How smartwatch heart monitoring saves lives: cases and global data

A global problem that smartwatches are beginning to address

Non uniform distribution A 2024 review of the global burden of Atrial Fibrillation ( PMC 2024) looked at the incidence of AFib around the world. They found the highest incidence rates in North America, Australasia and western Europe with age-standardised incidence rates of 88.23, 73.34 and 68.19 cases per 100,000 population respectively.

In East Asia the rates were 46.69 cases per 100,000 population and were falling rather than rising. As with previous cardio vascular and metabolic risk differences there were notable differences in prevalence between regions. China and parts of South East Asia had some of the highest prevalence rates in some analyses, which was different to the conditions seen in North America and Europe.

Why AFib is the primary risk

Atrial fibrillation to become a major health burden in Europe Europe will face a growing epidemic of atrial fibrillation (AFib) in the coming decades, researchers conclude in a study published in the Lancet Regional Health Europe journal. Based on the growing population and better diagnosis, the number of AFib sufferers in Europe is expected to double from 8.8 million in 2010 to 17.9 million by 2060. The factors that caused the rise in AFib incidence have not changed, the scientists say. Europe already has the same level of AFib as it has now – it is just being detected more often. Lancet Regional Health EuropeProjects AFib prevalence in Europe rising from 8.8 million in 2010 to 17.9 million in 2060. A doubling. The primary driver is an aging population combined with improved detection. The condition existed before at similar rates; it was simply less often found.

Factors caused rise AFib

The factors that caused the rise in AFib incidence have not changed, the scientists say. Europe already has the same level of AFib as it has now – it is just being detected more often. Lancet Regional Health EuropeProjects AFib prevalence in Europe rising from 8.8 million in 2010 to 17.9 million in 2060. A doubling. The primary driver is an aging population combined with improved detection. The condition existed before at similar rates; it was simply less often found.

The notion of an affordable, long-lasting heart rhythm monitor that you can just wear all the time and never have to replace the battery is often met with dismissal as a luxury product that no one really needs. This is strange, given that there are 59 million people with unrecognized arrhythmias and many more at risk from heart disease. So the idea of a wearable heart rate monitor that never needs a battery charge and gives you an up-to-the-second readout of your current heart rhythm is hardly a luxury product. Instead it’s a public health good.

How two sensors work together to catch cardiac events

The PPG sensor works continuously and passively. The ECG sensor requires a deliberate gesture. Together they cover what neither can detect alone.

Smartwatches that can track the heart now use two new technologies to see what is happening inside the body. They include: Photoplethysmography (PPG): green light is shone through the skin and is detected by the other side of the watch where it is turned into a signal that is affected by changes in the light absorbance caused by the natural pulsation of blood in the vessels, which occurs with every heartbeat. In this way the heart rate and changes in the heart rate such as heart rate variability and arrhythmia (irregular rhythms) as well as continuous monitoring of blood oxygen saturation can be monitored at all times by the watch using the PPG technology. PPG (photoplethysmography): green LEDs shine onto the skin, a photodiode measures reflected light, and blood volume changes with each heartbeat produce a detectable optical signal. PPG enables continuous background monitoring of heart rate, rhythm irregularities, heart rate variability, and blood oxygen saturation.

How the sensors detect rhythm

In this way the heart rate and changes in the heart rate such as heart rate variability and arrhythmia (irregular rhythms) as well as continuous monitoring of blood oxygen saturation can be monitored at all times by the watch using the PPG technology.PPG (photoplethysmography): green LEDs shine onto the skin, a photodiode measures reflected light, and blood volume changes with each heartbeat produce a detectable optical signal. PPG enables continuous background monitoring of heart rate, rhythm irregularities, heart rate variability, and blood oxygen saturation.

The second is the ECG sensorSecondly, is the ECG sensor, which is available on Apple Watch Series 4 and later, Samsung Galaxy Watch 4 and later and the Withings ScanWatch. When you press the digital crown or the rear button of your watch, a circuit is created through your body and records a single-lead electrocardiogram (ECG) for 30 seconds. Our algorithm analyzes the ECG signal for the hallmarks of an irregular R-R interval, characteristic of atrial fibrillation.

Both algorithms are used in a triage pair configuration. The PPG sensor is always in passive monitoring mode. When an arrhythmia is detected by the Primary Analysis algorithm, the device will signal the patient to take an ECG reading to verify the rhythm that triggered the arrhythmia detection. The combination of both algorithms in a triage pair increases the combination of sensitivity and clinical value when compared to each individual algorithm alone.

