Patent ID: 8401638

Claim:
A method for determining a cardiac shock strength, comprising the steps of: (a) sensing a change with respect to time in a T-wave of an electrical cardiac signal by calculating an extreme absolute value by a method selected from the group consisting of a finite difference, an ordinary derivative, a directional derivative, a gradient and a partial derivative, an implicit differential, a variance calculation, a bounded variation calculation, a radial displacement vector, and a tangent vector approximation, the extreme absolute value being one value selected from the group consisting of a minimum value and a maximum value; (b) delivering a test shock by: (i) delivering a test shock at a test-shock strength and at a test-shock time relating to sensing the change with respect to time in the T-wave; and (ii) sensing for cardiac fibrillation; and (c) if fibrillation is not sensed, repeating step (b) at the test-shock strength and at a different test-shock time relating to the change in the T-wave; and (d) if fibrillation is sensed, setting the cardiac shock strength as a function of the test-shock strength.