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Errors in manual measurement of QT intervals
A Murray1, N B McLaughlin, J P Bourke
1Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne.
British Heart Journal
|April 1, 1994
Summary
Manual QT interval measurements are significantly impacted by electrocardiogram paper speed and amplifier gain, leading to variations. Cardiologist differences also contribute to measurement errors in QT interval analysis.
Area of Science:
- Cardiology
- Medical Instrumentation
- Electrocardiography
Background:
- Accurate QT interval measurement is crucial for assessing cardiac repolarization.
- Manual QT interval measurement is susceptible to various technical and inter-observer factors.
Purpose of the Study:
- To quantify errors in manual QT interval measurements.
- To identify the sources of these measurement errors.
Main Methods:
- A randomized study involving four cardiologists measuring QT intervals on 512 electrocardiograms.
- Electrocardiograms were plotted with varying noise levels, paper speeds, and amplifier gains.
- Measurements were taken from four leads (I, aVR, V1, V5) in eight healthy subjects.
Main Results:
- Increased amplifier gain significantly lengthened QT intervals (8 ms per doubling).
- Slower paper speeds also significantly increased QT interval measurements (11-16 ms).
- Inter-cardiologist variability showed consistent differences, up to a 20 ms mean difference.
Conclusions:
- Manual QT interval measurement is significantly influenced by electrocardiogram paper speed and amplifier gain.
- T wave amplitude, affected by gain, also impacts QT measurements.
- Consistent differences exist between cardiologists performing manual QT interval measurements.