Make heart beat again: ICD
An arrhythmia is any disorder of heart rate or rhythm. It means that the heart beats too quickly, too slowly, or with an irregular pattern. Most arrhythmias result from problems in the electrical system of the heart. If the arrhythmia is serious, patient may need a cardiac pacemaker or an implantable cardioverter defibrillator (ICD). They are devices that are implanted in the chest or abdomen.
A pacemaker helps control abnormal heart rhythms. It uses electrical pulses to prompt the heart to beat at a normal rate. It can speed up a slow heart rhythm, control a fast heart rhythm, and coordinate the chambers of the heart. Find more information about pacemaker function in the previous article (make heart beat normally: pacemaker).
An implantable cardioverter-defibrillator (ICD) is a small battery-powered device placed in the chest to detect and stop irregular heartbeats. It is a device designed to administer lifesaving therapy in the event of a sudden cardiac arrest (SCA). When the ICD senses a dangerously high heart rate, it will send an electrical pulse to the heart to reset its normal rhythm and allow the heart to resume pumping blood through your body. This is known as defibrillation. ICDs have been used for decades and have prolonged hundreds of thousands of lives.
An ICD is used when patient is affected by dangerously fast heartbeat that keeps the heart from supplying enough blood to the rest of the body (such as ventricular tachycardia or ventricular fibrillation) or if the patient is at high risk of such a heart rhythm problem (arrhythmia), usually because of a weak heart muscle.
An ICD can give off a low-energy shock to speed up or slow down an abnormal heart rate or a high-energy shock, which can correct a fast or irregular heartbeat. If the low-energy shocks do not restore the normal heart rhythm, the device will switch to high-energy shocks for defibrillation. The device also will switch to high-energy shocks if the ventricles start to quiver rather than contract strongly.
ICDs are similar to pacemakers, but pacemakers deliver only low-energy electrical shocks.
Initially looked upon as a remote choice for patients with sustained ventricular tachycardia (VT), their effectiveness is unquestioned today. Over 200,000 ICDs are implanted worldwide every year, with rapidly expanding applications in modern day medicine
There are two basic types of ICD:
- A traditional ICD is implanted in the left shoulder area, near the collarbone, and the wires (leads) attach to the heart. The implant procedure requires invasive surgery: using X-ray imaging, the leads are fed through a vein into the heart and across the heart valve. Depending on the heart condition, one or two leads will be placed in the heart. Once the leads are put in place, they are attached to the heart wall for optimal connectivity.
- A subcutaneous ICD (S-ICD) is another option that’s implanted under the skin at the side of the chest below the armpit. It’s attached to an electrode that runs along the breastbone. An S-ICD is larger than a traditional ICD but doesn’t attach to the heart, so it leaves the heart and blood vessels untouched and intact.
Patient health care provider may recommend an ICD if he’s had signs or symptoms of a certain type of irregular heart rhythm called sustained ventricular tachycardia, including fainting. An ICD might also be recommended if a patient survived a cardiac arrest. Other reasons to use an ICD are:
- A history of coronary artery disease and heart attack that has weakened the heart;
- An enlarged heart muscle;
- A genetic heart condition that increases the risk of dangerously fast heart rhythms, such as some types of long QT syndrome;
- Other rare conditions that may affect the heartbeat.
A health care provider may recommend an S-ICD if there are structural defects in the heart that prevent attaching wires to the heart through the blood vessels.
How does an ICD work?
The ICD’s job is to quickly recognize and stop problems. It does this by keeping track of your heart rhythm at all times. If your heartbeat becomes irregular, the ICD delivers the treatment. Your doctor can program the ICD to do several things:
- Pacing: for mild ventricular tachycardia, the ICD can deliver several pacing signals in a row. These signals cause the heart to return to a normal rhythm.
- Cardioversion: this is used if pacing doesn’t work. Cardioversion sends a mild shock to the heart to stop the fast heartbeat.
- Defibrillation: For ventricular fibrillation, the ICD sends a stronger shock. This can stop the fast rhythm and help the heartbeat go back to normal.
- Pacemaker: The ICD can detect when the heart beats too slow. It can act like a pacemaker and bring your heart rate up to normal.
In the past, those at risk of sudden cardiac death from malignant tachyarrhythmias were managed pharmacologically with drugs such as amiodarone. The outcome of these treatments was varied and often poor. The first human to receive an implantable defibrillator, in 1980, was a young woman who had recurrent episodes of ventricular fibrillation. The device, however, was only able to identify ventricular fibrillation and responded with an unsynchronised shock. Today, the devices used are far more complex and consist of individually tailored algorithms, which provide a series of management strategies for episodes of ventricular tachycardia and ventricular fibrillation.
Risks
Possible risks of having an ICD implanted include:
- Infection at the implant site
- Swelling, bleeding or bruising
- Blood vessel damage from ICD leads
- Bleeding around the heart, which can be life-threatening
- Blood leaking through the heart valve (regurgitation) where the ICD lead is placed
- Collapsed lung (pneumothorax)
- Movement (shifting) of the device or leads, which could lead to cardiac perforation (rare)
Medical devices are not risk-free, but the ability to save our lives is so much greater that the risks take a back seat.
About me
I am 24 years old, graduated in Biomedical Engineering at the University of Padova. During my undergraduate courses I became more and more passionate about medical devices and clinical engineering. I enjoy sharing knowledge about this innovative, creative and important technology that we use every day.