Method and implantable system for constant current pacing
An implantable system includes an implantable medical device (IMD) and a non-transvenous lead that is configured to be implanted outside of a heart. The IMD includes an output configured to be connected at least to the lead, a current generator (CG) circuit configured to generate pacing pulses, a switching circuit coupled between the CG circuit and the output, one or more capacitors coupled in parallel with the CG circuit and the switching circuit, and a control circuit coupled to the CG circuit. The control circuit is configured to manage the CG circuit to generate the pacing pulses with a constant current at the output.
1 . An implantable medical device (IMD), comprising:
a case including an output configured to be connected to a lead;
a current generator (CG) circuit configured to generate pacing pulses at the output, the CG circuit having a transformer with a primary winding and a secondary winding, a switch device connected with the primary winding, and an output diode connected with the secondary winding, the switch device configured to control conduction of electrical energy from a power source to the CG circuit;
a switching circuit coupled in parallel with the CG circuit and the output between the output diode of the CG circuit and the output;
one or more capacitors coupled in parallel with the CG circuit and the switching circuit between the output diode of the CG circuit and the switching circuit; and
a control circuit coupled to the CG circuit and the switching circuit, the control circuit configured to manage the CG circuit during a low voltage mode to generate the pacing pulses, the control circuit configured to control the CG circuit and the switching circuit during a high voltage mode to charge the one or more capacitors and use the electrical energy stored in the one or more capacitors to deliver one or more shock pulses to the output,
wherein, during the low voltage mode, the control circuit is configured to close the switching circuit to provide a closed, electrically conductive pathway between the secondary winding and the output, and to control the CG circuit such that the pacing pulses are generated from the secondary winding and conducted through the switching circuit to the output without the one or more capacitors or any other capacitor between the CG circuit and the switching circuit generating the pacing pulses.
2 . The IMD of claim 1 , wherein the control circuit is configured to manage the CG circuit during the low voltage mode to generate the pacing pulses having a constant current at the output.
3 . The IMD of claim 1 , wherein the control circuit is configured to vary a duty cycle of control signals supplied to the CG circuit to define a shape of the pacing pulses.
4 . The IMD of claim 1 , wherein the control circuit is configured to vary a duty cycle of control signals supplied to the CG circuit to define a pulse width of the pacing pulses.
5 . The IMD of claim 1 , wherein the control circuit is configured to open and close the switch device of the CG circuit according to a duty cycle to generate the pacing pulses at the secondary winding.
6 . The IMD of claim 1 , wherein the switch device is a first switch device, and the switching circuit is arranged in an H-bridge configuration including the first switch device and a second switch device, a third switch device, and a fourth switch device, wherein the first and second switch devices are coupled in parallel on a first side of the output and the third and fourth switch devices are coupled in parallel on an opposite, second side of the output relative to the first and second switch devices.
7 . The IMD of claim 1 , further comprising the lead, wherein the lead includes an electrode segment for delivering the pacing pulses from the output to a patient during the low voltage mode and delivering the one or more shock pulses from the output to the patient during the high voltage mode, the electrode segment comprising one or more of a ring electrode, a tip electrode, or a coil electrode.
8 . The IMD of claim 7 , wherein the electrode segment of the lead is configured to be implanted proximate to a xiphoid process of the patient and a lead body of the lead is configured to extend from the electrode segment along an inter-costal area of the patient to the case.
9 . The IMD of claim 1 , further comprising the lead, wherein the lead includes a first electrode segment and a second electrode segment spaced apart from each other along a length of the lead, wherein the output is configured to convey the one or more shock pulses to at least one of the first electrode segment or the second electrode segment for delivering electrical stimulation therapy to a patient.
10 . The IMD of claim 1 , wherein the output includes a plurality of terminals electrically connected to different electrodes on at least one of the lead or the case, wherein the control circuit is configured to control the switching circuit to select a subset of the electrodes to define an electrode vector for delivering at least one of the pacing pulses or the one or more shock pulses.
11 . The IMD of claim 1 , further comprising one or more physiological sensors disposed on or within the case and communicatively connected to the control circuit, the one or more physiological sensors configured to monitor one or more of respiration rate, pH of blood, ventricular gradient, physical activity, body movement, posture, or minute ventilation of a patient in which the case is implanted.
12 . The IMD of claim 1 , wherein the control circuit is configured to manage the CG circuit to generate the pacing pulses by opening and closing the switch device of the CG circuit according to a duty cycle.
13 . The IMD of claim 1 , further comprising the power source within the case, the power source configured to supply the electrical energy to the CG circuit to power the CG circuit for generating the pacing pulses.
14 . A method comprising:
managing, via a control circuit, a current generator (CG) circuit of an implantable medical device (IMD) to generate pacing pulses at an output of the IMD during a low voltage mode, the pacing pulses configured to be delivered to a patient via a lead implanted within the patient, the CG circuit having a transformer with a primary winding and a secondary winding, a switch device connected with the primary winding, and an output diode connected with the secondary winding,
wherein the IMD further comprises a switching circuit and one or more capacitors, the switching circuit coupled in parallel with the CG circuit and the output between the output diode of the CG circuit and the output, the one or more capacitors coupled in parallel with the CG circuit and the switching circuit between the output diode of the CG circuit and the switching circuit;
controlling conduction of electrical energy from a power source to the CG circuit using the switch device;
closing, via the control circuit, the switching circuit to provide a closed, electrically conductive pathway between the secondary winding and the output during the low voltage mode so that the pacing pulses are generated from the secondary winding and conducted through the switching circuit to the output without the one or more capacitors or any other capacitor between the CG circuit and the switching circuit generating the pacing pulses;
switching from the low voltage mode to a high voltage mode; and
controlling the CG circuit and the switching circuit, via the control circuit, to charge the one or more capacitors during the high voltage mode and use electrical energy stored in the one or more capacitors to deliver one or more shock pulses to the output.
15 . The method of claim 14 , wherein managing the CG circuit to generate the pacing pulses during the low voltage mode comprises controlling the CG circuit to generate the pacing pulses independently of the one or more capacitors.
16 . The method of claim 14 , wherein managing the CG circuit to generate the pacing pulses during the low voltage mode comprises controlling the CG circuit to generate the pacing pulses that have a constant current at the lead.
17 . The method of claim 14 , further comprising:
monitoring, via one or more physiological sensors, signals indicative of heart activity, wherein the switching from the low voltage mode to the high voltage mode is responsive to detecting, via the control circuit, an arrhythmia based on the signals indicative of heart activity.