Cardioversion: Heart Rhythm Restoration Procedure

What Is Cardioversion and How Does It Work?

Cardioversion is a medical procedure that uses precisely timed electrical shocks to restore a normal heart rhythm in patients with arrhythmias such as atrial fibrillation or atrial flutter. The procedure is performed under general anesthesia, takes only 5-10 minutes, and has a success rate of 70-90% for converting the heart back to normal sinus rhythm.

Cardioversion is a treatment used when the heart is not beating in its normal rhythm. The most common reason for needing cardioversion is atrial fibrillation, a condition where the upper chambers of the heart (atria) beat irregularly and often too fast. This irregular heartbeat can cause symptoms such as palpitations, shortness of breath, fatigue, and dizziness, and it increases the risk of blood clots forming in the heart.

The word "cardioversion" comes from Latin, meaning "turning the heart." This accurately describes what the procedure does: it uses electrical energy to reset the heart's natural pacemaker cells and restore a normal, coordinated heartbeat. Unlike defibrillation, which is used in cardiac arrest emergencies, cardioversion delivers a precisely synchronized electrical shock that is timed to a specific point in the heart's electrical cycle. This synchronization is crucial for safety and effectiveness.

During cardioversion, two paddles or electrode pads are placed on your chest. A defibrillator device delivers a controlled electrical current through your heart. This current briefly stops all electrical activity in the heart, giving the heart's natural pacemaker (the sinoatrial node) the opportunity to resume control and establish a normal rhythm. The procedure itself takes only about 5 to 10 minutes, though you should expect to be at the hospital for several hours including preparation and recovery time.

Types of Cardioversion

There are two main approaches to cardioversion, and your doctor will recommend the most appropriate method based on your specific situation:

• Electrical cardioversion (DC cardioversion): Uses electrical shocks to reset the heart rhythm. This is the most common and effective method, with success rates of 70-90% for atrial fibrillation. It requires general anesthesia but is very quick.
• Pharmacological cardioversion: Uses medications (antiarrhythmic drugs) given intravenously or orally to restore normal rhythm. This approach may be tried first in some cases, particularly if the arrhythmia is recent. It does not require anesthesia but has lower success rates and takes longer to work.

This article focuses primarily on electrical cardioversion, as it is the more commonly performed procedure and the one most people are scheduled for when their doctor recommends "cardioversion."

When Is Cardioversion Recommended?

Your doctor may recommend cardioversion for several heart rhythm disorders. The most common indications include:

• Atrial fibrillation: The most common arrhythmia treated with cardioversion, where the atria beat chaotically and out of coordination with the ventricles
• Atrial flutter: A related condition where the atria beat very rapidly but in a more organized pattern than atrial fibrillation
• Supraventricular tachycardia: Rapid heart rhythms originating above the ventricles that do not respond to other treatments
• Ventricular tachycardia: In certain cases of stable ventricular tachycardia, synchronized cardioversion may be used

How Should I Prepare for Cardioversion?

Preparation for cardioversion typically includes taking blood-thinning medication (anticoagulants) for at least 3-4 weeks before the procedure, fasting from midnight the night before, and possibly undergoing a transesophageal echocardiogram (TEE) to check for blood clots. Inform your doctor about all medications you take, as some may need to be adjusted.

Proper preparation for cardioversion is essential for both safety and success. The most important aspect of preparation is anticoagulation (blood thinning), which significantly reduces the risk of stroke and other complications. When the heart is in an irregular rhythm like atrial fibrillation, blood can pool in the heart chambers and form clots. If cardioversion is performed and a clot is present, the restored normal heartbeat could dislodge the clot and send it to the brain, causing a stroke.

Your doctor will typically prescribe blood-thinning medication for at least three to four weeks before your scheduled cardioversion. Common anticoagulants include warfarin, rivaroxaban (Xarelto), apixaban (Eliquis), dabigatran (Pradaxa), and edoxaban (Savaysa). It is absolutely critical that you take this medication exactly as prescribed and do not miss any doses. Missing doses can significantly increase your risk of complications.

