Whenever you take an ECG on the Apple Watch, there’s a prominent warning that Apple Watch never checks for heart attacks.

Apple Watch does not check for heart attacks using its ECG (it does check for abnormal heart rhythms)

In this post, we’ll explain which heart conditions the Apple Watch ECG can detect, blood tests and imaging that do predict heart attack risk, and how to use Apple Watch as part of a comprehensive heart health plan.

Apple Watch’s ECG detects abnormal heart rhythms

Apple Watch’s ECG (electrocardiogram sensor) is FDA-cleared as a medical device to detect the most common abnormal heart rhythm, atrial fibrillation. Atrial fibrillation causes 1 in 4 strokes. In addition, Apple Watch’s heart rate monitor has an FDA clearance to alert people to likely atrial fibrillation via irregular rhythm notifications.

An irregular rhythm notification on Apple Watch, for an abnormal heart rhythm (not heart attack)

If you get an irregular rhythm alert, take it seriously. In the Apple Heart Study, 84% of participants who received an irregular rhythm notification while wearing an ECG patch were found to have atrial fibrillation.

Why Apple Watch’s ECG cannot detect heart attacks

A heart attack happens when bloodflow to part of your heart is stopped. In other words, when one of your coronary arteries—one of the arteries that supplies blood to the heart muscle itself—is blocked.

First, a normal ECG does not definitively rule out a heart attack. It’s possible to have a normal ECG but elevated troponin, even when using hospital equipment.

Second, the Apple Watch’s ECG only measures 1 of 12 ECG leads. The 12-lead ECG in a hospital measures 12 “angles” through the heart. Some of the angles may show the heart attack (if they go through the affected portion of heart muscle) and some won’t. This is why Apple Watch can’t detect heart attacks (but can detect abnormal heart rhythms, where the entire heart is in the same rhythm).

Heart attack risk can be predicted with blood biomarkers

While Apple Watch can’t predict a heart attack, blood tests can. It’s possible to predict both your lifetime and 10-year risk of a heart attack by using blood biomarkers like ApoB, LDL and HDL cholesterol, a1c, and your blood pressure.

Empirical Health’s advanced cardiovascular panel includes all the biomarkers you need to predict heart attack risk for under $200. It includes advanced heart health biomarkers such as ApoB, Lp(a), lipid particle size, LDL, HDL, total cholesterol, and 50+ other numbers.

During a heart attack, doctors use a 12-lead ECG and blood tests

When a patient arrives in the emergency room with a suspected heart attack, doctors use several tools to confirm a heart attack. First, they use a 12-lead ECG (placed on the chest, back, arms, legs) to view electrical signals that show many “angles” through of the heart. If they see that the ST segment (one part of the ECG) is elevated, then they know the patient is having a type of heart attack called a STEMI (ST elavation myocardial infarction). Second, they perform a blood test for troponin, a protein which is released when heart muscle is dying. Dependong on the results, the doctors will give the patient different types of treatment: clot-busting drugs, coronary artery bypass graft (CABG) surgery, stenting, and so on. Needless to say, if you’re currently having a heart attack, please call 911.

Research showed the Apple Watch’s ECG can be used as a 9-lead ECG for heart attack detection

Researchers at the Texas Heart Institute came up with a clever proof-of-concept study that uses the Apple Watch as a 9-lead ECG. In their study, participants wore the Apple Watch in a variety of different positions on the chest, arms, legs, and so on:

While this approach is very clever, it’s not necessarily a practical way to use an Apple Watch during a heart attack in the real world.

How to use your Apple Watch for comprehensive heart health

Do you want to create a comprehensive plan to improve heart health, including advanced biomarkers, nutrition, exercise, and medication? Download Empirical Health for Apple Watch or Android in order to create your customized plan.