Implantable Cardioverter-Defibrillator (ICD)

An implantable cardioverter-defibrillator, or ICD, protects against sudden cardiac arrest. It continuously monitors your heart rhythm, and if it detects a dangerously fast ventricular rhythm it responds within seconds — first by attempting rapid painless pacing to break the rhythm, and if that fails, by delivering a shock.

An ICD also functions as a pacemaker for slow rhythms. Its defining purpose, though, is to treat a rhythm that would otherwise be fatal within minutes.

Secondary prevention — for someone who has already survived a cardiac arrest or a sustained dangerous ventricular arrhythmia.

Primary prevention — for someone who has not had such an event but whose risk is high enough to warrant protection. Most commonly this means an ejection fraction of 35 percent or below that has persisted despite at least three months of optimal medication, because some hearts recover with treatment alone and would not need a device. It also includes certain inherited conditions such as hypertrophic cardiomyopathy, long QT syndrome, Brugada syndrome and arrhythmogenic cardiomyopathy, where risk is assessed individually.

A transvenous ICD places the generator below the collarbone with leads threaded through a vein into the heart — the standard configuration, and the one that can also provide pacing and resynchronization.

A subcutaneous ICD (S-ICD) places the generator at the side of the chest with a lead under the skin along the breastbone, with nothing inside the heart or blood vessels. It avoids the long-term risks of intravascular leads and is well suited to younger patients and to those with infection risk or difficult venous access, but it cannot provide long-term pacing.

A wearable defibrillator vest is sometimes used as a bridge while a decision is pending or while the heart is given time to recover.

Implantation takes roughly one to three hours under sedation with local anesthetic, and most patients stay overnight. Recovery follows the same rules as a pacemaker: keep the site clean and dry, avoid raising the arm above shoulder height and avoid heavy lifting for four to six weeks, and report fever, redness, drainage or increasing swelling at once.

If you receive a shock: a single shock while you feel otherwise well is not an emergency — contact your care team the same day so the recorded episode can be reviewed. Seek emergency care immediately for more than one shock in 24 hours, a shock accompanied by fainting, chest pain or breathlessness, or repeated shocks. Someone touching you during a shock may feel a mild tingle; it is not harmful to them.

Not every shock is appropriate — a fast atrial rhythm or a lead problem can trigger one, which is another reason every episode is reviewed and device settings adjusted.

Driving is restricted after implantation and after any shock, with rules that vary by state and by whether the device was placed for primary or secondary prevention. Ask directly rather than assuming.

Remote monitoring sends device data from home automatically. Batteries last roughly 5 to 10 years depending on how much therapy is delivered. Tell any clinician about the device before an MRI or any surgery using electrocautery, and keep strong magnets away from the site.

An ICD prevents sudden death; it does not treat heart failure or extend life in every circumstance. It is reasonable — and encouraged — to discuss what the device will and will not do, and under what future circumstances its shocking function might be deactivated. That decision can be made or revisited at any time, and deactivating shocks does not turn off pacing.