On QRS amplitude and other errors produced by direct-writing electrocardiographs

Abstract: From the Departments of Pharmacology and Electrical Engineering University of British Columbia and of Cardiology. Vancouver General Hospital Vancouver B. C. Canada. Supported by grants from the British Columbia Heart Foundation the Canadian Heart Foundation and the National Research Council of Canada. Received for publication June 18 1962. *Assistant Professor Department of Pharmacology University of British Columbia; Consultant Shaughnessy Hospital Vancouver Canada. Address: Faculty of Medicine Department of Pharmacology University of British Columbia. Vancouver 8 B. C. Canada. **Professor Department of Electrical Engineering University of British Columbia. ***Research Assistant Department of Pharmacology University of British Columbia. ****Assistant Director Cardiology Department Vancouver General Hospital. Several studies have been made of the effect of the speed of response of the recording instrument upon the wave form of the electrocardiogram. There have been many recommendations but the different methods used to express frequency response make comparison difficult. For example Einthoven considered that if after the application of a constant potential difference the galvanometer reached its new position of equilibrium within about 0.01 second distortion of the ECG would be negligible.1 The Council on Physical Medicine and Rehabilitation of the American Medical Association laid down as a (revised) minimum requirement for an acceptable electrocardiograph that the "one centimeter response to one millivolt peak sinusoidal voltage variation up to 15 cycles per second shall not fall below 90 per cent and up to 40 cycles per second shall not fall below 80 per cent of the square wave response to equivalent voltage variation."2 Rappaport and Rappaport considered that "a galvanometric speed of approximately 0.0015 second is ample for registering the fastest electrocardiographic complexes that may be found in a mammal as small as the white mouse whose average normal heart rate is approxilnately 570 beats per minute."3 Gilford4 recommended a frequency response flat to 200 cycles per second and more recently Geselowitz Langner and Okada have reported that "a recorder flat to at least 500 cps is necessary."5 An adequate low-frequency response on the other hand hardly seems to be a problem 6 but it has been pointed out in an excellent description of the types of distortion produced by instrument error that the 2-second time constant commonly used can give appreciable distortion in extreme cases e.g. electrocardiograms which show monophasic patterns.7 . . .

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