The repetitive nature of cardiac waveforms renders them suitable for processing by signal averaging. A flexible system is described, based on a general-purpose digital computer, capable of averaging a variety of cardiac signals in excess of 0.5 microV containing frequency components below a theoretical Nyquist limit of 5 kHz. Important features of the system include real-time processing capability at a high level of interactive control, and the facility to trigger the averaging process accurately from any part of either the data or a synchronous reference waveform. Application of the system to electrocardiographic and phonocardiographic signals at conventional gain has enabled clinically useful records to be obtained in the face of obtrusive environmental noise. The averaging of signals of a similar nature after considerably increased amplification has revealed cardiac activity unseen in conventional records in a total of 81 subjects.
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