KardiaMobile 6L device to measure QT intervals question

Has anyone ever used their KardiaMobile 6L device to measure QT intervals on Lead II (2) ?

What I measured on mine at home was pretty close to the computer-generated number several hours later on the ECG at my EP’s office. The EP office does wholeheartedly support use of KardiaMobile 6L in general, but the PA there told me it was known to be not always accurate for QT interval measurements.

Just wanted to know if anyone else had any experiences with or thoughts on this. Thx.

Quote
MarkL
Has anyone ever used their KardiaMobile 6L device to measure QT intervals on Lead II (2) ?

What I measured on mine at home was pretty close to the computer-generated number several hours later on the ECG at my EP’s office. The EP office does wholeheartedly support use of KardiaMobile 6L in general, but the PA there told me it was known to be not always accurate for QT interval measurements.

Just wanted to know if anyone else had any experiences with or thoughts on this. Thx.

How do you measure on your 6L?

Measuring QT can be done on the original Kardia, Apple Watch, or any device that shows an ECG waveform. All you need is a printed copy of the recording and a ruler. I would pick a sample of QRS complexes that aren't in the first few seconds of the recording, measure them, and then average them out.

Garabelli P, Stavrakis S, Albert M, Koomson E, Parwani P, Chohan J, et al.
J Cardiovasc Electrophysiol. 2016;27(7): 827-32."
Full

"QT Interval Readings With a Smartphone Heart Monitor (SMH). Introduction: A variety of medications
ranging from antiarrhythmics to psychotropics, as well as conditions such as bradycardia, can prolong the
QT interval, increasing the risk for life-threatening arrhythmias. Monitoring the corrected QT interval
(QTc) is therefore critical for patient safety. The recent development of smart phone heart monitors (SHM)
may allow for easier QTc monitoring. We sought to evaluate the accuracy of an SHM for assessing the QTc,
as compared to the standard 12-lead ECG.
Methods and Results: We compared the QTc interval in lead-I and lead-II between an SHM and 12-lead
ECG. Healthy volunteers and hospitalized patients in sinus rhythm being loaded on dofetilide or sotalol
were included. Manual and automatic measurements were studied. Across 99 healthy volunteers, the SHM
QTc demonstrated good agreement (bias = 4 milliseconds, standard deviation of bias = 11 milliseconds)
compared to the 12-lead ECG, using the Bland–Altman method of agreement. Across all hospitalized
patients, the SHM was capable of demonstrating QTc prolongation. Between the 12-lead ECG and SHM,
lead-I measurements had reasonable agreement (bias = 3 milliseconds, standard deviation of bias =
46 milliseconds). A QTc of > 500 milliseconds was associated with a higher likelihood (OR = 12.0; 95% CI
1.5–111.4; P = 0.02) to not achieve perfect agreement.
Conclusion: The SHM is accurate in measuring QTc interval in sinus rhythm when compared to
12-lead ECG in healthy volunteers. For patients receiving QT prolonging antiarrhythmics, SHM is capable of detecting"

" Between the 12-lead ECG and SHM, lead-I measurements had reasonable agreement (bias = 3 milliseconds, standard deviation of bias = 46 milliseconds)." This does look like a large standard deviation. "A QTc of > 500 milliseconds was associated with a higher likelihood (OR = 12.0; 95% CI 1.5–111.4; P = 0.02) to not achieve perfect agreement." Looks like a A QTc of > 500 ms is an issue, that CI range for the OR is huge.



Edited 1 time(s). Last edit at 01/11/2022 09:32PM by GeorgeN.

I email my ECG to myself from within the app. I than open the PDF on my wide monitor PC and manually count the blocks in the QT interval width on Lead II. I do this for 3 randon readable intervals and take the avg. Multply that by 40 for the QT interval total. I then use the Bazett formula for QT corrected:

QTc = QT/√RR
where RR = HR/60

this formula is valid when HR is between 60 - 100. For rates outside that range there are other better formulas to use.

Quote
MarkL
I email my ECG to myself from within the app. I than open the PDF on my wide monitor PC and manually count the blocks in the QT interval width on Lead II. I do this for 3 randon readable intervals and take the avg. Multply that by 40 for the QT interval total. I then use the Bazett formula for QT corrected:

QTc = QT/√RR
where RR = HR/60

this formula is valid when HR is between 60 - 100. For rates outside that range there are other better formulas to use.

Yep, that works equally well. QT and QTc aren't hard to measure, and it can be done off lead I as well.

Thank you. I'm reassured to now have my own KardiaMobile 6L and to benefit from others' wisdom and experience regarding best use.