Defibrillation pacing circuitry
Electrical circuit componentry is switchable into a defibrillator circuit to deliver a constant pacing current to a patient. The circuitry may include a constant current source inserted in a leg of the defibrillator circuit or a resistor of selected value inserted between a high voltage source and the high side of a defibrillator circuit.
1. An implantable apparatus for delivering electrical cardiac therapy to a patient, the implantable apparatus comprising:
power circuitry for creating a cardiac therapy signal, the power circuitry including a capacitive circuit chargeable to create the cardiac therapy signal;
an H-bridge circuit for delivering the cardiac therapy signal from the power circuitry to the patient, the H-bridge circuit comprising at least first and second legs each having high and low sides;
current controlling circuitry coupled to the H-bridge circuit for selectively controlling current passing through the H-Bridge; and
an implantable housing containing each of the power circuitry, H-Bridge Circuit, and current controlling circuitry;
wherein the implantable apparatus is configured to use at least:
a first configuration in which the current controlling circuitry modifies the cardiac therapy signal to provide a generally constant current signal to the patient, and
a second configuration in which the current controlling circuitry does not substantially modify the cardiac therapy signal so that the power circuitry provides a time-decaying signal to the patient.
2. The implantable apparatus of claim 1 , wherein the first configuration is a pacing configuration, and the second configuration is a defibrillation configuration.
3. The implantable apparatus of claim 1 , wherein the current controlling circuitry includes:
a transistor element;
a voltage source coupled to the transistor element to provide a control signal controlling a current output of the transistor element;
a resistor coupled to the transistor element to receive the current output of the transistor element; and
a bypass switch parallel to the resistor.
4. The implantable apparatus of claim 3 , wherein:
the current controlling circuitry further includes an amplifier having a first input, a second input, and an output;
the voltage source is coupled to the transistor element via the amplifier;
the first input of the amplifier is coupled to the voltage source;
the second input of the amplifier is coupled to the current controlling circuitry to provide a feedback signal to compensate for the transistor; and
the output of the amplifier is coupled to the transistor.
5. The implantable apparatus of claim 1 wherein the current controlling circuitry couples the power circuitry to the H-bridge circuit.
6. The implantable apparatus of claim 1 wherein the current controlling circuitry is coupled to a low side of at least one leg of the H-Bridge circuit.
7. An implantable apparatus for delivering electrical cardiac therapy to a patient, the implantable apparatus comprising:
power circuitry for creating a cardiac therapy signal, the power circuitry including a capacitive circuit chargeable to create the cardiac therapy signal;
an H-bridge circuit for delivering the cardiac therapy signal from the power circuitry to the patient;
current controlling circuitry for selectively controlling current passing through the H-Bridge; and
an implantable housing containing each of the power circuitry, H-Bridge circuit, and current controlling circuitry;
wherein the implantable apparatus is configured to use at least:
a first configuration in which the current controlling circuitry modifies the cardiac therapy signal to provide an approximately constant current signal to the patient, and
a second configuration in which the current controlling circuitry allows the power circuitry provides a time-decaying signal to the patient.
8. The implantable apparatus of claim 7 , wherein the first configuration is a pacing configuration, and the second configuration is a defibrillation configuration.
9. The implantable apparatus of claim 7 , wherein the current controlling circuitry includes:
a transistor element;
a voltage source coupled to the transistor element to provide a control signal controlling a current output of the transistor element;
a resistor coupled to the transistor element to receive the current output of the transistor element; and
a bypass switch parallel to the resistor.
10. The implantable apparatus of claim 9 , wherein:
the current controlling circuitry further includes an amplifier having a first input, a second input, and an output;
the voltage source is coupled to the transistor element via the amplifier;
the first input of the amplifier is coupled to the voltage source;
the second input of the amplifier is coupled to the current controlling circuitry to provide a feedback signal to compensate for the transistor; and
the output of the amplifier is coupled to the transistor.
11. The implantable apparatus of claim 7 wherein the current controlling circuitry couples the power circuitry to the H-bridge circuit.
12. The implantable apparatus of claim 7 wherein the current controlling circuitry is coupled to a low side of at least one leg of the H-Bridge circuit.