Deep Dive #3 ❤️ Cardiac-Related Wearable Features - The ECG app

If you haven’t read the overview article, start here: https://lnkd.in/g_DjivtU

The regulated ECG app allows users to receive a single lead (Lead 1) ECG waveform with a classification. Learn about how the ECG app works and see real patient examples that show how it can be a supplement for traditional methods of diagnosis or treatment.

Overview of the ECG App - Session-Based 30 Second Lead 1 Reading with Classification

The ECG app is a FDA-regulated feature and is intended for individuals 22 years and older. It is cleared for users who are previously diagnosed with AFib (note: the first version was not, but got expanded with the second version); however it is not recommended for users with other known arrhythmias. It is available on Apple Watch Series 4 or later and all models of Apple Watch Ultra. It is not available on the SE model. While the other deep dive features (high/low heart rate and irregular rhythm notifications) have utilized light sensors, this feature operates differently—using two separate electrodes, one on the back of the watch and one on the digital crown (dial that sticks out on the side of the watch). 

After a 30 second user-initiated session, the app provides a single-lead ECG (Lead I) with a categorization of either sinus rhythm, low heart rate, high heart rate, inconclusive reading or poor reading. There are no notifications that will remind you to use it. A user can export a PDF of the ECG reading, which matches the scale of traditional printed 12-lead ECGs.

Below are images showing from one of my sessions with normal sinus rhythm. The images show the message on the watch after the session, the corresponding ECG reading viewed in the Health App, and the PDF export. You can swipe through the reading in the Health App  and from that ECG detail screen, export the PDF by selecting the blue text “Export PDF”.

Detailed support article here: https://support.apple.com/en-us/HT208955

Category and Messages with Each ECG Reading: 

After manually taking an ECG, a category is listed with a corresponding message (these are taken directly from the regulatory document linked below):

• Sinus Rhythm: A sinus rhythm result means the heart is beating in a uniform pattern between 50-99 BPM.

• High Heart Rate—No Atrial Fibrillation Detected: A high heart rate results means that the heart is beating between 100-150 BPM and does not show signs of Atrial Fibrillation.

• Atrial Fibrillation: An AFib result means the heart is beating in an irregular pattern between 50-99 BPM.

• Atrial Fibrillation—High Heart Rate: An AFib High Heart Rate result means that the heart is beating in an irregular pattern between 100-150 BPM.

• Poor Recording: A poor recording result means that the recording could not be classified because of too much artifact or noise in the waveform. This can happen because for many reasons such as excess movement during a recording, or wearing your Apple Watch too loosely. Certain physiological conditions may prevent a small percentage of users from creating enough signal to produce a good recording.

• Low or High Heart Rate: The ECG app cannot check recordings with a heart rate under 50 BPM or over 150 BPM.

Important caution messaging is provided to help users recognize a key limitation:

• “The ECG app cannot check for signs of a heart attack. If you believe you’re having a medical emergency, call emergency services."

Personal Experience With ECG App And Undiagnosed PVCs:

I have inconclusive readings when I was having frequent PVCs (premature ventricular contractions). Turns out my body doesn’t do well when I have a second triple shot latte in a day combined with stress! For me (being both a patient and a physician), the single-lead ECG helped me identify the issue, though I still needed a 12-lead ECG for confirmation and a rhythm patch monitor for further quantification. The ECG app was useful as a supplement, but didn’t replace traditional diagnostic methods (which is inline with the official instructions for use).

Patient Stories With Undiagnosed AFib and SVT:

1. A 46-year-old discovered persistent AFib using the ECG app, initially disbelieving the results. https://abcnews.go.com/Health/apple-watch-told-46-year-man-irregular-heartbeat/story?id=59726093 

2. A patient with sporadic episodes of heart racing diagnosed with SVT (supraventricular tachycardia) using the ECG app and sharing the strips with their doctor. https://www.wkyt.com/2023/03/30/laurel-co-woman-credits-apple-watch-with-previously-elusive-diagnosis-heart-issue/ 

3. Another patient who had SVT shares ECG strips at baseline and in SVT: https://discussions.apple.com/thread/255123759?sortBy=best 

Troubleshooting for getting a good ECG reading:

If no ECG reading:

• Complete onboarding steps in the Health app.

• Ensure wrist and watch are clean and dry.

