Abstract: There is provided an implantable cardiac pacing system or other cardiac monitoring system having an enhanced capability to classify intracardiac signals through a combination of DSP techniques and software algorithms. The implantable device has one or more DSP channels corresponding to different signals which are being monitored. Each DSP channel most preferably amplifies the incoming signal, converts the signal from analog to digital form, digitally filters the converted signals to provide a filtered signal, operates on the filtered signal to provide a slope signal, determines from the filtered and slope signals when an intracardiac event has been detected, signal processes the filtered and slope signals for a predetermined analysis interval after threshold crossing, and generates a plurality of wave parameters corresponding to the signal.

Abstract: An implantable medical device and associated method perform ECG morphology monitoring. A subcutaneous ECG signal and a posture signal are sensed in a patient. A cardiac condition is detected in response to the ECG signal and the posture signal. In one embodiment, multiple ECG morphology templates corresponding to each of a number of different patient postures are acquired and stored for use in detecting a cardiac condition.

Abstract: A method and device for detecting the implanted orientation of an implantable medical device (IMD) in a patient. IMD includes an accelerometer for measuring acceleration signals in three orthogonal directional axes. A y-axis orientation of IMD is determined from the measured accelerometer signals using a gravitational force analysis. IMD includes a magnetic sensor that senses a varying magnetic field exerted on the magnetic sensor from an external magnet moved along a medial-lateral direction with respect to IMD. The z-axis orientation of IMD is determined from the location of the external magnet where the magnetic field exerted on the magnetic sensor is greatest. Based on a known relationship between the accelerometer and magnetic sensor, an orthogonal transformation calculation is performed on the y-axis and z-axis orientations to yield the x-axis orientation. The implanted orientation of IMD with respect to the patient is thus known and used to compensate accelerometer measurements.

Abstract: An implantable medical device and associated method perform ECG morphology monitoring. A subcutaneous ECG signal and a posture signal are sensed in a patient. A cardiac condition is detected in response to the ECG signal and the posture signal. In one embodiment, multiple ECG morphology templates corresponding to each of a number of different patient postures are acquired and stored for use in detecting a cardiac condition.

Abstract: A method of classifying arrhythmias using scatter plot analysis to define a measure of variability of a cardiac rhythm parameter such as for example, without limitation, R-R interval, A-A interval, and the slope of a portion of a cardiac signal, is disclosed. The variability measurement is derived from a scatter plot of a cardiac rhythm parameter, employing a region counting technique that quantifies the variability of the cardiac rhythm parameter while minimizing the computational complexity. The method may be employed by an implantable medical device or system, such as an implantable pacemaker or cardioverter defibrillator, or by an external device or system, such as a programmer or computer. The variability measurement may be correlated with other device or system information to differentiate between atrial flutter and atrial fibrillation, for example. The variability information may also be used by the device or system to select an appropriate therapy for a patient.

Abstract: An implantable medical device operates to promote intrinsic ventricular depolarization according to a pacing protocol. When a cardiac rate exceeds a predetermined threshold, the implantable medical device modifies the pacing protocol parameters to promote AV synchrony.

Abstract: A Ventricular Pacing Protocol (VPP) is provided that reduces ventricular pacing. The VPP has varying levels of aggressiveness that are more or less tolerant of an absence of intrinsic ventricular activity within a given interval. During periods of sleep, the VPP is adjusted to a more aggressive level to further reduce ventricular pacing based upon the reduced hemodynamic requirements of a patient during sleep.

Abstract: An implantable medical device operates to promote intrinsic ventricular depolarization according to a pacing protocol. The medical device determines a course of action based upon the presence or absence of sensed ventricular activity. The device further determines whether that activity is properly conducted or the result of a PVC or nodal rhythm.

Abstract: Systems and methods for distinguishing a valid sensed cardiac signal from an invalid signal, such as a myopotential. In one embodiment, sensing an electrical signal with one electrode causes a timing window to commence. When the electrical signal is sensed by another electrode in the timing window, the sense is deemed valid. When the electrical signal is not sensed by the other electrode in the timing window, the sense is deemed invalid. Therapy may be adjusted when an inordinate number of senses are invalid.

Abstract: There is provided a system and method of rate responsive pacing, having an intrinsic QT rate sensor. The system has the capability of sensing the QT interval of intrinsic cardiac signals and constructing from such intrinsic QT data a QT reference curve. The QT reference curve is used for comparison with beat-to-beat QT interval data, in order to provide sensor information for controlling pacing rate. The system of this invention preferably utilizes DSP circuitry for determining the occurrence of a Twave event and the timing of the Twave, from which the QT interval is calculated. The system also provides for compensation of any QT interval which is calculated following ventricular pacing, so that the QT sensor is operative at all times and throughout the entire rate range experienced by the patient. The system thereby provides an enhanced QT rate responsive pacing arrangement, and avoids the need of overdrive pacing in order to obtain QT reference data.

Abstract: Polarization signals, which represent voltages measured at a pacemaker electrode, are not constant and may drift. Polarization signal drift, which often precedes undesirable pace polarization artifacts, is more significant when the pacemaker is inhibited from providing an electrical stimulation to the patient's heart. The present invention provides an implantable system and methods for stabilization of a polarization signal. Electrical pulses may be applied to stabilize a polarization signal. In one implementation of the invention, polarization signal stabilization may be used as part of process to terminate tachycardia.

Abstract: There is provided a system and method of rate responsive pacing, having an intrinsic QT rate sensor. The system has the capability of sensing the QT interval of intrinsic cardiac signals and constructing from such intrinsic QT data a QT reference curve. The QT reference curve is used for comparison with beat-to-beat QT interval data, in order to provide sensor information for controlling pacing rate. The system of this invention preferably utilizes DSP circuitry for determining the occurrence of a Twave event and the timing of the Twave, from which the QT interval is calculated. The system also provides for compensation of any QT interval which is calculated following ventricular pacing, so that the QT sensor is operative at all times and throughout the entire rate range experienced by the patient. The system thereby provides an enhanced QT rate responsive pacing arrangement, and avoids the need of overdrive pacing in order to obtain QT reference data.

Abstract: Systems and methods for distinguishing a valid sensed cardiac signal from an invalid signal, such as a myopotential. In one embodiment, sensing an electrical signal with one electrode causes a timing window to commence. When the electrical signal is sensed by another electrode in the timing window, the sense is deemed valid. When the electrical signal is not sensed by the other electrode in the timing window, the sense is deemed invalid. Therapy may be adjusted when an inordinate number of senses are invalid.

Abstract: There is provided a system for regulating ventricular rate in the presence of abnormally high atrial rates, e.g., during episodes of atrial fibrillation. During such an episode, the system, preferably incorporated into an implantable pacemaker, applies subthreshold bursts of stimulus pulses to or proximate to the patient's AV node so as to inhibit conduction of electrical signals through to the ventricle during the bursts. The bursts are timed in relation to the last conducted ventricular signal, and in terms of burst length, to provide a rate of conducted signals through the AV node which results in a substantially regular and reduced ventricular rate. During the inhibition mode of operation, the system monitors to determine the efficacy of inhibition, by tracking the percentage of ventricular senses that occur during the burst periods.