Discussion
The novel Coronavirus has a high transmission rate in the community as well as within health care facilities, forcing a new emphasis on telemedicine and remote monitoring. While telehealth has been effective, this strategy precludes previously standard testing, including ECGs and application of mobile cardiac telemetry monitors. At the same time, cardiac complications related to COVID-19 infection and potential cardiac toxicity associated with common pharmacologic treatment prompts the need for easily accessible cardiac monitoring modalities that do not rely on physical contact or presentation to a health care facility. Remote patient management using smart device-based electrocardiography is therefore a valuable alternative to previously standard monitoring modalities.
The waveforms provided by smart device-based electrocardiograms have not been vigorously studied for the purpose of QT measurement and no outcome studies based on this strategy have been performed. The rhythm strip obtained by such devices is typically derived from the same vector as lead I of a standard 12-lead ECG; the waveforms are overlaid on standard ECG grids with recordings at 25mm/s and 10mm/mV, allowing QT and RR interval measurements in milliseconds. The corrected QT interval can therefore be derived in the same manner as on a standard 12-lead ECG. A recent validation performed in 129 healthy volunteers showed a reasonable concordance between QTc intervals measured from the Apple Watch and a 12-lead ECG (mean difference -11.67 +- 8.32 ms, r=0.57).(7) In addition, a prior study demonstrated the ability to use a smartphone based heart monitor to accurately detect QTc prolongation in patient receiving QT prolonging medications (bias=4 ms, sd =11 ms compared to 12-lead ECG).8 Another study found that QTc measurement using a single-lead handheld mobile device is feasible, but the QTc measurement was underestimated (23ms, 95%CI 13-34) when only a lead I rhythm strip was obtained; when a vector analogous to lead II could be recorded, QTc measurements had very close correlation to the maximum QTc interval by 12-lead ECG.9 Importantly, the change in QTc during treatment with QT prolonging medications has also been correlated with risk of torsades de pointes,10indicating that serial measurements using a single lead (such as with a smart device) may provide additional value in risk stratification even when the measured QTc value is imprecise.
Further validation and optimization of recording technique is required before this technology is promoted for routine QT interval assessment. If this approach is adopted, QTc measurement can likely be automated to improve the ease of measurement and reduce measurement error. The lack of multiple contiguous leads obtained by most wearable devices limits the sensitivity of these modalities for detection of QT abnormalities, which may be more pronounced in some leads than others. While lead II is most commonly utilized for QT measurement, the optimal lead for QT measurement does vary, and the use of the same lead for serial assessment is important to interpret QT changes with medication. Lead I is frequently adequate for interpretation, and the QTc measurement from lead I has been shown to differ by an average 7.5 ms from that obtained from lead II.11 Accordingly, single lead Mobile Cardiac Outpatient Telemetry units have previously been FDA-approved for QTc measurement. Additionally, the quality of the electrogram produced by smart devices may be effected by high skin-to-electrode impedance, which may be variable and impact waveform interpretation; nonetheless, electrogram quality produced by these devices has been generally consistent with other monitoring technologies and well validated for rhythm interpretation. Despite the limitations, the COVID-19 pandemic requires providers to use all resources at their disposal to manage patients safely and minimize the spread of infection, particularly in the health care environment.