High-fidelity ECGs. defined as ECG signals including high-frequency components, have been studied and variations in the incidence of fine notches and slurs on the QRS complex were reported in different myocardial pathologies. These observations might be of clinical importance since they suggested a noninvasive marker for cardiac dysfunctions. We studied high-fidelity ECG waveforms displaying pronounced notches and slurs. Signals were obtained from 12 anesthetized dogs. Computer analysis included digital averaging, followed by digital filtering in different frequency bands in order to determine the frequency range corresponding to notches and slurs. Low-pass filtering of the low-noise average waveforms was performed while gradually lowering the upper frequency limit, until the fine notch (or slur) could no longer be visually detected, thus determining the lower limit of its frequency content. A band cutoff filter was then applied to the original average waveform. The lower limit of the band cutoff filter was set at the frequency previously determined as the lower limit of the notch (or slur), and its upper limit was determined by gradual raising until the notch (or slur) was visually indistinct. Following this approach, the notches were found to contribute to a frequency range of 40-185 Hz, whereas the slurs contributed only to the lower subrange of this frequency band below 100 Hz. 'Q 1989 Academic Press. Lnc QRS notching has been extensively studied during the last decades (I-10). Various investigators observed changes in the notching pattern and an increased incidence of notches and slurs characteristic of different myocardial pathologies. They suggested that their findings might be of clinical importance and that appropriate analysis of the notches and slurs might constitute a step toward additional noninvasive diagnostic methods based on surface electrocardiograph y .
Yet, the distinction between the notches and the high-frequency noise is difficult to make and an accurate definition of the limits of the notching frequency range is needed to allow for reliable ECG recording devoted to notching examination. Nevertheless, few noticeable attempts have been made to determine the relevant frequency range. Van der Ark and Reynolds (II) suggested that the notches and slurs appearing on the QRS complex correspond to a wide frequency band of 80-300 Hz. However, this definition seems to lack necessary 18