Implanted Rhythm Protection
Implantable Cardioverter-Defibrillator (ICD)
An ICD is a small device that monitors the heart rhythm and can treat dangerous fast rhythms from the ventricles. It is used in selected patients after careful assessment.
On this page
Understanding the device
What Is an ICD?
An implantable cardioverter-defibrillator (ICD) is a small battery-powered device placed under the skin, usually near the collarbone. One or more thin wires, called leads, connect it to the heart. Some designs use a lead placed under the skin instead of inside the heart.
Its purpose is to recognise a dangerous fast rhythm from the ventricles and treat it. It does not prevent the rhythm from starting.
Continuous sensing
What an ICD Monitors
The device senses the heart’s electrical signals all the time. It measures the heart rate and the pattern of the signal and compares them with settings chosen by the care team.
If the rhythm stays within the set limits, the device does nothing. It records episodes it detects, so the team can review them at device checks.
Detection and treatment
How Therapy Can Be Delivered
The device follows a sequence. The settings differ between patients and are programmed by the care team.
Sense
The device senses the rhythm continuously.
Detect
It decides whether a rhythm is fast and abnormal.
Treat
It delivers the programmed therapy, if needed.
Record
The episode is stored for review at the next check.
Not every detected episode needs a shock. The device may try other therapies first.
Types of therapy
Pacing vs Shock Therapy
An ICD can deliver more than one kind of therapy. Which ones are available depends on the device.
Pacing therapy
Painless pacing
For some fast rhythms, a series of small pacing impulses can stop the rhythm. This is called antitachycardia pacing. Some devices can also pace the heart if it beats too slowly.
Usually not felt, or only mildly.
Shock therapy
Cardioversion or defibrillation
A stronger electrical shock resets the rhythm. It is used for rhythms that need faster or stronger treatment.
A shock can be uncomfortable and may be felt as a sudden blow in the chest.
Patient selection
Who May Be Assessed for an ICD
An ICD is considered when the risk of a dangerous ventricular rhythm is judged to be high enough to justify a device. The decision is made by the treating physician, with the patient.
After a dangerous rhythm
For some people who have had a life-threatening ventricular rhythm or cardiac arrest.
Heart muscle conditions
For some people with a weakened heart muscle or an inherited heart condition.
Other risk factors
Symptoms, test results and family history may be part of the assessment.
Individual decision
Having a condition does not mean a device is needed.
Clinical context
ICD and Ventricular Arrhythmias
Ventricular arrhythmias range from harmless extra beats to dangerous sustained rhythms. An ICD is only one part of care. Medicines, catheter ablation and treatment of any underlying heart condition may also be used.
Not every person with ventricular tachycardia needs an ICD. The choice depends on the rhythm, the heart condition and the overall risk.
Device types
ICD Systems: Transvenous and Subcutaneous
A transvenous ICD has one or more leads placed through a vein into the heart. It can deliver painless pacing therapy for some fast rhythms and, depending on the device, pace the heart for slow rhythms. Some systems have leads in more than one chamber, and a combined defibrillator with resynchronisation (CRT-D) is used in selected patients with heart failure.
A subcutaneous ICD (S-ICD) places the lead under the skin beside the breastbone, outside the heart and veins. It can deliver shocks but does not offer long-term pacing for slow rhythms or the painless pacing used to stop some fast rhythms.
Choice of system depends on the rhythm problem, whether pacing is needed, age, anatomy and other health factors. It is made with the treating team, and one type is not better in every case. See Pacemaker for pacing devices.
The procedure
Implantation Overview
Details vary with the device and the patient. The steps below are a general outline.
Assessment
Review of the heart condition, tests and the reason for the device.
Preparation
Discussion of the procedure and its risks, and of the type of device.
Anaesthesia
Usually local anaesthetic, often with sedation.
Lead placement
Leads are guided to the heart through a vein, or placed under the skin for some devices.
Device placement
The device is placed in a small pocket under the skin.
Testing
The team checks that the device senses and works as planned.
Recovery
Monitoring after the procedure before going home.
Recovery
After Implantation
The wound needs time to heal, and activity may be limited at first, particularly for the arm on the side of the device. You will be given instructions on wound care and activity.
Contact your care team if the wound becomes red, swollen or painful, or if you have a fever.
Ongoing care
Device Checks and Follow-up
The device is checked regularly, in clinic or by remote monitoring where available. Checks look at the battery, the leads and any recorded episodes, and the settings may be adjusted.
Battery
The battery life is checked. The device is replaced when the battery nears the end of its life.
Leads
Lead function is tested at each check.
Recorded episodes
The team reviews any episodes and the therapy delivered.
Settings
Settings are adjusted when needed.
Living with a device
Everyday Considerations
Most people return to normal daily activity. The care team will explain the details for your situation, including driving, sport and work, which depend on the reason for the device and on local rules.
Driving
Advice depends on the reason for the device and on local rules.
Activity and sport
Guidance is individual and given by your team.
Magnets and equipment
Your team will explain which equipment to keep away from the device.
Travel and security
Carry your device card when you travel.
If you receive a shock, contact your care team. Seek emergency care if you feel unwell, receive more than one shock, or faint.
Comparison
ICD vs Pacemaker
Both are implanted devices, but they have different main purposes.
Pacemaker
Treats slow rhythms
Sends small impulses to the heart when it beats too slowly or pauses.
See the Pacemaker page for more.
ICD
Treats dangerous fast rhythms
Detects a fast ventricular rhythm and treats it with pacing or a shock. Some devices can also pace for slow rhythms.
A person may need one device type or the other, depending on the assessment.
Questions