Abstract: An implantable medical device includes electrodes coupled to a patient's heart and sensing circuitry having inputs connected to the electrodes for sensing cardiac electrical signals. The sensing circuitry includes a digital waveform analyzer system which performs direct analysis of digitized ECG heart signals from the atrial and/or ventricular channels. This eliminates the need for the system microprocessor to perform direct analysis on raw ECG data. The benefit being that complex software algorithms are not required, saving microprocessor memory space. System current drain is also reduced since the microprocessor need not be active during every ECG sample.

Abstract: The subject invention integrates a two-channel defibrillator with a programmable stimulator to provide a means for assessing lethal ventricular tachyarrhythmias and determining defibrillation thresholds during implantable defibrillator procedures. The subject apparatus includes a number of features to aid doctors as well as improve patient care at substantially decreased patient risk. These features include an automatic charging circuit, as well as dual channel high voltage capacitor circuits to reduce the time in which a rescue shock can be delivered to a patient after an initial test defibrillation shock. Parameter storage is provided to allow the unit to be preprogrammed prior to the initiation of an electrophysiologic procedure. A microprocessor controlled display system provides the physician with information parameters regarding defibrillation shocks. This displayed information includes the energy delivered and the resistance in the patient.

Abstract: A method is disclosed for combined cardiac pacing and defibrillating with an implanted pacer/defibrillator having sensing and pacing leads connected to the atrium and the ventricle. P-waves and R-waves are sensed, and V--V timer and a V--A timer are reset if an R-wave is sensed. If an R-wave is sensed during the V--V timer interval, a pacing stimulus to the ventricle is inhibited. If a P-wave is sensed during the V--A timer interval, a pacing stimulus to the atrium is inhibited. In an R-wave is sensed during the V--V timer interval, arrhythmia therapy is provided if an arrhythmia is determined to be present. If the sensed ventricular rate is greater than a selected tachycardia rate but is less than a selected fibrillation rate, then a determination is made whether the sensed atrial rate is greater than a selected fibrillation rate, and if so, the V--V and V--A timers are reset, but if the sensed atrial rate is not greater than a selected fibrillation rate, then arrhythmia therapy is provided.

Abstract: An implantable cardiac defibrillator employing a switched capacitor filter stage having charge steering resistors connected in series with corresponding switched capacitors that are coupled to a sensitive node of an operational amplifier. The stored channel charges in associated switches when they are turned off are directed away from the sensitive node. The switches associated with the switched capacitors are operated by control signals having a generally trapezoidal shaped waveform so as to slowly turn off the same, thereby reducing clock feedthrough and charge injection induced offset voltage on the output of the operational amplifier.

Abstract: An implantable cardiac defibrillator includes electrodes coupled to a patient's heart, a sensing system having inputs connected to the electrodes for sensing cardiac electrical signals from the atrial and/or ventricular channels, means for storing a charge, and means for delivering a shock to the heart. The sensing system includes switched capacitor means for amplifying the cardiac electrical signal with non-binary gain changing steps.

Abstract: A cardiac therapy method with duration timer is disclosed, using an implanted cardiac pulse generator. A patient's heartbeat is sensed and the intervals between heartbeats are averaged. The number of temporary storage bins, in the form of RAM locations, are provided, including a sinus bin, a low rate tachycardia bin, a high rate tachycardia bin, and a fibrillation bin. The storage bin corresponding to the cardiac rhythm band of the determined average heartbeat interval is incremented. A maximum count limit is assigned to each storage bin. When the first bin reaches its maximum count limit, a diagnosis of the patient's cardiac rhythm is provided. Upon detection of a tachycardia, a duration timer is started and the tachycardia is treated in accordance with a programmed routine. If sinus is detected during the predetermined time period, then the duration timer is cleared.

