Q. What is QT Dispersion?

Is the difference between the QT interval measured from one part of the heart and the QT interval measured from another part of the heart. The QT interval must be measured in each leads, corrected for the heart rate and compared with all the other leads. The difference between the longest QT and the shortest is dispersion. QT dispersion has been studied extensively in patients with myocardial injury and has been found to correlate with the risk of serious ventricular arrhythmias and has also been measured before and after exercise. Patients with maximum QT dispersion with exercise are more likely to have ischaemia. It is found that when an increase in QT dispersion of greater than 20 msec is combined with ST depression, the specificity is 87 per cent. The measurements necessary to calculate dispersion however, are time consuming. Recently an automated method to measure dispersion has been reported. If it proves to be accurate and commonly available it may add to the parameters available identify ischaemia.