What happens during electrical cardioversion?

Q. I have been having bad symptoms from my atrial fibrillation and am scheduled for an electrical cardioversion. It sounds risky. What does this procedure involve?

A. Electrical cardioversion is a procedure to convert a rapid or irregular heartbeat back to a normal rhythm. While the idea of shocking your heart with electricity sounds scary and potentially risky, rest assured that this procedure is quite safe. It's not the same as cardiac defibrillation, which is an emergency procedure that uses high-energy shocks. Electrical cardioversion more often uses lower-energy shocks, and you're asleep during the brief procedure so you shouldn't feel the shock.

Atrial fibrillation (afib) causes blood to pool and stagnate in the heart's upper chambers (atria), increasing the risk of blood clots. Because these clots can break loose and cause a stroke, most people with afib take anti-clotting medications to lower this risk. Cardioversion can dislodge blood clots, and this elevated risk persists for about a month after the procedure.

If you're not already taking an anti-clotting medication, you'll probably need to take one for three to four weeks before the procedure. That usually allows any existing blood clots to stabilize or resolve. Another option is to receive a special ultrasound test called transesophageal echocardiography, which involves placing a thin, flexible tube down your esophagus (the tube connecting your throat and stomach) to get a closer view of the heart. If no blood clots are visible, an electrical cardioversion can be done without giving the anti-clotting pretreatment regimen for weeks ahead of time.

Before the cardioversion, you can't eat or drink for eight to 12 hours. You'll receive medications through a vein in your arm to make you sleepy. Two palm-sized electrode patches or paddles will be placed on your right upper chest and your lower left chest or back. (These areas will be shaved beforehand, if needed.) Wires from the electrodes connect to a cardioversion machine. The electricity momentarily stuns the heart. When the heart "wakes up," its internal pacemaker should take over and restore a regular, coordinated heartbeat.

After you're sedated, the procedure takes only a few minutes, but you'll be monitored for a few hours afterward. Cardioversion is successful about 90% of the time. But your heart may revert to an abnormal rhythm, sometimes shortly after the procedure, especially if you've had atrial fibrillation for many years. Your doctor may prescribe medications to help keep your heart in a normal rhythm. And you'll need to continue taking anti-clotting medications for at least another month — or indefinitely, depending on your risk of stroke.

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