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Implantable Cardioverter Defibrillators (ICDs): A Life-Saving Technology

An Implantable Cardioverter Defibrillator—commonly referred to as an ICD—is a powerful, life-saving device used by electrophysiologists to protect patients at risk of life-threatening heart rhythm disturbances, particularly ventricular arrhythmias.

One of the most serious risks for these patients is sudden cardiac death—a condition in which the heart suddenly stops beating. When this happens, there are only minutes to restore a normal rhythm before permanent damage or death occurs. Outside of a well-equipped public space, hospital, or emergency setting, the chances of accessing a traditional defibrillator in time are lower. That’s where an ICD can make all the difference.

What Is an ICD?

An ICD is a compact, implantable version of the external defibrillators found in airports, gyms, and other public spaces. While it resembles a pacemaker in appearance, its purpose is quite different. Rather than delivering steady pulses to regulate a slow heart rate, an ICD monitors the heart continuously and provides a powerful, high-voltage shock only when a dangerous rhythm is detected, specifically, when the heart stops or begins to quiver (as in ventricular fibrillation). Note: There are also ICDs that perform double duty and pace the heart.

Who Qualifies for an Implantable Cardioverter Defibrillator (ICD)?

An ICD is often recommended for patients at high risk of severe heart rhythm abnormalities. These include people with structural heart disease or a history of dangerous ventricular arrhythmias. The criteria are split into primary prevention (before a life-threatening event occurs) and secondary prevention (after a cardiac arrest or severe arrhythmia has already happened).

Primary Prevention (Preventing an Initial Event)

You may qualify for an ICD if you have not yet had a life-threatening arrhythmia, but have conditions that put you at high risk. These include:

  • Heart failure with reduced ejection fraction (HFrEF)
  • Post-myocardial infarction (heart attack)
  • Inherited arrhythmia syndromes (such as) Long QT syndrome, Brugada syndrome, Arrhythmogenic right ventricular cardiomyopathy (ARVC), and Catecholaminergic polymorphic ventricular tachycardia (CPVT)
  • Specific cardiomyopathies (like dilated cardiomyopathy)
  • Hypertrophic cardiomyopathy (with additional risk factors like syncope or family history of SCD)

Secondary Prevention (After a Serious Event)

You may qualify for an ICD if you’ve already had a life-threatening arrhythmia or cardiac arrest, including:

  • Surviving sudden cardiac arrest resulting from ventricular fibrillation (VF) or sustained ventricular tachycardia (VT)
  • Sustained VT with syncope (fainting)
  • History of prior myocardial infarction with sustained VT or VF, even if you’re not symptomatic now

Patients Who Are Not Typically Candidates:

  • Patients with severe heart failure (NYHA Class IV) may not be eligible for ICDs
  • When arrhythmias are reversible (e.g., drug overdose, electrolyte imbalance)

How Is an ICD Implanted?

The procedure to implant an ICD is very similar to that of a pacemaker and is typically performed under local anesthesia with sedation. A small incision is made near the collarbone, and the battery pacing device (called a pulse generator) is inserted beneath the skin. Thin wires (leads) are guided through the veins into the heart, where they will monitor electrical activity and deliver a shock if needed. The ICD can function for 10 to 12 years before a battery replacement is needed.

What Does an ICD Shock Feel Like?

Patients often describe an ICD shock as startling or intense—it can feel like a sudden jolt or thump in the chest. Fortunately, these devices have evolved significantly. Today’s ICDs are highly advanced and calibrated to minimize false detections. While inappropriate shocks can still happen, they are much less common due to improved technology and individualized programming.

Reducing the Risk of Unnecessary Shocks

While ICDs are lifesaving, their effectiveness depends on accurate rhythm detection. To reduce the chance of false positives (unnecessary shocks), patients are encouraged to follow all post-operative instructions carefully:

  • Maintain heart-healthy habits, including diet, exercise, and medication adherence.
  • Avoid trauma or impact to the area where the device is implanted
  • Attend regular follow-ups to ensure the device is functioning correctly and remains well-calibrated

Are There Alternatives to an ICD?

In some rare cases, patients may not be suitable candidates for an implanted ICD. For these individuals, an external option called a wearable defibrillator vest may be recommended. While bulkier and less convenient, it can still be lifesaving.

Some patients may choose not to have an ICD implanted, despite the associated risks. In such cases, it’s critical to have a well-informed caregiver or loved one nearby—someone who knows how to use an external defibrillator if sudden cardiac arrest occurs—every second counts.