Switched diverter circuits for minimizing heating of an implanted lead in a high power electromagnetic field environment
View Patent ↗An energy management system that facilitates the transfer of high frequency energy induced on an implanted lead or a leadwire includes an energy dissipating surface associated with the implanted lead or the leadwire, a diversion or diverter circuit associated with the energy dissipating surface, and at least one switch for diverting energy in the implanted lead or the leadwire through the diversion circuit to the energy dissipating surface. In alternate configurations, the switch may be disposed between the implanted lead or the leadwire and the diversion circuit, or disposed so that it electrically opens the implanted lead or the leadwire when diverting energy through the diversion circuit to the energy dissipating surface. The switch may comprise a single or multi-pole double or single throw switch. The diversion circuit may be either a high pass filter or a low pass filter.
1. A switched diverter circuit for minimizing heating of an implanted lead and/or providing EMI protection for an active implantable medical device (AIMD) in a high power electromagnetic field environment, comprising:
an implanted lead or a leadwire having a length extending between and to a proximal end and a tissue-stimulating or biological-sensing electrode at or near a distal tip end;
an energy dissipating surface comprising a housing for the AIMD, associated with the implanted lead or the leadwire;
a diversion circuit associated with the energy dissipating surface and disposed within the AIMD housing; and
at least one switch associated with the diversion circuit for diverting energy in the implanted lead or the leadwire through the diversion circuit to the energy dissipating surface.
2. The switched diverter circuit of claim 1 , wherein the switch is disposed between the implanted lead or the leadwire and the diversion circuit.
3. The switched diverter circuit of claim 1 , wherein the switch is disposed between the diversion circuit and the energy dissipating surface.
4. The switched diverter circuit of claim 1 , wherein the switch comprises a single or multi-pole single throw switch.
5. The switched diverter circuit of claim 1 , wherein the switch comprises a MEMS switch, a multiplexer switch, a mechanical switch, a reed switch, an electronic switch, a programmable switch, an automatically actuated switch, a Hall Effect switch, or a field effect transistor (FET) switch.
6. The switched diverter circuit of claim 1 , wherein the implanted lead or the leadwire has impedance characteristics at a selected RF frequency or frequency band, and wherein the diversion circuit has impedance characteristics at least partially tuned to the implanted lead's or the leadwire's impedance characteristics.
7. The switched diverter circuit of claim 6 , wherein the selected RF frequency or frequency band comprises an MRI center frequency or a range of MRI frequencies.
8. The switched diverter circuit of claim 6 , wherein the diversion circuit has a reactance and is vectorially opposite to a characteristic reactance of the implanted lead.
9. The switched diverter circuit of claim 8 , wherein the diversion circuit has a capacitive reactance generally equal and opposite to a characteristic inductive reactance of the implanted lead.
10. The switched diverter circuit of claim 9 , wherein the capacitive reactance and the inductive reactance each have a resistor component.
11. The switched diverter circuit of claim 1 , wherein the diversion circuit comprises a low pass filter, a resistor, or a short to the AIMD housing.
12. The switched diverter circuit of claim 11 , wherein the low pass filter comprises a capacitor, an inductor, a Pi filter, a T filter, an LL filter, or an “n” element filter.
13. The switched diverter circuit of claim 1 , wherein the diversion circuit comprises at least one series resonant L-C trap filter or a plurality of LC trap filters resonant respectively at different MRI center frequencies or frequency ranges.
14. The switched diverter circuit of claim 1 , including an impeding circuit associated with the diversion circuit, for raising the high-frequency impedance of the implanted lead.
15. The switched diverter circuit of claim 14 , wherein the impeding circuit comprises an inductor or a bandstop filter.
16. The switched diverter circuit of claim 1 , wherein the diversion circuit includes at least one non-linear circuit element.
17. The switched diverter circuit of claim 16 , wherein the non-linear circuit element comprises a transient voltage suppressor or a diode.
18. The switched diverter circuit of claim 1 , including an EMI shield conductively coupled to the housing and coaxially extending about the leadwire in non-conductive relation.
19. The switched diverter circuit of claim 18 , wherein the diversion circuit is conductively coupled to the EMI shield.
20. The switched diverter circuit of claim 1 , wherein the switch comprises a single pole double throw switch, wherein in normal operating mode the lead is conductively coupled to AIMD internal electrical circuits, and in an MRI compatible mode the lead is disconnected from the AIMD electrical circuits while at the same time the lead is conductively coupled to the diversion circuit.