What is the algorithm for cardioversion in various EKG (electrocardiogram) cases, including atrial fibrillation and ventricular tachycardia?

Cardioversion Algorithm for Various EKG Cases

Immediate Cardioversion Indications

Direct-current cardioversion must be performed immediately when hemodynamic instability is present, regardless of the underlying rhythm. 1

Class I (Must Do) - Emergent Situations:

• Atrial fibrillation with severe hemodynamic compromise (symptomatic hypotension, ongoing myocardial ischemia, intractable angina, or heart failure unresponsive to pharmacological rate control) requires immediate R-wave synchronized cardioversion 1
• Pre-excited atrial fibrillation (WPW syndrome) with rapid ventricular response and hemodynamic instability requires immediate direct-current cardioversion to prevent ventricular fibrillation 1
• Atrial fibrillation complicating acute MI with inadequate rate control despite pharmacological measures mandates immediate cardioversion 1

Technical Approach by Rhythm Type

Atrial Fibrillation - Paroxysmal

For paroxysmal AF, anteroapical (AA) or anteroposterior (AP) biphasic truncated exponential waveform (BTE) cardioversion is the most effective electrical strategy. 2

Pharmacological Cardioversion Options (in order of efficacy):

• Antazoline shows the largest effect (RR: 28.60) but has low-quality evidence 2
• Quinidine (RR: 2.23) likely results in large increase in sinus rhythm maintenance 2
• Ibutilide (RR: 2.00) is a reasonable option with moderate certainty 1, 2
• Propafenone (RR: 1.98) or flecainide (RR: 2.17) are effective, particularly for "pill-in-the-pocket" approach in patients without structural heart disease, sinus/AV node dysfunction, bundle-branch block, QT prolongation, or Brugada syndrome 1, 2
• Amiodarone (RR: 1.69) is reasonable when rapid restoration is not necessary 1, 2

Critical contraindication: Never use digoxin or sotalol for acute pharmacological cardioversion of AF as they may be harmful. 1

Atrial Fibrillation - Persistent

For persistent AF, use AP BTE maximum energy with patches as the first-line electrical approach (RR: 1.35 vs. incremental energy). 2

Electrical Cardioversion Protocol:

1. Start with biphasic waveform at maximum energy (≥200 J) - higher energy shocks reduce ventricular fibrillation risk and conversion to atrial flutter 1, 3, 2
2. Electrode placement: Anteroposterior positioning is more effective than anterolateral 1
3. If initial shock fails: Apply active compression at end of expiration with AP BTE incremental energy 2
4. For refractory cases: Consider simultaneous discharge from two defibrillators (required in 3.4% of cases) 4
5. Success rate with stepwise protocol: 99.3% 4

Pharmacological Options for Persistent AF:

• Bepridil (RR: 2.29) or quinidine (RR: 1.53) probably result in large increases compared to amiodarone 2
• Amiodarone remains a reasonable baseline option 1

Pre-treatment with amiodarone, flecainide, ibutilide, propafenone, or sotalol enhances cardioversion success and prevents early recurrence. 1

Atrial Flutter

Atrial flutter has extremely high electrical cardioversion success rates (97.9-100%) with any strategy. 2

Pharmacological Cardioversion (in order of efficacy):

• Ibutilide (RR: 21.45) - most effective pharmacological agent 5, 2
• Propafenone (RR: 7.15) 2
• Dofetilide (RR: 6.43) 2
• Sotalol (RR: 6.39) 2

For atrial flutter converting to atrial fibrillation during cardioversion, this occurs more frequently with shocks <200 J (20 of 930 shocks vs. 1 of 313 at ≥200 J). 3

Pre-excited Atrial Fibrillation (WPW Syndrome)

This is a distinct emergency requiring specific management. 1

Hemodynamically Unstable:

• Immediate direct-current cardioversion (Class I) 1

Hemodynamically Stable with Wide QRS (≥120 ms):

• Intravenous procainamide or ibutilide (Class I) 1
• Intravenous flecainide is reasonable (Class IIa) 1

