Cardioversion 

1️⃣ Definition of Cardioversion

Cardioversion refers to the conversion of an abnormal cardiac rhythm to normal sinus rhythm using either:

A. Electrical Cardioversion

• Delivery of synchronized electrical shock
• Timed with R wave
• Prevents shock during vulnerable period (T wave)

B. Pharmacological (Chemical) Cardioversion

• Antiarrhythmic drugs used to restore sinus rhythm

2️⃣ Physiology & Electrophysiological Basis

Why Cardioversion Works

Arrhythmias occur due to:

• Re-entry circuits(Continuous circular electrical impulse traveling repeatedly around a pathway, reactivating myocardium.)exp-AVNRT,AVRT,Atrial flutter
• Abnormal automaticity(Spontaneous impulse generation from cells that normally should NOT act as pacemakers.)Sinus tachycardia,Ectopic atrial tachycardia,Accelerated idioventricular rhythm
• Triggered activity(Extra depolarizations caused by afterdepolarizations occurring during or after repolarization.)👉 Torsades de Pointes,Bidirectional VT (classic digoxin),Ventricular tachycardia

Electrical cardioversion:

✔ Depolarizes entire myocardium simultaneously
✔ Terminates re-entry circuits
✔ Allows SA node to regain control

Why shock synchronized to R wave?

If shock delivered during:

👉 T wave (vulnerable repolarization phase)
→ Can trigger ventricular fibrillation
→ Called R-on-T phenomenon

Hence defibrillator uses:

• QRS detection
• Shock delivered at peak R wave

3️⃣ Types of Cardioversion

A. Electrical Cardioversion

✔ Synchronized shock

✔ Used in organized tachyarrhythmias

B. Unsynchronized Shock (Defibrillation)

4️⃣ Indications of Cardioversion (Guideline Based – ACLS / ESC / AHA)

 Immediate Electrical Cardioversion (Hemodynamic Instability)

Tachyarrhythmia with pulse + instability

Instability criteria:

• Hypotension
• Altered mental status
• Shock
• Ischemic chest pain
• Acute pulmonary edema

Arrhythmias Requiring Urgent Cardioversion

✔ Atrial fibrillation with instability
✔ Atrial flutter with instability
✔ Supraventricular tachycardia
✔ Monomorphic ventricular tachycardia with pulse

 Stable Arrhythmias – Elective Cardioversion

When rhythm control strategy selected:

• Persistent AF
• Symptomatic atrial flutter
• Drug-resistant SVT
• Selected VT cases

5️⃣ Contraindications

Absolute Contraindication- Digitalis toxicity arrhythmias (risk of VF)

Relative Contraindications

• Untreated AF > 48 hours
• Hypokalemia
• Inadequate anticoagulation
• Active thrombus in LA appendage

6️⃣ Anticoagulation Before Cardioversion(electrical/phamacological) (Very High Yield)

AF Duration < 48 Hours

👉 Cardioversion can be done
👉 Anticoagulation recommended based on CHA₂DS₂VASc

AF Duration > 48 Hours or Unknown

Two options:

Option 1 – Conventional Strategy

✔ Anticoagulate ≥ 3 weeks
✔ Cardioversion
✔ Continue anticoagulation ≥ 4 weeks

Option 2 – TEE Guided Strategy

✔ Perform TEE
✔ If no thrombus → immediate cardioversion
✔ Continue anticoagulation 4 weeks

7️⃣ Energy Settings for Electrical Cardioversion

Biphasic Defibrillators (Preferred – Modern Practice)

Monophasic (Older Machines)

Higher energy required.

8️⃣ Electrode Pad Placement

A. Anterior–Lateral

• Most common

B. Anterior–Posterior

• More effective in AF
• Useful in obese or COPD patients

9️⃣ Sedation & Analgesia 

Electrical cardioversion is painful → sedation mandatory in conscious patients.

Common Drugs

ICU Tip- Etomidate preferred in unstable patients.

 Complications of Cardioversion

Cardiac

• Ventricular fibrillation
• Bradyarrhythmia
• Asystole
• Myocardial injury

Thromboembolism

Most feared complication.

Cutaneous

• Burns
• Skin irritation

Sedation Related

• Hypotension
• Respiratory depression

 Pharmacologic Cardioversion

Drugs Used

ICU Pearls

👉 Amiodarone preferred in structural heart disease
👉 Class IC avoided in CAD / LV dysfunction

 Post-Cardioversion Care

Monitoring

• Continuous ECG
• Hemodynamics
• Electrolytes

Anticoagulation

Continue minimum 4 weeks regardless of rhythm outcome.

Why Anticoagulation Is Needed Even in Drug Cardioversion

The risk of thromboembolism is not due to the shock.It occurs because:

1️⃣ Atrial fibrillation causes atrial stasis

• Blood pools in the left atrium—>Especially in left atrial appendage—>Thrombus forms

2️⃣ Cardioversion restores atrial contraction

When sinus rhythm returns: Atrial contraction dislodges clot—>Leads to stroke or systemic embolism

3️⃣ Post-cardioversion atrial stunning

Even after sinus rhythm:Atria remain mechanically weak for weeks—>Clot risk persists

Antiarrhythmic Maintenance

Often required to prevent recurrence.

 Special ICU Situations

Cardioversion in Shock

• Perform immediately
• Sedation may be minimal

Cardioversion in Pregnancy

• Safe
• Fetal monitoring recommended

Cardioversion in Pacemaker Patients

• Pad away from device
• Check device after procedure