Patent ID: 7555338

Claim:
A method of inducing fibrillation in a patient, the method comprising applying an alternating current to the patient from an implantable cardioverter defibrillator (ICD), wherein: the alternating current comprises a series of alternating pulses each having a substantially constant current; the ICD comprises a stimulus delivery circuit having a high side and a low side, the high side having a first switch coupled to a first node and a second switch coupled to a second node, the first and second nodes being respectively coupled to first and second electrodes configured for delivering stimulus to the patient, the low side comprising a third switch coupling the first node to a low node and a fourth switch coupling the second node to the low node, and control circuitry coupled to the first, second, third and fourth switches and configured to perform an induction sequence including successively engaging the switches in an alternating sequence to produce an alternating output; the low node is coupled to ground or reference for the circuit via a stimulus switch in parallel with a feedback resistor; and a current modulation circuit is provided including a transistor having current inlet node, a current outlet node, and a control node, the control node being coupled to a feedback circuit that takes an input signal from the low node and a control voltage from the control circuitry to modulate current flow through the feedback resistor while the stimulus switch is open during the induction sequence such that a substantially constant current is maintained for the alternating current.