Browsing by Subject "QT interval"

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    Effect of exercise on QT dispersion
    (1998) Özçakır, Lütfü
    Electrocardiogram (ECG) is the measurement of potential differences occurring on the body due to the currents that flow on the heart during diastole and systole. Cardiac abnormalities cause uncommon current flows, leading to strange waveform morphologies in the recorded ECG. Since some abnormalities become visible in ECG only during activity, exercise ECG tests are conducted. Among all abnormalities, exercise induced ischemia is considered in this study. The previous studies have shown that exercise induced ischemia increases the QT dispersion (QTD). The patients in this study have been validated by cardiologists using ST segment analysis. However, the sensitivity and specifity of ST segment analysis is low. Some of the patients have been validated as ischemic using the coronary angiography results. A different method to measure the QT interval through out the exercise ECG test has been developed . The algorithm is designed to cope with the artifacts of exercise ECG. Such as high noise level and PT fusion. A different approach to obtain the QTD has been developed.We have shown that, QTD increases signiflcantly in patients who have ischemia during exercise. The sensitivity and specifity of exercise ECG test can be increased if QTD analysis is used as an additional tool to ST analysis.
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    Significance of QT dispersion as a diagnosis tool for cardiac patients
    (2000) Ben Ahmed Jemel, Nabil
    Electrocardiogram (EGG) is the recorded electrical potentials generated by the heart during a cardiac cycle. Gardiac abnormalities cause unknown current flows leading to strange waveform morphologies in the recorded EGG. Some of these abnormalities are only visible when the heart is under stress. Exercise EGG is conducted for this reason. Ischemia is one of the important cardiac abnormalities and is the focus of our study. It occurs when a part of the heart tissue dies or is injured. QT dispersion (QTd) is a proposed method for diagnosing Ischemia. The classical deflnition for QTd is the difference between the maximum and the minimum QT intervals within the 12 leads. In this study the effect of exercise on QT dispersion (QTd) is studied and whether QTd could give significant information for diagnosing patients with ischemic heart disease is investigated. A new method for measuring QT interval is developed and is compared with previous methods. QTd is measured on average beats calculated for 10 seconds intervals throughout the exercise ECG test and a trend curve which we call QTd, is generated. Several decision rules for the diagnosis of cardiac patients are proposed by analyzing these QTd trend curves and the accompanying heart rate curves. It is shown that despite the improvement in QT interval measurements, none of the decision rules proved to be a clinically useful discriminate of cardiac patients, with sufficient confidence.