Cardioversion

Cardioversion resets a heart that is beating in an abnormal rhythm — most often atrial fibrillation or atrial flutter — back to normal sinus rhythm. It can be done electrically, with a brief shock delivered through pads on the chest, or chemically, with a medication given under monitoring.

Electrical cardioversion is quick and highly effective at restoring rhythm in the moment. What it does not do is change why the arrhythmia started, which is why it is one part of a plan rather than a cure on its own.

When the atria have been fibrillating for more than about 48 hours, a clot can form inside the left atrial appendage. Restoring an organized rhythm makes the atria contract forcefully again — which can dislodge that clot and cause a stroke.

For this reason cardioversion is only performed once that risk has been addressed, by one of two routes:

• Three or more weeks of uninterrupted anticoagulation beforehand, with doses genuinely not missed
• Or a transesophageal echocardiogram (TEE) immediately beforehand to look directly into the appendage and confirm no clot is present

Anticoagulation continues for at least four weeks afterward regardless of which route was used, because the atria contract weakly for some time after rhythm is restored. Many patients continue indefinitely based on their overall stroke risk. If you have missed doses of your blood thinner, say so before the procedure — it is the single most important thing to disclose, and it will change the plan rather than simply delaying it.

Electrical cardioversion is brief. You will have nothing to eat or drink after midnight. Adhesive pads are placed on the chest and back, an IV is started, and an anesthesia provider gives a short-acting sedative — you are asleep for the shock itself and typically remember nothing of it. The shock is synchronized to your own heartbeat, which is what distinguishes cardioversion from defibrillation. If the first attempt does not restore rhythm, one or two more may be delivered at higher energy.

You wake within minutes and are monitored for a few hours. Because of the sedation, you must have someone drive you home and should not drive, work or make important decisions for the rest of the day.

Skin redness or irritation where the pads sat is common and settles in a few days. Mild chest muscle soreness can occur.

Medication can also convert the rhythm, given intravenously under continuous monitoring or, for selected patients, as an oral regimen an electrophysiologist has approved for use at home. It avoids sedation but works more slowly and less reliably, and the same anticoagulation rules apply in full.

Sometimes for years, sometimes only briefly. Recurrence is common, particularly when atrial fibrillation has been present a long time, or when sleep apnea, high blood pressure, thyroid disease, alcohol use or obesity are driving it. Cardioversion is often most useful as part of a plan that also addresses those factors and may include an antiarrhythmic medication or an ablation. A rhythm that returns is not a failure of the procedure — it is information about what else needs treating.