a container. Gas Exchange of carbon dioxide (PaCO₂) 35–45 mm Hg.
  • Start at 10/min.
• Targeted temperature management for comatose patient:
  • Improves neurologic outcome 
  • Use of cooling device with feedback loop, beginning at 32–36ºC (89.6–96.8ºF) for 24 hours
  • ↑ risk of death for each degree rise above 37ºC (98.6ºF)
• Other critical care management:
  • Continuous temperature monitoring
  • Maintenance of normoxia and normocapnia
  • Lung-protective ventilation
  • Maintenance of euglycemia ( insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin therapy to maintain a blood glucose of 150–180 mg/dL)
  • Electroencephalogram (EEG) monitoring
• Evaluation and treatment of causes:
  • Obtain brain computed tomography (CT) scan
  • Other imaging studies depending on the clinical picture
  • Laboratory tests
  • Remember the 5 Hs and Ts.

Prevention

Primary prevention

• Screen for risk factors for CHD ( lipid disorders Lipid disorders An abnormal amount of lipid in blood is called dyslipidemia, which includes abnormal levels of cholesterol, triglycerides, and/or lipoproteins. Dyslipidemia may be primary (familial) or secondary (acquired). Both primary and secondary causes can lead to the development of premature cardiovascular (atherosclerosis) disease. Lipid Disorders, hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension).
• Screen for CHD (in appropriate patients).
• Reduce risk factors:
  • Control hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension.
  • Treat hypercholesterolemia.
  • Treat diabetes.
  • Smoking cessation
  • Moderate alcohol consumption
  • Heart-healthy diet and regular exercise

Secondary prevention

• Implantable cardioverter-defibrillator (ICD):
  • Terminates ventricular arrhythmias when they recur
  • Recommended in the following:
    • Survivors of SCA (from VT/VF) with heart failure and 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
    • Patients with structural heart disease (associated with hemodynamically unstable VT or spontaneous sustained VT)
• Antiarrhythmic therapy:
  • Drugs (adjunctive treatment):
    • Amiodarone (preferred)
    • Sotalol
    • Mexiletine
  • Catheter ablation (adjunctive treatment)

Clinical Relevance

The following conditions are causes of cardiac arrest:

• Pericardial tamponade: a clinical syndrome caused by the accumulation of fluid in the pericardial space; results in reduced ventricular filling and subsequent hemodynamic compromise. Patients present with Beck’s triad ( 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, distended jugular veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins, and muffled heart sounds Heart sounds Heart sounds are brief, transient sounds produced by valve opening and closure and by movement of blood in the heart. They are divided into systolic and diastolic sounds. In most cases, only the first (S1) and second (S2) heart sounds are heard. These are high-frequency sounds and arise from aortic and pulmonary valve closure (S1), as well as mitral and tricuspid valve closure (S2). Heart Sounds). Tamponade can cause cardiac arrest. Treatment is with pericardiocentesis.
• Tension pneumothorax Pneumothorax A pneumothorax is a life-threatening condition in which air collects in the pleural space, causing partial or full collapse of the lung. A pneumothorax can be traumatic or spontaneous. Patients present with a sudden onset of sharp chest pain, dyspnea, and diminished breath sounds on exam. Pneumothorax: an abnormal collection of air in the pleural space due to laceration of the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs. Types of pneumothorax Pneumothorax A pneumothorax is a life-threatening condition in which air collects in the pleural space, causing partial or full collapse of the lung. A pneumothorax can be traumatic or spontaneous. Patients present with a sudden onset of sharp chest pain, dyspnea, and diminished breath sounds on exam. Pneumothorax include simple (spontaneous) and tension. Physical exam findings include decreased breath sounds, hyperresonance on percussion, and tracheal deviation. Treatment includes needle decompression and chest tube placement.
• Coronary heart disease Coronary heart disease Coronary heart disease (CHD), or ischemic heart disease, describes a situation in which an inadequate supply of blood to the myocardium exists due to a stenosis of the coronary arteries, typically from atherosclerosis. Coronary Heart Disease: acute anginal 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 because of partial or total occlusion of 1 or more 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 due to advanced coronary heart disease. Three clinical entities can be identified: unstable angina Unstable angina Precordial pain at rest, which may precede a myocardial infarction. Stable and Unstable Angina, non-ST-segment elevation 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), and ST-segment elevation 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. Diagnosis is by 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) and 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. Treatment is with percutaneous coronary intervention and/or medical management.
• Cardiomyopathies: a group of myocardial diseases associated with impaired systolic and diastolic function. Classified into dilated, hypertrophic, and restrictive cardiomyopathies. Potential complications include heart failure, arrhythmias, and sudden death. Treatment varies based on type and includes medications and/or surgery.