Shockable Cardiac Rhythms
The only shockable cardiac rhythms are ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT). 1, 2
Definition and Core Principles
The two rhythms requiring defibrillation are:
- Ventricular fibrillation (VF) - chaotic electrical activity with no organized QRS complexes 3
- Pulseless ventricular tachycardia (pVT) - organized wide-complex tachycardia without a palpable pulse 3
These are the only rhythms for which defibrillation is indicated as a primary intervention. 2
Non-Shockable Rhythms (Critical Distinction)
The following rhythms are NOT shockable and require a different treatment pathway:
- Asystole - flatline with no electrical activity 3, 1
- Pulseless electrical activity (PEA) - organized electrical activity without mechanical cardiac output 3, 1
These non-shockable rhythms have significantly worse prognosis and require CPR with epinephrine administration rather than defibrillation. 2
Clinical Significance
Patients presenting with shockable rhythms have substantially better outcomes compared to non-shockable rhythms, with improved survival to hospital discharge and favorable neurological outcomes. 1, 4 Over 80% of successful defibrillations occur within the first three shocks. 1, 2
Critical Caveat: Ventricular Tachycardia With a Pulse
Not all ventricular tachycardia is shockable. 1 This is a common source of confusion:
- VT WITH a pulse = synchronized cardioversion (lower energy, timed to QRS) 5
- VT WITHOUT a pulse (pulseless VT) = unsynchronized defibrillation (high energy, immediate) 5
The distinction depends entirely on whether the patient has a palpable pulse and adequate perfusion. Pulseless VT is treated identically to VF with immediate unsynchronized high-energy shocks. 2, 5
Treatment Approach
When VF or pVT is identified:
- Deliver immediate unsynchronized defibrillation without any delay 2
- Use 200J for monophasic or manufacturer-recommended dose (typically 120-200J) for biphasic defibrillators 3, 5
- Resume CPR immediately after the shock for 2 minutes before rechecking rhythm 2, 5
- Modern biphasic defibrillators achieve >90% first-shock efficacy 3, 2
Never use synchronized cardioversion for VF or pulseless VT, as the device may fail to sense a QRS wave and not deliver a shock, wasting critical time. 5