Session P71.6

Comparison of Two Automated Methods for QT Interval Measurement

R Gregg*, S Babaeizadeh, D Feild, E Helfenbein,
J Lindauer, S Zhou

Philips Medical Systems
Thousand Oaks, CA, USA

Background: In this work we compare two methods of automated QT interval measurement on standard ECG databases: the Root-Mean-Square (RMS) lead combining method aimed at QT monitoring and the method of median of lead-by-lead QT interval measurements.
Study Population: We used the Physionet PTB (N=548) and CSE measurement (N=125) standard databases. The last 10 seconds of each PTB record was downsampled from 1000sps and an amplitude resolution of 1µV to 500sps and 5µV in order to match the CSE set. PTB records #205 and #557 were excluded due to ventricular paced rhythm and artifact, respectively. Twenty five cases were excluded from the CSE set to match the selection of cases for IEC algorithm testing (IEC 60601-2-51).
Methods: We processed all records using the Philips resting ECG algorithm to generate representative beats for QT interval measurement. The RMS method measures QRS onset and end of T on an RMS waveform constructed from 8 primary leads I, II and V1-V6. The lead-by-lead method takes the median QT interval across leads. The automated QT intervals by the RMS and lead-by-lead methods were compared to the reference manual QT measurements.
Results: The lead-by-lead method results in a mean difference ± standard deviation(SD) of 14.7±21.4 and 0.62±11.0 on the PTB and CSE databases respectively. The RMS method results in a mean difference of 0.79±20.5 and -12.3±11.2 on the PTB and CSE databases. F-tests indicate that the standard deviation between methods is not significantly different (P=0.8 for PTB and P=0.3 for CSE). Since the mean difference between the methods is 13 ms for both databases (0.79-14.7 and -12.3-0.62), and the same 13 ms difference is seen across databases for each method (0.62-14.7 and -12.3-0.79), we suspect the measurements are 13 ms short on the PTB database. The bias may be due to the high gain which was being used during manual measurement of the CSE cases.
Conclusion: Lead-by-lead and RMS methods perform similarly, leading to the conclusion that the choice between them should be based on considerations such as the number of leads available or computational efficiency.

(Abstract Control Number: 71)