Absolute contraindication: Never give digoxin, diltiazem, or verapamil in pre-excited AF - these accelerate conduction over the accessory pathway and can precipitate ventricular fibrillation. 1

Pre-Cardioversion Requirements

Mandatory Corrections Before Procedure:

• Correct hypokalemia (potassium must be ≥4.0 mEq/L) 1, 5
• Correct hypomagnesemia 5
• Ensure patient is not digitalis toxic - cardioversion is absolutely contraindicated in digitalis toxicity 1
• Verify QTc <440 msec (if using QT-prolonging agents) 1

Anticoagulation Strategy:

• AF/flutter <48 hours duration: Initiate anticoagulation before or immediately after cardioversion 6
• AF/flutter ≥48 hours or unknown duration: Therapeutic anticoagulation for ≥3 weeks before cardioversion OR transesophageal echo to exclude thrombus 1
• Continue anticoagulation for ≥4 weeks post-cardioversion 6

Procedural Safety Measures

Monitoring Requirements:

Continuous ECG monitoring for minimum 4 hours post-cardioversion or until QTc returns to baseline is mandatory. 5

• Longer monitoring required if any arrhythmic activity noted 5
• 70% of conversions occur within 30 minutes of infusion start (for pharmacological cardioversion) 5
• Polymorphic VT can occur up to 3 hours post-infusion with ibutilide 5

Equipment and Personnel:

• Skilled personnel with defibrillator, intracardiac pacing facilities, and medications for sustained VT must be immediately available 5
• Short-acting anesthetics or conscious sedation preferred to enable rapid recovery 1

Special Populations:

Patients with Implanted Devices:

• Maintain ≥8 cm distance between paddle and pacemaker/ICD 1
• Use anteroposterior positioning 1
• Interrogate device post-cardioversion - anticipate increased pacing threshold 1

Post-Cardiac Surgery:

• Ibutilide highly effective: 78% conversion rate at 1 mg dose for atrial flutter occurring 1-7 days post-CABG 5

Patients with Heart Failure or Low EF:

• Higher risk of sustained polymorphic VT (5.4% vs. 0.8% in those without CHF) 5
• Consider amiodarone for rate control in acute MI with AF and severe LV dysfunction 1

Critical Safety Warnings

Proarrhythmia Risk:

• Sustained polymorphic VT occurs in 1.7% of patients 5
• Risk factors: History of CHF, low ejection fraction, female sex (for nonsustained VT), hypokalemia, hypomagnesemia 5
• Ventricular fibrillation more common with shocks <200 J (5 of 2959 vs. 0 of 3439 shocks ≥200 J) 3

Management of Polymorphic VT Post-Cardioversion:

1. Discontinue ibutilide or other QT-prolonging agents 5
2. Correct electrolyte abnormalities (especially potassium and magnesium) 5
3. Magnesium sulfate infusion 5
4. Overdrive cardiac pacing 5
5. Electrical cardioversion/defibrillation if sustained 5
6. Avoid additional antiarrhythmic drugs 5

Bradycardia Post-Cardioversion:

• Occurs in 0.95% of attempts but rarely requires emergency pacing 3
• Not related to energy level used 3
• Monitor for prolonged sinus arrest, especially in elderly patients with structural heart disease or sinus node dysfunction 1

Contraindications Summary

Absolute Contraindications:

• Digitalis toxicity 1
• Hypokalemia 1
• Digoxin, diltiazem, or verapamil in WPW with pre-excited AF 1

Relative Contraindications:

• Class IC drugs in acute MI setting 1
• Frequent repetitive cardioversions in patients with short sinus rhythm periods despite antiarrhythmic prophylaxis 1

Predictors of Success and Failure

Factors Favoring Success:

• Recent onset arrhythmia (<30 days: 42-50% success vs. >30 days: 16-31% success) 5
• Atrial flutter vs. atrial fibrillation (≥48% vs. ≤40%) 5
• Higher energy shocks (≥200 J) 3
• Biphasic waveform (94% vs. 79% for monophasic) 6

Predictors of Multiple Attempts Needed:

• High body mass index 4
• High transthoracic impedance 4