Recently there has been an explosion in consumer wearable smart devices. It is estimated that 1.1 billion devices were in use worldwide in 2022. These devices can detect and monitor a variety of health-related parameters including heart rate and arrhythmias (abnormal heart rhythms). Devices include smartwatches worn on the wrist, fitness bands with chest strap, and a stand-alone handheld single lead electrocardiogram (EKG) monitor. Smart devices can monitor heart rate and determine if there is an arrhythmia using two methods. The first method is photoplethysmography (PPG). The second way is to obtain an actual EKG strip, either a single lead or multiple leads, using electrotrodes as would be done with an EKG in a doctor’s office. PPG works by sending light pulses to the skin. The intensity and pulsatility of light reflected from the blood vessels can determine heart rate and algorithms can provide an estimate of whether there is an arrhythmia. Smartwatches such as Apple Watch (series 4 or later) and Samsung Galaxy Watch 3 utilize both PPG and EKG. PPG is used for routine monitoring, but the user can be prompted to obtain a single lead EKG by holding the crown of the watch for 30 seconds. The KardiaMobile device is connected to a phone but is a stand-alone monitor. It has two pads and the user places a finger on each pad to record a single lead EKG. Smartwatches using PPG can accurately detect heart rate, but accuracy drops off with activity. One study showed a 30% reduction in accuracy during exercise. For a more accurate determination of heart rate with exercise, a chest strap using PPG can be used. Patients often see their doctor for advice about arrhythmias that are detected on their smart devices. How accurate are the readings? What should one do if the device says there is atrial fibrillation (Afib)?
Before diving into wearable devices and Afib, a few words about Afib itself. Afib is a very common arrhythmia. In this condition, the upper chambers of the heart (the atria) fibrillate, beat chaotically, not in a regular coordinated manner. When the atria fibrillate, blood doesn’t flow into the lower heart chambers (the ventricles) efficiently and blood can stagnate in the atria. If blood is not flowing it can form clots. These clots break off and can cause a stroke. To treat this and prevent a second stroke in someone who already has had a stroke, blood thinners are prescribed. How important is the Afib/stroke connection? In a patient with a stroke, or a “mini-stroke” (TIA), a cause for the stroke cannot be found in 30%. This is called cryptogenic stroke, a stroke of unknown origin. It turns out that Afib is a major cause of cryptogenic stroke. If a patient is hospitalized with a stroke and a cause cannot be found, they often are prescribed a monitor to wear for one month to see if they have Afib. If Afib is found, they are prescribed a blood thinner. The use of blood thinners in Afib is quite effective, but comes at a cost. These medications can cause bleeding. In a patient with Afib, who should be placed on a blood thinner? The answer is not easy and there is lots we know, and still lots we don’t know. Some Afib patients are straightforward and should be on blood thinners. These include patients who are known to be in Afib for 48 hours of more. Also, patients with Afib and a history of stroke or mini-stroke should be on one of these agents. Patients with Afib who haven’t had a stroke but who are at high risk for a stroke (older patients, women, diabetics, heart failure patients, hypertensives, and patients with vascular disease) should be on a blood thinner. If a patient is not in one of these categories, how much Afib is needed before committing them to a blood thinner: an hour of Afib? several hours of Afib? a day of Afib? Unfortunately, we don’t yet know that answer, but a recent study did shed some light. The study looked at pacemaker patients without prior history of Afib. A pacemaker can be interrogated and can tell precisely how long a patient has an arrhythmia such as Afib. The study looked at pacemaker patients who had short duration episodes of Afib; the average time in Afib was about three hours. Patients who were given a blood thinner did not have fewer strokes than patients who were not on a blood thinner. In fact giving the blood thinner caused harm, more patients had bleeding. So, putting patients on a blood thinner for short duration episodes of Afib does not prevent strokes and may be causing harm. We still do not know the burden of Afib necessary to start treating to prevent a stroke.
How accurate are smartwatches and KardiaMobile devices in detecting Afib? More and more studies are being performed to check the validity of these devices. One study found that Apple Watch and Samsung Galaxy Watch were 80% accurate in picking out Afib, while KardiaMobile was 74% accurate. One issue with the devices was the high number of inconclusive tracings: Apple 18%, Galaxy 17%, KardiaMobile 26%. Another study of KardiaMobile also showed 74% accuracy and 16% of tracings could not be classified. The bottom line is that these devices are readily available, not very expensive (KardiaMobile is less than $100), reasonably accurate and the technology will only continue to improve.
So, what should you do if your smartwatch tells you that you are in Afib? First, realize that these devices should only be used as a screening tool. See your doctor, bring your phone or tracings for your doctor to review. Afib should be confirmed with medical grade devices such as a Holter monitor (worn for one to three days) or an event monitor (worn for two to four weeks) or an implantable recorder (used for months to years). Next discuss with your doctor whether you should be on a blood thinner, remembering that short duration episodes of Afib likely don’t need to be treated. However, if you have had a stroke, or mini-stroke (TIA) especially if cryptogenic, then starting a blood thinner may be appropriate. Even if the detection of Afib by your smart device doesn’t lead to a blood thinner, it can make a difference in your treatment plan. Medications may be changed to try to avoid Afib. In addition, triggers for Afib can be discussed and corrected (treating high blood pressure or sleep apnea, decreasing or eliminating alcohol, starting an exercise program or weight loss). Listen to your body and watch your watch.