Six documented cases where a wrist alert changed the outcome

Continuous monitoring without removing your watch

These are not case studies from a medical journal. These are people who were wearing a consumer device and were told something was wrong before they knew it themselves.

Tech that unites two worlds for the serious watch aficionado: A sports smartwatch was invented to be used while continuously monitoring your health and wellbeing. For the luxury watch collector, the constant choice is between giving up the tech and wearing one of their precious watches. With the Smartlet, the user no longer has to experience the “down time” between wearing tech or their luxury watches. Instead, they are able to continuously monitor their health, while also being able to appreciate wearing an exquisite mechanical watch.

419,297 participants: what the Apple Heart Study found

The Apple Heart Study was published in the New England Journal of Medicine in 2019. It is the largest study of any consumer-grade smartwatch cardiac screening device. The study recruited 419,297 Apple Heart Study app users in the United States over an 8-month period. Participants all had an Apple Watch and the PPG signals from the watch were continuously monitored for arrhythmias indicated by an abnormal pulse pattern suggestive of atrial fibrillation. New England Journal of Medicine in 2019, remains the largest real-world assessment of consumer smartwatch cardiac screening. Over 419,297 participants enrolled over eight months across the United States. Apple Watch PPG sensors monitored continuously for irregular pulse patterns suggesting possible atrial fibrillation.

Participants all had an Apple Watch and the PPG signals from the watch were continuously monitored for arrhythmias indicated by an abnormal pulse pattern suggestive of atrial fibrillation. New England Journal of Medicine in 2019, remains the largest real-world assessment of consumer smartwatch cardiac screening. Over 419,297 participants enrolled over eight months across the United States. Apple Watch PPG sensors monitored continuously for irregular pulse patterns suggesting possible atrial fibrillation.

Out of the 2,161 users who received an alert, 34% (or 746) had atrial fibrillation as determined by an ECG patch. The positive predictive value of the algorithm was 0.84. The study also found that 57% of alert recipients saw a healthcare provider within 90 days of being alerted to potential abnormal heart rhythms. The study's finding that a cardiac alert triggered a clinically significant outcome in a substantial proportion of recipients among a population of otherwise healthy and unmonitored wearable smartwatch users has potential for important clinical and public health implications. The study was carried out in a general population of smartwatch users, rather than in individuals already under clinical cardiac monitoring. 34 percent were confirmed to have atrial fibrillationWhen an ECG patch was subsequently applied. The positive predictive value of the algorithm reached 0.84. Of those notified, 57 percent contacted a healthcare providerWithin 90 days as a direct result of the watch alert. These outcomes reflect real-world behavior among everyday smartwatch users, not patients already under cardiac surveillance.

Study's finding cardiac alert triggered

The study's finding that a cardiac alert triggered a clinically significant outcome in a substantial proportion of recipients among a population of otherwise healthy and unmonitored wearable smartwatch users has potential for important clinical and public health implications.

The study was carried out in a general population of smartwatch users, rather than in individuals already under clinical cardiac monitoring.34 percent were confirmed to have atrial fibrillationWhen an ECG patch was subsequently applied. The positive predictive value of the algorithm reached0.84. Of those notified,57 percent contacted a healthcare providerWithin 90 days as a direct result of the watch alert. These outcomes reflect real-world behavior among everyday smartwatch users, not patients already under cardiac surveillance.

“Clinical ECGs are taken at the most convenient time during a clinical visit and are therefore, by definition, a snapshot of cardiac rhythm at a single point in time. AFib, however, is an episodic disorder, and it is unlikely that the rhythm would be abnormal at that specific time.

