Cardioversion: Electrical vs. Chemical, How It Works, and What to Expect

A 64-year-old man has been in atrial fibrillation for the last 10 days. He's tired, short of breath when walking up the stairs, and his heart rate has been bouncing around between 90 and 130 despite medications. His cardiologist recommends cardioversion to restore sinus rhythm. He's anxious because the word "shock" has been used. The procedure goes smoothly: a brief moment of general anesthesia, a single synchronized electrical shock, and his heart goes back to a regular rhythm. He wakes up 15 minutes later feeling tired but otherwise fine. Two days later, he's back to normal exercise tolerance.

I'm Dr. Damian Rasch, a cardiologist in Encinitas. Cardioversion is the process of converting an abnormal heart rhythm back to normal sinus rhythm. It can be done electrically (delivering a synchronized electrical shock to reset the heart's rhythm) or chemically (giving an antiarrhythmic medication that does the same thing pharmacologically). Both work, with different trade-offs. This article walks through what cardioversion is, when it's used, the differences between electrical and chemical approaches, the anticoagulation rules, and what to expect if you're scheduled for one.

What Cardioversion Is and Why We Do It

Cardioversion is used to restore normal rhythm in patients with sustained arrhythmias, most commonly atrial fibrillation and atrial flutter. The goal is to convert from the abnormal rhythm to sinus rhythm, where the heart's natural pacemaker (the sinus node) drives a regular, coordinated heartbeat.

For patients with atrial fibrillation, sinus rhythm is associated with better symptoms, better exercise tolerance, and (in some patients, especially those with heart failure or recent-onset AFib) better long-term outcomes. The EAST-AFNET 4 trial showed that early rhythm control improves cardiovascular outcomes compared to rate control alone in many patients. Cardioversion is one of the tools used in rhythm control strategies.

Cardioversion isn't a one-time fix. The same patient may need multiple cardioversions over the years if AFib recurs. Some patients maintain sinus rhythm for months to years after cardioversion, especially when combined with antiarrhythmic medications. Others recur within days or weeks. The persistence of sinus rhythm depends on the underlying disease, the duration of AFib before cardioversion, the patient's atrial size and substrate, and ongoing risk factors.

Electrical Cardioversion (DCCV)

Electrical cardioversion (also called direct current cardioversion or DCCV) uses a brief synchronized electrical shock to reset the heart's rhythm. The patient receives short-acting general anesthesia (typically propofol). Defibrillator pads are placed on the chest. The defibrillator is set to deliver a shock synchronized with the patient's QRS complex (the synchronized timing prevents the shock from being delivered during the vulnerable repolarization period, which could induce ventricular fibrillation).

The shock energy is typically 100 to 200 joules for atrial fibrillation, with biphasic waveforms more effective than older monophasic waveforms. If the first shock doesn't restore sinus rhythm, escalating energy levels are tried. Most patients convert with one or two shocks. Failed cardioversion is uncommon.

After the shock, the EKG is checked to confirm sinus rhythm has been restored. The anesthesiologist allows the patient to wake up. Total time from when the patient is sedated to when they're alert again is typically 15 to 30 minutes. The procedure is done as outpatient with discharge a few hours later.

Chemical Cardioversion (Pharmacologic Cardioversion)

Chemical cardioversion uses antiarrhythmic medications to convert the rhythm back to sinus. The medications work by altering ion channel activity in the atrial myocardium, terminating the chaotic atrial activity that defines AFib.

Several medications are used for chemical cardioversion of AFib.

Flecainide and propafenone (class IC antiarrhythmics) are highly effective for cardioversion of recent-onset AFib in patients without significant structural heart disease. They can be given orally as a "pill in the pocket" approach in selected patients (a single oral loading dose taken at home or in clinic, with conversion typically occurring within hours). They're contraindicated in patients with significant coronary disease or reduced ejection fraction.

Amiodarone is effective but slow-acting (takes hours to days to convert). It's used in patients with structural heart disease or reduced ejection fraction where flecainide and propafenone can't be safely used. Amiodarone has substantial long-term toxicity considerations (thyroid, lung, liver, eye effects), but for short-term use during cardioversion, the benefit usually outweighs the risk.

Ibutilide is an IV-only medication used in monitored settings. It's effective for cardioversion of recent-onset AFib and atrial flutter, with conversion typically occurring within an hour of administration. It carries a risk of torsades de pointes (typically 2 to 4 percent), so it's given with continuous EKG monitoring and magnesium readily available.

Dofetilide can be used for cardioversion in selected patients, but its use is restricted to inpatient initiation due to the risk of QT prolongation and torsades.

