Measuring your heart rate is quite simple. Place your finger on the inside of your wrist or on your neck and count the number of heart beats in one minute. A healthy heart rate at rest ranges from 60 anywhere up to 100 beats per minute. But a good heart rate does not tell you anything about your heart rhythm. How do you know if your heart rhythm is just as healthy?
Your heart is a pump that is activated by miniscule electrical pulses. These pulses cause the heart muscle to contract, pumping the blood via the aorta and the veins around the body. In normal situations, your heart fires off these tiny electrical pulses at a regular pace (rhythm). For example, if your heart rate is 60 beats per minute, this means your heart is beating at a pace (rhythm) of precisely once every second if you have a regular heart rhythm. This rhythm can be charted using various techniques.
The electrocardiogram or ECG
Do you have heart palpitations, experience shortness of breath after minimal exertion or feel dizzy sometimes? The first thing your GP or cardiologist will do is run an electrocardiogram. This is a straightforward and painless examination which only takes a few minutes, in which ten electrodes are attached to your body (4 on your limbs and 6 on your chest). These electrodes chart the electrical pulses that cause your heart to beat. If the ECG shows abnormalities or the doctor suspects there may be a problem, he may decide to run a second ECG, called an exercise stress test for which you are asked to ride a stationary exercise bike or walk on a treadmill.
An electrocardiogram (ECG) charts the electrical pulses of your heart.
Unfortunately, heart rhythm disorders sometimes stay under the radar in an ECG.
Dr Pieter Vandervoort, cardiologist with Hasselt University and the Ziekenhuis Oost-Limburg (ZOL) (East Limburg Hospital) in Genk: “The big problem with heart rhythm disorders such as atrial fibrillation is that they do not always show up during the examination by the cardiologist. Heart rhythm disorders sometimes occur and disappear again just as quickly. In addition, over 40% of patients don’t experience any symptoms at all. In a lot of cases, a stroke is the first sign of a heart rhythm disorder. By then, it may already be too late.”
The photopletysmogram or PPG
However, there is also another optical technique (a technique that uses light) to measure your heart rhythm.
A photophletysmogram or PPG does not focus on the electrical pulses themselves, but on the effect the beating of your heart has on your blood vessels. With every beat of your heart, blood is pushed out of the heart into the blood vessels. This blood flow that is pumped out of the heart puts pressure on the blood vessel walls, very briefly and ever so slightly stretching them with each beat of your heart. Between two heart beats, the diameter of the blood vessels ‘shrinks’ down again.
With each peak, the photophletysmogram (PPG) measures the dilation and relaxation of the blood vessels as a result of the electrical pulses of your heart.
In association with leading physician Dr Pieter Vandervoort, FibriCheck incorporated this tried and tested technique into a medically certified application for smartphones and smartwatches.
How exactly does this PPG technique work? By lighting your finger tip or your wrist for 60 seconds with the flash light of your smartphone camera or using the light sensors in your smartwatch, the app measures the miniscule changes in the amount of blood that flows through the dilating and relaxing capillaries (the very small blood vessels), based on the amount of light that is reflected. If the capillaries are dilated and therefore contain a lot of blood, a lot of light is absorbed by the blood and just a little is reflected back to the camera. If the capillaries are relaxing, this means they contain less blood which in turn also means the level of light absorbed drops.
Dr Pieter Vandervoort: “By incorporating this PPG technique into a digital application, we are overcoming all the limitations of the medical hardware. The FibriCheck app allows you to turn your smartphone and/or smartwatch into a budget-friendly and accessible medical device that enables you to take measurements on a regular basis either at home or wherever you are. Including at times when you are experiencing symptoms. This gives us valuable data for a timely diagnosis and an appropriate treatment.“