View as PDF version

Patient Safety Tip of the Week

November 22, 2022

The Apple Watch and Patient Safety



Your next patient safety tool might be right on your wrist already. You probably already know that the Apple Watch can detect atrial fibrillation and falls, but it also has several other potential patient safety uses. (Many of our comments likely also apply to several other smartwatches. The Apple Watch is simply the one we are most familiar with.)


Researchers at the Mayo Clinic recently applied a proprietary AI (artificial intelligence) algorithm using the single lead EKG function available on the smartwatch to see if it might predict patients at risk of cardiac dysfunction (Attia 2022). Almost 2500 patients used a Mayo Clinic iPhone application that sends watch ECG’s to a secure data platform. 421 participants had at least one watch-classified sinus rhythm ECG within 30 days of an echocardiogram, of whom 16 (3.8%) had an EF ≤ 40%. The Mayo AI algorithm detected patients with a low EF (ejection fraction) with a high degree of reliability.


That made us wonder whether the Apple Watch might also be able to detect QTc prolongation in patients at risk for Torsade de Pointes. We speculated on that in our February 16, 2021 Patient Safety Tip of the Week New Methods for QTc Monitoring. It turns out that such a study has already been done. Italian researchers (Spaccarotella 2021) did conventional ECG’s on 119 patients, then obtained via the Apple Watch ECG’s tracings on leads I, II, and V2. (Lead I was recorded with the smartwatch on the left wrist and the right index finger on the crown. Lead II was obtained with the smartwatch on the left lower abdomen and the right index finger on the crown. The V2 lead was recorded with the smartwatch in the fourth intercostal space left parasternal with the right index finger on the crown.) They found good agreement among the QT intervals of I, II, and V2 leads and the QT mean using the smartwatch and the standard ECG. A previous study (Strik 2020) had shown Apple Watch ECG tracings allowed adequate QT measurements, though performance depended on factors such as electrocardiographic tracing quality and T-wave amplitude. Those researchers suggested that identifying the best smartwatch position at baseline might improve accuracy. These 2 studies certainly suggest that in situations where monitoring of QTc intervals is important, such as when a patient is being treated with one of the many drugs known to increase the QTc, monitoring via a smartwatch may be useful.


Note that, with a bit of jockeying of placement, it is possible to obtain a 12-lead ECG using an Apple Watch (Cobos Gil 2020). That article includes a video demonstrating how to obtain the 12-lead ECG using the Apple Watch. The author concludes this could potentially revolutionize our approach to cardiac emergencies.


Though the Apple Watch can detect bradycardia and tachycardia, its most widely touted capability is detection of atrial fibrillation (AF). But its detection of AF is not infallible. In the Apple Heart Study, 34% of individuals who received a notification of arrhythmia were later found to have atrial fibrillation (AF), and the positive predictive value in participants notified of an irregular pulse was 0.84 (Perez 2019). Another study (Seshadri 2020) found that the single-lead electrocardiographic waveform saved as a PDF provided a more reliable means of detecting AF than the rhythm notification of the watch. Moreover, coexisting ECG anomalies may complicate the accuracy of smartwatch detection of atrial fibrillation (Racine 2022).


In addition to the functions related to cardiac function, the Apple Watch (and presumably several other smartwatches) have lots of other patient safety applications. 


Many smartwatches can now measure pO2. During the COVID-19 pandemic, some patients were using this capability rather than using a finger pulse oximeter to identify worrisome trends in oxygen saturation, though studies have not shown that such use had an impact on COVID-19 outcomes.


Measuring nocturnal pO2 has the potential to identify patients at risk for OSA (obstructive sleep apnea). However, most smartwatches with pO2 measurement capability only measure pO2 on demand. Periodic sampling of pO2 during the night while a patient is sleeping would be a major improvement in identifying potential OSA and some smartwatches will soon have the capability. In the meantime, identifying patients at risk for OSA can benefit from the ability of some smartwatches to identify snoring at night.


In addition to the potential to identify OSA risk, many smartwatches are now able to measure sleep duration, another important health indicator. 


The Apple Watch also offers fall detection, though you must enable that function. Remember those old “I’ve fallen and can’t get up!” commercials for medical alert devices and services? Now, when someone has fallen, they can use their Apple Watch (with cellular service) to call a friend or relative or summon 911 help. And it is not just the elderly who might use the Apple Watch after a fall. Recently, a teen slipped and fell 130 feet into a valley while hiking and was badly injured, breaking both ankles (Gallagher 2022). He did not have his smartphone with him but was able to call friends with his Apple Watch, leading to his rescue.


