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A Primer: Ambulatory Heart Rhythm Monitors

ECG pads positioned

Source: patient education brochure

By Steve S. Ryan, PhD,  Last updated: November 2, 2020

In order to make a diagnosis of an arrhythmia, some form of electrocardiographic recording (i.e. ECG/EKG) must be made at the time the arrhythmia is occurring.

If an arrhythmia becomes persistent and is present day-in and day-out, as often is the case for A-Fib, the diagnosis is quite easy with a routine ECG done in the physician’s office.

The challenge is when an arrhythmia occurs intermittently what doctors call “paroxysmal ” (on and off) or is self-limiting. In this case, when an ECG is performed in between A-Fib episodes, the ECG will appear completely normal. To circumvent this problem, one would go to the next level of evaluation with a long-term monitor.

Example: ECG tracing of Atrial Fibrillation shows tiny, irregular and erractic “fibrillation” waves between heart beats..

Long-term monitors

When your arrhythmia is intermittent, your doctor may have you wear a mobile type of heart rhythm monitor to capture the electrical activity of your heart.

Long-term monitors basically are ECG recorders that patients can take with them (ambulatory). They fall into two major categories: continuous recording (Holter) and intermittent recording (Event).

The Holter Monitor

Mortara H12+ Continuous 12-lead Holter recorder

Mortora H12+ Continuous 12-lead Holter recorder

A Holter Monitor (named after Dr. Norman Holter, go figure) records continuously the ECG of a patient, usually for 24 – 48 hours. More modern Holter units record onto digital flash memory devices. The data are uploaded into a computer where software analyzes the input, counting ECG complexes, calculating summary statistics such as average heart rate, minimum and maximum heart rate, and finding candidate areas in the recording worthy of further study.

The advantage of a Holter is that every single heartbeat during that day is recorded and can be analyzed. The disadvantage is that if an arrhythmia did not happen on that particular day, the Holter data would not be useful.

The Event Monitor

Cardionet wireless event monitor

Cardionet wireless event monitor

An Event Monitor, on the other hand, is a long-term monitor that can be used for up to 30 days or longer. The advantage is that the longer the recording period, the better chance of “catching” an intermittent arrhythmia. The disadvantage is that an Event Monitor must be activated by the patient and downloaded telephonically, a task that requires a certain amount of manual dexterity and may be difficult for some patients.

Some event monitors are patient activated when having an episode and save the last several minutes of data; others detect the irregular heart rate and automatically record the data.

Number of Electrodes

The number and position of electrodes varies by model, but most Holter monitors employ between three and eight, whereas the Event Monitors typically use two. Both the Holter and Event monitors record electrical signals from the heart via a series of electrodes attached to the chest. The Loop (event) monitor is not attached to the patient but is instead pressed to the chest by the patient when experiencing an A-Fib episode.

Implantable ambulatory event monitors

Medtronic Reveal® DX insertable cardiac monitor (ICM) continuously monitors

Medtronic Reveal® DX insertable continuous monitor

Implantable event monitors are also available for those instances where individuals experience such infrequent symptoms that extended monitoring is needed.

These devices are inserted just under the skin in the chest area during an outpatient surgical procedure. The device may remain implanted for over one year.

Implantable loop recorders have the ability to record events either automatically (auto activated) or by manual activation (self-activated).

Real Time Remote Cardiac Recording

CardioNet MCOTos Event wireless event monitor

CardioNet MCOTos wireless event monitor

An example of the newer monitoring technologies is the Ambulatory Cardiac Telemetry (ACT), a wireless cardiac telemetry system.  This event monitor is designed for remote arrhythmia monitoring in any location.

A small transmitter worn on the patient sends the ECG data to a portable handheld device where it is analyzed.  If an arrhythmia is identified, the data is automatically transmitted to a Monitoring Center for immediate review. Integrated into a state-of-the-art mobile phone, the ACT provides next generation cardiac arrhythmia monitoring. What’s interesting is the transmitter is a dongle type device worn around the neck with leads placed on the chest. You carry or have available what, in essence, is a mobile phone (it’s actually more than a phone). It is small and not cumbersome.

No patient input is required. Data collected from the monitors is transmitted to the monitoring center via a cellular network, the internet, or over the phone (based on model). Data from the monitors is not intended to be used directly by the patient but rather by the monitoring center and your cardiologist.

Next-Generation: the ‘Smart Band-Aid’ Patch

Steve wearing Carnation Ambulatory Monitor (for 1 week in Sept 2018 ) at

 BardyDx Carnation Ambulatory Monitor

The ‘Smart Band-Aid’ provides the next-generation ambulatory cardiac monitoring service with beat-to-beat, real-time analysis, automatic arrhythmia detection and wireless ECG transmission. The Zio XT Patch by iRhythm Technologies, the BardyDx Carnation Ambulatory Monitor by Davis Medical, and the BodyGuardian Mini by Preventice Solutions are next generation ambulatory monitors.

The sensors can be modified to monitor a number of different tasks as they can also provide a comprehensive suite of post-symptom, looping, and auto trigger event monitors as part of its turn-key cardiac event monitoring service.

For Steve’s first-hand account of the Medtronic Reveal LINQ loop recorder and the 7-day BardyDx Carnation Ambulatory Monitor, see our post: Has My A-Fib Returned? 21 Day Results from My LINQ Loop Recorder.

VIDEO: The Zio® Patch Ambulatory Cardiac Monitor


The single use Zio® Patch cardiac monitor (iRhythmi Technologies) looks similar to a 2-by-5-inch adhesive bandage and sticks to a patient’s chest. The single-use ambulatory, continuously cardiac monitor records for up to 14 days with no need to remove it during exercise, sleeping or bathing.  (2:04 min.) Go to video->

References for this article
Diagnosing Heart Disease: Ambulatory ECG, Cardionetics, Cardiac Intelligence. Last accessed, Sept 14, 2012.

Anderson, J, et al. New Methodlogies in Arrhythmia Monitoring, Touch Briefings 2008, European Cardiology, pp63-66.

Anderson, J., & Donnelly, N. New Methodologies in Arrhythmia Monitoring. Last accessed Nov 4, 2014. URL:

First posted: March 2013

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If you find any errors on this page, email us. Y Last updated: Monday, November 2, 2020

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