What Is Cardioversion?

Cardioversion is a technique used to treat several kinds of abnormal heart rhythm, called cardiac arrhythmias. Typically, it can be done using medication or, as is the case when someone uses a defibrillator, electricity. Which method is used would depend on your specific rhythm problem and your overall health and stability.

When someone needs cardioversion, they are often in a life-threatening situation. Both electricity and drugs may be used together to try to restore normal heart function. In other cases, as with an atrial fibrillation rhythm, you may be calm and awake as you have a scheduled procedure.

This article explains different kinds of heart rhythms that are treated by using cardioversion. It also discusses what to expect during your heart rhythm treatment, along with risks and side effects.

Man's chest with a defibrillator electrode on it
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Types of Cardioversion

Your heart has its own internal electrical system, and that's what keeps it beating throughout your life. Cardioversion is used when those electrical signals have been disrupted, causing the heart to beat erratically or stop altogether, leaving you without a pulse.

These rhythm disruptions can have quite a few causes, from medications to electrolyte imbalances or even simply age. Often, these arrhythmias are caused by heart disease.

Cardioversion can be done by using methods that, in most cases, rely on either electricity or medication. Which type of cardioversion is used will depend, in part, on the underlying causes of the arrhythmia. It also will depend on the precise heart rhythm that needs to be treated and your condition at the time.

Electrical Cardioversion

People who are alert and require electrical cardioversion will likely be experiencing signs and symptoms that may include:

An electrocardiogram, or EKG, is used to monitor the heart rhythm so that healthcare providers know what type of arrhythmia a person is having. An electrical shock is given using adhesive electrode patches connected to a defibrillator. If the person is awake, a sedation medication may be given beforehand.

During cardioversion, it's important that the electrode patches that conduct the electricity are in full contact with the skin. Some people may need to have chest hair removed.

Synchronized cardioversion may be used when a person still has a pulse but their heart rhythm is not normal and needs to be treated. In many cases that require cardioversion, however, the person does not have a pulse and the procedure is done with the goal of restoring the heart's electrical activity. This is known as defibrillation or unsynchronized cardioversion.

Defibrillation (Unsynchronized Cardioversion)

This type of cardioversion is used when a person has no pulse. Since this is obviously a life-threatening situation, rapid treatment with both cardioversion and drugs used to restore a heart rhythm is critical. Certain heart arrhythmias are common in the absence of any pulse.

Ventricular Fibrillation

Ventricular fibrillation happens when the heart chamber that pushes blood out into your body, called the left ventricle, is chaotic and quivering. The heart isn't able to pump any blood, so there is no pulse.

This is a primary cause of sudden cardiac arrest. A focused electrical shock delivered to most of the heart muscle is used to defibrillate, or stop, the disorganized electrical impulses that cause it.

Defibrillation causes most of the heart muscle cells to contract all at the same time. This sudden "shock" gives the natural pacemakers in the heart, located in the right atrium, a chance to regain control of the pace and rate of the heart's rhythm. This form of cardioversion is used in the hopes of restoring a cardiac rhythm with a pulse.

Pulseless Ventricular Tachycardia

Defibrillation also may be used in a less common cause of sudden cardiac arrest, known as pulseless ventricular tachycardia. In this cardiac arrhythmia, the patient's heart is beating in an organized rhythm, but it's too fast for the heart to fill with blood between beats and keep blood flowing.

A normal heart rate in most people is between 60 and 100 beats per minute. In ventricular tachycardia cases, the rate can reach as high as 220 beats per minute. The rapid rate and the heart's inability to pump blood make this a lethal rhythm.

Synchronized Cardioversion

Sometimes, the fast heart rates of tachycardia are still organized rhythms and people have a pulse. It's just too fast to be effective in pumping blood out to the body. Since you're likely to still be conscious with this rhythm, a different type of cardioversion is used.

The electrical impulse needs to be timed with precision so that it's synchronized to the heart's rhythm. Synchronization is done with an EKG to monitor the rhythm and time the shock, using the same type of electrodes used in defibrillation.

During cases of extremely rapid tachycardia, an electrical shock delivered at just the right moment in the cycle of a heartbeat can result in a higher chance of successful cardioversion.

Cardioversion by Medication

Medications can be used to speed up or slow down the rate of heart rhythm, or to completely change it into a different one. They also can be used for long-term control of atrial fibrillation.

One advantage of using drugs instead of electricity is that sedation isn't needed in people who are alert. Electrical cardioversion is preferred in patients who are unstable—that is, they have a dangerously abnormal blood pressure or other symptoms that need immediate intervention.

Drugs are used together with cardioversion in cases such as ventricular fibrillation, as healthcare providers work to try and restart a heart that's not pulsing. The medications used for cardioversion will be specific to the condition being treated.

People who've experienced both electrical and pharmacological cardioversion usually describe the cardioversion through medication as much less uncomfortable.

Adenosine

Adenosine is used for people experiencing a supraventricular tachycardia (SVT) that is not atrial fibrillation. It has a short-lived effect on ventricular tachycardia and on atrial fibrillation.