Vernakalant is approved in some countries (not the US) for atrial-selective cardioversion with a favorable safety profile.

Choosing Between Electrical and Chemical

Both approaches work. The choice depends on several factors.

Electrical Is Often Preferred When:

The arrhythmia has been present for more than 24 to 48 hours (chemical cardioversion success drops significantly with longer duration).

The patient is hemodynamically stable but symptomatic and needs prompt rhythm restoration.

The patient has structural heart disease or reduced ejection fraction, making flecainide or propafenone unsafe.

A planned, scheduled procedure is being arranged.

Chemical Is Often Preferred When:

The arrhythmia is very recent (within 24 to 48 hours of onset).

The patient prefers to avoid sedation and shocks.

A "pill in the pocket" approach is feasible (no significant structural heart disease, prior successful trial).

The patient is already being initiated on a long-term antiarrhythmic that will both convert and maintain sinus rhythm.

The Anticoagulation Rules

The biggest concern with cardioversion isn't the shock or the medication. It's stroke from a clot in the left atrial appendage that can be dislodged when the rhythm changes. The risk is real and the rules are strict.

Less Than 48 Hours of AFib

For patients with documented AFib of less than 48 hours duration who don't have other high-risk features, the stroke risk from cardioversion is low (around 0.7 percent), and cardioversion can usually proceed without the formal pre-cardioversion anticoagulation period. However, anticoagulation should be started at the time of cardioversion and continued for at least 4 weeks afterward, since the risk of post-cardioversion stroke remains for some weeks even when the pre-existing AFib was brief. Some experts recommend even a brief duration of AFib still warrants the same anticoagulation as longer-duration AFib if there are risk factors for stroke.

More Than 48 Hours or Unknown Duration

For patients with AFib of more than 48 hours duration or unknown duration, the standard approach is therapeutic anticoagulation (warfarin with INR 2 to 3, or a DOAC at appropriate dosing) for at least 3 weeks before cardioversion and at least 4 weeks afterward. The goal is to dissolve any pre-existing clot before the rhythm change and to prevent new clot formation during the post-cardioversion period when the atrium is "stunned" and slow-moving.

TEE-Guided Cardioversion

For patients who need cardioversion but haven't had 3 weeks of therapeutic anticoagulation, transesophageal echocardiography (TEE) can rule out left atrial appendage clot. If no clot is seen, anticoagulation is started, cardioversion is performed (often the same day), and anticoagulation continues for at least 4 weeks. The ACUTE trial established this approach as equivalent in stroke prevention to the 3-week pre-cardioversion anticoagulation strategy.

Long-Term Anticoagulation

After cardioversion, anticoagulation continues for at least 4 weeks. Long-term anticoagulation depends on CHA2DS2-VASc score. Patients with score of 2 or higher (or 3 in women) typically continue anticoagulation indefinitely, regardless of whether sinus rhythm is maintained, because subclinical AFib recurrence is common and stroke risk depends on the patient's risk factor profile rather than just whether AFib has been documented recently.

What to Expect

Before the Procedure

Plan to fast from midnight the night before. Take regular morning medications with sips of water unless told otherwise (anticoagulation should not be held). Arrange a ride home; you can't drive after sedation. Bring a list of all medications and a brief health history.

During the Procedure

A nurse places an IV. EKG monitoring is started. The anesthesiologist or the procedural team gives short-acting sedation. Once you're asleep (usually within a minute), the synchronized shock is delivered. The total time from sedation to wake-up is typically 15 minutes. You don't feel the shock; you're under anesthesia.

After the Procedure

You'll be in a recovery area for an hour or two until the sedation wears off completely. The EKG is checked to confirm sinus rhythm. Some patients have a sore chest from the shock pads; this resolves within hours to days. You'll be discharged with instructions about anticoagulation, antiarrhythmic medication if prescribed, and follow-up.

Success Rates and Outcomes

Electrical cardioversion successfully restores sinus rhythm in about 90 percent of patients on the first attempt. With escalating energy or repeat attempts, success rates approach 95 percent. The remaining 5 percent of patients have refractory AFib that doesn't convert.

Maintenance of sinus rhythm after cardioversion is variable. Without antiarrhythmic medication, only about 30 to 50 percent of patients remain in sinus rhythm at one year. With antiarrhythmic medications (amiodarone, dofetilide, sotalol, flecainide, propafenone), the rate climbs to 50 to 70 percent at one year. With AFib ablation as adjunctive therapy, the rate climbs further.

