Defibrillation Waveform Selection and Energy Settings
Waveform Types and Characteristics
- Monophasic defibrillators deliver current in a single polarity; the two main subtypes are monophasic damped sinusoidal (MDS) and monophasic truncated exponential (MTE). 1
- Biphasic defibrillators reverse current direction in two phases and are now incorporated in virtually all modern automated external defibrillators (AEDs) and manual defibrillators. 1, 2
Clinical Efficacy
First‑Shock Success and Energy Requirements
- Monophasic shocks require higher energies and achieve lower first‑shock success compared with biphasic shocks. 1
- Recommended initial energy for biphasic devices: 150–200 J for biphasic truncated‑exponential waveforms and 120 J for rectilinear biphasic waveforms (manufacturer‑specified). 3
- Recommended initial energy for legacy monophasic devices: 360 J for the first and all subsequent shocks. 3
Subsequent Shock Strategy
- For biphasic devices, the same or higher energy may be used for subsequent shocks; an optimal escalation algorithm has not been definitively established. 1, 2
- For monophasic devices, continue delivering 360 J for each subsequent shock. 3
- Human studies have found no evidence of harm from biphasic energies up to 360 J. 1, 2
Survival Outcomes
- No specific waveform (biphasic or monophasic) has been consistently associated with higher rates of return of spontaneous circulation (ROSC) or survival to hospital discharge. 1, 2
Resuscitation Protocol Implications
- The high first‑shock efficacy of biphasic defibrillators (>90 %) prompted adoption of a single‑shock strategy followed immediately by chest compressions, replacing the older three‑stacked‑shock sequence. 4, 3
- After each shock, CPR should be resumed immediately without a pulse or rhythm check. 4, 3
- The former three‑shock protocol caused 29–37 second interruptions in chest compressions, which are now avoided. 4, 3
Common Pitfalls
- Shock success (termination of ventricular fibrillation) does not guarantee ROSC or survival; high‑quality CPR must continue regardless of waveform type. 1, 2
Defibrillator Effectiveness
Key Differences
- The American Heart Association recommends biphasic defibrillators over monophasic defibrillators for treating ventricular fibrillation due to their higher first-shock success rates and lower energy requirements 5, 6
- Biphasic waveforms demonstrate higher first-shock success rates (85-98%) for terminating ventricular fibrillation compared to monophasic waveforms 6, 7
- Biphasic defibrillators can effectively terminate ventricular fibrillation at lower energy levels (typically 200 J or less) compared to monophasic defibrillators 6, 7
Clinical Recommendations
- The American College of Cardiology recommends defibrillators using biphasic waveforms (BTE or RLB) for treatment of both atrial and ventricular arrhythmias (Class IIa, LOE B-R) 8, 7
- No specific biphasic waveform has been proven superior to others for termination of ventricular fibrillation 6, 7