When someone’s heart rhythm becomes irregular, two electrical treatments often come to mind: cardioversion and defibrillation. They might sound alike, but they serve different purposes and occur in very different situations.
Electrical cardioversion is not the same as defibrillation—it’s a controlled procedure used to restore a normal rhythm in non-emergency cases, while defibrillation is a life-saving shock used during cardiac arrest.
We often see both methods used in hospitals and emergency settings, but the goals and timing set them apart. Cardioversion uses a synchronized shock to correct abnormal rhythms like atrial fibrillation.
Defibrillation, on the other hand, delivers an unsynchronized shock to restart the heart when it stops beating effectively.
Key Takeaways
- Cardioversion and defibrillation both use electric shocks but serve different purposes.
- Cardioversion corrects certain irregular heart rhythms in a controlled setting.
- Defibrillation treats cardiac arrest by restoring the heart’s normal rhythm immediately.
Key Differences Between Electrical Cardioversion and Defibrillation
Both electrical cardioversion and defibrillation use controlled electric shocks to correct abnormal heart rhythms. They differ in purpose, timing, and urgency, which influence how and when each procedure is performed in patient care.
Purpose and Clinical Indications
We use electrical cardioversion to treat arrhythmias in patients who have a pulse but an irregular rhythm, such as atrial fibrillation or atrial flutter. The goal is to restore a normal sinus rhythm and improve heart efficiency.
Defibrillation, on the other hand, is an emergency intervention. We use it when a patient has no pulse due to life-threatening rhythms like ventricular fibrillation or pulseless ventricular tachycardia.
These conditions stop the heart from pumping blood effectively.
| Procedure | Typical Rhythm Treated | Pulse Present | Example Use |
| Cardioversion | Atrial fibrillation, atrial flutter | Yes | Planned rhythm correction |
| Defibrillation | Ventricular fibrillation, pulseless VT | No | Cardiac arrest |
Cardioversion is usually elective or semi-urgent. Defibrillation is performed immediately to prevent death.
Synchronization and Shock Timing
The key difference lies in timing. In synchronized cardioversion, we deliver the shock at a specific point in the heart’s electrical cycle—aligned with the R wave of the QRS complex.
This timing avoids shocking during the T wave, which could trigger dangerous rhythms.
Defibrillation uses an unsynchronized shock. We deliver the energy as soon as possible, without waiting for a specific point in the cardiac cycle.
This approach is essential in cardiac arrest when no organized rhythm exists.
Energy Levels and Delivery
Energy levels differ between the two procedures. We typically use lower energy for cardioversion, often in the range of 50–200 joules, depending on the arrhythmia and equipment type.
The goal is to restore rhythm without causing unnecessary tissue damage.
Defibrillation requires higher energy, usually 200–360 joules, because it must depolarize a larger portion of the heart muscle instantly.
The stronger shock helps reset the heart’s electrical system during chaotic rhythms.
Both procedures use adhesive electrode pads or paddles placed on the chest. Proper placement and firm contact help deliver energy effectively and reduce skin burns.
Urgency and Setting
Cardioversion is usually performed in a controlled setting, such as a hospital or clinic. We often sedate the patient to reduce discomfort.
The procedure is planned, and continuous monitoring ensures safety during and after the shock.
Defibrillation is an emergency procedure done wherever cardiac arrest occurs—in hospital rooms, ambulances, or public spaces using automated external defibrillators (AEDs). Speed is critical, as every minute without defibrillation lowers survival chances.
Understanding Electrical Cardioversion
We use electrical cardioversion to restore a normal heart rhythm when medications alone cannot correct an irregular or rapid heartbeat. It helps treat specific arrhythmias safely and effectively through a controlled, synchronized electrical shock delivered under medical supervision.
Mechanism of Action
Electrical cardioversion works by sending a synchronized electrical shock to the heart at a precise moment in the cardiac cycle. The shock is timed with the R-wave on an ECG to avoid triggering dangerous rhythms like ventricular fibrillation.
