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1. (WO1999037362) SYSTEM FOR INDUCING TACHYCARDIA UTILIZING NEAR FIELD T-WAVE SENSING
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CLAIMS:

1. A system for inducing an abnormally high rate in a patient's heart, comprising:
stimulus pulse means for generating and delivering a series of stimulus pulses at a predetermined rate to a heart chamber of said patient,
sensing means for sensing a predetermined portion of each repolarization wave which follows each depolarization wave evoked by a said stimulus pulse, and
inducing means for triggering said stimulus pulse means to generate an inducing pulse following each said sensed predetermined repolarization wave portion, said inducing means comprising timing means for timing each said inducing pulse in a predetermined time relation to said repolarization wave portion, whereby a series of inducing pulses are delivered.

2. The system as described in claim 1, further comprising means operative before delivery of said series of stimulus pulses for controlling said stimulus pulse means to generate pacing signals at a rate higher than the patient's spontaneous depolarization rate, whereby said stimulus pulse means delivers a series of pacing pulses which overdrive said chamber of said patient's heart.

3. The system as described in claim 1, wherein said stimulus pulse means comprises series means for generating a series of 1 to 5 pairs of pulses, each said pair comprising a said stimulus pulse and a said inducing pulse.

4. The system as described in claim 1, wherein said inducing means comprises means for generating each said inducing pulse immediately upon the sensing of a said repolarization wave portion.

5. The system as described in claim 1 , wherein said inducing means comprises means for generating each said inducing pulse after a predetermined short time delay following the sensing of said repolarization wave portion.

6. The system as described in any of claims 1 - 5, wherein said stimulus pulse means, said sensing means and said inducing means comprise components of an implantable stimulator.

7. The system as described in claim 1, further comprising confirmation means for confirming when a tachycardia has been induced.

8. The system as described in claim 7, comprising rate means for sensing said patient's spontaneous depolarization rate, and wherein said control means has rate control means for setting the rate of said stimulus pulses just higher than said spontaneous depolarization rate, and wherein said confirmation means has means for identifying tachycardia when a spontaneous depolarization is sensed before a said stimulus pulse is due to be delivered.

9. The system as described in claim 8, further comprising means responsive to a spontaneous depolarization which is sensed before a next said stimulus pulse is due to be delivered, for inhibiting delivery of a next said stimulus pulse.

10. The system as described in claim 1, comprising means operative after said series of stimulus pulses has been delivered for confirming whether tachycardia has been induced.

11. The system as described in any of claims 1 - 10 wherein said heart chamber is a ventricle, and said sensing means comprises means for sensing T waves and for sensing a predetermined portion of each sensed T wave.

12. The system as described in claim 1, wherein said stimulus pulse means comprises a lead with at least one electrode for delivery of stimulus pulses at a location of a predetermined one of the patient's heart chambers, said lead having a conductor for conducting said pacing pulses from said generator to said electrode and wherein said sensing means comprises near field means electrically connected to said electrode for sensing repolarization waves from near said location and for determining the timing of a portion of each said repolarization wave.

13. The system as described in claim 12, wherein said heart chamber is a ventricle, and said near field means has means for sensing T waves and for determining the timing of a predetermined portion of each sensed T wave.

14. The system as described in claim 12, wherein said near field means comprises an FDC circuit with an input connected to said at least one electrode, and said lead is a unipolar lead and said one electrode is a tip electrode.

15. The system as described in claim 12, wherein said lead is a bipolar lead and said at least one electrode is a tip electrode, said lead having a ring electrode proximal to said tip electrode, the spacing between said tip and ring electrodes being less than about 0.75 mm.

16. The system as described in claim 15, wherein said tip electrode has a surface area of 2-6 square mm, and said ring electrode has a surface area greater than 10 square mm.