Cardioversion is a medical procedure that restores a normal heart rhythm when the heart’s upper chambers are beating chaotically or too fast, most commonly during atrial fibrillation. It can be done with a controlled electric shock delivered through pads on the chest or with specific medications given intravenously. The procedure itself is brief, but the preparation, anticoagulation strategy, and follow-up decisions around it are where much of the complexity lives.
Electrical Versus Drug-Based Cardioversion
There are two broad approaches. Electrical cardioversion uses a synchronized direct-current shock to reset the heart’s rhythm. Pharmacological cardioversion uses antiarrhythmic drugs, typically given through an IV in a monitored setting, to coax the heart back into a normal pattern. Both aim for the same result, but they differ in speed, success rates, and trade-offs.
When electrical cardioversion is used as the first strategy, it converts atrial fibrillation to normal sinus rhythm in roughly 90 to 95 percent of attempts. A registry study from emergency departments found a first-attempt success rate of about 95 percent for electrical cardioversion, compared with about 28 percent for pharmacological cardioversion as a standalone initial approach.1PubMed Central. Pharmacological Cardioversion Versus Electrical Cardioversion in the Acute Treatment of Atrial Fibrillation in the Emergency Department: The Recufa-Hula Register That gap narrows, though, when you account for the fact that patients who fail drug therapy often get shocked afterward as a backup. A systematic review and meta-analysis pooling several trials found that when the entire treatment strategy was considered, overall success was similar between the two approaches, around 86 to 89 percent.2PubMed Central. Electric Cardioversion vs. Pharmacological with or without Electric Cardioversion for Stable New-Onset Atrial Fibrillation: A Systematic Review and Meta-Analysis An earlier trial also found comparable initial-attempt success between the two methods (about 74 versus 73 percent), but the drug-first strategy ended up more effective overall because patients who didn’t convert on medication could still be shocked afterward.3PubMed. Effectiveness and costs of chemical versus electrical cardioversion of atrial fibrillation
From a side-effect standpoint, one notable difference is that pharmacological cardioversion carries a higher risk of low blood pressure. The meta-analysis found significantly less hypotension in the electrical-cardioversion group.4PubMed Central. Electric Cardioversion vs. Pharmacological with or without Electric Cardioversion for Stable New-Onset Atrial Fibrillation: A Systematic Review and Meta-Analysis Electrical cardioversion, on the other hand, requires sedation, which introduces its own considerations.
Where the Pads Go and Why It Matters
For electrical cardioversion, adhesive electrode pads are placed on the chest. Two configurations are common: anterior-posterior, where one pad sits on the front of the chest and the other on the back between the shoulder blades, and anterior-lateral, where one pad is near the right collarbone and the other is on the left side of the ribcage. You might assume one position would be clearly better, but the evidence is surprisingly close. A meta-analysis of randomized controlled trials found that cumulative success rates were similar regardless of pad placement, though the anterior-posterior position did produce lower resistance to the electrical current passing through the chest.5PubMed Central. Anterior-Posterior versus anterior-lateral electrodes position for electrical cardioversion of atrial fibrillation: A meta-analysis of randomized controlled trials A randomized comparison using biphasic shocks confirmed this, finding that both positions achieved success rates above 94 percent.6PubMed. Randomized comparison of anterolateral versus anteroposterior electrode position for biphasic external cardioversion of atrial fibrillation
Modern defibrillators almost universally use biphasic waveforms, which deliver current in two directions. Older monophasic machines pushed current in one direction only and generally required higher energy levels. The meta-analysis on pad positioning found no significant interaction between waveform type and electrode position, meaning the choice of pad location is largely a matter of clinician preference and patient body habitus rather than a rigid protocol.7PubMed Central. Anterior-Posterior versus anterior-lateral electrodes position for electrical cardioversion of atrial fibrillation: A meta-analysis of randomized controlled trials
The Blood Clot Problem
