Abstract: A method for analyzing a cardiac signal, e.g. an electrocardiogram signal, comprises continuously generating values RR(t) and QT(t), representing the RR and QT intervals respectively as functions of time, and operating on one or both values to compensate for the naturally occurring delay between the change in the RR interval and the resulting change in the QT interval. A delay may be introduced into the RR(t) value by a resistor-capacitor network having two time constants T1 and T2. After compensating for the delay, S(t), the slope of the graph of the QT interval against the RR interval may be found and used to generate Qtc(t), the corrected QT interval at a standard RR interval. Alternatively, an advance may be introduced into the value QT(t). Apparatus for generating Qtc(t) may include a hybrid digital/analog circuit applying an “xth root law.

Abstract: A method and apparatus for monitoring recurrent waveforms such as electrocardiogram (e.c.g.) waveforms. The e.c.g. apparatus comprises integrators and stores for storing integrated segments of a normal, reference waveform complex. A timing circuit derives timing signals from the e.c.g. waveform to be monitored. The timing signals represent the time location of particular selected parts of the waveform which are to be compared with the corresponding parts of the stored waveform. The e.c.g. waveform is corrected by subtracting a version of the waveform after it has passed through a low pass filter from a delayed version. Corrected segments of the waveform are integrated and subtracted from the corresponding stored segments of the reference waveform to provide a difference signal and the difference signals are quantitatively summed. An output signal is produced if the total sum of the magnitudes of the difference signals exceeds a predetermined value to indicate an abnormal complex.