Accuracy of various techniques in the measurement of the duration of the Q wave: a possible source of error in diagnosing myocardial infarction by electrocardiography.

Abstract

The method of measuring the width of the Q wave on electrocardiogram is one of the variables contributing to conflicting findings regarding the accuracy of the ECG in the diagnosis of myocardial infarction. This study assesses the accuracy of a variety of methods of measuring the width of the Q wave recorded by direct-writing electrocardiographic instruments. The assessment was made by comparing the width of the Q wave as inscribed by thermal direct-writing electrocardiographs to the width of the Q wave as measured from an oscilloscopic display, the latter representing the "true" width of the Q wave. The measurement of the width as obtained from the upper edge of the tracing obtained with direct-writing electrocardiographs underestimated the true width of the Q wave, while the opposite was the case by measuring the width along the lower edge of the tracing. The most reliable ways to obtain the true width of the Q wave are: (1) to average the measurements as obtained along the upper and lower edge, (2) to measure the width along an ideal line in the middle of the tracing, or (3) to measure the width along the trailing edge of the deflection.