In addition to the Apple Watch capabilities, newer iPhone models may provide important information about certain patient safety risks, such as walking steadiness.

Most users of the Apple Watch or other smartwatches are well aware of the fitness applications like step counting, heart rate monitoring, etc. But collection of such health data over time can also identify trends that might be important. For example, trends in the 6-minute walk test measured via the Apple Watch (Apple 2021) might provide evidence of deterioration of physical function. Conversely those trends might provide evidence of improvement in physical function after a medical event.


Gait speed is an important potential indicator of frailty (see our August 14, 2012 Patient Safety Tip of the Week Gait Speed: A New Vital Sign?) and the Apple Watch can provide a measure of gait speed. Of course, you can also just use the timer on the Apple Watch to do the Timed Up-and-Go Test (see our November 2011 What's New in the Patient Safety World column Timed Up-and-Go Test and Surgical Outcomes). Note also that an iPhone app from the University of Toronto, iWalkAssess, provides easy access to stroke-specific walk test protocols, timing tools, a 6-minute walk test length counter, and algorithms for comparing test performance to normative and community ambulation values.


Newer smartwatches are expected to have temperature sensors that could identify febrile patients. But even older smartwatches, that can measure heart rate, can identify potential fever by identifying the elevated heart rate that usually accompanies fever.


Beware that false alarms may be triggered by the smartwatch. We’ve had the “It looks like you have fallen” alert trigger on our Apple Watch after doing a twist entry into a kayak off a dock. And it might trigger if you are wearing the watch on your dominant arm when serving a tennis ball! And once, after an awkward bicycle dismount, we even accidentally triggered the emergency call function of the Apple Watch (fortunately, we were able to cancel that before EMT’s were summoned!).


Also keep in mind that the Apple Watch and iPhone might have unintended consequences related to implanted cardiac devices (see our October 2021 What's New in the Patient Safety World column More on Smartphones and Watches Effect on Cardiac Devices).


In this era where most remote monitoring is fairly expensive, it is refreshing to see that many important patient safety monitoring capabilities can be provided relatively inexpensively.






Attia ZI, Harmon DM, Dugan J, et al. Prospective evaluation of smartwatch-enabled detection of left ventricular dysfunction. Nat Med 2022; November 14, 2022


Spaccarotella CAM, Migliarino S, Mongiardo A, et al. Measurement of the QT interval using the Apple Watch. Scientific Reports 2021; 11: 10817 May 24, 2021



Strik M, Caillol T, Ramirez FD, et al. Validating QT-interval measurement using the Apple Watch ECG to enable remote monitoring during the COVID-19 pandemic. Circulation 2020; 142(4): 416-418



Cobos Gil MA. Standard and Precordial Leads Obtained with an Apple Watch. Ann Intern Med 2020; 172(6): 436-437



Perez MV, Mahaffey KW, Hedlin H, et al; Apple Heart Study Investigators. Large-scale assessment of a smartwatch to identify atrial fibrillation. N Engl J Med 2019; 381: 1909-




Seshadri DR, Bittel B, Browsky D, et al. Accuracy of Apple Watch for Detection of Atrial Fibrillation. Circulation 2020; 141(8): 702-703



Racine H-P, Strik M, van der Zande J, et al. Role of Coexisting ECG Anomalies in the

Accuracy of Smartwatch ECG Detection of Atrial Fibrillation. Canadian Journal of Cardiology 2022; 38(11): 1709-1712 November 01, 2022



Gallagher W. Apple Watch gets help for badly injured teen after 130-foot fall.

AppleInsider 2022; November 17, 2022



Apple. Using Apple Watch to Estimate Six-Minute Walk Distance. May 2021 wjIxfqph737AhXQjYkEHZXpA_YQFnoECAsQAw&url=https%3A%2F%2Fwww.appl e_Walk_Distance.pdf&usg=AOvVaw3kBjmQ9ObMQx8sW_A7spCW


Apple. Measure your walking steadiness with your iPhone.



University of Toronto. iWalkAssess (app). Apple Store




 Print PDF version












Tip of the Week Archive


What’s New in the Patient Safety World Archive