The electrical current temporarily stops abnormal electrical activity in the heart. This pause allows the heart’s natural sinus node to regain control and reestablish a normal sinus rhythm.
We place electrodes or paddles on the patient’s chest, sometimes one on the chest and one on the back, to deliver the current. The energy level varies depending on the arrhythmia type and patient size.
Unlike defibrillation, which delivers an unsynchronized shock during cardiac arrest, cardioversion is planned and controlled. It is often combined with antiarrhythmic medications such as amiodarone to help maintain rhythm after the procedure.
Indications for Use
We perform electrical cardioversion to treat arrhythmias that do not respond to medication or cause troubling symptoms. The most common conditions include atrial fibrillation, atrial flutter, and supraventricular tachycardia.
These arrhythmias cause the heart to beat irregularly or too fast, reducing its ability to pump blood efficiently. When left untreated, they can increase the risk of blood clots and stroke.
Before cardioversion, we often prescribe anticoagulant therapy for several weeks to lower stroke risk. If urgent treatment is needed, a transesophageal echocardiogram may be performed to check for clots in the heart chambers.
Electrical cardioversion is not used for life-threatening rhythms like ventricular fibrillation; those require immediate defibrillation instead.
Procedure Steps and Sedation
The procedure takes place in a hospital or cardiac care unit under the supervision of a cardiologist and a trained medical team. We attach ECG leads to monitor the heart rhythm continuously.
Before the shock, we give sedation or short-acting anesthesia so the patient remains comfortable and unaware of the brief shock. Oxygen and vital signs are monitored throughout.
We position the electrodes on the chest or chest and back. After confirming synchronization with the ECG’s R-wave, we deliver a controlled electrical shock.
In some cases, more than one shock may be needed. The heart rhythm is then reassessed to confirm restoration of sinus rhythm.
The patient usually recovers within a short observation period.
Risks and Complications
Electrical cardioversion is generally safe, but it carries some risks. Skin burns or mild irritation can occur at the electrode sites.
Irregular heart rhythms may briefly appear after the shock but usually resolve quickly. The main concern is stroke from dislodged blood clots, especially in patients with atrial fibrillation.
Proper use of anticoagulants before and after the procedure reduces this risk.
Rare complications include low blood pressure, heart muscle injury, or reaction to sedation. We monitor patients closely during and after the procedure to detect and manage these issues.
Compared with chemical cardioversion using drugs alone, electrical cardioversion acts faster and often restores rhythm more reliably when performed under controlled conditions.
Defibrillation in Cardiac Emergencies
Defibrillation delivers a controlled electric shock to the heart to restore a normal rhythm in life-threatening situations such as cardiac arrest. It is a critical step in resuscitation when the heart’s electrical system stops functioning properly, especially during ventricular fibrillation or pulseless ventricular tachycardia.
How Defibrillation Works
During defibrillation, we deliver an unsynchronized electric shock across the chest using paddles or adhesive pads. The goal is to depolarize the heart muscle cells all at once, allowing the heart’s natural pacemaker to regain control.
The shock interrupts the chaotic electrical activity seen in ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT). By resetting the electrical system, the heart may resume a coordinated rhythm that can support blood flow.
Modern biphasic defibrillators deliver current in two directions, which improves efficiency and reduces the energy needed for success compared to older monophasic defibrillators.
Energy levels typically range from 120 to 200 joules for biphasic devices.
Safety is essential. We ensure no one touches the patient during the shock, verify proper pad placement, and confirm the device is charged and ready.
Shockable Rhythms and Indications
Defibrillation is indicated only for shockable rhythms, specifically VF and pulseless VT. These rhythms cause the heart to quiver or beat too fast to pump blood effectively, leading to cardiac arrest.
