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.