When Tracking Your Heart: Is a Wrist-Worn Heart Rate Monitor Just as Good as a Chest Strap Monitor?

Wrist-worn heart rate fitness trackers like Fitbit and Apple Watch have become trendy wrist accessories, but are they accurate enough for Atrial Fibrillation patients? How do fitness trackers compare to chest strap heart rate monitors (HRMs)?

What’s Behind the Discrepancies? Different Technologies

Chest strap style heart rate monitors are consumer products designed for athletes and runners, but used by A-Fib patients, too. They measure the electrical activity of the heart. They’re usually a belt-like elastic band that wraps snugly around your chest with a small electrode pad against your skin and a snap-on transmitter.

The pad needs moisture (water or sweat) to pick up any electrical signal. That information is sent to a microprocessor in the transmitter that records and analyzes heart rate and sends it to a wrist watch display or smartphone app.

Wrist fitness trackers typically sit on your wrist and don’t measure what the heart does. Most glean heart-rate data through “photoplethysmography” (PPG) with small LEDs on their undersides that shine green light onto the skin on your wrist.

The different wavelengths of light interact differently with the blood flowing through your wrist, the data is captured and processed to produce understandable pulse readings on the band itself (or transmitted to another device or app).

HRMs Research Study

A 2016 single-center study was designed to find out whether wrist-worn heart rate monitors readings are accurate. Four brands of fitness trackers were compared against the Polar H7 chest strap heart monitor (HRM) and, as a baseline, with a standard electrocardiogram (ECG).

Researchers at the Cleveland Clinic enrolled 50 healthy adults, mean age, 37 years. In addition to ECG leads and the Polar chest-band heart rate monitor, patients were randomly assigned to wear two different wrist-worn heart rate monitors (out of the four).

Participants completed a treadmill protocol, in which heart rate was assessed at rest and at different paces: between two and six miles per hour. Heart rate was assessed again after the treadmill exercise during recovery at 30 seconds, 60 seconds and 90 seconds.

In total, 1,773 heart rate values ranging from 49 bpm to 200 bpm were recorded during the study. Accuracy was not affected by age, BMI or sex. The four wrist-worn heart rate monitors assessed were the Apple Watch (Apple), Fitbit Charge HR (Fitbit), Mio Alpha (Mio Global) and Basis Peak (Basis).¹

HRMs Study Results

Chest Strap Monitors: The chest strap monitor was the most accurate, with readings closely matching readings from the electrocardiogram (ECG).

In general, the chest straps were more accurate because the sensor is placed closer to the heart (than a wristband), allowing it to capture a stronger heart-beat signal.

Wrist-Worn Monitors: Accuracy of wrist-worn monitors was best at rest and became less accurate with more vigorous exercise, which presumably is when you’d most want to know your heart rate.

None of the wrist-worn monitors achieved the accuracy of a chest strap-based monitor. According to the electrocardiograph, some wrist-worn devices over- or underestimated heart rate by 50 bpm or more.

What Patients Need to Know

Wrist-band optical heart-rate monitors may be more convenient or comfortable and have advanced over the years. But in this small study, researchers found that chest-strap monitors were always more accurate than their wrist counterparts and more reliable and consistent.

When monitoring your heart beat rate is important to you (while exercising or doing heavy work), you’ll want to stick with an electrode-containing monitor (chest band-style, shirts or sports bras with built-in electrode pads, etc.).

To help you choose a HRM, see Steve’s Top Picks: DIY Heart Rate Monitors for A-Fib Patients at Amazon.

Bottom line 
Leave the wrist-worn trackers for the casual fitness enthusiasts

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