Abstract: An improved automatic sensing threshold control for cardiac rhythm detection in an implantable device. The improvement includes setting the sensing threshold according to the amplitude of both sensed signals corresponding to cardiac activity and sensed noise, for setting the threshold substantially below the sensed signal amplitude, but above the noise amplitude. The invention provides absolute refractory periods after pacing or sensing, followed by a retriggerable noise refractory period. Following sensing the device sets the sensing threshold to approximately one-fourth of the measured amplitude, and then increases the threshold when it detects noise.

Abstract: A method and apparatus for optimizing the sensing circuit of a tachyarrhythmia detector for use with direct heart (cardiac) electrodes. The method is applied to detection of ventricular fibrillation and multifocal ventricular tachyarrhythmia, with rejection of T wave and pacing artifact. The sensing circuit optimized with this method includes a third-order high-pass filter followed by at least one comparator, with the filter corner frequency near 16 Hz and the comparator threshold near 0.40 mV referred to the input, in-band.

Abstract: A configuration for generating single capacitor multiphasic shocks is disclosed, using an H-bridge with four switches to connect an energy storage capacitor to a load with selectable polarity. The improvement concerns referring the negative side of the shock generator to a supply voltage which is negative with respect to pacing and sensing ground, and to connect the battery positive terminal to this same ground. This configuration permits operating the low side switches in the H-bridge, the pace/sense circuits, and the control circuitry from negative supplies derived without inversion from the negative battery terminal.

Abstract: A process and device to control a cardiac pacemaker enslaved to at least one physiological parameter. The pacemaker also possesses a mode of desynchronization of the ventricular stimulation when the atrial rhythm is too rapid for synchronous operation. One compares a detected coupling interval (PP) with an escape interval calculated by the enslavement (EI.sub.ASSERV). The calculated enslavement escape interval is preferably decreased by a prematurity factor (x), for example, 0 to 50%, preferably approximately 37.5%, of the calculated escape interval. After the comparison, one counts the number of cardiac cycles for which the coupling interval detected is less than the calculated escape interval, and one triggers the mode of desynchronization (FALLBACK) when the count exceeds a given threshold (y), for example 50 to 75%, preferably approximately 75% of the total number (N) of cardiac cycles analyzed.

Abstract: Process of control of an implantable active medical device. The device is under the responsive control of (enslavement to) a sensed physiological parameter. A representative magnitude of the physiological parameter is measured in the presence of a useful signal to determine a value of the parameter. Then, in the absence of the useful signal, another measure is made to determine the noise. The noise is compared to a threshold corresponding to an unacceptable level of noise. In case of crossing the noise threshold, this crossing is taken in account by a control device with a view to possible suspension of a function of the device if there is too much noise.

Abstract: This invention provides an improved Holter function in an implantable device for arrhythrnia monitoring or therapy. One improvement consists of a zoom feature which stores information about an arrhythmia episode at several levels of detail, with increasing levels of detail corresponding to shorter recording periods, and with a way to display the relation in time of the recordings at different levels of detail. The invention also introduces a novel implantable Holter function called an event log, which records time-stamped events once each minute, on changes in detected rhythm, or on application of antiarrhythmia therapy. The invention also provides logic for arbitrating which arrhythmia episodes the device saves in its memory.

Abstract: Process for controlling a double atrial triple chamber pacemaker having a right atrial electrode and a left atrial electrode connected to one and the same atrial circuit for the detection/stimulation of the atrium, as well as a ventricular electrode connected to a ventricular circuit for the detection/stimulation of the ventricle.

Abstract: A heart signal sensor 11 is connected by a flexible cord 13 to a catheter 17. The sensor 11 and the catheter 17 are attached to install the sensor in the cardiac wall, and thereafter are disunited and separately attached to the cardiac wall 1. The sensor is attached to the cardiac wall by claws projecting from the sensor surface, and may be installed by rotating or by deformation of the sensor.

Abstract: Methods and apparatus for classifying cardiac rhythm by analyzing sensed atrial and ventricular heartbeats, and determining if the rhythm might be pace-terminable in a given chamber. The method maintains a histogram of the sensed beat interval in the chamber of interest and a second histogram of conduction time from the other chamber. The method classifies a rhythm as pace terminable in the given chamber when the intervals in that chamber are stable, and the conduction times to that chamber are unstable. It applies further criteria when the intervals in the given chamber are stable, and the conduction times are also stable. Antitachycardia pacing is deliverable to terminate tachyarrhythmias determined to be pace terminable.

Abstract: During a calibration phase, the representative characteristics of a parameter are determined, a reference value is deduced for determining pacing efficiency, and during a threshold search phase, the value of the capture threshold is determined as a function of pacing efficiency.

