Cardioversion

Cardioversion is a procedure that resets an abnormal heart rhythm back to a normal one by delivering a brief, controlled electrical shock to the heart.

In a healthy heart, electrical signals fire in an organised pattern that keeps the heartbeat steady. When those signals become chaotic, the heart beats too fast, too slowly, or unevenly — a condition doctors call arrhythmia (an abnormal heart rhythm). Cardioversion works by sending a precisely timed burst of electricity through the chest wall. This brief shock interrupts the disordered signals and gives the heart's own natural pacemaker a chance to take over and restore a normal rhythm. The entire electrical event lasts only a fraction of a second, and the patient is asleep under a short-acting sedative (a medicine that causes temporary sleep) during the shock.

Cardioversion is used when the heart is beating in an abnormal rhythm that either causes symptoms or puts the patient at risk of serious complications. It is most commonly planned as an elective (non-emergency, scheduled) procedure, but it can also be performed urgently when an arrhythmia becomes dangerous.

• Atrial fibrillation (AF) — a rapid, irregular quivering of the upper chambers of the heart; the most common reason cardioversion is performed.
• Atrial flutter — a fast but more organised abnormal rhythm in the upper chambers.
• Supraventricular tachycardia (SVT) — a broad term for rapid rhythms that start above the lower chambers of the heart.
• Ventricular tachycardia (VT) — a fast, potentially dangerous rhythm originating in the lower chambers, when medicines alone are not enough.
• Other sustained (long-lasting) abnormal rhythms that cause chest discomfort, breathlessness, dizziness, or fainting.

Cardioversion is generally not suitable in certain situations. A cardiologist (heart specialist) will review the patient's full history before deciding.

• A blood clot (thrombus) is known or suspected to be present inside the heart — particularly in the left atrial appendage (a small pouch in the upper-left chamber) — because the shock could dislodge it.
• The patient has not taken blood thinners (medicines that reduce clotting) for long enough beforehand, unless an imaging test confirms no clot is present.
• The abnormal rhythm is caused by a reversible trigger, such as a low potassium level or an overactive thyroid, that can be treated directly.
• The patient has a condition that makes sedation (sleep medicine) unsafe without specialist anaesthetic (anaesthesia) support that is not available.

Cardioversion is generally considered a low-risk procedure when performed in a properly equipped setting with appropriate preparation, but like any medical intervention it carries some recognised risks.

• Return of the abnormal rhythm — the most common outcome concern; the heart may revert to the arrhythmia hours, days, or weeks after a successful shock.
• Stroke or clot travelling to another organ (embolism) — a blood clot that was sitting in the heart may be dislodged by the shock and travel to the brain or elsewhere; this is the reason doctors prescribe blood thinners before and after the procedure.
• Skin redness or mild burn at the electrode (pad) sites on the chest — usually temporary.
• Temporary low blood pressure (hypotension) immediately after the procedure.
• Temporary irregular rhythm in the minutes following the shock, which usually resolves on its own.
• Reactions to the sedative medicine, including nausea or brief confusion on waking.
• In rare cases, the shock may trigger a more serious arrhythmia that requires immediate further treatment; a defibrillator (a device that can deliver a stronger corrective shock) is always kept ready in the room for this reason.
• Muscle soreness in the chest area lasting a day or two from the electrical energy.

Preparation for cardioversion usually begins days or weeks before the procedure, not just on the day itself. Because a sedative is given, patients are asked to fast (have nothing to eat or drink) for several hours beforehand — the exact time will be specified by the care team. Alcohol should be avoided in the days leading up to the procedure, and smokers are usually advised to stop as early as possible before any heart procedure.

Medicines play an important role in preparation. Most patients will be asked to take blood thinners for several weeks before cardioversion to reduce the risk of stroke. Some patients may have their heart rhythm or rate managed with specific heart medicines in the days before. The doctor will review all current medications and advise which ones to continue or hold on the day; patients should not start, stop, or adjust any medicine without that guidance.

Before the procedure is confirmed, the care team will usually arrange the following tests to assess heart structure and rule out clots:

• ECG (electrocardiogram) — a quick, painless recording of the heart's electrical activity using stickers on the skin.
• Echocardiogram (an ultrasound scan of the heart, sometimes called a "heart echo") — to check the structure and pumping function of the heart.
• Transoesophageal echocardiogram (TOE) — a specialised ultrasound where a thin probe is guided down the throat to get a close-up view of the heart's upper chambers and check for clots; this is done if the doctor needs more certainty before proceeding.
• Blood tests — to check kidney function, thyroid function (the thyroid is a gland in the neck that affects heart rate), potassium levels, and the level of any blood-thinning medicine in the blood.
• Chest X-ray — to look at the size and shape of the heart and the condition of the lungs.

On the day of the procedure, the steps typically follow this order:

• The patient arrives at the hospital or cardiology unit and changes into a hospital gown.
• A nurse places sticky electrode pads on the chest and back (or two positions on the chest) — these both monitor the heart and deliver the shock.
• An intravenous (IV) line (a small tube in a vein, usually in the arm) is placed to give the sedative and any other medicines needed.
• The care team confirms the patient's identity, medicines, fasting time, and allergy history.
• The sedative is given through the IV line; the patient falls into a light sleep within a minute or two.
• Once the patient is asleep and monitored, the cardiologist programmes the cardioversion machine to deliver a shock that is synchronised (timed) to a specific moment in the heartbeat cycle to maximise safety.
• The shock is delivered. It lasts only a fraction of a second.
• The team immediately checks the ECG to see whether the heart has returned to a normal rhythm.
• If the first shock does not restore a normal rhythm, the doctor may repeat the shock at a higher energy setting, usually up to a small number of attempts.
• The sedative wears off within minutes and the patient begins to wake up in a monitored recovery area.

Most patients spend a few hours in a monitored recovery area after cardioversion before going home the same day, as long as the heart rhythm is stable and the sedative has fully worn off. An escort is required — patients must not drive or travel alone on the day of the procedure because the sedative affects coordination and judgment for several hours. The care team will confirm the heart rhythm with an ECG before discharge and will usually schedule follow-up appointments to track the rhythm over the coming days and weeks.

• Rest at home for the remainder of the day; most patients feel well enough to return to light daily activities the following day, but individual recovery varies.
• Avoid driving, operating machinery, or making important decisions for at least 24 hours after the sedative was given, or as directed by the care team.
• Continue any blood thinners prescribed — these are usually continued for at least several weeks after cardioversion, because the upper chambers of the heart may take time to regain full normal pumping motion, which means clot risk remains elevated for a period.
• Any redness or mild soreness on the chest skin where the pads were placed usually fades within a day or two; cool compresses (not ice directly on the skin) can ease discomfort.
• Return to the hospital or seek urgent care immediately if chest pain, severe breathlessness, palpitations (the feeling of a racing or fluttering heart), one-sided weakness, sudden difficulty speaking, or any other concerning symptom develops.
• Attend all follow-up ECG or Holter monitor (a device worn on the body that records the heart's rhythm continuously over one or more days) appointments — these are essential to check whether the normal rhythm is being maintained.
• Lifestyle changes such as reducing alcohol, managing body weight, treating sleep apnoea (interrupted breathing during sleep), and controlling blood pressure and blood sugar are commonly recommended alongside cardioversion to help the heart stay in normal rhythm.
• The doctor will discuss long-term rhythm management, which may include continuing heart-rhythm medicines or considering additional procedures if the arrhythmia returns.