The biggest concern with cardioversion isn’t the shock itself but what can happen to blood clots sitting inside the heart. When the upper chambers fibrillate, blood pools and can form clots, particularly in a small pouch called the left atrial appendage. The moment the heart snaps back into a normal rhythm, those clots can be ejected into the bloodstream and travel to the brain, causing a stroke. Without anticoagulation, the risk of a thromboembolic event after cardioversion has been reported at anywhere from 1 to 7 percent, but proper blood-thinning therapy can reduce that to under 1 percent.8International Journal of Clinical Cardiology. Electrical Cardioversion: A Review
Guidelines recommend at least three weeks of oral anticoagulation before cardioversion for anyone whose atrial fibrillation has lasted longer than 48 hours.9PubMed Central. Are Three Weeks of Oral Anticoagulation Sufficient for Safe Cardioversion in Atrial Fibrillation? After the procedure, anticoagulation continues for at least four more weeks. Whether you stay on blood thinners long-term depends on your individual stroke risk profile, which clinicians assess with a scoring system that accounts for age, sex, heart failure history, high blood pressure, diabetes, prior stroke, and vascular disease.10PubMed Central. Cardioversion in Non-Valvular Atrial Fibrillation
Skipping the Three-Week Wait With Imaging
Three weeks of anticoagulation before cardioversion can feel like a long time, especially when your heart is racing and symptoms are miserable. There is a shortcut: transesophageal echocardiography, or TEE. This involves passing a small ultrasound probe down the esophagus, which sits right behind the heart, to look directly at the left atrial appendage for clots. Guidelines uniformly recommend TEE for this purpose.11PubMed. Roles of Transesophageal Echocardiography and Cardiac Computed Tomography for Evaluation of Left Atrial Thrombus and Associated Pathology
The large ACUTE trial randomized patients whose atrial fibrillation had lasted more than two days to either the standard three-week anticoagulation approach or a TEE-guided strategy. In the TEE group, clots were found in about 14 percent of patients. Those with clots received extended anticoagulation before any cardioversion attempt, while those without clots were cardioverted immediately and put on at least four weeks of anticoagulation afterward.12US Cardiology. Early Cardioversion of Atrial Fibrillation Guided by Transesophageal Echocardiography The TEE-guided strategy was safe and allowed earlier cardioversion for most patients. TEE remains the gold standard for ruling out atrial clots before the procedure.13PubMed Central. Diagnosis and Management of Left Atrium Appendage Thrombosis in Atrial Fibrillation Patients Undergoing Cardioversion
What the Sedation Feels Like
Electrical cardioversion is not done while you’re awake. You receive brief intravenous sedation, enough to put you under for the few seconds the shock takes, and then you wake up. The two most commonly used sedation drugs are propofol and etomidate, and each has a distinct profile.
Propofol is smooth and fast-acting but tends to drop blood pressure. In one comparative study, about a third of patients receiving propofol experienced hypotension, compared with roughly a sixth of those given etomidate.14PubMed Central. Cardioversion: What to choose? Etomidate or propofol Etomidate keeps blood pressure more stable and allows quicker recovery, but it has a well-known side effect: involuntary muscle jerking, called myoclonus, which is harmless but can be startling. A meta-analysis confirmed this trade-off: propofol carried higher rates of hypotension and breathing depression, while etomidate carried significantly higher rates of myoclonus and nausea.15PubMed. Etomidate versus propofol sedation for electrical external cardioversion: a meta-analysis An earlier comparison noted that giving propofol as an infusion rather than a single bolus can blunt the blood-pressure drop, making it a reasonable choice for people with arrhythmias.16PubMed. A comparison of propofol and etomidate for cardioversion In emergencies, midazolam is sometimes used alongside propofol.17European Heart Journal Supplements. Acute rate control in atrial fibrillation: an urgent need for the clinician
Why the Rhythm Often Doesn’t Stay Fixed
Getting cardioverted and waking up in normal rhythm feels like a fix, but the reality is more sobering. Atrial fibrillation recurs in a large proportion of patients. One study of 124 patients with persistent atrial fibrillation found that only about 37 percent were still in normal rhythm four weeks after cardioversion.18PubMed Central. Factors predicting success rate and recurrence of atrial fibrillation after first electrical cardioversion in patients with persistent atrial fibrillation That is not a typo: roughly two-thirds had reverted to fibrillation within a month.