Abstract: A cardiac therapy method is disclosed, using an implanted cardiac pulse generator. A patient's heartbeat is sensed and the intervals between heartbeats are averaged. The number of temporary storage bins, in the form of RAM locations, are provided, including a sinus bin, a low rate tachycardia bin, a high rate tachycardia bin, and a fibrillation bin. The storage bin corresponding to the cardiac rhythm band of the determined average heartbeat interval is incremented. A maximum count limit is assigned to each storage bin. When the first bin reaches its maximum count limit, a diagnosis of the patient's cardiac rhythm is provided. Upon detection of a tachycardia, a duration timer is started and the tachycardia is treated in accordance with a programmed routine. If sinus is detected during the predetermined time period, then the duration timer is cleared.

Abstract: An implantable cardiac defibrillator includes electrodes coupled to a patient's heart, sensing circuitry having inputs connected to the electrodes for sensing cardiac electrical signals, charging means for storing a charge, and discharge means for delivering a shock to the heart. The sensing circuitry includes switched capacitor gain/filter means for providing an output signal which is transient-free during a gain change operation and which maintains a constant filter bandwidth for each gain setting.

Abstract: An implantable cardiac defibrillator employing a switched capacitor stage wherein the switches are clocked in a non-50%/50% ratio such that an operational amplifier has greater than 50% of the clock period to acquire the desired voltage and less than 50% of the clock period to hold the acquired voltage, thereby allowing the circuit to run at an overall lower current drain.

Abstract: A low battery detect circuit shuts down high current circuitry in the system in the event that battery voltage drops to a level such that the regulated output voltage is endangered. The trigger voltage is dependent upon capacitor ratios and a reference voltage. The output of the detection circuitry is a digital signal which can be used to disable high current circuitry in an implantable medical device and, thus, allow the battery voltage to recover. Alternatively, the output of the detection circuitry can be used as a battery status indicator flag.

Abstract: A method for cardiac defibrillation is described, for use with an implanted defibrillator. A patient's R-waves are sensed to detect the R-R intervals. If an arrhythmia is detected, the charging of a capacitor is commenced. Determination are made whether the arrhythmia is still in progress and whether the capacitor is charged a predetermined amount. If the arrhythmia is not still in progress, the charging is discontinued. If the arrhythmia is still in progress and the capacitors are charged a predetermined amount, another R-R interval is detected and if the R-R interval is shorter than a selected amount, a shock is delivered to the heart.

Abstract: A power supply down-conversion, regulation, and low battery detection system has application in an implantible defirillator but is also directly applicable to any battery powered implantible device. Battery voltage is down-converted by a high efficiency switched capacitor voltage divider to a suitable intermediate voltage. This voltage is then linearly regulated down to the desired output voltage. A second regulator, which takes current directly from the battery, supports the output voltage in the event that the load current cannot be supplied by the voltage downconverter. A low battery detect circuit shuts down high current circuitry in the system in the event that battery voltage drops to a level such that the regulated output voltage is endangered.

Abstract: A voltage measurement circuit is provided which can be used in a single supply situation, which has a measurement range from rail to rail and which uses a reference voltage which can lie anywhere between the rails but not at the rail to which measurements are to be referenced. The unknown voltage is sampled to a first plate of a capacitor. The second plate of the capacitor is connected to ground. The first plate of the capacitor is then connected to the first input of a comparator, the second input being connected to receive the reference voltage. If the unknown voltage is less than the reference voltage, the second plate of the capacitor is disconnected from ground and then connected to receive the reference voltage. Otherwise it remains connected to ground. The first plate of the capacitor is then connected to a constant current source, causing the voltage at the first comparator input to decrease linearly with time.

Abstract: An implantable defibrillation electrode of a shape requiring minimal incision in the body is disclosed. The electrode has a flexible insulated guide and terminates in a preconfigured flexible distal portion with an exposed conductive element. The electrode may be straightened, as for example by insertion of a stylet into the body of the electrode, for ease of insertion into the body.

Abstract: A combination two-channel defibrillator and programmable pacing stimulator for assesses lethal ventricular tachyarrhythmias and determine defibrillation thresholds during implantable defibrillator procedures. A pair of switching transistors are provided to protect the pacing circuit when a defibrillation shock is delivered. These switching transistors provide symmetric voltage protection and prevent the defibrillation energy from being shunted back to the patient through the pacing leads.