The Ultimate Cardiologist's Guide to the Smartwatch ECG

Author: Marina

May. 20, 2024

The Ultimate Cardiologist's Guide to the Smartwatch ECG

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Introduction to Smartwatch ECG: Revolutionizing Heart Monitoring

The advancement in ECG technology is nothing short of revolutionary. Previously, experiencing concerning symptoms meant a visit to the doctor for an ECG, dialing emergency services, or rushing to the hospital. The introduction of the Holter monitor in 1962 changed this landscape by enabling continuous ECG recording at home, albeit only for 24 hours. Next, extended ECG monitors, such as the convenient ECG patch monitors, pushed the boundaries to weeks-long monitoring with a doctor's prescription as a requisite.

Fast forward to the present, and we now have heart monitors that reside on your wrist, the smartwatch, which requires no prescription. It allows seamless pulse checks multiple times a day, and an ECG can be taken merely by touching the watch’s crown. Such an innovation was unimaginable to Dr. Holter fifty years ago, and even today, the sophistication of these devices continues to impress, including myself when I first tried the Apple Watch ECG.

So, what can your smartwatch ECG do? What details about your heart can it reveal? What functionalities does this wrist-worn heart monitor encompass? In this article, I’ll guide you through these questions to clarify your smartwatch’s intentions and limitations.

Understanding the Electrocardiogram for Cardiologists

For cardiologists, the ECG is a fundamental diagnostic tool, offering an electrical snapshot of the heart’s activity. It helps ascertain whether the heart's electrical pathways are functioning properly, detect heart injuries, identify an enlarged heart, and diagnose other medical conditions.

Smartwatch ECGs provide a limited perspective compared to the comprehensive 12-lead ECGs available in medical facilities. You get a single lead, “lead I,” instead of multiple angles. Though limited, this single-lead ECG is invaluable for those random moments when a quick check becomes essential. Much like a professional photographer’s notion that the best camera is the one you have, the ability to take a single-lead ECG on demand is priceless.

Notably, the ECG function on smartwatches like the Apple Watch is designed specifically to detect Atrial Fibrillation (AFib). AFib is a prevalent arrhythmia affecting over 1% of the US population and is linked to an increased risk of stroke and other adverse outcomes. Hence, focusing the device’s features on identifying this abnormal heartbeat makes sense. The Apple Watch ECG is FDA-approved primarily for this purpose, flagging only AFib as a diagnosable condition when you use it.

The accuracy of smartwatches in detecting AFib from the ECG is commendable, though not perfect. Some limitations exist, such as difficulty in interpreting very fast heart rates, potential misreadings due to electrical noise from arm movement, or low signal strength. Despite these challenges, the smartwatch ECG remains proficient in AFib detection.

Moreover, the ECG app stores recordings, allowing you to convert them into PDFs for healthcare provider consultation or personal review. As a cardiologist, I find the quality of these tracings adequate for analysis. On numerous occasions, patients identified AFib through their smartwatches, and I verified it by examining their PDF tracings. While the smartwatch only provides a single lead, much can still be inferred by a skilled professional beyond AFib detection.

A clean ECG recording can illuminate the heart’s rhythm—how it beats electrically. In a “normal sinus rhythm,” the heart's top chambers (atria) and bottom chambers (ventricles) contract in an organized manner. AFib is one among various abnormal heart rhythms that can cause palpitations, fatigue, or shortness of breath. While the ECG app won’t identify other abnormalities besides AFib, you can send the ECG PDF to your healthcare provider or use services like Qaly for a technician’s interpretation.

In certain cases, a single-lead ECG can detect heart attacks—caused by blood vessel blockages around the heart—but this method is unreliable for such diagnoses. Structural heart anomalies also require a multi-lead ECG and additional tests. The smartwatch ECG cannot diagnose strokes, lung issues, or other serious cardiovascular conditions either. Hence, new symptoms should always be discussed with your doctor instead of solely relying on your smartwatch ECG.

Can a Smartwatch with ECG Accurately Detect AFib?

You might have come across accounts of individuals who first learned about their irregular heartbeat through their ECG-capable smartwatch. As the smartwatch user base grows, such narratives are becoming increasingly common.

