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. The treatment of cardiac arrest begins with basic life support (BLS) when out-of-hospital and advanced cardiac life support (ACLS) when in-hospital. Basic life support comprises checking the patient’s mental status, activating the emergency response system, and cardiopulmonary resuscitation (CPR). An automated external defibrillator (AED) should be used once available. High-quality CPR (with early defibrillation in shockable rhythms) is crucial to survival in cardiac arrest. Advanced cardiac life support includes CPR, securing the airway, administering medications (such as epinephrine), and identifying and treatment of the cause of cardiac arrest. Post-cardiac arrest care follows return of spontaneous circulation (ROSC).

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


  • 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 (associated with sudden cardiac death (SCD) and ventricular arrhythmia after a myocardial infarction)

Etiology and Clinical Presentation

Cardiac causes of cardiac arrest

  • Structural heart disease: 
    • Coronary heart disease (CHD): associated with up to 70% of SCAs
    • Congenital heart diseases
    • Cardiomyopathies
    • Valvular heart diseases
    • Myocarditis
    • Aortic dissection
    • Acute pericardial tamponade
  • No structural heart disease:
    • Complete heart block
    • Brugada syndrome
    • Idiopathic ventricular fibrillation
    • Long QT syndrome
    • Preexcitation syndrome
    • Familial sudden cardiac death
    • Chest wall trauma (commotio cordis)

Non-cardiac causes of cardiac arrest

  • Trauma
  • Electrocution 
  • Excessive hemorrhage
  • Hypoglycemia
  • Pulmonary embolism
  • Drowning
  • Sudden infant death syndrome (SIDS)
  • Sudden unexplained death in epilepsy (SUDEP)


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

  • 5 Hs:
    1. Hypoxia
    2. Hypovolemia
    3. Hypokalemia or hyperkalemia
    4. Hypothermia
    5. Hydrogen ion (acidosis)
  • 5 Ts:
    1. Toxins
    2. Tamponade
    3. Tension pneumothorax
    4. Thrombosis (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
      • Dyspnea
    • Up to 80% of patients have symptoms 1 hour before and 50% have symptoms 1 month before the SCA.

Cardiac Rhythms

Four major cardiac rhythms are associated with SCA. These rhythms are divided into shockable and non-shockable rhythms.

Shockable rhythms

Shockable rhythms are usually caused by primary cardiac disease (most commonly ischemia). Less commonly, they are caused by systemic conditions (electrolyte disturbances, toxins, autoimmunity).

  • Ventricular fibrillation (VF):
    • Disorganized high-frequency electrical activity in the ventricles
    • No mechanical contraction, which means no pulse
  • Pulseless ventricular tachycardia (VT):
    • Rapid, regular ventricular rate with a wide QRS complex
    • More than 100/min on rhythm strip

Non-shockable rhythms

  • Asystole:
    • No discernible electrical activity
    • Flatline on electrocardiogram (P waves and QRS complexes are not present)
  • Pulseless electrical activity (PEA): 
    • Electrocardiogram (ECG) shows a cardiac rhythm without a palpable pulse.
    • May be organized (with normal-appearing ECG complexes) or unorganized (no discernible complexes on ECG)
    • From electromechanical dissociation, or no cardiac filling (“empty heart”)

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 is indicated, continue chest compressions until just before shock is ready to be given.
  6. Resume chest compressions immediately after delivery 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 thrust without head extension
    • Deliver breath mouth-to-mouth or via bag-mask ventilation.
General cardiopulmonary resuscitation (CPR) cycle

General CPR cycle: (start: bottom image)
1. Upon recognition of cardiac arrest, give 30 firm chest compressions.
2. Follow the compressions with 2 rescue breaths.
3. When an AED arrives, place pads in appropriate areas.
4. When prompted by the AED, check rhythm and deliver the shock when indicated (after making sure that no one is in physical contact with the patient).
Resume CPR cycle after shock delivery.

Image: “Aed ablauf” by Jörg Rittmeister. License: Public Domain

Management with Advanced Cardiac Life Support (ACLS)

Circulation, airway, breath (CAB)

Circulation, airway, breath is the advanced cardiac life support mantra. Since 2010, management has focused on starting chest compressions first to address circulation, then airway access and rescue breathing.

  • C (circulation):
    • High-quality CPR
    • Determine rhythm; in PEA/asystole, continue CPR.
    • Defibrillate shockable rhythms:
      • Shock at 120–200 joules on a biphasic defibrillator (lower peak electric current efficient in terminating ventricular tachyarrhythmias).
      • Shock at 360 joules on a monophasic defibrillator. 
    • Establish intravenous (IV) or intraosseous (IO) access.
    • Epinephrine 1 mg IV and repeat every 3–5 minutes for all rhythms.
    • Medications for shockable rhythms (ventricular tachycardia/fibrillation):
      • Amiodarone 300 mg IV with repeat dose of 150 mg IV as indicated
      • Consider lidocaine.
      • For torsades de pointes: magnesium sulfate (not for routine use)
  • A (airway): 
    • Bag-mask device (if not intubated)
    • Use of an advanced airway (endotracheal tube or ETT): 10/min
  • B (breathing): 
    • Oxygenate patient with 100% oxygen.
    • Use quantitative waveform capnography (check end-tidal (ETCO₂)): If ETCO₂ is low or decreasing, check CPR quality.
  • Differential diagnosis: 5 Hs and 5 Ts; treat accordingly
Adult cardiac arrest diagram

