Ambulatory Monitors

How do ambulatory monitors work?

All ambulatory monitors rely on the fact that your heart has its own electrical system. That system controls the entire cycle of your heartbeat, using electrical pulses to cause the four chambers of your heart to act in a specific order. This ensures that your heart pumps in an organized, efficient sequence.

The electrical activity of your heart is strong enough that it’s easy to detect by devices that are attached to or implanted just under your skin. When it’s done with a live or printed readout of the electrical activity, it’s called an electrocardiogram (EKG or ECG for short).

When parts of your heart aren’t working correctly, the electrical activity in those areas changes. That’s how a trained healthcare provider can read the EKG data and tell how well the different parts of your heart are performing. An EKG is done in a hospital or clinic setting and usually takes just a few minutes.

Ambulatory monitors use a similar method, but they do so for days, weeks or even years. Depending on the monitor used, they can track your heart’s activity while you’re sleeping, working or going about most parts of your daily routine.

What are the different types of ambulatory monitors?

Most ambulatory monitors are external devices that you can carry with you. They read your heart’s activity through sensors called electrodes that are attached to your skin using a special adhesive. Most of these monitors are roughly the size and weight of a cell phone (and some use cell phones that have been specially modified just for this kind of use).

External ambulatory monitors include:

• Holter monitors. This type of monitor is most often used to record heart activity for 1-2 days. However, some variants of this device can record for 1-2 weeks.
• Event monitors. These devices only record your heart’s activity when it’s most likely that an arrhythmia is happening. Some devices let you activate them when you feel symptoms. Others passively “listen” to your heart rhythm and automatically start recording when they detect an arrhythmia. These devices largely fall into two types:
  • Looping. These devices have a memory loop of a few minutes (the exact amount of time varies). The loop includes a set amount of time into the past and the future. When it’s not activated, new data that’s added pushes older data out of the loop. If you activate it, a few minutes in the past will be saved for later review, along with a few minutes after you activate the device.
  • Non-looping. These devices only record a set period after they’re activated. With some of these devices, the electrodes can be taken off. Then, when you feel symptoms, you put the electrodes on and activate the device to record your heart rhythm.
• Real-time monitors. These devices are very similar to event monitors but can transmit heart activity data to a monitoring center for immediate review by a healthcare provider. Real-time monitors can automatically gather and send data when they detect an arrhythmia. They can also gather and send data when activated by a wearer who feels symptoms. These devices are especially useful with severe arrhythmias where expert medical guidance is needed quickly.
  • Certain types of real-time monitors are meant only for use during check-ins over a phone call. This type of device lets you call a monitoring center and transmit your data while you’re on the phone. You can also check in with clinical staff, during which they will likely ask you questions related to symptoms, your medications or recent activities.

There are two other types of ambulatory monitors that work similarly to the above monitors but with key differences.

• Patch recorders. These devices stick to your skin like an adhesive patch but contain all the hardware needed to detect, record and save heart activity data. You can wear them for up to two weeks. The size of these devices varies, but in general, they are small enough that you could wear one under a t-shirt and it wouldn’t be easy to spot.
• Implantable loop recorders. These small devices can be inserted under your skin and monitor your heart activity for much longer periods. They can record automatically or can when activated by the wearer. Data can be downloaded from them wirelessly in a clinic or doctor’s office. Some of these monitors can stay in place for up to two years. A major advantage of this device is you don’t have to worry about activating it, and you don’t have to worry about issues when bathing, swimming, etc.

What should I expect before the test?

A healthcare provider, usually a specialist, will explain the test options and recommend one that’s most likely to help diagnose your problem. They’ll also consider your circumstances (such as your job) and your preferences in choosing the type of monitor.

How do I prepare for the test?

Before the test, you may want to bathe because, depending on the test, it may be a day or two before you can remove the electrodes and bathe again. Whether or not you choose to bathe, you should make sure that the skin on your chest is clean.

You should not use any oils, lotions, creams or other skin care products on the skin of your chest because these can make it hard for the electrodes to stick to your skin or detect your heart activity. You should also wear a shirt that’s easy to take off and put on, as this makes it easier to place the electrodes.

What to expect on the day the monitoring period begins?

A technician or other healthcare professional will explain how to use the device, including how to operate it. Depending on the device, they will also instruct you on taking off and putting on the electrodes yourself after bathing, swimming, etc.

They’ll also tell you specific situations or devices that you’ll need to avoid to prevent them from interfering with the monitor. This usually includes certain types of electronics or devices that contain magnets. They may provide you with a list of devices to avoid, or you can request one.

In the case of monitors that use electrodes, they’ll use alcohol to clean the skin where they’ll place the electrodes. They’ll also shave or remove any hair you might have in that area, ensuring that the electrode can stay attached and get a clear signal.

What to expect during the monitoring period?

Ambulatory monitor tests are extremely safe and painless. In general, all you’ll need to do is wear and use the monitor as instructed. Your healthcare providers, including technicians and nurses, will tell you anything else you’ll need to know for the monitoring period.

What to expect after the monitoring period is over?

Once the test is over, you’ll be able to remove the electrodes (if the device uses them) and return the device. You may have some lingering skin irritation from the adhesive used with the electrodes with external monitors. This usually goes away in a few days. Your provider may be able to give you guidance on how to treat the irritation to help it clear up more easily.

Are there risks with these devices?

In general, the most common side effect with most external ambulatory monitors is skin irritation. The irritation is usually caused by the adhesive used to stick the electrodes to your skin. If you have sensitive skin or an allergy (confirmed or suspected) to adhesives, you should mention it before it’s applied to your skin.

With implantable loop recorders, there are some side or complications — most of them minor — that can happen:

• Irritation or pain. This usually happens around where the device is implanted. In the majority of these cases, it will improve or go away on its own.
• Infection. In rare cases, the area where the device was implanted might become infected. This is usually treated with antibiotics, but the device might need to be moved in some cases.
• Allergic reaction. Another rare complication is an allergy to a material used in the implantable recorder device. If you have such an allergy, the device may need to be removed and another type of monitor used.
• Poor signal. Implantable loop recorders can sometimes have trouble picking up electrical activity in certain parts of your heart. When this happens, it’s usually necessary to move the device to a location where the signal is clearer.