The present invention relates to digital signal processing using waveform morphology. In particular, the invention relates to processing signals, such as sensed cardiac signals distorted by cross talk or other noise, to identify a signal component of interest.
Implantable medical devices (IMD's) are used for a variety of monitoring and therapy delivery purposes. Many IMD's sense physiologic signals and provide outputs, either in the form of delivered therapy or in the form of monitored physiologic activity. For example, pacemakers and implantable cardioverter defibrillators (ICD) include electrodes (and in some cases other sensors) to sense cardiac activity. The sensed signals representing cardiac activity are processed in signal processing channels, and are used in the detection of cardiac arrhythmias and other conditions that require the delivery of therapy. The types of therapy that can be delivered include, for example, pacing pulses and cardioversion/defibrillation shocks delivered to the heart.
An IMD that is monitoring or delivering therapy to the heart must accurately process sensed signals that may contain noise, such as cross talk, that distorts the signal waveform. For example, a sensed signal from an atrial electrode will typically contain a P-wave signal representing depolarization of the atrium and a Far Field R-wave (FFRW) signal, which occurs when an atrial electrode detects an electrical signal resulting from ventricular depolarization.
The Far Field R-wave is normally an unwanted atrial sensed signal, and can be considered cross talk or noise. Various techniques have been developed in the past to distinguish between P-waves and Far Field R-waves, so that a Far Field R-wave is not erroneously identified as P-wave.
Signal processing of physiologic signals, such as signals representing cardiac activity, has generally been performed in IMDs by analog circuitry. Digital signal processing offers potential benefits that have been used in IMDs. In digital signal processing, the incoming sensed signal is converted to a digital signal at a specified rate. Sampled waveform data representing the input signal can then be processed digitally, which permits more sophisticated signal analysis and has generally been available with analog circuitry.
The Wohlgemuth et al. U.S. Pat. No. 6,556,859 describes the use of digital signal processing to classify sensed atrial signals as P-wave or Far Field R-waves, based upon form factor histograms. In this technique, there must be some time separation between the P-wave form factor histogram and the R-wave form factor histogram, so that each has a specific form or shape. Other techniques are required if there is an overlap or near overlap.
If a P-wave signal and a Far Field R-wave signal occur to close in time, the resulting atrial signal will have a waveform which is a combination of the two overlapping signal components. The sensed atrial waveform may be distorted to the extent that it does not resemble either of the two waveform components (P-wave and FFRW) that are overlapping. Digital signal processing techniques with the ability to extract and identify the waveform component of interest, such as the P-wave in an atrial sensed signal, would be advantageous.