We do not use defibrillation for non-shockable rhythms such as asystole or pulseless electrical activity (PEA), as these require CPR and medications instead.
| Rhythm Type | Shockable? | Defibrillation Indicated? |
| Ventricular Fibrillation (VF) | Yes | ✅ |
| Pulseless Ventricular Tachycardia (VT) | Yes | ✅ |
| Asystole | No | ❌ |
| Pulseless Electrical Activity (PEA) | No | ❌ |
Quick recognition and immediate defibrillation improve survival rates. Each minute without defibrillation reduces the chance of survival by about 7–10%.
Types of Defibrillators and AEDs
Defibrillators come in several forms: manual, biphasic, monophasic, and automated external defibrillators (AEDs).
Manual defibrillators are used mainly by trained medical professionals who interpret rhythms and select energy levels. AEDs, by contrast, are designed for public use.
They automatically detect a shockable rhythm and guide users through voice or visual prompts.
AEDs are common in airports, schools, and workplaces. They use adhesive pads instead of paddles and deliver biphasic shocks, which are safer and more effective.
By making AEDs widely available, we increase the likelihood that someone can deliver a life-saving shock before emergency responders arrive.
Types and Techniques of Cardioversion
We use cardioversion to restore a normal heart rhythm when the heart beats too fast or irregularly. The method can involve an electrical shock timed with the heart’s rhythm or medications that act on the heart’s electrical system.
Synchronized Electrical Cardioversion
In synchronized cardioversion, we deliver a controlled electric shock that aligns with the R wave on the electrocardiogram (ECG). This timing prevents the shock from striking during the heart’s vulnerable repolarization phase, which could cause dangerous rhythms like ventricular fibrillation.
We perform this procedure under sedation for patient comfort. The energy level varies depending on the arrhythmia type—lower for atrial fibrillation or flutter, higher for stable ventricular tachycardia.
The device automatically detects the proper timing for discharge, ensuring precision.
Common indications include atrial fibrillation, atrial flutter, and supraventricular tachycardia when medications fail or symptoms persist. We attach adhesive pads to the chest or chest and back, confirm synchronization on the ECG monitor, and then deliver the shock.
Afterward, we monitor the heart rhythm and vital signs to confirm successful conversion and to detect any recurrence or complications.
Pharmacologic Cardioversion
Pharmacologic, or chemical cardioversion, uses antiarrhythmic medications instead of electricity to restore sinus rhythm. We choose this method when electrical cardioversion is not urgent or when sedation poses a risk.
Drugs such as amiodarone, flecainide, propafenone, or ibutilide are common options. The choice depends on the type of arrhythmia, underlying heart disease, and patient tolerance.
We monitor the patient continuously with an ECG to detect changes in rhythm or potential side effects like QT prolongation. Conversion can take minutes to hours, and success rates vary by medication and arrhythmia type.
Types and Applications of Defibrillators
Defibrillators come in several forms designed for different settings and patient needs. Each type delivers an electric shock to restore a normal heart rhythm, but they vary in how they are operated, who uses them, and where they are applied.
Manual Defibrillators
We often use manual defibrillators in hospitals or advanced medical settings. These devices require trained professionals to interpret heart rhythms and set the correct energy level before delivering a shock.
Manual defibrillators can be monophasic or biphasic.
- Monophasic defibrillators send current in one direction through the heart.
- Biphasic defibrillators reverse the current flow midway, using less energy and reducing heart muscle damage.
Biphasic models have largely replaced monophasic ones due to their efficiency and safety. We rely on manual defibrillators during cardiac arrest, ventricular fibrillation, or unstable ventricular tachycardia when immediate expert intervention is available.
Automated External Defibrillators
Automated external defibrillators (AEDs) are designed for public use and emergency response outside hospitals. They analyze the heart’s rhythm automatically and give clear voice or visual prompts to guide users.
Most AEDs are biphasic, which improves success rates while minimizing injury to heart tissue. These devices are common in airports, schools, gyms, and workplaces, making early defibrillation possible before medical teams arrive.
We use AEDs to treat sudden cardiac arrest, especially when the heart stops due to ventricular fibrillation or pulseless ventricular tachycardia. Their simple design allows bystanders with minimal training to act quickly and increase survival chances.
