Abstract: A filtering scheme for an implantable medical device mitigates potentially adverse effects that may be caused by MRI-induced signals. In some aspects filtering is provided to attenuate MRI-induced signals on an implanted cardiac lead that is coupled to an implanted device. In some aspects the filter may be configured to complement a capacitor circuit (e.g., a feedthrough capacitor) that reduces the amount of EMI that enters the implanted device via the cardiac lead. In some implementations the filter consists of a LC tank circuit and a series LC circuit, where the LC tank circuit is in series with the cardiac lead and a cardiac stimulation circuit and the series LC circuit is in a shunt configuration across the cardiac stimulation circuit.

Abstract: Constant voltage or current is applied to high-voltage leads to determine impedance across medical device leads. Thyristors are used for upper switching components in an H-bridge. Current is sourced into a thyristor's gate from a ground-referenced source. This current then passes from the gate to the cathode and out to the patient. By keeping the current sufficiently low, the thyristors will not conduct from the anode to the cathode. Current passes through the thyristor, lead and patient and is sensed as it returns from the other lead. The sensed current is used to regulate the injected current. Pulses of constant current on the order of tens of milliamperes can be injected and the resulting voltage can be measured. Alternatively, a constant voltage can be applied and the resulting current can be measured to determine lead impedance.

Abstract: A medical device (implantable or external) is provided that comprises a power source, a charge storage member, a terminal connector, a switch network, a controller and a leak detection module. The charge storage member is configured to receive and store energy from the power source. The terminal connector is configured to be coupled to a lead to be implanted in a patient proximate to tissue of interest. The switch network is electrically disposed between the charge storage member and the terminal connector. The switch network changes between open and closed states to disconnect and connect the charge storage member and the terminal connector. The controller controls storage of energy in the charge storage member and delivery of stimulating pulses from the charge storage member to the lead coupled to the terminal connector. The leak detection module obtains a leakage measurement by sensing at least one of i) a voltage potential of the charge storage member and ii) current flow from the charge storage member.

Abstract: A filtering scheme for an implantable medical device mitigates potentially adverse effects that may be caused by MRI-induced signals. In some aspects filtering is provided to attenuate MRI-induced signals on an implanted cardiac lead that is coupled to an implanted device. In some aspects the filter may be configured to complement a capacitor circuit (e.g., a feedthrough capacitor) that reduces the amount of EMI that enters the implanted device via the cardiac lead. In some implementations the filter consists of a LC tank circuit and a series LC circuit, where the LC tank circuit is in series with the cardiac lead and a cardiac stimulation circuit and the series LC circuit is in a shunt configuration across the cardiac stimulation circuit.

Abstract: Current usage from a battery in an implantable cardiac device is tracked. The apparatus includes a battery current sensor having multiple current ranges. The current sensor produces a first signal representative of current drawn from a battery. A current range selector selects a current range for the battery current sensor and produces a second signal representative of the current range. An accumulator accumulates the first signal based on the second signal over time to generate an output signal representing usage of the battery.

Abstract: Methods and systems for increasing capacitor reformation efficiency in an implantable cardiac device (ICD) are presented. In one embodiment, a method and system provide for: (1) fully charging a first capacitor, (2) transferring energy from the first capacitor to an inductor, (3) transferring energy from the inductor to the second capacitor, and (4) completing charging of the second capacitor. In another embodiment, a method and system provide for: (1) fully charging a first capacitor, (2) sharing energy from the first capacitor with a second capacitor, and (3) completing charging of the second capacitor. In yet another embodiment, a method and system provide for: (1) fully charging a first capacitor, (2) sharing energy from the first capacitor with a second capacitor, (3) transferring remaining energy from the first capacitor to an inductor, (4) transferring energy from the inductor to the second capacitor, and (5) completing charging of the second capacitor.

Abstract: A method of operating an implantable medical device containing a Lithium Silver Vanadium Oxide battery. In response to a detected need for therapy, a current flow is delivered from the battery to a charge storage device. After the battery is at least partly depleted by one or more such deliveries of current or other power consumption, the battery is recharged. The recharging may be initiated in response to a selected time threshold, a selected number of current flow delivery events, a selected voltage level, an excess charge time duration, or other operating characteristics. A limited number of recharging cycles may be provided if the charging is done under controlled conditions with respect to charge current and voltage.

Abstract: A processor controlled implantable cardiac stimulation device may be placed into a shelf mode for extending the shelf life of the device. The device includes a real time clock circuit, a watch dog timer circuit having a duty cycle, a telemetry circuit capable of operation in either an active mode or a standby mode, and ancillary circuits that sense cardiac activity and provides stimulation pulses to a heart. The device includes a power source for providing power to all of the circuits of the device and a shelf mode circuit that places the device into the shelf mode. The shelf mode circuit disables power to the ancillary circuits, decreases the duty cycle of the watch dog timer, sets the processor into a static state, and sets the telemetry circuit to the standby mode. The shelf mode circuit places the device into the shelf mode in response to shelf mode commands received by the telemetry circuit to set the device from an active powered mode to the shelf mode.

Abstract: A circuit within an implantable cardiac stimulation device monitors impedance of an electrode configuration including first and second electrodes in electrical contact with a heart. The circuit is within the implantable cardiac stimulation device which applies stimulation pulses having a current and a voltage magnitude across the electrode configuration. The circuit that monitors impedance of an electrode configuration provides an impedance digital output proportional to the ratio of a stimulation pulse voltage and current.

Abstract: An implantable cardiac stimulation device possessing pacing, cardioversion and defibrillation functions and automatic capture capabilities, for automatically verifying capture during stimulation operations and, as necessary, automatically delivering back-up stimulation pulses when capture is lost, and subsequently adjusting the stimulation energy to a level safely above that needed to achieve capture. The stimulation device utilizes a method for maintaining capture by means of a capture search algorithm, so that whenever loss of capture is detected, it re-determines the minimum stimulation energy required to achieve capture. Another aspect of the stimulation device is the automatic threshold testing which is invoked to determine the minimum stimulation pulse energy needed to ensure capture.

Abstract: An implantable cardiac stimulation device possessing pacing, cardioversion and defibrillation functions and automatic capture capabilities, for automatically verifying capture during stimulation operations and, as necessary, automatically delivering back-up stimulation pulses when capture is lost, and subsequently adjusting the stimulation energy to a level safely above that needed to achieve capture. The stimulation device utilizes a method for maintaining capture by means of a capture search algorithm, so that whenever loss of capture is detected, it re-determines the minimum stimulation energy required to achieve capture. Another aspect of the stimulation device is the automatic threshold testing which is invoked to determine the minimum stimulation pulse energy needed to ensure capture.