What do all cardiac arrest rhythms have in common?

Common Characteristics of All Cardiac Arrest Rhythms

All cardiac arrest rhythms are characterized by the absence of effective cardiac output and pulselessness, resulting in inadequate tissue perfusion regardless of the electrical activity present on the ECG. 1, 2

Pathophysiological Features Common to All Cardiac Arrest Rhythms

• Absence of effective mechanical contraction: Despite potentially different electrical patterns, all cardiac arrest rhythms fail to generate adequate cardiac output 1
• Pulselessness: No detectable peripheral pulses regardless of rhythm 1
• Inadequate tissue perfusion: Critical organs (brain, heart, kidneys) receive insufficient blood flow 1
• Progressive metabolic derangement: As arrest continues, all rhythms lead to worsening acidosis, hypoxia, and depletion of high-energy phosphate stores 1, 3

The Four Main Cardiac Arrest Rhythms

1. Ventricular Fibrillation (VF)

   • Chaotic, irregular electrical activity
   • No organized ventricular contraction
   • Most common initial rhythm in witnessed cardiac arrests 1

2. Pulseless Ventricular Tachycardia (pVT)

   • Organized rapid ventricular rhythm without effective output
   • Often precedes VF if untreated 1

3. Pulseless Electrical Activity (PEA)

   • Organized electrical activity visible on ECG
   • No detectable mechanical contraction
   • Often associated with potentially reversible causes 1

4. Asystole

   • Complete absence of electrical activity
   • "Flatline" on ECG
   • Often represents end-stage of untreated cardiac arrest 1

Management Implications

• All cardiac arrest rhythms require high-quality CPR: Regardless of rhythm, immediate chest compressions at adequate depth (2 inches/5 cm) and rate (100-120/min) with minimal interruptions are essential 1

• All require assessment for reversible causes: The "H's and T's" should be considered for all cardiac arrest rhythms 1:

  • Hypovolemia
  • Hypoxia
  • Hydrogen ion (acidosis)
  • Hypo/hyperkalemia
  • Hypothermia
  • Tension pneumothorax
  • Tamponade (cardiac)
  • Toxins
  • Thrombosis (coronary)
  • Thrombosis (pulmonary)

• All require continuous monitoring: Regardless of initial rhythm, continuous assessment is needed to detect rhythm changes that might require different interventions 1

• All benefit from early epinephrine: While timing may vary by rhythm (earlier for non-shockable rhythms), all cardiac arrest rhythms eventually benefit from epinephrine administration 1, 4

Clinical Pearls and Pitfalls

• Pitfall: Focusing solely on the electrical rhythm while neglecting high-quality CPR

  • Solution: Prioritize minimizing interruptions to chest compressions regardless of rhythm 1

• Pitfall: Missing fine VF misdiagnosed as asystole

  • Solution: Always confirm "asystole" in at least two ECG leads 2

• Pitfall: Delayed recognition of rhythm changes during resuscitation

  • Solution: Assign a team member to continuously monitor for rhythm changes during CPR 1

• Pitfall: Overlooking potentially reversible causes

  • Solution: Systematically evaluate for all reversible causes regardless of presenting rhythm 1

While treatment approaches may differ based on the specific rhythm (defibrillation for VF/pVT versus focusing on reversible causes for PEA/asystole), the fundamental pathophysiology of absent cardiac output and the need for high-quality CPR remains universal across all cardiac arrest rhythms.