Accuracy of computer measurements of QRS duration using spatial magnitude--agreement with human readers

The beginning and end of the QRS complex in the ECG are often poorly defined, leading to poor agreement between measurements of QRS duration made by computer and human readers. In the spatial magnitude tracing, on the other hand, definition of QRS onset and offset points is less ambiguous. In 50 normal subjects, 345 QRS durations were measured by computer and visually. The correlation coefficient between the two methods was 0.93; the typical discrepancy was less than 3 msec. For a series of 100 inpatients, similar results were obtained even though one of the human readers was unfamiliar with the spatial magnitude display. Although the spatial magnitude is obtained from vectorcardiographic xyz signals, it could be derived from three simultaneous ECG leads, and applied to computer programs analyzing the 12-lead ECG.