Medications to Discuss with Your Doctor

Before your cardioversion, inform your doctor about all medications you are currently taking. Some medications can affect the heart's electrical activity or interact with anesthesia. Pay particular attention to:

• Heart medications: Beta-blockers, calcium channel blockers, antiarrhythmic drugs, and digoxin
• Blood thinners: Ensure your doctor knows exactly which anticoagulant you are taking and confirm you have been taking it correctly
• Diabetes medications: You may need to adjust your insulin or oral diabetes medications since you will be fasting
• Supplements and herbal remedies: Some supplements, such as fish oil, vitamin E, and certain herbs, can increase bleeding risk

Fasting Requirements

Because cardioversion requires general anesthesia, you must have an empty stomach to prevent aspiration (inhaling stomach contents into your lungs) during the procedure. You will be instructed not to eat or drink anything after midnight on the night before your procedure. If you need to take essential morning medications, your doctor may allow you to take them with a small sip of water.

Transesophageal Echocardiogram (TEE)

Some patients may need a special ultrasound examination called a transesophageal echocardiogram before cardioversion. During this test, a small ultrasound probe is passed down your throat into your esophagus, which lies just behind your heart. This position provides very clear images of the heart, particularly the left atrial appendage, where blood clots most commonly form in atrial fibrillation.

A TEE may be recommended if:

• You have not been on adequate anticoagulation for the required 3-4 weeks
• There is any question about whether you have been taking your blood thinner correctly
• You have certain risk factors that increase the likelihood of clot formation
• Your doctor wants additional assurance that no clots are present

If the TEE shows no clots, cardioversion can proceed immediately. If a clot is found, cardioversion will be postponed, and you will continue anticoagulation treatment until the clot resolves.

What Happens During the Cardioversion Procedure?

During cardioversion, an IV is placed, ECG monitoring is set up, and you are given general anesthesia. While you sleep, two paddles are placed on your chest, and a synchronized electrical shock is delivered. The actual procedure takes only 5-10 minutes, and you will not feel or remember the shocks. Sometimes 2-4 shocks are needed to restore normal rhythm.

Understanding what happens during cardioversion can help reduce anxiety about the procedure. The entire process is carefully controlled and monitored by an experienced medical team, typically including a cardiologist, anesthesiologist, and nurses. Here is what you can expect step by step:

Step 1: Arrival and Preparation

When you arrive at the hospital or outpatient facility, you will change into a hospital gown and a nurse will review your medical history, confirm your fasting status, and check your current medications. Your vital signs (blood pressure, heart rate, temperature, and oxygen levels) will be measured.

Step 2: IV Placement and Monitoring Setup

A small intravenous (IV) catheter will be placed in a vein in your arm or hand. This IV line serves multiple purposes: it allows the medical team to administer anesthesia, provide any necessary medications during the procedure, and give you fluids. ECG electrodes will be attached to your chest to continuously monitor your heart rhythm throughout the procedure. A blood pressure cuff and pulse oximeter (finger clip) will also be applied.

Step 3: Anesthesia Administration

Once everything is ready, the anesthesiologist will administer a short-acting general anesthetic through your IV. Within seconds, you will fall into a deep sleep. You will not be aware of anything happening during the procedure and will not feel or remember the electrical shocks. This is fundamentally different from the "awake" defibrillation shown in movies; cardioversion is performed under anesthesia specifically to ensure your comfort.

Step 4: Delivery of Electrical Shocks

With you safely asleep, the doctor places two large paddles or adhesive electrode pads on your chest. These are positioned to direct electrical current through your heart in the most effective path. The defibrillator is set to "synchronized" mode, meaning it will analyze your heart rhythm and deliver the shock at precisely the right moment in the cardiac cycle.

The doctor then delivers an electrical shock. The amount of energy used varies depending on your specific arrhythmia and body size, typically ranging from 50 to 200 joules. After each shock, the medical team watches the ECG monitor to see if normal rhythm has been restored. If the first shock is not successful, additional shocks at higher energy levels may be delivered. It is common for the procedure to require two to four shocks to achieve the desired result.

Step 5: Recovery

Once the procedure is complete, the anesthesia is stopped, and you will begin to wake up within a few minutes. You may feel groggy or confused at first, which is completely normal. You will be moved to a recovery area where nurses will monitor your heart rhythm, blood pressure, and oxygen levels. An ECG will be performed to confirm that your heart is now beating normally.

What Should I Expect After Cardioversion?

After cardioversion, you will rest in the recovery area for 1-2 hours while being monitored. Most patients go home the same day. You may experience mild chest soreness and muscle aches for a day or two. You must continue taking blood thinners for at least 4 weeks after the procedure and should not drive or make important decisions on the day of the procedure due to residual anesthesia effects.

The recovery period after cardioversion is generally straightforward, but there are important things to know about what to expect and how to take care of yourself in the hours, days, and weeks following the procedure.

