Apple Watch is a consumer-oriented smart watch and wearable activity monitor (also called fitness tracker) made by Apple Inc. The device runs on the watchOS operating system, allowing for native apps as well as installation of third party apps. Supported wireless connectivity include Bluetooth, wifi, and cellular standards. Many of its core functions depend on a connection with a nearby iPhones. Its health-related features originally include exercise detection, fitness tracking, pedometer, and calorie counter. Users can customize individual goals and allow the watch to track progress over time. In 2018, improved accelerator and gyroscope sensors supported a fall detection feature by "analyz[ing] wrist trajectory and impact acceleration." After a fall is recognized, the watch offers to reach out to an emergency contact. If the wearer is stationary for more than 60 seconds after the fall, the watch will automatically notify the authorities and user-defined emergency contacts.
This product line initially obtained FDA approval as a Class II medical device with the Series 4 hardware version for its novel electrocardiogram (ECG) feature. Class II devices under FDA regulation represent a moderate potential for harm for consumers—they are neither associated with minimal risk nor are used for critical life support purposes. Apple Watch is the first over-the-counter product for consumers to feature this functionality. Although AliveCor's KardiaBand accessory for Apple Watch received a similar Class II clearance in 2014, the first ECG from this device must be unlocked by a U.S. board-certified cardiologist prior to viewing; this is not the case for the Apple Watch.
Electrocardiogram (ECG) Functionality
Apple introduced two integrated electrodes—one on the back crystal and one in the digital crown—into the watch design in Series 4 to support the ECG feature. With the back crystal in constant contact with the wrist, the user touches the digital crown with a finger from the contralateral hand to complete a closed circuit and allow sensors to record a single channel, closely resembling a Lead I tracing in a 12-lead ECG. The software uses an algorithm to analyze the pulse rate to determine whether the cardiac rhythm is regular or irregular, with the latter case being indicative of possible atrial fibrillation (a-fib). Once activated, users receive results from the watch within 30 seconds. The ECG waveform, rhythm classification, and associated notes are then stored in PDF format in Apple's Health app for later review by a physician. Select users are also able to directly transmit the results directly to their providers using Apple Health Records.
These two individual software components, the ECG app and the cardiac rhythm algorithm, received regulatory clearance under FDA Section 513(f)(2) with De Novo numbers DEN180044 and DEN180042, respectively. Applications for classification were both submitted in August 2018 and both approved on September 11, 2018. The collected data are only indicated for informational use and cannot be used for diagnostic or screening purposes. Further, the software is not approved for identification of any other cardiac arrhythmias besides atrial fibrillation. Several risks to consumer health were identified in the application review process:
- Poor quality ECG signal resulting in failure to detect arrhythmia
- Misinterpretation and/or over-reliance on device output, leading to:
- Failure to seek treatment despite acute symptoms
- Discontinuing or modifying treatment for chronic heart condition
- False negative resulting in failure to identify arrhythmia and delay of further evaluation or treatment
- False positive resulting in additional unnecessary medical procedures
Clinical data from two studies accompanying the applications showed the a-fib detecting software has a sensitivity of 79% and specificity of 99.6%. After eliminating ECG recordings that were not interpretable by the app, sensitivity rises to 98%. Positive predictive value was estimated at approximately 45%.
Cardiologist reception of this Apple Watch feature is mixed. The American Heart Association demonstrated implicit support when the organization's president, Ivor Benjamin, took part onstage in the product launch presentation on September 12, 2018. Notable cardiologists have described the functionality as "a game changer" and as a tool to engage and empower patients. Others disagree, however. Some cardiologists are concerned about false positives, especially among a patient population with low pre-test probability, such as younger consumers, who are more likely to purchase an Apple Watch. Unnecessarily alarming asymptomatic patients may induce anxiety and put them at risk of complications from testing procedures or therapies. The extra data may "increase the burden on physicians" to filter out additional noise as opposed to facilitating healthcare. Given these limitations, formal atrial fibrillation screening based on watch ECG results are more suitable for certain groups: patients with a history of a-fib, palpitations, or family history of arrhythmias.
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Submitted by Stephen Pun