Cardiac Arrest

Definition

• The absence of a carotid or femoral pulse is the primary diagnostic criterion for healthcare professionals.
• Cardiac arrest differs from heart attack (myocardial infarction): MI is a plumbing problem; cardiac arrest is an electrical/mechanical problem.
• Sudden cardiac arrest (SCA) accounts for ~50% of all cardiovascular deaths.

Types of Cardiac Arrest (by Underlying Rhythm)

1. Ventricular Fibrillation (VF) - Shockable

• The most "electrical" form of cardiac arrest.
• Chaotic, disorganized electrical activity with no recognizable QRS complexes.
• The ventricles quiver rather than contract - no effective cardiac output.
• Historically the most common initial rhythm in out-of-hospital cardiac arrest (OHCA), particularly in ischemic heart disease.
• Currently estimated at ~20-25% of first-recorded rhythms (frequency has declined as VF-related MI presentations have changed).
• Best prognosis of all arrest rhythms when treated promptly with defibrillation.
• Causes: acute MI, coronary artery disease, cardiomyopathies, electrolyte disturbances, Brugada syndrome, long QT syndrome.

2. Pulseless Ventricular Tachycardia (Pulseless VT) - Shockable

• Organized wide-complex tachycardia at high rates (>100-150 bpm), but insufficient cardiac output to generate a palpable pulse.
• May degenerate into VF if untreated.
• Also estimated at ~20-25% of first-recorded OHCA rhythms.
• Treated identically to VF: immediate defibrillation.
• Patients with sustained VT (even without immediate pulselessness) can persist longer with marginal blood flow before full arrest.
• Sustained VT carries a better prognosis than VF when intervened upon quickly.

3. Asystole - Non-Shockable

• Complete absence of all electrical activity in the heart - a "flat line" on ECG.
• Currently the most common first-recorded rhythm in OHCA (~50%).
• Results from failure of the heart's electrical system to generate or propagate any ventricular depolarizations.
• Two types:
  • Primary asystole: failure of the electrical system itself (e.g., sick sinus syndrome, complete heart block, advanced coronary disease).
  • Secondary asystole: external factors suppress the electrical system (e.g., hypoxia, hypercarbia, drug overdose, hypothermia, stroke).
• Common causes: myocardial ischemia/infarction, asphyxiation, hypoxia, opiates, beta-blockers, calcium channel blockers, parasympathomimetics.
• Poorest prognosis - return of spontaneous circulation (ROSC) is rare; long-term neurologically intact survival is extremely uncommon.
• Not treated with defibrillation. Management focuses on CPR, epinephrine, and treating reversible causes.

4. Pulseless Electrical Activity (PEA) - Non-Shockable

• Organized electrical activity visible on ECG (identifiable QRS complexes), but no palpable pulse - no effective mechanical contraction.
• Estimated at ~20-25% of OHCA rhythms. In in-hospital cardiac arrest (IHCA), PEA has become increasingly common (up to 70% of pediatric IHCA).
• Important distinction: "pseudo-PEA" exists when a rescuer cannot detect a pulse but there is actually adequate perfusion (e.g., profound vasoconstriction in hypothermia).
• Mechanism: profound myocardial depression OR mechanical factors that reduce venous return or impede blood flow.
• Reversible causes (the H's and T's):

• Prognosis is poor except when a reversible cause is identified and corrected rapidly.

Summary Comparison Table

Classification by Setting

• Out-of-Hospital Cardiac Arrest (OHCA): Most common setting. Dominated by asystole (~50%), followed by VF/pVT and PEA. Survival to discharge is ~10-20% overall.
• In-Hospital Cardiac Arrest (IHCA): VF/pVT accounts for only ~33%; respiratory arrest, asystole, and PEA dominate (~61%). Survival rates differ - VF/VT has ~27% survival vs. ~8% for PEA/asystole.
• Pediatric Cardiac Arrest: Asystole is the most common rhythm (~2/3 of cases), with PEA increasing significantly over time. VF/pVT is rare (~9%) in children, contrasting with adults.

Major Causes of Cardiac Arrest

1. Ischemic heart disease - most common overall cause
2. Structural heart disease - cardiomyopathies (dilated, hypertrophic, arrhythmogenic)
3. Primary arrhythmia syndromes - long QT, Brugada, catecholaminergic polymorphic VT (CPVT)
4. Valvular disease - severe aortic stenosis
5. Congenital heart disease - ALCAPA, Tetralogy of Fallot, aortic coarctation
6. Non-cardiac causes - pulmonary embolism, aortic aneurysm rupture, aortic dissection, intracranial hemorrhage
7. Electrolyte disorders - severe hyperkalemia (can cause VF, PEA, or asystole)
8. Drug toxicity - beta-blockers, digoxin, tricyclic antidepressants, cocaine

Time to Biologic Death

• Irreversible brain damage begins within 4-6 minutes of circulatory arrest.
• Biologic death rapidly follows in unattended arrest.
• Exceptions exist - some patients resuscitated after >8 minutes of basic life support delay or >16 minutes without advanced life support.
• Probability of neurologically intact survival deteriorates sharply with each passing minute.

Management Overview

1. BLS (Basic Life Support): High-quality CPR - 100-120 compressions/min, 5-6 cm depth, allow full chest recoil, minimize interruptions.
2. Defibrillation: For VF/pVT - earliest possible shock. "Chain of Survival" principle.
3. ACLS (Advanced Cardiac Life Support): Airway management, IV/IO access, epinephrine (1 mg IV every 3-5 min), amiodarone/lidocaine for shockable rhythms.
4. Treat reversible causes (H's and T's): Especially for PEA and asystole.
5. Post-cardiac arrest care: ICU admission, targeted temperature management (TTM, 32-36°C), coronary angiography if indicated, neuroprotection.