ICD: The Implantable Defibrillator

An implantable defibrillator is a device that watches the heart’s rhythm continuously and is designed to stop a life-threatening acceleration when it finds one. Its medical name is ICD, implantable cardioverter defibrillator. A conventional pacemaker speeds the heart up when it slows; an ICD intervenes when it races dangerously. One detail matters: the device does not deliver a shock in every case — it first tries to correct the rhythm by a method that does not involve a shock.

What Is an ICD?

An ICD consists of a body placed under the skin below the collarbone and one or more electrode leads running to the heart.

The device watches every beat. While the rhythm is normal it does nothing and waits quietly. When it finds a dangerous acceleration it acts within seconds.

The same device also works as a conventional pacemaker where needed, supporting the heart with an impulse when the rhythm slows.

How Does It Differ from a Conventional Pacemaker?

This is what is most often confused. The two devices look similar from outside but work against different problems.

• A conventional pacemaker: delivers an impulse when the heart beats more slowly than it should. The aim is to prevent fainting, dizziness and the symptoms that come with a slow pulse.

• An ICD: intervenes when the heart goes into a very fast and ineffective rhythm arising from the ventricles. The aim is to stop that rhythm continuing.

In short, a conventional pacemaker works against slowness and an ICD against dangerous acceleration. An ICD also includes the pacemaker function; the reverse is not true.

Which Rhythm Disorders Does It Protect Against?

The ventricles, the lower chambers of the heart, are the part that pumps blood out to the body. If they begin to work very fast and irregularly, there is no effective contraction and the circulation stops.

• Ventricular tachycardia: a fast, regular rhythm arising from the ventricles. The person may faint, or feel palpitations and dizziness.

• Ventricular fibrillation: the ventricles quivering instead of contracting. The circulation stops and consciousness is lost within seconds.

An ICD is programmed to recognise these two rhythms and bring them to an end.

Who Is an ICD For?

Secondary Prevention

These are people who have already had one of those rhythms: those who have survived a cardiac arrest, or who have had an episode of ventricular tachycardia that caused them to faint.

Here the event has already happened, and the likelihood of it happening again is taken into account.

Primary Prevention

These are people who have not had such an event but are considered to be at high risk. The group most often seen is patients with heart failure whose pumping strength has fallen markedly.

An important condition applies here: the decision is made after heart failure medication has been brought to its optimal level and a period has been allowed to pass. In some patients the pumping strength recovers with medication and no device is needed.

Other situations include certain inherited rhythm disorders and diseases of the heart muscle. A family history of sudden death at a young age is assessed separately.

When It May Not Be Suitable

• Where the rhythm disorder is due to a temporary, correctable cause, such as the effect of a medicine or a disturbance in the blood

• An active infection

• Another condition that markedly shortens expected life span

• Heart failure treatment not yet brought to its optimal level

Whether it suits you is decided by weighing your rhythm recordings, the pumping strength of your heart and your general condition together.

How Do You Prepare?

• Screening for infection: because a permanent device and lead are being placed in the heart, there must be no active infection in the body. A dental check is part of that assessment and is often skipped.

• Your list of medicines: bring everything you take, with the doses. Your doctor decides how blood thinners are managed around the procedure; do not stop them on your own.

• Your heart failure treatment: where the device is being considered for primary prevention, the medication must have been brought to its optimal level and a period allowed to pass.

• Which arm you use: the device is usually placed on the non-dominant side. Say beforehand if there is anything about your work or your shoulder that matters.

• Your expectations and your questions: what a shock is, when it will be delivered and what you should do afterwards are discussed beforehand. Your written consent is taken.

It helps to write down whatever is on your mind about living with the device; driving, work and sport should all be made clear at that consultation.

How Is the Device Fitted?

The procedure is done under local anaesthetic with sedation. A small incision is made below the collarbone and a pocket is prepared under the skin. The electrode leads are advanced through a vein to the heart and their positions confirmed with imaging.

Once the leads are in place, measurements are taken: is the device sensing the heart’s signals well enough, and is the impulse capturing the heart? When the measurements are right, the body of the device is placed in the pocket and the incision closed.

Your arm movements are restricted for a period afterwards, which is needed for the leads to settle. Your doctor sets how long.

What Does an ICD Shock Feel Like?

A shock is described as a sudden, strong blow in the chest. It is unpleasant. A shock delivered while you are unconscious is not felt.

But the most important information on this page is this: not every intervention is a shock.

Trying Without a Shock First: ATP

When the device finds a dangerous acceleration, its first response is not a shock. It sends the heart a run of impulses slightly faster than the rhythm it is in. That run usually breaks the rhythm and the heart returns to normal.

This is called anti-tachycardia pacing, or ATP. It lasts a few seconds and most patients do not notice it at all.

A shock is delivered only if that attempt does not work, or if the rhythm is of a kind that calls for a shock directly. This is why many people with an ICD live for years without ever receiving one.

What Should You Do If You Receive a Shock?

Having a clear plan matters:

• One shock and you feel well: sit down, rest, and get in touch with your doctor. The device’s record will be examined.

• More than one shock in a short time: go to an emergency department.

• A shock with fainting, chest pain or breathlessness: go to an emergency department.

• If somebody is touching you as the shock is delivered: they may feel a slight tingling; this does no harm.