Several factors predict whether normal rhythm will hold. Having been in atrial fibrillation for less than three months before cardioversion made sustained success about two and a half times more likely. Being on a beta-blocker was the strongest protective factor, increasing the odds of maintained rhythm sevenfold. Smaller atrial size also helped substantially.19PubMed Central. Factors predicting success rate and recurrence of atrial fibrillation after first electrical cardioversion in patients with persistent atrial fibrillation A more recent analysis added left atrial diameter and the number of prior cardioversions to the list of recurrence predictors, suggesting that each additional cardioversion raises the odds that the next one will also fail.20PubMed Central. Investigation of predictive parameters for recurrence in patients undergoing electrical cardioversion for atrial fibrillation
This is the core frustration for many patients: cardioversion works well as a reset, but it does nothing to fix whatever structural or electrical problem caused the fibrillation in the first place. That’s why it is almost always paired with ongoing medication or followed by a discussion about catheter ablation, which targets the triggers more directly.
Atrial Stunning and Post-Procedure Clot Risk
Even after a successful cardioversion, the left atrial appendage doesn’t snap back to full mechanical function right away. There is a period known as “stunning” during which the appendage contracts weakly, allowing blood to pool and potentially clot. This is why anticoagulation continues for at least four weeks after the procedure, even if normal rhythm is restored. Stunning occurs in patients cardioverted from atrial flutter as well, though it is less pronounced than in atrial fibrillation, which likely explains the lower (but still real) stroke risk after flutter cardioversion.21PubMed. Left atrial appendage “stunning” after electrical cardioversion of atrial flutter: an attenuated response compared with atrial fibrillation as the mechanism for lower susceptibility to thromboembolic events
When Cardioversion Happens in an Emergency
Everything described so far applies to elective, planned cardioversion. When atrial fibrillation causes dangerously low blood pressure, chest pain, or heart failure that threatens the patient’s life, there is no time for three weeks of anticoagulation or a TEE. Emergent electrical cardioversion is performed immediately. There is broad consensus that immediate electrical cardioversion is the right call for hemodynamically unstable patients, and it is considered safer and more effective than trying to use intravenous drugs like amiodarone in that setting. Amiodarone’s slow onset, modest conversion rates, and side effects make it a poor choice when someone is crashing.22European Heart Journal Supplements. Acute rate control in atrial fibrillation: an urgent need for the clinician Even in emergencies, equipment for temporary pacing should be available, because one potential complication is the heart slowing too much or pausing after the shock.
Complications and Side Effects
Electrical cardioversion is a safe procedure in the vast majority of cases, but it is not without risks. More than a quarter of patients experience a brief period of slow heart rate right after the shock, and this is more common in people who already have problems with their heart’s natural pacemaker (the sinus node).23International Journal of Clinical Cardiology. Electrical Cardioversion: A Review Dangerous ventricular arrhythmias after cardioversion are uncommon as long as the shock is synchronized properly and there is no digitalis toxicity, which is a hard contraindication to the procedure.
Skin irritation and mild burns under the pad sites are common. One study found that 84 percent of patients had some pain at the electrode sites, and about 23 percent reported moderate to severe pain. Burns tended to be worse at the edges of the sternal pad than at the center.24PubMed. The incidence and severity of cutaneous burns following external DC cardioversion The discomfort typically resolves within a few days.
People With Pacemakers and Implanted Defibrillators
If you have a pacemaker or implantable cardioverter-defibrillator, cardioversion can still be performed, but it requires extra caution. The electrical shock can potentially alter the device’s pacing thresholds or sensitivity settings.25PubMed Central. Electrical cardioversion In practice, significant device malfunction after cardioversion is rare with contemporary devices, but because the consequences of a malfunction could be serious, routine device interrogation afterward remains standard care.26PubMed. External cardioversion of atrial fibrillation and flutter in patients with cardiac implantable electrical devices The electrode pads are generally placed so that current does not flow directly across the device generator.
