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      Which Lead for Q-T Interval Measurements?



      S. Karger AG

      ECG, Q-T interval measurement, methodology, Lead determination, Q-T interval

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          There are several Q-T interval measures (individual lead, mean Q-T interval or Q-T dispersion) from a 12-lead ECG. Which should be used? As the ECG provides twelve different measures of the heart’s ‘true’ Q-T interval, and as, ‘a priori’, no one measure is any better or worse than any other measure at estimating the ‘true’ Q-T interval, the best measure is the average of these twelve measures, i.e., the mean Q-T interval. The best single lead to measure the Q-T interval is the lead that relates most closely to the mean Q-T interval which in 49 subjects with cardiac diseases was lead V<sub>3</sub>, then lead II. The longest lead Q-T interval relates poorly to the mean and to the individual lead Q-T intervals and therefore carried information different to and quite unique from these measures. This unique information is Q-T dispersion which relates well to the longest lead Q-T interval (r = 0.71, p < 0.001).

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          QT interval and mortality from coronary artery disease.

           P. Davey (2000)
          Abnormalities in the QT interval can be divided into 3 types, prolongation of the QT interval, increases in the dispersion of the QT interval, and abnormalities in the heart rate dependent behavior of the QT interval. Abnormalities may be found in short or long-term recordings. Prolongation of the QT interval may reflect factors associated with an adverse prognosis in coronary disease and may in itself be arrhythmogenic. The data to date suggest that there is an association between adverse prognosis and QT interval prolongation in coronary disease, both before and after acute myocardial infarctions. This relationship is weak, however, and is not clinically useful. The data as to whether increased QT dispersion postmyocardial infarction relates to adverse prognosis is weak because there is no convincing evidence yet. If there is a relationship it is weak. Abnormalities in the rate dependent behavior of the QT interval are widely found, but as no large scale prospective study with mortality as an endpoint has yet been undertaken the significance of rate dependent abnormalities is uncertain. The widespread introduction of beat-to-beat QT analysis of 24 hour Holter tapes may take QT intervalology into the realm of clinical practice.

            Author and article information

            S. Karger AG
            February 2001
            02 March 2001
            : 94
            : 3
            : 159-164
            Department of Cardiovascular Medicine, John Radcliffe Hospital, Oxford, UK
            47311 Cardiology 2000;94:159–164
            © 2001 S. Karger AG, Basel

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            Page count
            Figures: 2, Tables: 4, References: 12, Pages: 6
            Arrhythmias, Electrophysiology and Electrocardiography


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