Electric Cardioversion in Unstable Tachycardia - AHA 2025 Guidelines

Note on "2026 Guidelines": As of July 2026, the most recent AHA ACLS guidelines are the 2025 AHA Guidelines for CPR and Emergency Cardiovascular Care (published October 21, 2025 in Circulation; PMID 41122884). No separate 2026 AHA tachycardia guidelines have been issued. The information below reflects the latest official AHA guidance.

Step 1: Identify Clinical Instability

The 2025 AHA highlights a key nuance: arrhythmias can be both the cause of AND a manifestation of clinical instability. Evaluating the proximal cause (e.g., sinus tachycardia from sepsis, pain, or hypovolemia) is essential before immediately cardioverting - sinus tachycardia should NOT be cardioverted.

Step 2: Immediate Synchronized Cardioversion

Key Principles

• Sedate whenever feasible (e.g., midazolam, propofol, etomidate) - do not delay cardioversion for sedation if the patient is rapidly deteriorating
• Synchronize to the R-wave to avoid shocking during the vulnerable T-wave period (which can precipitate VF)
• After each shock, re-engage sync mode - most defibrillators default back to unsynchronized mode after a shock
• Escalate energy if the first shock fails

Step 3: Energy Doses by Rhythm Type (Biphasic Defibrillator)

2025 AHA Updated Energy Recommendations

Key 2025 Update on Energy: Previous guidelines recommended lower starting energies. The 2025 AHA now recommends ≥200 J as the starting energy for AF and atrial flutter based on randomized trials and a network meta-analysis of >3,000 patients showing >90% cumulative cardioversion success with 200 J across all biphasic platforms. Higher energies cause NO increase in cardiac enzyme elevation, post-cardioversion arrhythmias, or cardiac dysfunction.

If device-specific energy is unknown: Use the maximum energy setting (per the 2025 AHA Official Algorithm).

Special Considerations by Rhythm

Narrow-Complex (SVT/AF/Flutter) - Unstable

• Proceed directly to synchronized cardioversion
• If regular narrow-complex: adenosine may be considered first as a brief diagnostic/therapeutic trial before cardioverting (if it can be given immediately)
• For AF: ≥200 J biphasic (Class IIa)
• For flutter: 200 J biphasic (Class IIa)

Wide-Complex Tachycardia (Monomorphic VT) - Unstable

• Synchronized cardioversion is recommended (2025 AHA, Class I)
• Do NOT administer adenosine to unstable, irregularly irregular, or polymorphic wide-complex tachycardia - it may cause profound hypotension or precipitate VF

Wide-Complex Tachycardia (Polymorphic VT / TdP) - Always Unstable

• All forms of polymorphic VT are considered hemodynamically and electrically unstable by definition
• Use UNSYNCHRONIZED shock (defibrillation) - synchronization is unreliable due to differing QRS morphology
• If the patient is pulseless → manage as VF/pulseless VT

Pre-excited AF/Flutter (Wolff-Parkinson-White)

• Synchronized cardioversion is first-line
• Do NOT use AV nodal blockers (adenosine, digoxin, calcium channel blockers, beta-blockers) - these can precipitate VF via the accessory pathway

Step 4: If Cardioversion Fails (Refractory)

1. Search for and treat underlying cause
2. Increase energy level for the next cardioversion attempt
3. Add an antiarrhythmic drug (amiodarone 150 mg IV over 10 min; or procainamide for stable wide-complex)
4. Expert consultation (cardiology, electrophysiology)

Procedure Checklist (Step-by-Step)

1. Establish IV access, apply monitor leads, pulse oximetry
2. 12-lead ECG if available (do not delay if unstable)
3. Sedate the patient if time permits
4. Turn on defibrillator and engage SYNC mode - confirm sync markers align with R-waves
5. Select initial energy (see table above)
6. Announce "Charging - stand clear!"
7. Confirm all personnel are clear
8. Deliver shock
9. Immediately reassess rhythm - if tachycardia persists, re-engage SYNC mode and escalate energy
10. Monitor for post-cardioversion arrhythmias

Summary Algorithm (2025 AHA)

Tachycardia with pulse
        |
        v
Signs of instability? ──NO──→ Stable pathway (medications ± elective cardioversion)
        |
       YES
        |
        v
Synchronized Cardioversion
• Sedate if feasible
• Sync to R-wave
• Energy: ≥200 J (AF/flutter), 50-200 J (SVT/mono VT)
• Polymorphic VT → Defibrillation (unsynchronized)
        |
        v
Rhythm restored? ──YES──→ Monitor, treat underlying cause
        |
       NO
        |
        v
Escalate energy + antiarrhythmic + expert consult