Contemporary ReviewRemote and wearable ECG devices with diagnostic abilities in adults: A state-of-the-science scoping review
Introduction
The electrocardiogram (ECG) is the most widely used diagnostic tool in clinical cardiology and is also one of the most widely collected body signals in wearable devices intended for diagnostic use. The ECG is abnormal in a significant proportion of cardiac pathologies other than arrhythmias (eg, coronary artery disease, heart failure, valvular heart disease.), making it suitable for screening purposes before subsequent evaluation by more specific diagnostic tests (eg, echocardiography, coronary angiography). The ECG is commonly acquired from 12 body surface leads to enable the spatial assessment of the heart in a 3-dimensional model. However, the 12-lead ECG traditionally is acquired by clinicians and trained personnel via a highly regulated procedure, which limits the scope of its clinical utility beyond the clinic. If one could trigger ECG recordings at the onset of worrisome cardiac symptoms, anytime and anywhere, clinicians would be provided with evidence of cardiac diseases that might no longer be apparent on the 12-lead ECG taken later at a medical appointment.1 The latter objective has led to widespread use of consumer-oriented remote and wearable ECG devices in recent years.
Information provided by the 12-lead ECG is interpreted following recommendations and expert-consensus statements. Fortunately, identifying basic arrhythmias only requires 1 ECG lead,2 which drastically simplifies the task to the point of making possible its assignment to untrained individuals. Some solutions lie in the scope of wearables, which allow for a long-term ECG recording with an ergonomic design. There also are portable options that do not provide continuous monitoring but allow a patient to quickly record one or multiple ECG leads in a range of nonclinical settings. These 2 types of devices—wearables and portables—make up the broader class of remote ECG devices.
In this review, we summarize the recent contributions, examine the reliability, and discuss the limitations of commercially available remote ECG devices in adult population. We restrict our investigation to wireless products that claim a diagnostic value with a reduced set of electrodes. This article also elaborates on how remote ECG devices overcome the disadvantages of the standard 12-lead ECG, as well as their clinical utility in diagnosing cardiac disease.
The 12-lead ECG can be used for the noninvasive assessment of a plethora of abnormalities, including arrhythmias and ectopic rhythm abnormalities, conduction defects and heart blocks, chamber hypertrophies and cardiomyopathies, inherited syndromes and channelopathies, myocardial ischemia and infarction, electrolyte abnormalities, medication toxicity, secondary cardiopulmonary manifestations, and other noncardiac etiologies.3 Thus, practice guidelines by the American Heart Association/American College of Cardiology grouped the diagnostic statements for automated ECG interpretation into a list to promote uniformity of ECG diagnosis, yielding 117 potential diagnostic statements.4 Figure 1 shows the ECG acquisition method and an example of the tracing and diagnostic statements available to clinicians.
The ECG signal needs to be filtered before it is analyzed for diagnostic purposes. This is done by keeping a frequency band that preserves important prognostic physiological signatures needed for proper diagnostic statements. Guidelines specify the lower and upper filtering frequency bounds to guarantee an interpretable signal, equal to 0.05 and 150 Hz, respectively, for adults.5 Measuring abrupt events such as peak amplitude is more accurate when higher frequencies are kept in the signal after filtering.6
This review was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines.7 A database search was conducted using PubMed to screen research articles with the following search term: “(((wearable or portable) and (ECG or electrocardiogram)) and adult) and diagnosis) not PPG”. The most recent search was performed on March 1, 2021, and was limited to the past 5 years. The search yielded 243 articles, which subsequently were filtered, first based on their title and abstract, then based on whether they were suitable for the study of the review's topic. The targeted studies were those that discussed commercially available, Food and Drug Administration–cleared devices validated in an adult population. Moreover, a manual search was carried out to identify commercially available remote ECG devices and link them to relevant research articles, thus forming a complete summary of state-of-the-art products. Data extraction regarding study characteristics, device description, and diagnostic utility metrics reported in that study was done by a single reviewer (ZB).
Section snippets
Commercially available ECG devices
Table 1 summarizes the available remote ECG devices from published validation studies. Figure 2 illustrates the configuration and placement of these 8 remote ECG systems. Figure 3 compares the functionality of these systems against the standard 12-lead ECG.
Real-time capabilities
Many remote ECG devices have real-time monitoring capabilities. For example, intermittent portable ECGs recorded by AliveCor (Mountain View, CA) devices can be used as near real-time systems because of wireless communication through a
Factors that jeopardize signal quality
An ECG signal can be seriously compromised by noise, which might be the result of baseline wander and abrupt drift, power line interference, or muscle artifact.10 ECG signals corrupted with noise are unreliable and either must be filtered using noise-specific signal processing techniques before any manipulation or discarded if recovery of a good-quality signal is impossible.10 Ambulatory data recording from wearable devices are more likely to result in signals with artifacts than data obtained
Diagnostic capabilities of remote ECG devices
Most clinical guidelines are based on 12-lead ECGs, which limits the diagnostic capabilities of reduced-set ECGs. Thus, most reduced-set ECG devices have primarily focused on abnormal rhythm detection, namely, the detection of AF. This was recently highlighted by a collaborative statement on mHealth in arrhythmia management by leading societies in the field.27 Figure 4 summarizes the diagnostic significance of remote ECG devices for AF detection. Yet, some other studies focused on the role of
Signal filtering bandwidth
Recording higher-frequency signals consumes more battery and memory, which is problematic for remote ECG systems. Guidelines relax the upper frequency to 60 Hz in ambulatory devices. Such frequency can suppress the excessive noise and interferences introduced by daily activities and excessive movement. The downside is that a frequency as low as 40 Hz affects the QRS complex and nullify amplitude measurements. This impacts the performance of R peak detection used in almost all ECG signal
Conclusion
Remote ECG devices provide incremental benefits over the standard 12-lead ECG or ambulatory Holter monitors in multiple aspects. They can facilitate the accurate and timely diagnosis of heart rhythm abnormalities, namely, AF. The potential integration of these tools in clinical settings or in patients' homes gives unprecedented flexibility for patients to self-monitor their heart health without interrupting daily activities or scheduling doctor visits. They also improve diagnostic value by
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Funding Sources: This work was supported by National Institutes of Health grant # R01HL137761.
Disclosures: The authors have no conflicts of interest to disclose.