Electrical ablation devices and methods

1. A method for delivering energy to tissue having a necrotic threshold, the method comprising:

inserting an electrode array comprising a plurality of electrodes into the tissue;

inserting a central electrode into the tissue;

positioning a ground pad proximal to the tissue;

applying a first sequence of electrical pulses to the electrode array less than the necrotic threshold to induce thermal heating in the tissue;

applying a second sequence of electrical pulses to the central electrode equal to or greater than the necrotic threshold to induce cell necrosis in the tissue by irreversible electroporation; and

applying a ground potential to the ground pad.

2. The method of claim 1 comprising coupling the electrode array and the central electrode to an energy source operative to generate the first sequence of electrical pulses and the second sequence of electrical pulses.

3. The method of claim 1 comprising positioning each of the plurality of electrodes spaced apart from the other of the plurality of electrodes, and positioning the central electrode intermediate the plurality of electrodes.

4. The method of claim 1 comprising applying the first sequence of electrical pulses to the central electrode.

5. The method of claim 1 , wherein the second sequence of electrical pulses is not applied to the electrode array.

6. The method of claim 1 , wherein the first sequence of electrical pulses is sufficient to create at least one thermal zone in a portion of the tissue induced by thermal heating in an area near an electrode-tissue-interface of each of the plurality of electrodes, and wherein the second sequence of electrical pulses is sufficient to create a necrotic zone in a portion of tissue induced by irreversible electroporation in an area surrounding each of the plurality of electrodes and the central electrode.

7. The method of claim 6 , wherein the thermal zone of each of the plurality of electrodes contacts the thermal zone of the other of the plurality of electrodes.

8. The method of claim 6 , wherein the thermal zone of at least one of the plurality of electrodes contacts the central electrode.

9. The method of claim 6 , wherein the thermal zone of each of the plurality of electrodes contacts the central electrode.

10. The method of claim 6 , wherein the central electrode is positioned within the thermal zone of each of the plurality of electrodes.

11. The method of claim 6 , wherein the volume of the necrotic zone is greater than the volume of the thermal zone.

12. The method of claim 6 , wherein the thermal zone has a volume of about 4 cm 3 to about 6 cm 3 .

13. The method of claim 6 , wherein the thermal zone has a temperature greater than about 37° C.

14. The method of claim 6 , wherein the thermal zone has a temperature of about of 55° C.

15. The method of claim 1 comprising:

delivering a first energy dose to the tissue that is less than the necrotic threshold to induce thermal heating by the first sequence of electrical pulses; and

delivering a second energy dose to the tissue equal to or greater than the necrotic threshold to induce cell necrosis in the tissue by irreversible electroporation by the second sequence of electrical pulses.

16. The method of claim 1 comprising:

forming a pre-heated zone by applying an electric field that is less than about 800 V/cm by the first sequence of electrical pulses; and

forming a necrotic zone by applying an electric field that is greater than about 800 V/cm by the second sequence of electrical pulses.

17. The method of claim 1 comprising:

heating a mass of tissue by applying an electric field that is less than about 800V/cm by the first sequence of electrical pulses to lower the necrotic threshold; and

inducing cell necrosis by irreversible electroporation by applying an electric field that is greater than about 800 V/cm by the second sequence of electrical pulses.

18. The method of claim 1 comprising:

applying the first sequence of electrical pulses to the electrode array less than the necrotic threshold to lower the necrotic threshold; and

applying the second sequence of electrical pulses to the central electrode to induce cell necrosis by irreversible electroporation.

19. The method of claim 1 comprising:

lowering the necrotic threshold by heating the tissue by applying an electric field that is less than about 800 V/cm by the first sequence of electrical pulses.

20. The method of claim 1 comprising:

measuring at least one of temperature and pressure adjacent at least one of the electrode array and central electrode;

applying the first sequence of electrical pulses to the electrode array to achieve at least one of a predetermined temperature and a predetermined pressure; and

applying the second sequence of electrical pulses to the central electrode when the at least one of the predetermined temperature and the predetermined pressure is achieved.

21. The method of claim 1 comprising:

applying a sequence of electrical pulses to the electrode array, the sequence of electrical pulses having amplitudes in the range of about ±100 VDC to about ±10,000 VDC, pulse widths in the range of about 1 μs to about 100 ms, and frequencies in the range of about 1 Hz to about 10,000 Hz; and

re-applying the sequence of electrical pulses to the central electrode.

22. A method for delivering energy to tissue having a necrotic threshold, the method comprising:

inserting an electrode array comprising a plurality of electrodes into the tissue;

inserting a central electrode into the tissue;

measuring at least one of temperature and pressure in the tissue adjacent at least one of the electrode array and central electrode;

applying a first sequence of electrical pulses to the electrode array less than the necrotic threshold to induce thermal heating in the tissue until at least one of a predetermined temperature and a predetermined pressure is achieved; and

applying a second sequence of electrical pulses to the central electrode equal to or greater than the necrotic threshold to induce cell necrosis in the tissue by irreversible electroporation when the at least one of the predetermined temperature and the predetermined pressure is achieved.

23. A method for delivering energy to tissue having a necrotic threshold, the method comprising:

inserting an electrode array comprising a plurality of electrodes into the tissue;

inserting a central electrode into the tissue;

applying a first sequence of electrical pulses to the electrode array less than the necrotic threshold to induce thermal heating and lower the necrotic threshold in the tissue; and

applying a second sequence of electrical pulses to the central electrode equal to or greater than the necrotic threshold to induce cell necrosis in the tissue by irreversible electroporation.