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Three-lead measurement of QTc dispersion
J M Glancy1, C J Garratt, K L Woods
1Department of Medicine and Therapeutics, University of Leicester, United Kingdom.
Insights
Calculating QTc dispersion using three electrocardiogram (ECG) leads may be as effective as using all 12 leads. This simpler method maintains prognostic value for post-myocardial infarction patients, aiding in risk stratification.
Area of Science:
- Cardiology
- Clinical Electrophysiology
Background:
- Traditionally, QTc dispersion is calculated from 12-lead electrocardiograms (ECGs).
- Exploring alternative, simpler methods for QTc dispersion calculation is warranted.
Purpose of the Study:
- To determine if QTc dispersion differences between post-myocardial infarction patients who died and survivors persist when calculated using fewer than 12 ECG leads.
- To evaluate the utility of simplified QTc dispersion measurements for risk stratification.
Main Methods:
- QTc dispersion was recalculated from 270 12-lead ECGs using four methods: excluding extreme leads, using six precordial leads, using three "likeliest" leads (aVF, V1, V4), and using three quasi-orthogonal leads (aVF, I, V2).
- Comparison of QTc dispersion fall from early to late ECGs between patients who died and survivors was performed for each method.
Main Results:
- A significant difference in QTc dispersion fall was observed between groups using the standard 12-lead method (P=0.016) and two three-lead methods (quasi-orthogonal leads: P=0.003; "likeliest" leads: P=0.05).
- The difference was not maintained when excluding extreme leads (P=0.13) or using only precordial leads (P=0.76).
- The quasi-orthogonal three-lead method showed a significant difference (P=0.003) between groups.
Conclusions:
- QTc dispersion calculated from three quasi-orthogonal leads may be a viable and simpler alternative to the standard 12-lead measurement.
- This simplified approach retains prognostic value for identifying high-risk post-myocardial infarction patients.
Introduction:
QTc dispersion has traditionally been calculated from all 12 leads of a standard electrocardiogram (ECG). It is possible that alternative, quicker methods using fewer than 12 leads could be used to provide the same information.
Methods And Results:
We have previously shown a difference in QTc dispersion from ECGs recorded at least 1 month after myocardial infarction between patients who subsequently died and long-term survivors. In the current study, we recalculated QTc dispersion in these ECGs using different methods to determine if the observed difference in QTc dispersion measurements between the two groups, as calculated from 12-lead ECGs, persisted when using smaller sets of leads. QTc dispersion was recalculated by four methods: (1) with the two extreme QTc intervals excluded; (2) from the six precordial leads; (3) from the three leads most likely to contribute to QTc dispersion (aVF, V1, V4); and (4) from the three quasi-orthogonal leads (aVF, I, V2). For each of the 270 12-lead ECGs examined, a mean of 9.9 leads (SD 1.5 leads) had a QT interval analyzed; the QT interval could not be accurately measured in the remaining leads. Using the standard 12-lead measurement of QTc dispersion, there was a difference in the fall in QTc dispersion from early to late ECG between the groups: 9.1 (SD 60.8) msec for deaths versus 34.4 (55.2) msec for survivors (P = 0.016). This difference in QTc dispersion between early and late ECGs was maintained using either three-lead method (quasi-orthogonal leads: -2.6 [56.2] msec for deaths vs 26.9 [54.3] msec for survivors [P = 0.003]; "likeliest" leads: 8.6 [64.9] msec vs 29.5 [50.2] msec [P = 0.05]), but not when using the other two methods (precordial leads: 19.1 [55.5] msec vs 22 [50.8] msec [P = 0.76]; extreme leads removed: 9.2 [50.1] msec vs 21.8 [42] msec [P = 0.13]).
Conclusion:
QTc dispersion calculated from three leads may be as useful a measurement as QTc dispersion calculated from all leads of a standard ECG. Its advantages over the standard measurement are its simplicity and the lack of problems with lead adjustment.