Device Resets Rhythm without Touching Heart

August 28, 2013

News Review From Harvard Medical School -- Device Resets Rhythm without Touching Heart

A new kind of device shocks the heart back into normal rhythm without the need for implanted wires that actually touch the heart, a study finds. The device is called a subcutaneous implantable cardioverter defibrillator (ICD). A standard ICD is implanted under the skin and is attached to wires that touch the heart. The wire on the new device is implanted under the skin. The study included 314 people using the new device. In a 6-month period, 21 people had episodes of a fast heart rhythm that can lead to cardiac arrest. This occurred 38 times in all. Each time, the device shocked the heart back to a normal rhythm. The device detected and fixed 100% of the life-threatening rhythms. However, 41 patients received shocks at times when there was no dangerous rhythm. Cameron Health Inc. makes the device. The U.S. Food and Drug Administration approved it last year. However, long-term studies were required. The journal Circulation published the study. HealthDay News wrote about it August 27.

By Reena L. Pande, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

For several decades, doctors have been able to implant a device in the body to shock the heart out of an abnormal rhythm. These devices are called implantable cardioverter-defibrillators (ICDs). They serve as a sort of insurance policy for the heart if there's a risk it will develop a dangerous fast rhythm. If this happens, the ICD detects the abnormality. Then it delivers a shock to restore a normal heart rhythm.

These devices are very similar to the automated external defibrillators (AEDs) found in airports, schools and stores. But they also are different, because they are inside a person's body. ICDs have been proven to save lives in patients with weakened heart muscles or those who have survived sudden cardiac death (when an abnormal rhythm makes the heart stop working).

All ICDs have to be implanted under the skin of the upper chest. This is usually quite straightforward. Wires are then implanted to connect the device to the heart. This is done by passing the wires through the veins in the chest and into the heart. The device can then deliver the shock if necessary.

However, these ICDs pose some challenges. Over time, the veins can get scarred or develop blood clots, which can cause more problems. If the tissue around the device or the wires ever gets infected, removing the wires is a major challenge.

New research, published this week in the journal Circulation, describes testing of a new type of ICD device. It is planted under the skin, but there's no need for a wire connected to the heart. The study included more than 300 people. This new ICD was found to be just as safe and effective as the standard kind.

The new device has advantages. It avoids the need for implanting wires next to the heart, and the scarring and clots that wires can cause.

But there are also some technical limitations that make the new device not suitable for all patients. For example, the wires of a standard ICD allow it to also serve as a pacemaker (keeping the heart beating when it beats too slowly). The newer ICDs will not have this function.

These new devices are not ready for prime time just yet. Though they are available in Europe, they are not yet available in the United States for widespread use.

What Changes Can I Make Now? 

Some people have the following questions about these devices.

How do you know if you need a defibrillator?

The decision to implant an ICD is one that you and your doctor would make together.  ICDs are helpful for some people with heart disease, but not all. Appropriate patients include:

• People with a severely weakened heart muscle who are at risk for dangerous heart rhythms
• People with factors that increase their risk of developing dangerous heart rhythms
• Survivors of sudden cardiac death

What's the difference between a defibrillator and a pacemaker?

They are indeed different, but some devices have both a pacemaker and a defibrillator. A defibrillator delivers a small shock when the heart is beating in an abnormally fast rhythm. This puts the heart back into a normal rhythm. A pacemaker typically works only when the heartbeat is abnormally slow. The purpose is to keep the heart beating at a normal pace.

How long are these devices left in place?

Once they are put in, they usually are left in place. Sometimes the battery needs to be changed. This is done with a simple procedure under the skin. Sometimes an ICD is removed because of infection in the area under the skin or in the bloodstream around the wires. This is a much more complicated procedure.

Are there other side effects?

Some people can feel the device under the chest wall, but that is usually not uncomfortable. The most troublesome "side effect" occurs if a shock is delivered at the wrong time (when the heart is not actually in an abnormal rhythm). This can be very uncomfortable and sometimes is described as feeling like a kick in the chest by a horse.

What Can I Expect Looking to the Future? 

In the era of new and improved medical devices with wireless capabilities, expect to see even more high-tech devices that will be simpler to implant. The new ICD studied here has some real advantages. However, the lack of wires also makes it unsuitable for some patients. I suspect we will see it used more widely when available. Future research will no doubt make these devices easier to implant. As they get easier to put in, the challenge will remain for doctors to make sure we implant them only in the right patients.