Cardioversion During Pregnancy
Arrhythmias can develop or worsen during pregnancy due to the increased blood volume and hormonal changes. When medication fails or the patient is unstable, electrical cardioversion can be used. A review of available data concluded that it is safe and effective during pregnancy, provided there is continuous fetal heart rate monitoring and a multidisciplinary team is involved, with the ability to perform an emergency cesarean section if needed.27PubMed Central. Electrical cardioversion during pregnancy: safe or not? The amount of current that reaches the fetus is negligible, and cardioversion is generally preferred over prolonged exposure to antiarrhythmic drugs, which carry their own fetal risks.28PubMed. Maternal arrhythmias during pregnancy
Cardioversion in Children
Atrial arrhythmias in children are less common than in adults and are often associated with congenital heart disease or prior cardiac surgery. Biphasic cardioversion works well in pediatric patients and young adults, often at very low energy levels. A study of 16 patients, many with complex congenital heart disease including single-ventricle repairs, found that all were successfully cardioverted. Most required less than 0.5 joules per kilogram of body weight, a fraction of the energy used in adults.29PubMed. Low energy biphasic waveform cardioversion of atrial arrhythmias in pediatric patients and young adults
The Pill-in-the-Pocket Approach
For people with infrequent, well-tolerated episodes of atrial fibrillation, there is an appealing alternative to repeated hospital visits: carrying a dose of an antiarrhythmic medication to take at home when symptoms start. This is known as the “pill-in-the-pocket” strategy, and it functions as a self-administered pharmacological cardioversion.
The landmark trial enrolled patients with recent-onset atrial fibrillation and had them take either flecainide or propafenone outside the hospital when episodes occurred. Over a mean follow-up of about 15 months, roughly 79 percent of participants had recurrences. Of the episodes treated with the pill approach, 94 percent converted successfully, with symptoms resolving in about two hours on average. Emergency room visits and hospitalizations dropped significantly compared with the year before the patients started the program.30PubMed. Outpatient treatment of recent-onset atrial fibrillation with the “pill-in-the-pocket” approach
The strategy is not risk-free. A safety analysis of 273 patients found serious adverse events in about 3 percent, including fainting, dangerously slow heart rates, and conversion of atrial fibrillation into atrial flutter with a fast ventricular response. All significant events occurred at the higher dose levels of flecainide or propafenone.31PubMed. Safety of Pill-in-the-Pocket Class 1C Antiarrhythmic Drugs for Atrial Fibrillation Another study found that about a quarter of patients screened for the approach failed their initial monitored trial dose, underscoring why the first dose is always given under observation in a hospital before sending patients home with the medication.32PubMed. Clinical effectiveness of a systematic “pill-in-the-pocket” approach for the management of paroxysmal atrial fibrillation When it works, though, it dramatically reduces the need for emergency department visits and formal electrical cardioversions.
Does Early Rhythm Control Actually Help Long-Term?
For years, there was genuine debate about whether actively restoring and maintaining normal rhythm (rhythm control) was better than simply managing heart rate and accepting the fibrillation (rate control). Older trials suggested no clear survival benefit to rhythm control, which led many clinicians to take a more conservative approach. More recent evidence has shifted that thinking. A systematic review and meta-analysis of studies comparing early rhythm control to rate control found that pursuing normal rhythm early was linked to about a 24 percent lower risk of death from any cause, a roughly 32 percent lower risk of cardiovascular death, and a 23 percent lower risk of stroke.33PubMed Central. Early rhythm control vs. rate control in atrial fibrillation: A systematic review and meta-analysis The key word is “early.” The benefit appears strongest when rhythm control is pursued soon after diagnosis rather than years into the disease, when the heart’s structure has already remodeled.
Quality of Life After Cardioversion
Beyond survival statistics, how patients feel matters. A comparative study measuring anxiety, sleep quality, and overall quality of life in atrial fibrillation patients found significant improvements after cardioversion. Quality-of-life scores went up by about 11 points on a validated atrial fibrillation questionnaire, and both anxiety and sleep quality improved meaningfully.34PubMed Central. A Comparative Analysis of the Effects of Cardioversion and Ablation on Anxiety, Sleep, and Quality of Life in Patients Diagnosed With Atrial Fibrillation Catheter ablation produced even larger gains in that study, with a 21-point quality-of-life improvement. This makes intuitive sense: ablation targets the triggers and can produce a more durable result, while cardioversion often requires repeat procedures or ongoing medication. Still, the relief patients feel after a successful cardioversion, even temporary, is real and measurable. For many people, it serves as both a bridge and a proof of concept, showing them what life in normal rhythm feels like and sometimes motivating the conversation about more definitive treatment options.