By Nicholas Tullo, MD

The Apple Watch, first released in April of 2015, is a technological breakthrough in many ways. Although it was designed to allow users to interact with their phone to perform tasks like making calls, retrieving email, and playing music, the hidden feature that could potentially save lives is the heart rate sensor. The watch is able to utilize software that monitors heart rates quite accurately, and this is now being studied by Stanford University to see how capable it might be to detect atrial fibrillation.

Atrial fibrillation (AF) is the most common heart rhythm disturbance that affects adults.  Most people with atrial fibrillation have symptoms like palpitations, weakness, lightheadedness, shortness of breath, and exercise intolerance.  However, as many as 1/3 of AF patients may have little or no symptoms. Although AF can adversely affect quality of life in patients with symptoms, this is a minor problem compared with the most serious consequence of AF, which is stroke. AF increases the risk of stroke 5-fold, especially if you are 65 years or older, have hypertension, diabetes, vascular disease, a history of heart failure, or especially if you have had a prior stroke. Detecting AF in patients with little or no symptoms is challenging. Often, heart monitors are used on a short-term basis (one day, one week or one month) to see if AF occurs. These monitors are cumbersome to wear and usually miss AF episodes that occur less than once a month.

Heart rate trackers, mostly used by athletes or people who want to stay healthy, are generally worn on the wrist. These devices are capable of detecting color changes in the skin, using a form of photocell, to indirectly measure the pulse rate. Companies such as FitBit, Garmen, and Everlast market devices intended to help people track their activity and heart rate during exercise or throughout the day. The Apple Watch is capable of detecting the heart rate through a sophisticated system of green LED lights and light-sensitive photodiodes. The device gathers signals from four distinct points on the wrist, and comparative studies have suggested that the accuracy of the Apple Watch exceeds that of any of the other devices on the market. Since atrial fibrillation usually results in a sudden change in heart rate, the Apple Watch is well suited to monitor such changes, and a variety of apps are currently available that will display a graphical representation of heart rates over the course of a few hours or a few days.

Stanford University is now working with Apple, and together they created the Apple Heart Study app, which is designed to prospectively study how effective the Apple Watch is to detect heart rhythm changes. Potentially, a patient with atrial fibrillation would receive an alert from their watch, so they can then inform their physician. The physician might recommend blood thinners in high-risk patients with AF, since anticoagulant therapy can reduce the risk of potentially fatal strokes in AF patients. 

There are additional advantages of having an accurate means of tracking your heart rate throughout the day. Some patients complain of palpitations and feel their heart racing. It is very helpful for their doctor to be able to review their actual heart rates as measured by the Apple Watch. Heart rates in the range of 90 to 110 beats per minute usually indicate sinus tachycardia (a benign rhythm), while heart rates in excess of 150 bpm usually suggest more serious arrhythmias like supraventricular tachycardia or atrial flutter / fibrillation.

The Apple Heart Study is another way that technology companies are helping patients to become more involved with their own health. Hopefully, engaged patients will partner with their physicians to identify problems before they become serious. If your doctor has mentioned to you that you might have atrial fibrillation, you can discuss whether monitoring your heart rate with an Apple Watch would be worthwhile, since it may provide valuable long-term information about the existence of intermittent AF.

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