Heart smart watches

August 19, 2019| Health and Wellbeing /

If you look closely, you will see them on people’s wrists everywhere. Smart watches or fitness trackers claim to count your steps, measure your sleep, calculate calories, document your heart rate, and now, some even test your heart function with an ECG.

The new Apple Watch Series 4 comes with simplified electrocardiogram to measure your heart’s rhythm and electrical activity. It’s the first mainstream wearable gadget to include diagnostic technology that doctors use to detect a range of potentially serious heart problems, including arrhythmia and coronary heart disease.

So, what do smart watches actually do and are they reliable?

Here’s a list of some of the things they measure and the technology involved:

  • Motion - All smart watches generally measure acceleration, frequency, duration, intensity and patterns of your movement. This is done with an accelerometer and gyroscope

  • Height - Some include an altimeter to measure altitude, which is handy if you’re climbing hills or stairs

  • Body fat mass - Some clock the time taken for an electrical signal to make it through the upper part of your body and return to the device. This estimates fat and muscle mass

  • Heart rate - Optical sensors illuminate your capillaries to see how fast your blood is pumping

  • Sleep quality - Wrist movements are interpreted to determine periods of sleep and wake time

  • Calories burned - The device takes information you’ve supplied such as your sex, age, weight and height and combines it with the activity it has detected and the activity you’ve logged to estimate calories used

  • Heart function - Apple is yet to explain how its ECG will work, but experts have already raised concerns that healthy people without any symptoms of heart problems might be misled by ‘false positive’ results indicating a problem where none really exists

Studies of reliability

While it’s too early for independent studies to test the reliability of Apple’s ECG - not to mention its impact on users and whether it picks up legitimate problems or not - studies of other smart watch features have been done.

One by Stanford University in the US evaluated the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2. It found that:

  • Factors such as skin colour and your body mass index (how heavy or thin you are) can affect the measurements

  • None of the devices measured calorie use accurately, so don’t use it to excuse more cake or fried food! The most accurate device was off by an average of 27% and the least accurate was off by 93%

  • Most measured heart rate well. Six out of seven of the devices measured beats per minute with an error rate of less than 5%

Another study looking at how well these devices measure sleep quality found that they tend to overestimate both sleep time and quality, which could be dangerous if you’re relying on your watch to pick up a serious sleep problem.

So, if you want a smart watch to keep track of your heart rate while you exercise, it’s likely to be money well spent. But if you’re worried about your heart function or sleep, it’s best to talk to your GP about it. They can always recommend a specialist to conduct more accurate tests if required.

Dr Andris Ellims a cardiologist of Victoria Heart who practices at Epworth Richmond and Epworth Freemasons advises:

I encourage my patients to consider purchasing a fitness-specific watch, particularly if it helps motivate them to improve their regular exercise habits. However, we need to be mindful that these new technologies do have limitations (such as false measurements) which restricts their clinical benefit currently. Newer generations of devices are likely to overcome these problems in coming years
— Dr Andris Ellims, Cardiologist, Epworth HealthCare


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