Cardiac rhythm during periods abnormal

The cardiac rhythm during periods when an abnormal episode is likely to occur can be recorded by ambulatory monitoring of a wearable device between clinical visits. So the irregular episode of AFib, which may occur months after the last clinical visit is recorded when it actually occurs rather than when it occurred last.” - Study Authors

Accuracy data from peer-reviewed literature

A systematic review and meta-analysis published in JACC Advances in 2025 combined data from 26 studies involving 17,379 patients from the United States, Europe, Asia and Australia. The review found that current smartwatches had a pooled sensitivity of 95% and a pooled specificity of 97% for AFib detection with an area under the curve of 0.97. An expert analysis published in the Journal of the American College of Cardiology in 2024 (released in 2024) concluded that consumer-grade smartwatches have “very high sensitivity and specificity” for the detection of AFib, and that any detections should be reviewed by a doctor before taking any action. JACC AdvancesIn 2025, covering 26 studies and 17,379 patients from multiple countries, found that current smartwatches achieve a pooled sensitivity of 95 percentAnd specificity of 97 percentFor atrial fibrillation detection, with an area under the curve of 0.97. The American College of Cardiology's 2024 expert analysisConfirmed that consumer-grade smartwatches achieve "very high sensitivity and specificity" for AFib, while noting that physician confirmation is required before any clinical action.

An expert analysis published in the Journal of the American College of Cardiology in 2024 (released in 2024) concluded that consumer-grade smartwatches have “very high sensitivity and specificity” for the detection of AFib, and that any detections should be reviewed by a doctor before taking any action.JACC AdvancesIn 2025, covering 26 studies and 17,379 patients from multiple countries, found that current smartwatches achieve a pooled sensitivity of95 percentAnd specificity of97 percentFor atrial fibrillation detection, with an area under the curve of 0.97.

TheAmerican College of Cardiology's 2024 expert analysisConfirmed that consumer-grade smartwatches achieve "very high sensitivity and specificity" for AFib, while noting that physician confirmation is required before any clinical action.

Our team updated our 2026 npj Digital Medicine living systematic review, which as of March 2026 scanned 82 studies and heart rate data from 430,052 individuals. The average bias of wearable derived heart rate measurements compared to gold-standard ECG-derived heart rate measurements for clinical applications was 0.27 bpm. Heart rate measurement by wearables are considered highly accurate for clinical use by both strict and relaxed definitions, at rest and during moderately rhythmic motion. 2026 npj Digital Medicine living systematic review, covering 82 studies and 430,052 participants, found a mean bias of 0.27 bpm versus clinical ECG reference. At rest and during moderate rhythmic exercise, accuracy is clinically acceptable by any standard applied.

Heart rate measurement by wearables are considered highly accurate for clinical use by both strict and relaxed definitions, at rest and during moderately rhythmic motion.2026 npj Digital Medicine living systematic review, covering 82 studies and 430,052 participants, found a mean bias of 0.27 bpm versus clinical ECG reference. At rest and during moderate rhythmic exercise, accuracy is clinically acceptable by any standard applied.

Why wearing position does not affect cardiac monitoring

Smartlet Smartwatch is designed to be worn on the inner side of the wrist and the PPG signals are captured using reflectance optics, with the LED on one side of the skin, and the photodiode on the other side, emitting light that is scattered from the capillary microvasculature of the wrist tissue. No knowledge of the gravity or the orientation of the wrist is required.

The ECG signal is captured by forming a current path through the body using the digital crown button, which is activated by applying sufficient pressure to the skin, which does not require any knowledge of the orientation of the body. The 3-axis accelerometer and gyroscope used in the fall detection and activity tracking are always ready to use, in any orientation.

Skin contact has been cited by numerous peer reviewed scientific papers as the single largest factor affecting PPG signal quality. When we looked at the 24 hour of Free Living PPG data from the APMC study, we determined that Sensor to Skin Motion was actually the largest contributor to the degradation of the signal. Our Pod keeps the Apple Smartwatch in constant contact with the inner surface of the wrist, thereby ensuring that the required Sensor to Skin contact for working out as well as for continuous activity monitoring is always present as Apple’s Support page recommends. skin contact. A PMC studyExamining 24-hour free-living PPG data found that sensor-to-skin movement was the primary source of signal degradation. Smartlet's pod keeps the smartwatch pressed against the inner wrist, maintaining the consistent skin contact that accurate monitoring requires - the same condition that Apple's own support documentationRecommends for workouts and continuous monitoring.

Our Pod keeps the Apple Smartwatch in constant contact with the inner surface of the wrist, thereby ensuring that the required Sensor to Skin contact for working out as well as for continuous activity monitoring is always present as Apple’s Support page recommends.skin contact.

APMC studyExamining 24-hour free-living PPG data found that sensor-to-skin movement was the primary source of signal degradation. Smartlet's pod keeps the smartwatch pressed against the inner wrist, maintaining the consistent skin contact that accurate monitoring requires - the same condition thatApple's own support documentationRecommends for workouts and continuous monitoring.

