What are the key differential diagnoses to consider post cardiac arrest?

Post-Cardiac Arrest Differential Diagnoses

Primary Cardiac Causes

Acute coronary syndrome is the most common etiology of out-of-hospital cardiac arrest in adults with no obvious extracardiac cause, with coronary lesions amenable to emergency treatment found in 96% of patients with ST elevation and 58% without ST elevation. 1

Key Cardiac Etiologies to Consider:

• Acute myocardial infarction/ischemia - Most frequent cardiac cause, particularly in adults 1
• Acute valvular dysfunction - Including acute mitral regurgitation, prosthetic valve dysfunction 1
• Ventricular septal defect - Complication of myocardial infarction 1
• Free-wall rupture with tamponade - Mechanical complication of MI 1
• Cardiomyopathy - Including hypertrophic cardiomyopathy, dilated cardiomyopathy 1, 2
• Inherited arrhythmia syndromes - Long QT syndrome, sudden arrhythmic death syndrome (particularly in young adults and athletes) 2

Non-Cardiac Causes

Pulmonary Etiologies:

• Pulmonary embolism - Accounts for 4.8% of cardiac arrests; initial rhythm typically pulseless electrical activity (63%) or asystole (32%), rarely ventricular fibrillation (5%) 1, 3
• Tension pneumothorax - Part of reversible "T's" 1, 4
• Respiratory insufficiency - Accounts for 15-40% of in-hospital cardiac arrests 5

Cardiovascular Structural:

• Aortic dissection - Consider in chest trauma or severe deceleration injury 1
• Cardiac tamponade - Frequent cause requiring immediate echocardiographic identification 1, 4

Metabolic/Toxic:

• Drug overdose - Including illicit drugs and QT-prolonging medications; common in young adults 2
• Hyperkalemia/hypokalemia - Part of reversible "H's" 4
• Severe acidosis - Hydrogen ion excess 4
• Hypothermia - Requires continued CPR until rewarming achieved 4

Neurological:

• Acute ischemic stroke - Cardiac arrest occurs in 3.9% of acute ischemic stroke patients (2.5% when palliative patients excluded) 6
• Intracranial hemorrhage - Particularly right hemisphere/insular involvement; presents with pulseless electrical activity (50%), asystole (40%), or ventricular fibrillation (10%) 7
• Subarachnoid hemorrhage - Noncardiac cause in young adults 2
• Seizure - Can precipitate cardiac arrest 2

Other Critical Causes:

• Hypovolemia - From hemorrhage or other fluid losses 4
• Anaphylaxis - Allergic/anaphylactic shock 1, 2
• Sepsis/infection - Systemic infection 2, 6

Diagnostic Approach Using Echocardiography

Emergency echocardiography should be performed to identify unexpected causes of cardiac arrest including tamponade, pulmonary embolism, hypovolemic heart, and hypertrophic cardiomyopathy to guide CPR. 1

Echocardiography is Recommended For:

• Rapid identification of pericardial effusion, left or right ventricular dysfunction, acute valvular dysfunction 1
• Detection of structural abnormalities - Myocardial contusion, regional wall motion abnormalities, ventricular septal defects 1
• Absence of cardiac motion on sonography is highly predictive of inability to achieve ROSC (only 2 of 218 patients without cardiac activity achieved ROSC) 1

Echocardiography is NOT Recommended:

• As routine procedure during CPR if it interferes with chest compressions 1

Initial Evaluation for Young Adults (<40 years)

For young adults with out-of-hospital cardiac arrest, 55-69% have underlying cardiac causes at autopsy, including sudden arrhythmic death syndrome and structural heart disease. 2

Mandatory Initial Workup:

• Basic metabolic profile and serum troponin 2
• Urine toxicology test 2
• 12-lead electrocardiogram - Obtain as soon as possible after ROSC 1
• Chest x-ray 2
• Head-to-pelvis computed tomography 2
• Bedside ultrasound - Assess for pericardial tamponade, aortic dissection, hemorrhage 2
• Transthoracic echocardiography - If initial evaluation non-diagnostic, screen for structural heart disease, valvular disease 2

Special Population Considerations

Obstetric Patients:

Amniotic fluid embolism should be considered in the differential diagnosis of sudden cardiorespiratory compromise in any pregnant or recently postpartum patient. 1

Post-Surgical Patients (Prone Position):

• Pulmonary embolism, gas embolism, acute myocardial infarction - Key differentials after spine surgery in prone position 8

Common Pitfalls to Avoid

• Do not assume apparent diagnosis is correct - Referral diagnosis may be misleading; always confirm with objective testing 1
• Do not delay echocardiography when clinically indicated, but never interrupt high-quality CPR 1
• Do not overlook reversible causes - Systematically evaluate all "H's and T's" 4
• Consider thrombolysis for massive PE - Significantly higher rate of ROSC (81% vs 43%) compared to no thrombolysis 3