Apple Watch Series 4 at the Steve Jobs Theater during an event to announce new Apple products Wednesday, Sept. 12, 2018, in Cupertino, Calif.

This column originally ran on Medium on Sept. 17, 2018.

Apple's new watch sounds like a win for anyone interested in their heart health. It will notify wearers of a slow or irregular heart rhythm, and it can take a basic electrocardiogram (ECG), a recording of the electrical activity of the heart.

During Apple's presentation of the new watch on Sept. 12, the company boasted of its FDA clearance and basked in praise from American Heart Association president Dr. Ivor Benjamin.

As a heart doctor, my opinion is that if you think an Apple Watch is nifty, buy one. But do not buy it for your health. It will not improve your health, and it could even bring you harm.

In particular, I'm concerned about the problems that arise when we screen healthy people.

I concede that early detection seems like a good idea, especially for atrial fibrillation (AF). AF can increase a person's risk of stroke, and many people who have AF don't know it. We also have effective ways to treat it, including drugs that block clotting—called anticoagulants—that can reduce the risk of stroke in patients with AF and other risk factors, such as high blood pressure or diabetes.

The first obstacle when it comes to AF screening is understanding that the vast majority of people do not have AF, but most people do have normal variation of their heart rhythm, which can mimic AF. Benign premature beats, for instance, can make your rhythm irregular.

This makes ECG accuracy a problem. Recently, I co-wrote an editorial in JAMA-Internal Medicine, where my co-authors and I reviewed studies of AF screening with medical-grade 12-lead ECGs, which are more accurate than the one-lead ECG used in the Apple Watch.

The specificity of an ECG (its ability to correctly identify people who don't have AF) is around 90 percent. That may sound good, but the 10 percent of the time that an irregular rhythm is falsely labeled as AF will exert a massive effect in large populations—like the millions of people who may soon own the new Apple Watch.

To put this into perspective, let's use a round number of 1 million watch owners. We know that about 1 percent, or 10,000 people, will have AF, and 990,000 will not have AF. If the watch is wrong 10 percent of the time, that means nearly 100,000 people will be falsely diagnosed with AF.

Sending hundreds of thousands of wrongly diagnosed people to the doctor scares me. In addition to needless anxiety and costs, this is hazardous because while some doctors will simply reassure the patient, many other doctors will order tests. Since all medical interventions come with risks, many people will suffer harm from unnecessary tests and procedures.

Another snag in heart rhythm screening stems from a poor understanding of AF. Despite decades of research, doctors still argue about the causes of AF and its treatments.

In 2017, Harvard researchers published a paper exposing a core deficit in AF knowledge. In their review of 34 studies of hundreds of thousands of patients with AF who were not treated with clot-blocking drugs, they found wide variation in the rate of stroke, which means we don't really know the stroke risk of having an AF diagnosis.

Even if the Apple Watch identifies true AF, we can't be sure the treatment will do more good than harm. While anticoagulants reduce the rate of stroke when used in patients with multiple risk factors—like high blood pressure, diabetes, and older age—these patients are typically diagnosed with AF using ECGs done in doctor's offices, usually because they are experiencing symptoms.

I worry that the Apple Watch will discover lots of short-duration AF or AF occurring in younger people with fewer risk factors. Given their lower risk of stroke, it's unlikely that anticoagulant drugs will deliver similar benefits. But anticoagulants do increase the risk of bleeding.



The truth is that preventive health is far more complicated than identifying irregular rhythms from a watch. When you endeavor to make healthy people healthier, you always risk making them worse.

John Mandrola is a cardiac electrophysiologist at Baptist Health Louisville.