Conflict of Interest:Employment: Gopi Krishna Panicker, Rajesh Joshi, Sheetal Shetty, Niraj Vyas, and Snehal Kothari are employees of Quintiles ECG Services, Mumbai. Consultant or Advisory Role: Dilip Karnad and Dhiraj Narula. Stock Ownership: None. Honoraria: None. Research Funding: None. Expert Testimony: None. Other Remuneration: None.
Z-Score for Benchmarking Reader Competence in a Central ECG Laboratory
Article first published online: 16 JAN 2009
©2009, Copyright the Authors Journal compilation ©2009, Wiley Periodicals, Inc.
Annals of Noninvasive Electrocardiology
Volume 14, Issue 1, pages 19–25, January 2009
How to Cite
Panicker, G. K., Karnad, D. R., Joshi, R., Shetty, S., Vyas, N., Kothari, S. and Narula, D. (2009), Z-Score for Benchmarking Reader Competence in a Central ECG Laboratory. Annals of Noninvasive Electrocardiology, 14: 19–25. doi: 10.1111/j.1542-474X.2008.00269.x
- Issue published online: 16 JAN 2009
- Article first published online: 16 JAN 2009
- thorough QT/QTc study;
- reader variability;
- quality assurance;
- phase I studies;
- drug-induced QT prolongation
Background: ECGs from thorough QT studies must be read in a central laboratory by trained experts. Standards of expertise are not presently defined. We, therefore, studied the use of Z-scores to define reader competence.
Methods: Two hundred ECGs were read by 24 experts and the mean and standard deviation (SD) of QT measurements calculated for each ECG. Z-scores ([QTreader– mean QTexperts]/ SDexperts) for each ECG and mean of absolute Z-scores of all ECGs read by a reader were calculated. The highest mean absolute Z-score of experts was considered the cutoff to define competence. Hundred of these standardized ECGs were used to assess performance of readers from the central laboratory.
Results: All experts had mean absolute Z-scores ≤ 1.5. Using this cutoff, one of 28 experienced readers and 7 of 15 trainees had unacceptable Z-scores. After re-training, all achieved Z-scores <1.5. Comparing histograms of actual Z-scores of the 100 ECGs of readers with unacceptable scores with that of the reader with the best Z-score showed two patterns. Readers with histograms having a peak and tails similar to that of the best reader, but with leftward or rightward shift, consistently made shorter or longer QT measurements, respectively. A histogram with a flatter peak and wider tails, suggested that measurements were long in some ECGs and short in others.
Conclusion: Mean absolute Z-score is useful to assess competence for measuring the QT interval on ECGs. Analysis of histograms can pinpoint problems in QT measurements.