Validation of a 6-lead smartphone ECG against 12-lead ECG in athletes
Authors: Orchard J , Orchard JW , Raju H , La Gerche A , Puranik R , Semsarian C 
Published: May 2021

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): JO is supported by an Australian Government Research Training Program scholarship. CS is the recipient of a National Health and Medical Research Council (NHMRC) Practitioner Fellowship (#1154992).

Background
Athletes sometimes experience transient arrhythmias during intense exercise, which may be difficult to capture with traditional monitors. New highly portable technology, such as smartphone electrocardiogram (ECG) devices, may be useful in documenting and diagnosing exercise-induced arrhythmias. Accuracy of the Kardia single-lead ECG (1L) has been documented, but little data exists for the 6-lead device (6L).

Purpose
To examine the level of similarity between resting 6L and 12L readings to build evidence for the utility of the 6L as a practical diagnostic tool in athletes.

Methods
Participants (n = 30 healthy athletes, mean age 18.9 years, 57% male) had a resting supine 12-lead ECG (12L) as part of cardiac screening required by their sport. Within 1 hour, a 30 second 6L reading (leads I, II, III, aVR, aVL, aVF) was taken whilst seated.
Data were analysed by 4 expert cardiologists. Manual measurements were taken for PR, QT and RR intervals and QRS duration using EPS digital calipers. To calculate mean 6L RR interval and QT prior to QTc, &lt;10 sequential RR/QT measurements were taken from the middle 10 seconds. QTc was calculated using Bazett’s formula. ECGs were reviewed for rhythm and presence of atrial/ventricular ectopics.
Continuous variables were expressed as the mean of 4 cardiologists’ values ± standard deviation. Two-tailed paired t-tests were used to compare continuous variables (p &lt; 0.05 significant). Bland-Altman plots were used to assess quantitative agreement between QRS axis and mean values for QTc interval, QRS duration and PR interval for paired 6L and 12L ECGs.

Results
There were relatively high levels of agreement between the mean 6L and 12L measures for QTc and PR interval and QRS duration, with the 6L readings slightly but significantly shorter on average. The largest difference was seen in the QTc intervals (391ms vs 401ms, p = 0.003). The 6L QRS durations were shorter on average by 3ms (89ms vs 92ms, p = 0.025) and PR intervals were shorter on average by 6ms (163ms vs 169ms, p &lt; 0.001).
There was complete agreement for all cardiologists for sinus rhythm and the presence of ectopics for the 6L and 12L readings.

Conclusions
The 6L readings had relatively high agreement with the 12L. All 6L measures (except heart rate) were slightly shorter on average than 12L. These small differences are unlikely to have any clinical significance, and are similar to findings comparing the 1L to 12L. 6L heart rates were slightly higher, which is best explained by seated compared to lying position. The reading with the greatest variation was QT interval, some of which is explained by heart rate variation.
These pilot data suggest the 6L is sufficiently accurate to be useful in an athletic population as an event monitor for exercise-induced arrhythmias. This may provide more useful diagnostic data than the 1L. Larger studies showing higher levels of agreement with 12L would be required to expand the role of 6L beyond an event monitor.
Abstract Figure 1: 6L device, Bland-Altman plots