Adult cardiac arrest diagram
Upon recognition of cardiac arrest, rapid evaluation of breathing, pulse and rhythm (once cardiac monitor is available) is done and cardiopulmonary resuscitation (CPR) is initiated. Defibrillate shockable rhythms, ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT). If with pulseless electrical activity/asystole, CPR continues. Simultaneously through the process, intravenous (IV) access (or intraosseous access) is obtained to administer needed medications. IV epinephrine is given every 3–5 minutes.
Endotracheal intubation (advanced airway) is performed. Quantitative waveform capnography (which shows end-tidal (et)CO₂) is monitored. If (et)CO₂ is low, reassess CPR quality.
Cycle of steps (defibrillation and/or CPR with minimal interruption + airway support → rhythm, pulse and blood pressure check → IV medication administration) continues until return of spontaneous circulation (ROSC). Continuation of the cycle is also assessed if there is no ROSC. Signs of ROSC are: pulse and blood pressure present, abrupt sustained increase in etCO₂ (about ≥ 40 mm Hg) and spontaneous arterial pressure waves with intra-arterial monitoring.

Image by Lecturio.

Special populations

  • Pediatric advanced life support (PALS): 
    • In asystole/PEA, administer epinephrine as soon as possible (within 5 min).
    • Use cuffed ETT to reduce air leaks.
    • Respiratory rate increased to 20–30/min
    • Medications and shock energy are given based on weight.
  • Pregnant patient in-hospital ACLS:
    • More prone to hypoxia: oxygenation and airway management prioritized during resuscitation from cardiac arrest 
    • Adult ACLS + IV placement above the diaphragm (ensures the uterus does not obstruct IV administration)
    • If receiving IV magnesium: Stop and give calcium chloride or gluconate.
    • Provide lateral uterine displacement to relieve aortocaval compression.
    • Obstetric and neonatal care:
      • If no ROSC in 5 minutes: immediate perimortem cesarean delivery
      • Neonatal team to receive neonate
    • Consider etiologies of maternal cardiac arrest (A, B, C, D, E, F, G, H):
      • Anesthetic complications
      • Bleeding
      • Cardiovascular
      • Drugs
      • Embolic
      • Fever
      • General nonobstetric causes (5 Hs and 5 Ts)
      • Hypertension
  • Coronavirus disease 2019 (COVID-19):
    • Whenever possible, patients are placed in negative pressure rooms.
    • Don appropriate personal protective equipment (PPE) prior to entry.
    • Limit personnel performing CPR.
    • Oxygenation, preferably with low aerosolization risk
    • Pause chest compression for endotracheal intubation.
    • When possible, connect patient to a ventilator with inline HEPA (high-efficiency particulate air) filter.


Return of spontaneous circulation signs

  • Pulse and blood pressure
  • Abrupt sustained increase in ETCO₂ level (about ≥ 40 mm Hg)
  • Spontaneous arterial pressure waves with intra-arterial monitoring

Criteria for termination of resuscitation:

  • Several factors considered in making the decision to stop:
    • Duration of resuscitation (> 30 minutes without perfusing rhythm)
    • Initial rhythm: asystole
    • Absence of brainstem function
    • Long interval between arrest and resuscitation
    • Patient age and comorbidities
    • Normothermia
  • In out-of-hospital resuscitation, the criteria are:
    • Arrest not witnessed by emergency medical services (EMS)
    • Asystole/PEA (no shocks delivered)
    • No ROSC before the 3rd dose of epinephrine
  • ETCO₂ level:
    • Indicates CO₂ production, which increases with perfusion and pulmonary circulation (↑ in ROSC)
    • When low, confirm endotracheal tube placement first.  
    • A confirmed low EtCO₂ (< 10 mm Hg) in > 20 min of resuscitation: absent circulation and predicts acute mortality

Post-resuscitation Care


  • 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 > 65 mm Hg.
    • Emergent cardiac intervention in cases of ST-segment elevation myocardial infarction and/or cardiogenic shock
  • Mechanical ventilation:
    • Titrate fraction of inspired oxygen (FiO2) for oxygen saturation (SPO2) > 94%.
    • Titrate to partial pressure 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 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.


Primary prevention

  • Screen for risk factors for CHD (lipid disorders, hypertension).
  • Screen for CHD (in appropriate patients).
  • Reduce risk factors:
    • Control 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
      • 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, distended jugular veins, and muffled heart sounds). Tamponade can cause cardiac arrest. Treatment is with pericardiocentesis.
  • Tension pneumothorax: an abnormal collection of air in the pleural space due to laceration of the lungs. Types of 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: acute anginal pain because of partial or total occlusion of 1 or more coronary arteries due to advanced coronary heart disease. Three clinical entities can be identified: unstable angina, non-ST-segment elevation myocardial infarction (MI), and ST-segment elevation MI. Diagnosis is by ECG and cardiac 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.


  1. Marine, J., Russo, A., Knight, B., Levy, S., Yeon, S. (2020) Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy. UpTodate. Retrieved December 19, 2020, from
  2. Panchal, A. et al. (2020). Part 3: Adult Basic and Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 142 (16): S366–S468.
  3. Podrid, P. (2019). Overview of sudden cardiac arrest and sudden cardiac death. UpToDate. Retrieved December 5, 2020, from
  4. Rittenberger, J and Callaway, C. (2020). Post-cardiac arrest management in adults. UpToDate. Retrieved December 5, 2020, from
  5. Podrid, P. (2019). Pathophysiology and etiology of sudden cardiac arrest. UpToDate. Retrieved December 5, 2020, from
  6. Rittenberger, J and Callaway, C. (2020). Post-cardiac arrest management in adults. UpToDate. Retrieved December 5, 2020, from
  7. Topjian, A. et al. (2020). Part 4: Pediatric Basic and Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 142(16):S469–S523.

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