Every shock is recorded. At your review the device’s memory is read to see which rhythm the shock was delivered for.

What Is an Inappropriate Shock?

This is where the device misreads a rhythm that is not dangerous and delivers a shock. The commonest reason is the pulse becoming very fast during atrial fibrillation. A problem with an electrode lead, or settings that are not right, can also cause it.

Inappropriate shocks are a preventable problem. Reprogramming the device, medication, or ablation for the underlying rhythm disorder can all reduce the risk.

Is There an ICD Without a Lead in the Heart?

Yes. A type of ICD has been developed with no lead inside the heart (a subcutaneous ICD). Its body is placed on the side wall of the chest and the electrode under the skin in front of the breastbone. Nothing enters the heart or the blood vessels.

What that means in practice is this: because there is no lead inside a vein, lead-related problems and lead-related infection do not arise with this device.

It has an important limitation, though: since the device is not inside the heart, it cannot work as a pacemaker. It is not suitable for patients with a slow rhythm, those who need pacing support, or those who need CRT. The method of ending a rhythm without a shock cannot be used with it either.

It is therefore considered particularly in younger patients, in people with problems of venous access, and in those who have had a device infection before. Which device suits you is decided by taking the type of your rhythm disorder together with whether you need pacing.

Where pacing support is needed but a lead is not wanted, a leadless pacemaker may come onto the table as a separate option.

Driving

This is hardly covered anywhere, yet it affects daily life directly.

The restriction is not because of the device but because of the underlying rhythm disorder. A loss of consciousness at the wheel is a risk both to you and to those around you.

The general approach is as follows:

• Driving is not allowed for a period after the device is fitted.

• Where there has been a rhythm that caused fainting, that period is longer.

• If the device delivers a shock, the period starts again.

• Driving commercial vehicles, buses and heavy goods vehicles is generally not permitted.

The periods differ from country to country and with the regulations in force. Always ask your doctor what applies in your case, and follow what you are told.

Daily Life

• Reviews: the battery level, the lead measurements and the events recorded are checked at set intervals. Remote monitoring systems can also be used.

• MRI: a large proportion of devices today are MRI-compatible. Always say that you have a device before a scan.

• Mobile phones: you can use one; do not carry it in a chest pocket on the same side as the device.

• Security gates: tell the staff you have a device and ask to be checked by hand. Walking through without stopping is also fine — just do not stand still in the gate.

• Strong magnetic fields: ask your doctor if you work around welding equipment, industrial generators and the like.

• Your device card: always carry the identification card you are given.

What Are the Possible Risks?

• Bleeding, bruising or swelling at the pocket

• Infection; one of the most serious problems in device treatment, which is why screening, including a dental check, is done beforehand

• An electrode lead moving out of position or wearing over time

• An inappropriate shock

• Injury to the lining of the lung or to a vessel while the leads are being placed; rare

• Anxiety about living with the device; fear of a shock is marked in some patients and should be talked about

That last point should not be dismissed. Anxiety is common in patients who have had a shock, and it is something to seek support for.

How Long the Device Lasts, and Follow-Up

Battery life depends on how heavily the device is used, how many treatments it has delivered and its settings. It is followed regularly at reviews and the decline is seen in advance.

When its life is over, the body of the device is replaced. If the leads are sound they are left in place and connected to the new body; that procedure is shorter than the first fitting.

Implantable Defibrillators in Antalya

Prof. Dr. Umuttan Doğan is a cardiologist who trained in electrophysiology at the Gülhane Military Medical Academy in 2012; pacemaker and defibrillator work is one of the areas he works in. The procedures are carried out in the catheter laboratory at Antalya American Hospital.

If an ICD has been suggested to you, or you are having a problem with the device you already have, you can be seen at the clinic in Konyaaltı with your rhythm recordings and test results. You may also want to look at CRT, used in heart failure, and the leadless pacemaker. You will find his background and contact details on their own pages.

Frequently Asked Questions

Are an ICD and an ordinary pacemaker the same thing?

No. A conventional pacemaker delivers an impulse when the heart beats more slowly than it should. An ICD intervenes when the heart races dangerously. An ICD also includes the pacemaker function; a conventional pacemaker has no shock function.

Is a shock painful?

A shock delivered while you are conscious feels like a sudden, strong blow in the chest, and it is unpleasant. A shock delivered while you are unconscious is not felt. A shock lasts less than a second.

Is a shock delivered for every dangerous rhythm?

No. The device tries a method without a shock first: it sends the heart a short, fast run of impulses to break the rhythm that way. Most patients do not feel it. A shock is delivered only when that attempt does not work, or when the rhythm calls for a shock directly.

I have had a shock — should I go to an emergency department?

If you have had one shock and feel well, sit down, rest and get in touch with your doctor. If you have had more than one in a short time, or the shock came with fainting, chest pain or breathlessness, go to an emergency department.

Will an ICD treat my heart failure?

No. An ICD protects against a life-threatening rhythm disorder; it does not treat heart failure. Your medication, your salt and fluid management and your reviews all continue independently of the device. For a different kind of device aimed at regulating the heart’s contraction, CRT is considered.

The information on this page is for general guidance and does not replace a consultation. Decisions about diagnosis and treatment are made by your doctor after assessing your own situation.