Differences between QT and RR intervals in digital and digitized paper electrocardiograms: contribution of the printer, scanner, and digitization process.
BACKGROUND
Prints of electrocardiograms (ECGs) are often sent to core laboratories, where they are scanned, converted to a digital format, and read on-screen. These ECGs may differ from the original ECG because of variability introduced by the printer, scanner, or digitization software.


METHODS
Digital ECGs were recorded in 50 volunteers simultaneously using electrocardiographs from 2 different manufacturers. QT and RR intervals were measured on-screen on the digitized ECGs. To study the contribution of individual steps in the digitization process, differences in RR interval between 2 prints each of 50 digital ECGs, 2 scanned files of 50 prints, 2 digitized files from 50 scanned files, and 2 readings of 50 digitized ECGs (intrareader variability) were analyzed.


RESULTS
Repeatability coefficient for RR interval measurement was 18.5 milliseconds for machine 1 and 21 milliseconds for machine 2. Contributions of the printer were 6.5 milliseconds for machine 1 and 9.0 milliseconds for machine 2, digitization process was 5.5 milliseconds, and reader variability was 8.0 milliseconds. Variability of the scanner was negligible.


CONCLUSIONS
The printer and digitization process account for significant differences in interval measurements in digitized ECGs.
Hingorani
Pooja
P
Research Section, Quintiles ECG Services, Mumbai, India. pooja.hingorani@quintiles.com
Karnad
Dilip R
DR
Panicker
Gopi Krishna
GK
Deshmukh
Sheetal
S
Kothari
Snehal
S
Narula
Dhiraj
D
D000328:Adult; D016477:Artifacts; D016287:Computer Peripherals; D004562:Electrocardiography / Q000295:instrumentation* / Q000379:methods*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010209:Paper; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*