US 6,675,042 B2 · Defibrillation shock strength determination technology

Abstract

A method for determining a cardiac shock strength, for example the programmed first-therapeutic shock strength of an implantable cardioverter defibrillator (ICD), including the steps of sensing a change in a T-wave of an electrogram with respect to time such as the maximum of the first derivative of a T-wave of an electrogram; delivering a test shock by (i) delivering a test shock at a test-shock strength and at a test-shock time relating to the maximum of the first derivative of the T-wave with respect to time; and (ii) sensing for cardiac fibrillation. If fibrillation is not sensed, test-shock delivery is repeated at the same test-shock strength and at specific, different test-shock times relating to the maximum of the first derivative of the T-wave. If fibrillation is still not sensed, the shock strength is decreased and test shocks are repeated at the same specific test shock times relative to the maximum of the first derivative of the T-wave. And if fibrillation is sensed, the programmed therapeutic shock strength of the ICD is set as a function of the incrementally greater test-shock strength. Also disclosed is an apparatus for selecting a programmed first-shock strength of an ICD, including a shock subsystem for delivering therapeutic shocks and test shocks to the heart, and a ULV subsystem connected to the shock subsystem, to provide test shocks of test-shock strengths and at test-shock times relating to the maximum of the first derivative of the T-wave with respect to time, and to determine the therapeutic shock strength of the ICD as a function of the test-shock strengths.

Claims112

Dependent claims

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, the change with respect to time being a derivative of T wave amplitude with respect to time;
(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 derivative of T wave amplitude with respect to time;
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 derivative of T wave amplitude with respect to time;
and
(d) if fibrillation is sensed, setting the cardiac shock strength as a function of the test-shock strength.

6 more elements

A method for determining an optimal programmed strength of a first therapeutic shock of an implantable cardioverter defibrillator relative to the upper limit of vulnerability, the implantable cardioverter defibrillator having at least one sensing electrode, at least one pacing electrode, and at least one shocking electrode, comprising the steps of:

(a) setting an initial test-shock strength, up to four offset times, and a shock strength decrement;
(b) delivering a set of up to four test shocks with the implantable cardioverter defibrillator to the patient, each test shock member of the set of test shocks comprising the sub steps of:
(i) sensing an electrogram from the patient;
(ii) detecting at least one predetermined base timing point prior to the T-wave of the electrogram;
(iii) differentiating the electrogram with respect to time;
(iv) detecting at least one maximum of the first derivative with respect to time of a T-wave of the differentiated electrogram;
(v) measuring at least one base time interval from the at least one base timing point to the at least one maximum of the first derivative with respect to time of a T-wave;
(vi) delivering a test shock to the patient at the test-shock strength and at a test-shock time corresponding to the base time interval plus one of the offset times;
(vii) sensing for an induction of cardiac fibrillation for a predetermined sensing time period;
and
(viii) if fibrillation is not sensed in step b(vii), then repeating sub steps b(vii), at the same test-shock strength, up to the fourth test shock, each test shock member of the set of test shocks having a different test-shock time corresponding to a base time interval plus an offset time;
and
(c) if fibrillation is not sensed in step (b) by the fourth test shock, then repeating step (b) at a lower test-shock strength corresponding to the shock strength decrement, to deliver at least one additional set of up to four test shocks;
and
(d) if fibrillation is sensed in step (b), then:
(i) defibrillating the patient;
and
(ii) setting the programmed first-shock strength of the implanted cardioverter defibrillator at a predetermined higher level than the weakest test-shock strength at which fibrillation was not induced, which test-shock strength represents the upper limit of vulnerability.

15 more elements

Dependencies are inferred from the claim text.

Defibrillation shock strength determination technology

Life of this patent

Defibrillation shock strength determination technology

Life of this patent

Abstract

Claims112