Measurement of high resolution ECG QT interval during controlled euglycaemia and hypoglycaemia

During hypoglycaemia, typically there is a change in the surface ECG charac terized by a flattened and prolonged T wave, often accompanied by a fused U wave. The QT interval is a useful parameter for quantifying the ECG morpho logy. However, reliable measurement of QT is not straightforward, particula rly for hypoglycaemic ECG morphology. The objective of this study was to co mpare the ability of two methods of QT measurement to distinguish between E CGs recorded during euglycaemia and hypoglycaemia. The first method involve s manually setting the intersection of the isoelectric line and the T wave or, where this is not possible, the nadir between the T and U wave. The sec ond method is semi-automatic and fits a tangent to the point of maximum gra dient on the downward slope of the T wave. Two independent observers used b oth methods to measure the QT for high resolution ECG data recorded during a study of 17 non-diabetic subjects undergoing controlled euglycaemia and h ypoglycaemia. Using the mean results of the two observers, the mean +/- SD increase in heart rate corrected QT, QTc, for ECGs recorded during euglycae mia and hypoglycaemia was 32 +/- 25 ms for the non-tangent method and 60 +/ - 24 ms for the tangent method. Therefore, the tangent method provides grea ter distinction between ECGs recorded during euglycaemia and hypoglycaemia than the non-tangent method. A potential clinical application could be the non-invasive detection of impending hypoglycaemia at night, which would be of significant benefit to adults and young children with diabetes.