May 12, 2022

ECG vs PPG: A Comprehensive Comparison

Prevayl is no ordinary sportswear. Hidden within each SmartWear® garment are integrated knitted electrodes created by our in-house team of experts to record the electrical activity of your heart and deliver clinical-grade ECG data to the Prevayl App in real time, giving you professional-level performance insights whilst negating the need for clunky chest straps.

But what’s an ECG? And how does it stack up to PPG, which is more widely accessible in the fitness tracker market? In this article, we’re addressing some of the questions you may have regarding the differences between ECG and PPG to deepen your understanding of your wearables.

What are ECG and PPG?

Essentially, both ECG (electrocardiography) and PPG (photoplethysmography) are technologies used to examine how your heart is functioning, but with different methods.

ECG measures the bio-potential (or voltage) generated by electrical signals that control the expansion and contraction of the heart's chambers. Since ECG measures the electrical activity of the heart directly, it’s always best to take the measurement as close to the heart as possible, hence most ECG-based sensors utilise a chest strap with built-in electrodes. That’s also why we’ve positioned our electrodes in the chest band of our SmartWear® garments – for maximum accuracy.

On the other hand, PPG-based wearables shine a light source through the surface of skin and use a photodetector to measure the volumetric variations of blood circulation controlled by the heart's pumping action. Such wearables are typically wrist-worn devices, think Apple Watch, Fitbit, Garmin, Whoop, etc.

Is ECG or PPG more accurate?

When it comes to accuracy, ECG presents a clear advantage over PPG, as it’s considered to be the non-invasive gold standard for cardiac monitoring.

ECG is used in the healthcare industry to help diagnose and monitor conditions affecting the heart, as well as to investigate symptoms of possible heart problems, such as chest pain, palpitations (suddenly noticeable heartbeats), dizziness and shortness of breath. While PPG relies on ECG signals as a reference for static HR comparison.

 

Can ECG and PPG measure heart rate (HR)?

Since it captures measurement directly from the source: your heart, ECG can measure your HR more accurately. That’s why the Prevayl Sensor is designed to sit right below your chest, where we can capture the most precise data.

This is not to say that PPG-based wearables can’t do the same, but it tends to produce less accurate data during physical activity or cyclic wrist motions, thereby making ECG-based counterparts a much more reliable workout companion for high-performance athletes.

 

Can ECG and PPG measure heart rate variability (HRV)?

HRV analysis is traditionally performed on ECG, which is capable of extracting R-Peak Intervals (RRI) with millisecond accuracy. In other words, HRV data can be obtained with short-duration measurements. In fact, using ECG, Prevayl is able to examine your HRV and determine your readiness to perform  in three minutes – learn more about BodyCheck™.

For PPG sensors, peak interval accuracy is limited by usable sampling rate due to the high power consumption of LEDs. Not to mention that with PPG, pulse rate variation correlates with HRV for longer periods of measurement (more than five minutes), thus requiring long-duration windows of data to establish an accurate HRV.

Which has the lowest power consumption?

ECG sensors tend to have extremely low power consumption, operating at low mW or µW. This is why our Prevayl Sensor can often outlast even the most impressive wrist-based PPG-based wearables in terms of power consumption. 

In contrast, most PPG sensors require higher power consumption – often orders of magnitude greater – due to the need of driving one or more LEDs approximately 30mW of operating power, which can reduce your wearable’s battery life.

Are there any downsides to ECG or PPG?

The key challenges with PPG technology are cancelling the effects of ambient light, accommodating different skin colours and conditions (tattoos, eczema, etc.) and dealing with physical motion artefacts caused by movement. Not to mention that PPG can only be used on parts of the body that have a high concentration of blood vessels – for example, it can be difficult to get an accurate PPG signal from the wrist. 

ECG sensors bypass these issues by collecting data directly from your heart, which ultimately enables them to deliver the widest range of heart health metrics thanks to their capability to capture a more complete signal of overall heart performance, including both HR and HRV.

May 12, 2022 - Written by Prevayl

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