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Errors in the visual determination of corrected QT (QTc) interval during acute myocardial infarction
Insights
Investigator differences significantly impact corrected QT (QTc) interval measurements, highlighting challenges in comparing study data. Random error is minimal with sufficient measurements, but inter-observer variability is a major concern.
Area of Science:
- Cardiology
- Medical Imaging Analysis
Background:
- The corrected QT (QTc) interval is a critical indicator in electrocardiogram (ECG) analysis, particularly for patients with acute myocardial infarction.
- Variability in QTc measurements can arise from both intra- and inter-individual factors, complicating clinical interpretation and research comparisons.
Purpose of the Study:
- To quantify intra- and inter-individual variations in corrected QT (QTc) interval measurements.
- To assess the impact of different investigators on QTc interval readings.
- To evaluate the significance of random error in QTc measurements.
Main Methods:
- Duplicate sets of 50 twelve-lead electrocardiograms (ECGs) from 100 patients with acute myocardial infarction were analyzed.
- Nine investigators independently measured the QTc interval from these ECGs in a randomized order.
- Two-way analysis of variance was employed to analyze 900 QTc measurements.
Main Results:
- Significant inter-investigator differences in QTc measurements were observed (p < 0.001), indicating major variability.
- A significant interaction between investigator and electrocardiogram was also found (p < 0.001).
- Random error was found to be negligible (< 0.5 mm) when over 11 measurements were performed.
Conclusions:
- Substantial inter-observer variability exists in QTc interval measurements, posing challenges for comparing data across studies and applying normal limits.
- Standardization of measurement techniques and observer training is crucial for reliable QTc interval assessment.
- While random error is minimal, systematic differences between investigators are a primary source of measurement variability.
Abstract:
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 QTc measurements. Significant differences in these measurements were registered among investigators and were of major importance (p less than 0.001). This finding illustrates the difficulty in comparing mean values from different studies and emphasizes the difficulties in applying limits for a normal QTc interval to data obtained by different observers. Of less but still significant importance was the interaction between the investigator and electrocardiogram (p less than 0.001). Finally, the random error was calculated and proven to be of no importance (less than 0.5 mm) when more than 11 measurements were performed.