What are the causes of cardiac arrest?

Causes of Cardiac Arrest

The primary causes of cardiac arrest include ischemic heart disease, cardiomyopathies, genetic arrhythmia syndromes, and non-cardiac conditions such as pulmonary embolism, electrolyte abnormalities, and trauma. 1

Cardiac Causes

Ischemic Heart Disease

• Primary ischemic heart disease is the most common cause of cardiac arrest in adults 1
• Manifests as:
  • Ventricular fibrillation (most common primary rhythm of cardiac arrest)
  • Pulseless ventricular tachycardia
  • Asystole
  • Electromechanical dissociation (PEA)

Cardiomyopathies

1. Nonischemic Dilated Cardiomyopathy (DCM)

   • High risk for recurrent cardiac arrest 1
   • Often presents with ventricular tachycardia or ventricular fibrillation

2. Hypertrophic Cardiomyopathy (HCM)

   • Most common cause of cardiac arrest in individuals younger than 40 years 1
   • Affects approximately 1 in 500 persons
   • Risk increases during physical exertion
   • Sudden death may be the first manifestation of disease 2

3. Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy (ARVD/C)

   • Characterized by fibrofatty infiltration of the right ventricle
   • Usually manifests with sustained monomorphic VT
   • More common in young individuals during exercise 1

Genetic Arrhythmia Syndromes

• Primary electrical conditions that exist without structural heart disease 1
• Include:
  • Long QT syndrome
  • Short QT syndrome
  • Brugada syndrome
  • Idiopathic ventricular fibrillation
  • Catecholaminergic polymorphic ventricular tachycardia
  • Wolff-Parkinson-White syndrome 3

Non-Cardiac Causes

Pulmonary Causes

• Pulmonary embolism
• Tension pneumothorax
• Drowning (accounts for 25-31% of pediatric out-of-hospital cardiac arrests) 1

Metabolic/Electrolyte Disturbances

• Hyperkalemia - can cause cardiac arrhythmias and cardiac arrest 1

  • Presents with:
    • Peaked T waves (early sign)
    • Flattened P waves
    • Prolonged PR interval
    • Widened QRS complex
    • Eventually sine-wave pattern and asystole

• Other electrolyte abnormalities that can contribute to cardiac arrest:

  • Hypokalemia
  • Hypocalcemia/hypercalcemia
  • Hypomagnesemia/hypermagnesemia

Traumatic Causes

• Cardiac tamponade - increasing fluid and pressure in the pericardium reduces cardiac filling 1
• Commotio cordis - blunt trauma to the chest 1
• Hemorrhagic shock

Toxicological Causes

• Drug overdose (particularly tricyclic antidepressants)
• Medication side effects (QT-prolonging drugs)
• Proarrhythmic effects of antiarrhythmic drugs 3
• Anaphylaxis

Special Considerations

Cardiac Arrest in Young Adults

• In young adults (<40 years), cardiac arrest incidence ranges from 4-14 per 100,000 person-years 2
• 55-69% have underlying cardiac causes, including:
  • Sudden arrhythmic death syndrome (normal heart by autopsy)
  • Structural heart disease
  • Genetic cardiac disease (found in 2-22% of survivors) 2
• Non-cardiac causes more common than in older adults:
  • Drug overdose
  • Pulmonary embolism
  • Subarachnoid hemorrhage
  • Seizure
  • Anaphylaxis
  • Infection 2

Cardiac Arrest in Athletes

• Age-dependent causes:
  • Younger athletes: genetic heart conditions and unexplained cases (normal autopsy)
  • Veteran/Masters athletes: coronary artery disease 4

Diagnostic Approach for Survivors

For survivors of cardiac arrest, a comprehensive evaluation should include:

• Basic metabolic profile and serum troponin
• Urine toxicology
• ECG
• Chest x-ray
• Head-to-pelvis CT
• Bedside ultrasound to assess for pericardial tamponade, aortic dissection, or hemorrhage 2
• Transthoracic echocardiography to screen for structural heart disease 1
• Electrophysiologic study (may demonstrate life-threatening tachycardias in patients with apparently normal hearts) 5

Pitfalls and Caveats

1. Idiopathic Ventricular Fibrillation

   • In approximately 5% of victims, no structural heart disease is found 6
   • Requires exclusion of all other potential causes before diagnosis
   • Patients require careful follow-up with annual non-invasive testing

2. Misdiagnosis

   • Up to 6.5% of presumed cardiac arrests may have an erroneous diagnosis 3
   • Conditions like focal cardiomyopathy, myocarditis, or transient electrolyte abnormalities may remain silent despite evaluation 6

3. Drug-Induced Cardiac Arrest

   • Amiodarone, while used to treat arrhythmias, can itself cause asystole/cardiac arrest/PEA as an adverse reaction 7
   • QT-prolonging medications should be avoided in patients with long QT syndrome 1

Understanding the specific cause of cardiac arrest is crucial for determining appropriate treatment and prevention strategies, particularly for survivors who require targeted interventions to prevent recurrence.