An implantable cardioverter-defibrillator (ICD) is a small device fitted under the skin, usually near the collarbone, that continuously monitors heart rhythm. If it detects a dangerous arrhythmia, it can deliver a controlled electrical shock to restore a normal rhythm.
Some devices also provide pacing support and a therapy called ATP (anti-tachycardia pacing), which can correct certain arrhythmias without a full shock. ATP works silently and the person often has no awareness that it has activated.
ICDs are used both for people who have already experienced a life-threatening cardiac event and for those considered at elevated risk of one, as a precautionary measure. The device records data continuously, which your ICD clinic can download and review remotely or at a scheduled appointment.