Immediately After the Procedure

When you wake from anesthesia, you will be in the recovery area with nurses monitoring you closely. It is normal to feel groggy, slightly confused, or tired for the first 30 minutes to an hour. You may not remember the moments immediately before and after the procedure due to the anesthesia. Your nurse will check your heart rhythm with an ECG and monitor your blood pressure and oxygen levels.

Once you are fully awake and your vital signs are stable, you will typically be offered something to eat and drink. Since you have been fasting, starting with water and light snacks is recommended. Most patients are ready to go home within 2-4 hours after the procedure.

Physical Sensations After Cardioversion

After cardioversion, it is common to experience some mild physical effects:

• Chest skin irritation: The areas where the paddles or electrode pads were placed may be slightly red or tender. This typically resolves within a few days.
• Muscle soreness: Some people experience mild muscle aches throughout their body for a day or two after the procedure. This is caused by the brief muscle contraction that occurs with the electrical shock.
• Fatigue: You may feel more tired than usual for a day or two. This is a combination of the anesthesia wearing off and your body adjusting to the new heart rhythm.
• Mild throat soreness: If you had a transesophageal echocardiogram, you may have a sore throat for a day or two.

Restrictions and Precautions

On the day of your cardioversion, the residual effects of anesthesia can impair your judgment, reaction time, and coordination even if you feel normal. For your safety:

• Do not drive: You must have someone drive you home. Do not drive for at least 24 hours after the procedure, or as directed by your doctor.
• Do not operate machinery: Avoid using power tools, heavy equipment, or anything requiring precise coordination.
• Do not make important decisions: Avoid signing legal documents or making significant financial decisions on the day of the procedure.
• Do not drink alcohol: Alcohol can interact with residual anesthesia effects.

Continuing Anticoagulation

One of the most important aspects of your post-cardioversion care is continuing your blood-thinning medication for at least four weeks after the procedure. Even though your heart rhythm may now be normal, the atria (upper heart chambers) take time to recover their normal mechanical function. During this recovery period, there remains an increased risk of blood clot formation.

Some patients will need to continue blood thinners indefinitely, depending on their individual risk factors for stroke (assessed using a scoring system called CHA2DS2-VASc). Your doctor will discuss your specific anticoagulation plan with you.

How Successful Is Cardioversion?

Cardioversion has an immediate success rate of 70-90% for restoring normal heart rhythm in patients with atrial fibrillation. However, the arrhythmia may return over time in some patients. Long-term success depends on factors including the duration of the arrhythmia, underlying heart disease, and whether contributing factors are addressed.

Cardioversion is highly effective at restoring normal heart rhythm in the short term. Studies consistently show that 70-90% of patients with atrial fibrillation are successfully converted to normal sinus rhythm with electrical cardioversion. This success rate is significantly higher than pharmacological cardioversion (using medications alone), which typically has success rates of 30-60%.

However, it is important to understand that cardioversion treats the immediate rhythm problem but does not necessarily cure the underlying condition that caused the arrhythmia in the first place. For many patients, especially those with longstanding atrial fibrillation, the irregular rhythm may return over time. Studies suggest that without additional treatment:

• Approximately 50% of patients remain in normal rhythm at 1 month
• About 30-40% remain in normal rhythm at 1 year
• Recurrence rates are higher for patients who have had atrial fibrillation for longer periods

Factors Affecting Success

Several factors influence both the immediate success of cardioversion and the likelihood of maintaining normal rhythm long-term:

• Duration of arrhythmia: The shorter the time you have been in atrial fibrillation, the higher the success rate. Cardioversion within 48 hours of onset has the best outcomes.
• Size of the left atrium: An enlarged left atrium makes successful cardioversion less likely and increases the chance of recurrence.
• Underlying heart disease: Conditions like heart valve disease, heart failure, or coronary artery disease can reduce success rates.
• Other health conditions: Uncontrolled hypertension, sleep apnea, obesity, and thyroid disorders can contribute to arrhythmia recurrence.
• Age: Older patients may have somewhat lower success rates, though age alone is not a contraindication.

Improving Long-Term Success

To improve the chances of maintaining normal rhythm after cardioversion, your doctor may recommend:

• Antiarrhythmic medications: Drugs such as amiodarone, flecainide, propafenone, or sotalol can help maintain normal rhythm after cardioversion.
• Treating underlying conditions: Controlling blood pressure, treating sleep apnea, managing thyroid disease, and achieving a healthy weight all reduce recurrence risk.
• Lifestyle modifications: Reducing alcohol intake, caffeine, and stress; getting regular exercise; and ensuring adequate sleep can all help.
• Catheter ablation: For patients with recurrent atrial fibrillation despite medication, catheter ablation may be recommended as a more definitive treatment.

