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From the Fall 2005 Issue
You Asked. We Answered.
Cardiac Devices: The Inside Story
You know your cardiac device is designed to help your heart. But what's inside your device that makes it work? How does it sense what's going on in your heart — and then deliver the right treatment at just the right time?
In response to many questions from readers, LifeBeat Online looks inside three types of cardiac devices. We tell you what conditions each type of device treats. We also explain how the devices get their energy. And how the devices deliver that energy — to help improve the way your heart works. We also take you on a behind-the-scenes video tour of how we make these devices.
What Do the Devices Treat?
Three types of cardiac devices treat electrical problems in the heart.
| Device | What It Does |
|---|---|
| Pacemaker | Delivers electrical energy in amounts so small that you can't feel them. The energy "paces" the heart to beat at a normal rate. Pacemakers treat abnormally slow heartbeats (bradycardia). |
| Implantable cardioverter defibrillator (ICD) | Delivers electrical energy to the heart to treat heart rhythms that lead to sudden cardiac death. ICDs, also called defibrillators, stop fast rhythms (arrhythmias) by delivering low amounts of energy to the heart. If the device senses a dangerously fast arrhythmia, it delivers a high-energy shock called defibrillation. All ICDs have pacemakers inside them and may be referred to as a "combination" pacemaker and defibrillator. |
| Heart failure device | Delivers cardiac resynchronization therapy (CRT), also known as biventricular pacing. A CRT device sends tiny amounts of electrical energy to both of the heart's lower chambers, the ventricles. The energy causes the ventricles to contract, or pump, at the same time. A CRT device treats the uncoordinated beating (dyssynchrony) of the heart's ventricles. Many people with heart failure are at higher risk of sudden cardiac death. Some of these people may receive CRT-D devices, which are CRT devices with built-in defibrillators. Other people may have CRT in a pacemaker, known as a CRT-P device. |
Along with the benefits, there are risks associated with these devices. Talk to your doctor about important safety information.
Where Are the Devices Implanted?
A doctor implants each type of device in much the same way. The device itself is typically implanted just under the skin near the shoulder (Figure 1). Cardiac devices send electrical energy to the heart through thin, specially coated wires called leads. Leads are positioned inside or on the surface of the heart.
What's Inside My Device?
All cardiac devices contain two parts: circuitry and a battery. Devices that send higher levels of energy to your heart have a third part called a capacitor.
Behind the Scenes:
How Cardiac Devices Are Made
Do you wonder what's inside your device? Our videos take you on a tour showing the many critical steps involved in manufacturing each type of cardiac device.
Defibrillators |
Pacemakers |
Heart Failure |
Talk to your doctor about important safety information.
Circuitry
The circuitry — called the "brains" of the device — acts somewhat like a mini-computer. The leads in your heart sense your heart rhythms. The circuitry reads the information from the leads and determines whether the rhythm is normal or abnormal. The circuitry then determines what treatment to deliver if the rhythm is abnormal.
For example, let's say a patient has a pacemaker. Imagine that the patient's heart is beating only 45 times per minute. The circuitry senses that rate from the leads. Depending on how the doctor has programmed the pacemaker, the circuitry then may tell the pacemaker to increase the patient's heart rate.
Battery
The battery powers everything that your device does. For example, the battery provides the energy for the circuitry to constantly track your heart rhythms. The battery also provides the energy to treat abnormal rhythms as needed.
Capacitor
A device that delivers high-energy treatment, such as an ICD, has a third part. In addition to a battery and circuitry, a high-energy device has a high-energy capacitor. It takes a number of seconds for the capacitor to collect and hold the electrical energy from the battery. The device then delivers a life-saving shock.
Imagine that a patient with an ICD develops a dangerously fast arrhythmia. To stop the arrhythmia, a high-energy shock is needed. For a few seconds the battery sends energy to the capacitor. The device then delivers a shock. And the patient's heart beats normally again.
The battery, circuitry, and capacitor each plays a critical role in enabling your device to do its job. By working together, the parts of a cardiac device ensure that you get the treatment you need for your heart rhythm.
Important Safety Information
Cardiac Resynchronization Therapy Devices
Cardiac resynchronization therapy pacemakers (CRT-P) and defibrillators (CRT-D) are used to treat heart failure patients who have symptoms despite the best available drug therapy. These patients also have an electrical condition in which the lower chambers of the heart contract in an uncoordinated way and a mechanical condition in which the heart pumps less blood than normal. CRT-Ps and CRT-Ds are not for everyone including people with separate implantable cardioverter-defibrillators (CRT-P only) or certain steroid allergies. Procedure risks include infection, tissue damage, and kidney failure. In some cases, the device may be unable to respond to your heart rhythm (CRT-P only) or may be unable to respond to irregular heartbeats or may deliver inappropriate shocks (CRT-D only). In rare cases severe complications or device failures can occur. Electrical or magnetic fields can affect the device. Only your doctor knows what is right for you. These devices are available by prescription only. Individual results may vary.
Implantable Cardioverter Defibrillators
An implantable cardioverter defibrillator can protect you from the effects of sudden cardiac arrest by reviving your heart rhythm. But it is not for everyone, including people with certain steroid allergies. Procedure risks include infection and tissue damage. In some cases, the device may not respond to irregular heartbeats or may deliver inappropriate shocks. In rare cases severe complications or device failures can occur. Electrical or magnetic fields can affect the device. Only your cardiologist knows what is right for you. This device is available by prescription only. Individual results may vary.
Pacemakers
A pacemaker system can monitor and treat your heart rhythm by delivering electrical energy to pace your heart when it senses a slow rhythm. But it is not for everyone, including patients with certain steroid allergies. Patients who have additional medical conditions that may not allow the pacemaker to function appropriately should not receive a device. Procedure risks include infection, tissue damage and kidney failure. In some cases, the device may not respond to your heart rhythm. In rare cases severe complications or device failures can occur. Electrical or magnetic fields can affect the device. Only your doctor knows what is right for you. This device is available by prescription only. Individual results may vary.