Predictors of successful long-term sinus rhythm maintenance include shorter duration of AFib before cardioversion, smaller left atrial size, absence of significant structural heart disease, no untreated sleep apnea, and good blood pressure control. Patients with these favorable features often maintain sinus rhythm for years after cardioversion.

Risks and Complications

Electrical cardioversion is generally safe, with low complication rates.

The most concerning complication is stroke, with risk highly dependent on adherence to anticoagulation rules. With proper anticoagulation, stroke risk is low (under 1 percent).

Skin burns from the shock pads are minor and resolve within days. Modern adhesive electrode pads have largely eliminated this issue compared to older paddles.

Anesthesia-related complications (allergic reactions, transient hypotension, transient hypoxemia) are typically minor and managed by the anesthesia team.

Pro-arrhythmia from the shock is rare. Ventricular fibrillation immediately following cardioversion is theoretically possible but nearly never happens with properly synchronized shocks.

Post-cardioversion bradycardia or pauses occur in some patients, especially those with sinus node dysfunction. Most resolve spontaneously, but a small number need pacemaker placement.

Common Patient Questions

Will I feel the shock?

No. You'll be under general anesthesia (or deep sedation) during the shock. You go to sleep, the shock is delivered, and you wake up about 15 minutes later. The procedure happens while you're unconscious.

How long does the procedure take?

The actual cardioversion takes seconds. The total time from sedation to recovery is typically 15 to 30 minutes. Plan to be at the hospital for 3 to 4 hours total when you include preparation, anesthesia recovery, and discharge.

Why do I need anticoagulation for so long?

For at least three reasons. First, any pre-existing clot in the left atrial appendage needs to be dissolved before changing the rhythm. Second, the atrium is "stunned" for several weeks after cardioversion, with reduced contractile function and increased clot risk. Third, AFib often recurs (sometimes silently), and the stroke risk depends on your underlying risk factors rather than just on whether you're currently in AFib.

What if my rhythm comes back into AFib after cardioversion?

Recurrence is common. The next steps depend on your situation: starting an antiarrhythmic medication if not already on one, considering AFib ablation, repeating cardioversion in the right context, or transitioning to a rate control strategy if rhythm control is challenging. The decision is individualized based on symptom burden, what's been tried, and patient preference.

Can cardioversion damage my heart?

No. The shock is brief and synchronized to avoid the vulnerable period. The energy delivered is well below what would cause myocardial injury. Patients can have multiple cardioversions over their lifetime without long-term cardiac damage from the procedure itself.

Can I have cardioversion if I have a pacemaker or ICD?

Yes, with appropriate precautions. The cardiologist or technician adjusts pad placement to avoid direct current passage through the device, and the device is interrogated after the procedure to confirm normal function. Most modern devices tolerate cardioversion without issue.

What's the difference between cardioversion and defibrillation?

Both deliver electrical shocks to the heart, but with different timing. Cardioversion is synchronized with the QRS complex (delivered at a specific moment in the heart cycle), used for organized rhythms like AFib and atrial flutter. Defibrillation is unsynchronized (delivered at any moment), used for ventricular fibrillation or pulseless ventricular tachycardia where there's no organized rhythm to synchronize to.

Can I have a "pill in the pocket" approach?

In selected patients, yes. The approach uses a single oral dose of flecainide or propafenone taken at the onset of an AFib episode, with cardioversion typically occurring within hours. The first dose is usually given in a monitored setting (clinic or hospital) to confirm safety. Subsequent episodes can sometimes be managed at home if the first trial was successful and uncomplicated. The approach requires absence of significant structural heart disease and reduced EF, normal QT interval, and reliable patient.

Is there an alternative to cardioversion?

For atrial fibrillation, alternatives include rate control alone (allowing the AFib to continue but controlling the heart rate), AFib ablation (a procedure that can produce more durable rhythm control), or antiarrhythmic medications without cardioversion (allowing slower spontaneous conversion). The right choice depends on symptom burden, AFib duration, and patient preference.

When to Escalate Care

Call 911 immediately for severe chest pain after cardioversion, severe shortness of breath, syncope, or any concerning symptoms suggestive of stroke (sudden weakness, slurred speech, vision changes). The risks of cardioversion are early; significant complications usually present within hours to days.

Contact your cardiologist the same day for new palpitations after cardioversion (suggesting recurrence), unusual chest discomfort, severe pain at the shock site, or any concerns about anticoagulation. Same-day evaluation lets us assess whether intervention is needed.

Schedule a clinic visit within one to two weeks for routine post-cardioversion follow-up to assess rhythm status, medication tolerability, and any ongoing symptoms. Long-term anticoagulation decisions and rhythm management are reviewed at this visit.

