Ventritex, Inc.

John G Ryan

Benjamin D Pless

Roubik Gregorian

James M Culp

The present invention is directed to various features of an implantable combined defibrillation/pacemaker system. The system's defibrillation delivery circuit provides for delivery of a multi-phase defibrillation waveform. It also includes features for insuring low patient current leakage. Protection circuitry is provided for protecting the pacing circuitry from damage by the high voltage defibrillation output. The dual channel cardiac pacing circuit accommodates bipolar and pseudo-unipolar pacing. The system includes the ability to detect defibrillator lead breaks without delivering a defibrillation pulse to the patient. An additional advantage of the disclosed system is its ability to use the pacing output stage for extremely high rate pacing to induce ventricular fibrillation.

System configuration for combined defibrillator/pacemaker

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.

Power supply down-conversion, regulation and low battery detection system

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.

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. By measuring the elapsed time between the connection of the first capacitor plate to the constant current source and a change of state of the comparator due to the voltage decrease at its first input, the difference in voltage between the unknown voltage and the reference voltage or ground can be determined based on the linearity of the time-voltage relationship.

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San Jose, CA, United States of America

John G Ryan