Computerized measurement of the first derivative of the QRS complex: Theoretical and practical considerations

Abstract

The first derivative ( dV dt ) of the QRS complex has been used to assess high-frequency QRS notching. However, prior investigators did not evaluate the amplitude of QRS dV dt . Theoretically, myocardial infarction should decrease QRS dV dt by slowing ventricular conduction and by reducing electromotive potentials. To further study QRS dV dt , we employed a high-fidelity, microprocessor-based electrocardiograph with a signal-averaging algorithm to reduce noise. The analog ECG output of 256 averaged beats was digitized at 4000 samples/sec and QRS dV dt was obtained using a five-point Lagrangian polynomial. Two parameters were then measured in leads I and aVL in 12 normal subjects and 19 patients with anterior wall infarction: (1) The number of isoelectric baseline corssings of QRS dV dt , an index of QRS notching, and (2) the root-mean-square (rms) value of QRS dV dt , an index of its effective amplitude. QRS notching in both leads was greater ( p < 0.025) but rms dV dt was lower among infarct patients ( p < 0.0025 in lead I). Furthermore, a negative correlation was obtained between QRS notching and rms dV dt in both lead aVL ( r = −0.61) and lead I ( r = −0.73). These data support a previous computer model which suggested that QRS notching should correlate negatively with QRS slope. Measurement of the amplitude of QRS dV dt is a new application of computer methodology to ECG analysis with theoretical and potential clinical relevance.