A Final Note From Me

Cardioversion is one of the more effective and well-tolerated procedures in cardiology when done with appropriate anticoagulation safeguards. Patients who walk into the hospital exhausted from weeks of AFib often walk out feeling substantially better. The downside is that AFib often recurs, especially when the underlying risk factors (hypertension, sleep apnea, alcohol, weight) aren't addressed. Cardioversion buys you a window of sinus rhythm; what you do during that window determines how long it lasts.

If you're scheduled for cardioversion, the most important things are following the anticoagulation plan exactly, fasting before the procedure, arranging a ride home, and addressing the modifiable risk factors that influence whether sinus rhythm sticks. The patients who do best long-term aren't necessarily the ones with the easiest anatomy or the youngest age; they're the ones who lose weight if needed, treat their sleep apnea aggressively, control their blood pressure, moderate their alcohol, and stay engaged with their cardiologist.

If your AFib has recurred after multiple cardioversions, the conversation evolves. Options include adding or escalating antiarrhythmic medications, considering AFib ablation, or transitioning to a rate control strategy with continued anticoagulation. The decision depends on your symptoms, your tolerance of medications, and your preferences. There's rarely a single right answer; the right answer is the one that best fits your situation.

If you have AFib and you've never been cardioverted, the conversation about whether to attempt rhythm restoration is worth having. For some patients, rate control alone is the right strategy. For others, especially those with recent-onset AFib or significant symptoms, rhythm control with cardioversion as the starting point produces better outcomes. Talk to your cardiologist about which approach fits your situation.

References

1. January, Craig T., L. Samuel Wann, Hugh Calkins, et al. "2019 AHA/ACC/HRS Focused Update of the 2014 AHA/ACC/HRS Guideline for the Management of Patients with Atrial Fibrillation." Journal of the American College of Cardiology 74, no. 1 (2019): 104-132.

2. Hindricks, Gerhard, Tatjana Potpara, Nikolaos Dagres, et al. "2020 ESC Guidelines for the Diagnosis and Management of Atrial Fibrillation." European Heart Journal 42, no. 5 (2021): 373-498.

3. Klein, Allan L., Richard A. Grimm, Robert D. Murray, et al. "Use of Transesophageal Echocardiography to Guide Cardioversion in Patients with Atrial Fibrillation." New England Journal of Medicine 344, no. 19 (2001): 1411-1420.

4. Kirchhof, Paulus, A. John Camm, Andreas Goette, et al. "Early Rhythm-Control Therapy in Patients with Atrial Fibrillation." New England Journal of Medicine 383, no. 14 (2020): 1305-1316.

5. Crijns, Harry J. G. M., Hans-Heinrich Weijs, Annick W. Fairley, et al. "Contemporary Real-Life Cardioversion of Atrial Fibrillation: Results from the Multinational RHYTHM-AF Study." Heart 100, no. 17 (2014): 1364-1372.

6. Alboni, Paolo, Giovanni L. Botto, Nicola Baldi, et al. "Outpatient Treatment of Recent-Onset Atrial Fibrillation with the 'Pill-in-the-Pocket' Approach." New England Journal of Medicine 351, no. 23 (2004): 2384-2391.

7. Mittal, Suneet, Sergei Ayati, Kenneth M. Stein, et al. "Transthoracic Cardioversion of Atrial Fibrillation: Comparison of Rectilinear Biphasic versus Damped Sine Wave Monophasic Shocks." Circulation 101, no. 11 (2000): 1282-1287.

8. Stiell, Ian G., Catherine M. Clement, Robert Symington, et al. "Variation in Management of Recent-Onset Atrial Fibrillation and Flutter among Academic Hospital Emergency Departments." Annals of Emergency Medicine 57, no. 1 (2011): 13-21.

9. Roy, Denis, Mario Talajic, Stanley Nattel, et al. "Rhythm Control versus Rate Control for Atrial Fibrillation and Heart Failure." New England Journal of Medicine 358, no. 25 (2008): 2667-2677.

10. Stiell, Ian G., Marc-Andre Sirois, Vidya Vaillancourt, et al. "Electrical versus Pharmacological Cardioversion for Emergency Department Patients with Acute Atrial Fibrillation (RAFF2): A Partial Factorial Randomised Trial." Lancet 395, no. 10221 (2020): 339-349.

Published on damianrasch.com. The above information was composed by Dr. Damian Rasch, drawing on individual insight and bolstered by digital research and writing assistance. The information is for educational purposes only and does not constitute medical advice.