Accuracy of Apple Watch to Measure Cardiovascular Indices in Patients With Cardiac Diseases: Observational Study

Introduction:

Measuring the heart rate (HR) is important to estimate the suitable exercise training intensity and to determine the recommended exercise intensity (1). The 12-leads electrocardiogram (ECG) is the gold standers to measure heart rate, but it may be not suitable to be used outside the laboratory, therefore using the polar chest strap is the alternative to be used outside the lab and it has been tested against the 12-leads ECG during exercise and at rest in healthy subjects [2,3,4] and cardiac patients [5]. The HR following exercise is called heart rate recovery and it is important to predict mortality risk and cardiorespiratory fitness [6].

There is a liner relationship between the HR and oxygen consumption [7]. The Oxygen saturation (Spo2) is recommended to be monitored in patients with hypoxemia to extend their survival [8]. Some cardiac patients have hypoxemia particularly cardiac patients after cardiac arrest [9]. Pulse oximeter is a gold standard to measure the Spo2 [10].

The Apple Watch all versions can measure heart rate, but the latest versions-6 and 7 can measure blood Spo2. Photoplethysmography (PPT) is a non-invasive measurement procedure to evaluate the HR through wrist-worn devise by detecting each heartbeat changes in blood flow and changes colors in blood flow. The PPT has been used to measure Spo2, cardiac output, and blood pressure in many medical devices [11]. The PPT technology can help in early detection of some cardiovascular diseases such as atherosclerosis and atrial fibrillation [12].

A pilot study measured the HR agonist the telemetry in 50 cardiac patients (half of them with atrial fibrillation (AF) and other half with normal HR rhythm) during rest, through assessments of the HR 3-times/ day for two days. They found that the HR accuracy in patients with AF (r=86) was more than the cardiac patients who have normal rhythm (r= 0.64) and the overall accuracy was (r=070) but this still pilot study and more studies with large sample size are needed to confirm this findings in addition to presence of some limitations in this pilot study, as including of 3 black participants that could affect the accuracy of the results, presence of other interfering devices near the Apple Watches devices during evaluations in the cardiac wards and the fluid and edema after operation[13]. Moreover, the accuracy of the Apple Watch in measuring the HR during exercise is still unknown with cardiac patients and cardiac patients with AF.