What Are the Risks and Complications?

Cardioversion is generally very safe when proper preparation is followed. The main risks include blood clot formation and stroke (greatly reduced by anticoagulation), skin irritation at paddle sites, temporary muscle soreness, and rarely, other rhythm disturbances. Serious complications are uncommon, occurring in less than 1% of cases.

Like any medical procedure, cardioversion carries some risks, but it is considered a very safe procedure when performed correctly with appropriate preparation. Understanding these risks can help you have an informed discussion with your doctor.

Blood Clots and Stroke

The most serious potential complication of cardioversion is stroke caused by blood clots. When the heart is in atrial fibrillation, blood can pool and form clots in the heart, particularly in a structure called the left atrial appendage. If cardioversion dislodges one of these clots, it can travel to the brain and cause a stroke.

This is why anticoagulation is so critically important. When patients are properly anticoagulated for at least 3-4 weeks before and after cardioversion, the risk of stroke is very low, approximately 0.5-1%. Without proper anticoagulation, this risk increases significantly to 5-7%.

Skin Reactions

Mild skin irritation, redness, or tenderness at the sites where the paddles or electrode pads were placed is common and generally resolves within a few days. In rare cases, more significant skin burns can occur, but this is uncommon with modern equipment and techniques.

Muscle Soreness

Some patients experience generalized muscle aches for a day or two after the procedure. This is caused by the brief muscle contraction that occurs when the electrical shock is delivered and is not a cause for concern.

Other Rhythm Disturbances

Occasionally, cardioversion can trigger other heart rhythm abnormalities. In most cases, these are brief and resolve on their own. Rarely, more serious rhythm problems may occur that require additional treatment. The medical team monitors your heart continuously during and after the procedure to detect and manage any such issues promptly.

Anesthesia Risks

General anesthesia, even the short-acting type used for cardioversion, carries its own small risks, including allergic reactions, breathing problems, and in very rare cases, more serious complications. These risks are minimized by the use of experienced anesthesiologists and appropriate monitoring.

What Are the Alternatives to Cardioversion?

Alternatives to electrical cardioversion include pharmacological cardioversion (using medications), rate control strategy (accepting the arrhythmia but controlling heart rate), and catheter ablation (a more invasive procedure that can cure atrial fibrillation). The best approach depends on your specific situation, symptoms, and overall health.

Cardioversion is not the only treatment option for atrial fibrillation and other arrhythmias. Your doctor will work with you to determine the most appropriate treatment strategy based on your individual circumstances, including how long you have had the arrhythmia, your symptoms, your overall health, and your preferences.

Pharmacological Cardioversion

Medications can sometimes restore normal heart rhythm without the need for electrical cardioversion. Antiarrhythmic drugs such as flecainide, propafenone, amiodarone, ibutilide, or vernakalant may be given intravenously or orally. This approach may be tried first, especially if the atrial fibrillation is recent (less than 48 hours) and you do not have significant heart disease. However, pharmacological cardioversion has lower success rates (30-60%) compared to electrical cardioversion and may take longer to work.

Rate Control Strategy

For some patients, especially those with longstanding atrial fibrillation or those who have had multiple unsuccessful cardioversions, a "rate control" strategy may be recommended instead of trying to restore normal rhythm (a "rhythm control" strategy). With rate control, medications such as beta-blockers, calcium channel blockers, or digoxin are used to slow the heart rate to a more normal level, even though the rhythm remains irregular. This approach can effectively relieve symptoms and reduce complications while avoiding repeated cardioversion attempts.

Catheter Ablation

Catheter ablation is a more invasive procedure that can potentially cure atrial fibrillation by destroying the heart tissue responsible for generating the abnormal electrical signals. During ablation, thin flexible tubes (catheters) are threaded through blood vessels to the heart, where radiofrequency energy or cryotherapy (freezing) is used to create small scars that block the abnormal electrical pathways. Catheter ablation is typically considered for patients who have recurrent atrial fibrillation despite medication or cardioversion, or for those who prefer a more definitive treatment approach.

Choosing the Right Approach

The decision between cardioversion, rate control, and ablation depends on many factors. Discuss these options with your cardiologist, who can help you weigh the benefits and risks of each approach based on your specific situation.