While these stories might seem almost too good to be true, they highlight the potential role of smartwatches with ECG functionalities in identifying lurking heart issues.

Dr. Maged Amine, an interventional cardiologist at Houston Methodist, affirms that smartwatches can indeed assist in the screening and monitoring of Atrial Fibrillation (AFib)—a common arrhythmia. The FDA has even recognized Apple's AFib History Feature as a qualified tool for evaluating AFib burden in clinical settings.

"AFib involves an irregular, often rapid heart rhythm, which compromises heart function," explains Dr. Amine. "It's common and frequently asymptomatic, with a stroke sometimes being the first sign due to heart-related blood clots."

AFib significantly elevates stroke risk, emphasizing the need for early detection. Dr. Amine points out, "With constant wearable ECG monitoring, we have a novel, widespread screening method for AFib," improving both initial detection and long-term monitoring.

How ECG Helps in Detecting AFib

"Our goal is to detect AFib before it leads to stroke," says Dr. Amine. "Whether conducted in-office or through home-worn devices, ECG has been a reliable method for AFib detection for decades." 

An ECG tracks your heart's rate, revealing if your rhythm is normal or irregular. Traditionally, it requires electrodes on your chest and other body parts, transmitting data to a computer for doctor-reviewed analysis. This is essential for symptoms like palpitations, chest pain, or shortness of breath, and is part of routine screening for those at high cardiovascular risk or with a familial history of heart disease.

"AFib's asymptomatic nature means broader, simpler screening is beneficial," Dr. Amine adds. "Smartwatches with ECG capabilities might bridge this screening gap, especially for asymptomatic individuals." Past studies have shown home-based ECG devices to be more effective than traditional screenings for AFib.

Are Smartwatches with ECG Really Capable of Detecting AFib?

The ECG technology in smartwatches uses LEDs to detect blood flow and heart rate through your skin. This data is processed by algorithms to determine heart rhythm irregularities. Throughout the day, your smartwatch collects these measurements and alerts you if an abnormal rhythm is detected.

Considering the difference from conventional clinical ECG technology, skepticism about a smartwatch’s capability is understandable. However, Dr. Amine asserts, "The ECG technology in smartwatches is highly accurate, with brands like Apple, Fitbit, and Samsung leading the way." Several smartwatch series from these brands are FDA-approved for AFib detection.

Receiving an alert from your smartwatch warrants a doctor's consultation for proper testing and confirmation or exclusion of AFib.

ECG-Capable Smartwatches and Long-Term AFib Monitoring

The significance of on-demand ECG technology in wearable devices is evident, especially for AFib screening. However, these devices are equally valuable for long-term monitoring in diagnosed AFib patients.

AFib can recur intermittently, necessitating continuous monitoring to promptly catch any recurrence. Implantable ECG devices are sometimes used for extended rhythm tracking post-treatment, but such procedures aren't suitable for everyone.

Dr. Amine acknowledges, "Smartwatches offer almost the same accuracy as implantable devices, minus the invasive procedure. They’re incredibly efficient."

In addition, smartwatch monitoring might someday help reduce the dependency on blood thinners after AFib treatment. "Treatment often involves rhythm-regulating medications or ablation therapy along with blood thinners to mitigate stroke risk. The dilemma lies in determining when it's safe to discontinue blood thinners due to their inherent risks," explains Dr. Amine. Enhanced smartwatch monitoring could guide timely treatment re-initiation, potentially reducing reliance on blood thinners.

"Smartwatches could revolutionize long-term AFib monitoring, ensuring prompt intervention if the condition recurs," adds Dr. Amine.

Smartwatch ECG Isn't a Substitute for Healthy Lifestyle Choices

Despite the advantages of smartwatch ECG, managing AFib also necessitates consistent check-ins with your cardiologist and maintaining heart-healthy lifestyle habits, including:

  • Following a balanced diet
  • Regular physical activity
  • Avoiding excessive alcohol
  • Maintaining a healthy weight

Dr. Amine emphasizes, "Your smartwatch serves as an additional protective measure, providing valuable data for your doctor and aiding in condition monitoring, potentially reducing emergency visits. I envision prescribing these devices for AFib management in the future, despite their current cost."

(Related: Can a Fitness Tracker Help Improve Your Heart Health?)

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