Several types of STV can be treated with adenosine, including Wolff-Parkinson-White syndrome and undifferentiated regular wide complex tachycardia.

Beta Blockers

Certain SVT rhythms can be slowed with a class of drugs called beta blockers. These medications help to restore a rhythm that improves blood flow and reduces symptoms. Beta blockers may be used to achieve long-term control over rapid heart rates.

They also are used to treat hypertension (high blood pressure). Beta blockers that are often used to manage episodes of STV include:

  • Lopressor (metoprolol)
  • Tenormin (atenolol)
  • Inderal (propranolol)
  • Brevibloc (esmolol) 

Calcium Channel Blockers

Like beta blockers, calcium channel blockers can either be used in some cases of acute SVT or be prescribed for long-term control of tachycardia and hypertension.

Depending on the type of SVT, some of the calcium channel blockers that are used in cardioversion include:

  • Calan (verapamil)
  • Cardizem (diltiazem)
  • Procardia (nifedipine)

Atropine, Dopamine, and Epinephrine

Some drugs are used for cardioversion of rhythms that are too slow rather than too fast. For these rhythms, called bradycardia, medications to speed up the heart rate include:

  • Atropen (atropine)
  • Intropin (dopamine)
  • Epinephrine

Implanted Devices

Some abnormal heart rates can be stabilized over the long term by using a surgically implanted device. People with bradycardia may have an implanted pacemaker, while people at risk of lethal rhythms (ventricular tachycardia or fibrillation) may consider an implantable defibrillator.

Risks and Contraindications

The risks and contraindications of electrical cardioversion depend on the type that's used and the condition that's being treated. For example, no one who has a pulse should be defibrillated. And there's an obvious risk to using a defibrillator when someone is in contact with water, such as a swimming pool.

There are a few common situations in which a "shock" is more risky than others.

Atrial Fibrillation

Cardioversion that's used on a person with an atrial fibrillation rhythm can potentially lead to life-threatening conditions. These risks include:

People who have this heart rhythm problem are often given blood thinners called anticoagulants to prevent blood clots if they will be having a procedure for cardioversion. Heparin and Coumadin are among the most common of these drugs.

Alert Patients

Sedation is common for people who will be awake and alert while having an electrical cardioversion procedure. This is to avoid the discomfort and apprehension they may experience, even when the procedure is a success in treating their signs and symptoms.

Sedation also may be used after a cardioversion procedure. This is often the case for people whose condition was too unstable to wait for sedation.

Medications used to restore stable heart rhythms are effective but may have serious risks. This can lead to complications such as blood clots, pain, or other unintended heart rhythms.

After Cardioversion

Many people will experience significant and immediate improvement of their signs and symptoms when cardioversion is successful. The underlying cause of the heart arrhythmia then becomes the focus of treatment.

If the procedure doesn't convert the rhythm on a first attempt, there is often a second try. In most cases, patients can receive multiple electrical shocks or doses of medication without harm.

Side Effects

It's possible to experience side effects after electrical cardioversion. Some of these general side effects are:

  • Irritation near electrode sites
  • Pain and soreness in the chest
  • Anxiety

When people are treated with drugs for their arrhythmias, they may experience heart palpitations as the medication is working to change the cardiac rhythm. This typically lasts for a few seconds.

Patients who receive medications to achieve cardioversion can sometimes feel heart palpitations as the medication is working to change the cardiac rhythm. In some cases, the feelings can be prolonged a few seconds.

Summary

Cardioversion is a method of managing abnormal heart rhythms by restoring the proper electrical impulses within the heart.

Some of these rhythms, such as atrial fibrillation, require treatment but are typically not life-threatening. In other cases, the abnormal heart rhythm is lethal and cardioversion can be life-saving.

Cardioversion can be achieved through medications designed to restore heart rhythm, electricity to "shock" and reset its function, or a combination of both. When the heart rhythm has been successfully stabilized, your healthcare provider will likely focus next on the underlying cause.

A Word From Verywell

Cardioversion to treat cardiac arrhythmia is safe and effective, although in an emergency your health care team may not have time to offer a lot of information about the procedure. If you are awake during the procedure, you can ask your provider to walk you through it as it happens.

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7 Sources
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  1. American Heart Association. Cardioversion.

  2. Goyal A, Sciammarella JC, Chhabra L, Singhal M. Synchronized electrical cardioversion. In: StatPearls.

  3. American Heart Association. Ventricular fibrillation.

  4. American Academy of Family Physicians. Diagnosis and management of common types of supraventricular tachycardia.

  5. January CT, Wann LS, Alpert JS, et al. 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation. J Am Coll Cardiol. 2014;64(21):e1-e76. doi:10.1016/j.jacc.2014.03.022

  6. Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay: executive summary. J Am Coll Cardiol. 2019;74(7):932-987. doi:10.1016/j.jacc.2018.10.043

  7. January CT, Wann LS, Alpert JS, et al. 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation. J Am Coll Cardiol. 2014;64(21):e1-e76. doi:10.1016/j.jacc.2014.03.022