For poor readings with artifact, noise, or interference:

• Rest arms on a table or lap.

• Ensure the watch band is snug.

• Move away from electronics that can cause interference.

As a medical provider, you are not required to troubleshoot technical issues with the Apple Watch (or any other consumer device). Refer patients to the official support site, which for the Apple Watch is: https://getsupport.apple.com/ 

Want to learn even more? For those wanting to dive deeper, official regulatory documents are available. Although technical, you can focus on the feature details, study, and performance.

These are the three documents I recommend:

1. Official IFU (Instructions For Use): An official document required for regulatory features. The language is straightforward and includes details on safety, performance, and cautions. This is the link for version 2.0. Available in multiple languages: https://www.apple.com/legal/ifu/ecg/ecg-ifu-2-en_GB.pdf 

INDICATIONS FOR USE:

“The ECG app is a software-only mobile medical application intended for use with the Apple Watch to create, record, store, transfer, and display a single channel electrocardiogram (ECG) similar to a Lead I ECG. The ECG app determines the presence of atrial fibrillation (AFib), sinus rhythm, and high heart rate (no AF detected with heart rate 100-150 bpm) on a classifiable waveform. The ECG app is not recommended for users with other known arrhythmias.

The ECG app is intended for over-the-counter (OTC) use. The ECG data displayed by the ECG app is intended for informational use only. The user is not intended to interpret or take clinical action based on the device output without consultation of a qualified healthcare professional. The ECG waveform is meant to supplement rhythm classification for the purposes of discriminating AFib from sinus rhythm and is not intended to replace traditional methods of diagnosis or treatment.”

1. De Novo Classification Request for ECG app: An official FDA document with the request and grant for the feature. It includes Indications of Use, Limitations, Device Description, and a summary of the testing completed: https://www.accessdata.fda.gov/cdrh_docs/reviews/DEN180042.pdf.

2. 510(K) for the ECG 2.0 App (the second version): https://www.accessdata.fda.gov/cdrh_docs/pdf20/K201525.pdf this document is a summary of the expanded use with this 2.0 version: https://www.apple.com/healthcare/docs/site/Apple_ECG_app_during_COVID-19.pdf 

Current Focus on AFib, but Broader Applications Exist:

A study comparing ECG morphology and interval characteristics of single-lead ECG to 12-lead ECG (74 patients) suggests that improved signal processing could enhance reliability. https://www.heartrhythmjournal.com/article/S1547-5271(22)01091-8/fulltext 

There Are Multiple Wearable Devices with a Single-Lead ECG:

While the above information is specific for the Apple Watch, other devices also offer similar features: 

Samsung ECG Monitoring Application (compatible with Samsung Galaxy Watch): 

• User facing information: https://www.samsung.com/us/apps/samsung-health-monitor/  

• FDA 510(k) document: https://www.accessdata.fda.gov/cdrh_docs/pdf20/K201168.pdf 

Fitbit ECG app: 

• User facing information https://www.fitbit.com/global/dk/technology/ecg  

• FDA 510(k) document: https://www.accessdata.fda.gov/cdrh_docs/pdf20/K200948.pdf 

KardiaMobile (A non-wearable device used in active sessions to generate a single-lead ECG):

• User facing information: https://store.kardia.com/products/kardiamobile 

• FDA 510(k) document: https://www.accessdata.fda.gov/cdrh_docs/pdf21/K211668.pdf 

About the Author: Bronwyn Harris is a practicing physician who enjoys building digital clinical tools that utilize patient-generated health data.

Intended Audience: Any health professional curious about PGHD, whether it is because they come across it in clinical care, are conducting related research, building digital tools or just want to better understand it. If you have any specific questions or topics that you would like to see in the future, please message me!

What is PGHD? There is not a singular definition, but I like this one "Patient-generated health data (PGHD) are health-related data created, recorded, or gathered by or from patients (or family members or other caregivers) to help address a health concern.” https://www.healthit.gov/topic/scientific-initiatives/pcor/patient-generated-health-data-pghd

Examples of PGHD include: symptoms tracked by a patient, heart rate data, step count, BP measurements and treatment history

Disclaimer: The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. It is also not a complete review of the topic. Specifics about wearable data and smartphones often change with new software updates, so information above may become out of date. While I worked at Apple in the past, I wasn’t directly involved in any of these features and all the information provided here is from publicly available sources.