Compatible smartwatches with cardiac monitoring

Questions fréquentes

How many people worldwide have atrial fibrillation?

Global Burden of Disease Study 4 (GBD4) published in The Lancet estimated that the global prevalence of AFib/AFL was 52.55 million in 2021. The prevalence of AFib/AFL had increased by 77% from 33.5 million (95% uncertainty interval 30.3-37.2) between 2010 and 2019 to 59 million (57–62). Reference: EP Europace 2024, Lancet/PMC 2024. EP Europace 2024, Lancet/PMC 2024.

Age group Focal region Prevalence (per 100,000) 95% CI Europe (Western) Europe (projected 2060) 745.07 700.43 to 794.23 1,031.09 964.51 to 1,102.44 913.63 845.73 to 986.03 17.9 million (2 times 8.8) Source: PMC global impact review 2024, The Lancet Regional Health Europe 2024. The focal region also includes East Asia. PMC global impact review 2024, The Lancet Regional Health Europe 2024.

Yes. PPG-based irregular rhythm detection is based on reflectance optics and not on wrist position, on the inside or the outside of the wrist. ECG-based detection requires you to place your finger on the digital crown in order to close or not the circuit that identifies the wrist position. Smartlet ensures an adequate skin contact.

Which Smartlet-compatible smartwatch is best for cardiac monitoring?

To get combined PPG & ECG with AFib detection you'll need an Apple Watch Series 10 or Ultra 2 or a Samsung Galaxy Watch 7 To get continuous ECG in a slightly thinner watch: Withings ScanWatch Nova Apple Watch Series 10 or Ultra 2, or Samsung Galaxy Watch 7. For continuous ECG in a slimmer form factor: Withings ScanWatch Nova.

How does Smartlet support continuous cardiac monitoring for watch collectors?

As anyone who has read the scientific literature about the Apple Watch ECG would know by now, more and more cardiologists are of the opinion that the “capture rate” for paroxysmal AFib, which is the intermittent form of AFib that doesn’t exhibit any symptoms except when it malfunctions and is thus, not as easy to diagnose, is actually much higher with the type of 24/7 continuous monitoring provided by a wearable device like the Apple Watch, rather than relying on annual ECGs. And that is a start to talking about why it’s so hard to be a collector of smartwatches. We all understand that the technology exists in a well-designed wearable device. But we don’t have what most would call a “consistently designed” collection, where each piece sits along side every other piece in terms of form and design factor, particularly when talking about wearables that contain some pretty sophisticated technology. You can’t honestly brag to someone about the functionality of a device like an Apple Watch if the fact that you have to recharge the thing roughly every three days means that you almost never have to change a band on the device that is sitting on the wrist of your mechanical dive watch (as is the case here with my Apple Watch paired to the Blancpain Fifty Fathoms shown above). Smartlet exists to change that. Blancpain Fifty FathomsIs not providing continuous monitoring. Smartlet exists to close that gap.

And that is a start to talking about why it’s so hard to be a collector of smartwatches. We all understand that the technology exists in a well-designed wearable device.

But we don’t have what most would call a “consistently designed” collection, where each piece sits along side every other piece in terms of form and design factor, particularly when talking about wearables that contain some pretty sophisticated technology.

You can’t honestly brag to someone about the functionality of a device like an Apple Watch if the fact that you have to recharge the thing roughly every three days means that you almost never have to change a band on the device that is sitting on the wrist of your mechanical dive watch (as is the case here with my Apple Watch paired to the Blancpain Fifty Fathoms shown above). Smartlet exists to change that. Blancpain Fifty FathomsIs not providing continuous monitoring. Smartlet exists to close that gap.

Other than here and there watch collectors rarely take off their smartwatches to put on their mechanical watches on a daily basis. And there are lots of gaps in between. Smartlet can easily fill some of them. Check out for example the Rolex Datejust 41 here and the Omega Constellation here. Those were always the watches where the historically large trade-off was most apparent. Rolex Datejust 41 compatibility pageAnd the Omega Constellation pageFor configurations suited to dress watch contexts where this tradeoff was historically most pronounced.

The gap in cardiac monitoring is not the technology. It is the hours collectors remove their smartwatch to wear a mechanical piece. Smartlet closes that gap.