Written by Dimitrios Vrachatis, Specialist Cardiologist, PhD, National and Kapodistrian University of Athens.
What is an implantable defibrillator?
An implantable cardioverter-defibrillator (ICD) is a device placed inside the body. Among its functions is delivering an electrical shock, or defibrillation, to the heart.
What is it used for?
It aims to prevent sudden arrhythmic cardiac death in patients considered at high risk.
How is it implanted?
The procedure resembles pacemaker implantation:
- A small skin incision is made under local anaesthesia.
- Venous access is obtained.
- One or more leads are advanced to the appropriate cardiac positions.
- The leads are connected to the device.
- The device is placed in a pocket beneath the skin.
Read more about implantation on the pacemaker page.
How does it work?
When a life-threatening arrhythmia is detected, the response depends on its type:
- For ventricular tachycardia, the device first attempts faster pacing of the right ventricle, called antitachycardia pacing. If unsuccessful, it delivers a shock.
- For ventricular fibrillation, it delivers a shock directly.
Can a shock be delivered unnecessarily?
Despite substantial software advances, an ICD can occasionally mistake a non-fatal arrhythmia for a life-threatening one and deliver an inappropriate shock. The cardiologist then optimises treatment settings for the individual patient.
How does an ICD differ from a pacemaker?
All defibrillators can also provide pacing, but the reverse is not true. The main difference is the right ventricular lead, which is designed to support defibrillation.
The cardiologist selects single-chamber, dual-chamber or biventricular pacing according to need. If pacing is unnecessary, that function remains inactive and the simplest suitable system, usually single-chamber, is chosen.
Size is another difference. ICDs are larger because they require a larger generator or battery.
What are the possible complications?
Small but real risks include:
- Procedure-related swelling, infection or haematoma at the pocket, pneumothorax, haemothorax or blood around the heart
- Long-term infection of the pocket or system
Indications are therefore specific and strict, so that the expected benefit exceeds the potential risks.
When can I go home?
In uncomplicated cases, patients stay overnight and return to usual activities the next day, while taking care with movements of the arm on the implantation side for a few weeks.
When should I contact the doctor after implantation?
Some pain around the incision and pocket is possible in the first days. You should be assessed if you develop:
- Marked local inflammation, including redness, swelling or severe pain, or fever
- A large haematoma; minor bruising can occur depending on blood-thinning medicines
- Strong, uncomfortable muscle contractions
- Severe, persistent breathlessness or chest pain
- Persistent palpitations
- Loss of consciousness or fainting
How often is the ICD checked?
Routine checks are usually annual, using an external programmer. This brief interrogation provides information about battery life, lead function and significant rhythm events.
An additional check is required after every shock.
What precautions should I take?
People with an ICD can live normally. Follow your cardiologist’s medication instructions, usually for heart failure, and lifestyle advice carefully.
Other precautions mainly concern avoiding extreme physical activity with the arm on the side of the device.
Can I have an MRI?
This depends on the model, identified on the device card. If MRI is permitted, special programming is required immediately before and after the scan.
What about airport checks and magnetic fields?
Strong magnetic fields, such as those encountered during airport security checks, should be avoided because they may interfere with ICD function. Modern devices have stronger electromagnetic protection, making this less likely. Settings may be temporarily affected and require reprogramming; during that time the patient may not have the device’s protection. For the same reason, phones containing strong magnets, for example for wireless charging, should not be placed near the ICD pocket.