Author + information
- Received April 23, 1984
- Revision received October 8, 1984
- Accepted October 22, 1984
- Published online March 1, 1985.
- ↵*Address for reprints: Staffan Ahnve, MD, Division of Cardiology, University of California, San Diego Medical Center, 225 Dickinson Street, San Diego, California 92103.
To estimate variations in intra- and interindividual measurements of the corrected QT (QTc) interval, duplicates of 50 twelve lead electrocardiograms (100 photocopies, paper speed 50 mm/s) were given to each of nine investigators in random order. The electrocardiograms were recorded from patients with acute myocardial infarction consecutively admitted to a coronary care unit. Patients receiving drug therapy and those manifesting various arrhythmias were included. Two-way analysis of variance was used to evaluate the results from all 900 QTcmeasurements. Significant differences in these measurements were registered among investigators and were of major importance (p < 0.001). This finding illustrates the difficulty in comparing mean values from different studies and emphasizes the difficulties in applying limits for a normal QTcinterval to data obtained by different observers. Of less but still significant importance was the interaction between the investigator and electrocardiogram (p < 0.001). Finally, the random error was calculated and proven to be of no importance (<0.5 mm) when more than 11 measurements were performed.
- Received April 23, 1984.
- Revision received October 8, 1984.
- Accepted October 22, 1984.
- American College of Cardiology Foundation