Abstract: A circuit for use in an implantable cardiac pacemaker for use in processing intracardiac signals and methods of processing such signals. The circuit includes a passive filter 1 has a bandwidth of 0.1 to 80 Hz approximately. An amplifier 2 with switched capacitors presents at the output a dynamics of 0.8V approximately and a gain lower than 50. An analog-to-digital converter 3 with delta modulation, which is controllably variable in step and functions at two frequencies, one of 1 kHz approximately, the other of 4 kHz approximately. The circuit may be used for both processing said signals to identify spontaneous cardiac events and to telemeter an intracardiac ECG.

Abstract: An extractable cardiac probe comprising a catheter (4) and a sleeve (3) that is at least partially deformable and mountable to the catheter. The procedure for application of the extractable probe uses an extractor device (11) equipped to pass between the sleeve and catheter to deform the sleeve (3) elastically to permit removal and replacement of the catheter.

Abstract: Control of an anti-tachycardia device such as a defibrillator to apply a preselected programmed therapy in the event of ventricular tachycardia. The control includes comparison of the atrial and ventricular rhythms, and examination of the criteria of stability of the P-R intervals, of the stability of the R-R intervals, and of the acceleration of the ventricular rhythm subsequent to an atrioventricular desynchronization, thereby to ensure control of the antitachycardia device solely in the event of ventricular tachycardia.

Abstract: A method for automatic control of sensitivity, for implanted pacemaker, cardioversion and/or cardiac defibrillation device. Prior to the start of the cardiac cycle, the sensitivity threshold is set to a low value (Smax) so as to have maximum sensitivity. Upon detection of a ventricular complex, the amplitude is measured and the sensitivity threshold S is set to the value of that amplitude. The sensitivity threshold subsequently decreases in stages to return to the low value Smax.

Abstract: A pacemaker with patient effort-controlled stimulation frequency that responds to a control parameter. Accelerometers (1) with capacity variation are placed on a substratum. Each of the accelerometers is sensitive in one direction of a Cartesian coordinate system. The output of the accelerometers are combined and integrated over a small time constant to produce a signal representative of the patient's metabolic power exerted. The signal is then used to control the stimulation frequency of the pacemaker. The integration may be based on the sum of the absolute value of the acceleration signals or the square root of the sum of the squares of the acceleration signals.

Abstract: The difference between the divergences between the determined PR and RR intervals (dPR-dRR) is measured, cycle by cycle, and compared to two selected thresholds S1 and S2. If the difference exceeds threshold S1, a signal corresponding to a ventricular tachycardia is triggered. If the difference is below threshold S2, a signal corresponding to a supraventricular tachycardia related signal is triggered. The trigger signals may be used to control the therapeutic treatment of an implantable tachycardia treatment device accordingly.

Abstract: A cardiac pacemaker that is programmable to have one of a DDD and an AAI pacing mode of operation such that the pacing mode best suited to the patient's physiological condition is selected and implemented. The heart is paced in the AAI mode during periods of atrio-ventricular conduction. It automatically switches to pacing the heart in the DDD mode in response to a lack of atrio-ventricular conduction, and automatically switches back to the AAI mode after occurrence of a restoration event including restoration of atrio-ventricular conduction. Time delays for use in the DDD mode are calculated during operation in the AAI mode prior to loss of atrio-ventricular conduction and other timing delays for monitoring the patient's current physiological condition for mode switching are calculated.

Abstract: Upon detection of a ventricular extrasystole, a pacing control algorithm is brought into play to trigger: a stimulation of the atrium, a controlling of the atrium at a faster pacing rate than that of the ventricle during some cycles, a synchronous controlling of the ventricle during a period that is a multiple of a programmed number of cycles, and subsequent to the programmed number of cycles, a slowing of the ventricular rate until either the programmed base rate is reached or a further sinus detection occurs. The algorithm is inactivated on certain conditions, inhibited on certain conditions, and reactivated on further sensed ventricular extrasystoles.

Abstract: A cardiac pacemaker having a pacing rate responsive to a control function of a physiological parameter indicative of activity levels. The coefficients of the function are automatically calculated and modified in response to the trend of the measured physiological parameter in order to correspond to the patient real needs. For monitoring the physiological parameter minute ventilation (VE), the basic value VE low and maximum value VE max are calculated in order to vary the slope and intercept of the straight line representative of the control relation of the pacing rate FC by the minute volume VE.

Abstract: A method for calculating the atrial escape interval. A calculation is made of the average value of the delays between two "P" waves measured over 8 heart cycles, and this average value is taken as the value of the atrial escape interval. The "P" wave is monitored to identify atrial extrasystole so that only competent "P" waves are used in determining the average value and, hence, the atrial escape interval.