Implantable Cardioverter Defibrillators
An implantable cardioverter defibrillator (ICD) is a small device placed under the skin, usually near the collarbone. It monitors heart rhythms continuously and delivers an internal shock when it detects a dangerous arrhythmia.
ICDs help patients at high risk of sudden cardiac arrest, such as those with severe heart failure or prior life-threatening arrhythmias. The device can perform cardioversion or defibrillation automatically, depending on the rhythm detected.
We program ICDs to adjust their response based on the patient’s condition. This long-term protection makes them essential for preventing sudden death in people with chronic heart rhythm disorders.
Comparing Outcomes, Risks, and Considerations
Electrical cardioversion and defibrillation both aim to restore a normal heart rhythm, but their outcomes, risks, and follow-up needs differ. We assess each method based on how well it works, possible complications, and what patients may need for long-term care.
Success Rates and Recurrence
Electrical cardioversion has a high success rate, often restoring normal sinus rhythm in over 90% of patients with atrial fibrillation or other irregular heart rhythms. However, recurrence is common, especially in people with underlying heart disease or untreated risk factors such as high blood pressure or thyroid problems.
Defibrillation, used in emergencies like cardiac arrest, focuses on life-saving rhythm restoration rather than long-term control. Its success depends on how quickly it is performed and the cause of the arrhythmia.
In some cases, antiarrhythmic drugs or catheter ablation can reduce recurrence. Patients may also need close monitoring by cardiologists to track their rhythm over time.
| Procedure | Typical Success Rate | Common Use | Recurrence Risk |
| Electrical Cardioversion | 85–95% | Stable arrhythmias | Moderate to high |
| Defibrillation | Variable | Cardiac arrest | Not applicable |
Potential Complications
Both procedures carry risks, though serious events are uncommon when performed correctly. Electrical cardioversion can cause skin burns, minor chest discomfort, or short-term arrhythmia recurrence.
In rare cases, it may trigger a stroke if blood clots are present in the heart. We reduce stroke risk by giving anticoagulants before and after the procedure, especially for atrial fibrillation.
Defibrillation, because of its higher energy levels, can lead to muscle soreness, temporary confusion, or heart muscle injury, though these effects are usually short-lived.
Patients with implanted devices such as a pacemaker or implantable cardioverter-defibrillator (ICD) require special care to avoid damage. We use specific pad placements and energy settings to protect these devices during treatment.
Long-Term Management and Follow-Up
After cardioversion, maintaining a normal rhythm often requires ongoing medication and lifestyle adjustments. We monitor patients for recurrent arrhythmias and adjust therapy as needed.
Regular follow-up visits help us assess heart function. We also manage contributing conditions like sleep apnea or hypertension.
Defibrillation patients, especially those who survive cardiac arrest, usually need a comprehensive evaluation to find the cause of the event. They may receive an ICD to prevent future episodes.
Long-term management includes stroke prevention and rate control. Patient education is also important.
We emphasize adherence to medications and follow-up appointments. This helps reduce complications and improve quality of life.
Conclusion: Knowing the Difference Helps You Respond with Confidence
Electrical cardioversion and defibrillation may seem similar, but understanding how they differ is essential for recognizing when each treatment is needed. Cardioversion is a controlled, scheduled procedure used to correct irregular rhythms like AFib or atrial flutter, restoring a steady rhythm in patients who still have a pulse. Defibrillation, on the other hand, is an emergency, lifesaving shock used during cardiac arrest to restart the heart when no effective rhythm is present. Both treatments rely on electrical energy, but their timing, energy levels, goals, and clinical settings set them apart. By knowing the purpose and application of each, patients and families can feel more confident in the care being provided and better understand the steps taken during urgent or non-urgent rhythm correction.
If you’re experiencing symptoms of an irregular heartbeat or want expert guidance on rhythm management, Cardiovascular Group (CVG Cares) offers advanced diagnostics and compassionate, personalized care.
