US 2003/0195569 A1 · 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.

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Claims135

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;
(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.

5 more elements

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

(a) setting an initial test-shock strength, 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(i-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 implantable 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

An implantable cardioverter defibrillator system for determining and delivering an optimal programmed first-shock strength based on the upper limit of vulnerability, comprising:

(a) a plurality of implantable electrodes;
(b) a shock delivery subsystem, connected to the electrodes;
and
(c) a ULV subsystem comprising;
i) a sensor, connected to the electrodes, for sensing the electrical activity of the heart, including a change with respect to time of the T-wave of a cardiac signal and including the presence of fibrillation;
ii) a timer connected to the sensor for providing a series of shock times, timed relative to the maximum derivative of the T-wave;
iii) a test-shock driver, connected to the timer, for transmitting timing and amplitude information regarding T-wave test shocks;
iv) a memory unit, connected to the test shock driver and the shock subsystem, for storing programmable values such as pacing cycle length, timing intervals, an initial shock strength, and values for incrementing and decrementing shock strength;
and
v) a controller, connected to the sensor, test-shock driver, and shock subsystem for incrementally varying shock strength and the shock times;
whereby the system provides a test shock having a shock strength and shock time selected by the controller;
(d) whereby:
(i) the shock subsystem delivers an initial test shock to the heart at an initial shock strength and an initial shock time;
and if the heart does not fibrillate
(ii) the system delivers a sequence of test shocks to the heart at the same shock strength and different shock times;
and if the heart does not fibrillate
(iii) the system decreases the shock strength, a strength decrement and delivers test shocks at a sequence of intervals;
and if the heart does not fibrillate
(iv) the system repeats steps (d) (i)-(iii) until the heart fibrillates, whereby the shock strength of the test shock immediately prior to the test shock that induces fibrillation represents the upper limit of vulnerability, and whereby the optimal programmed first shock strength of an implantable cardioverter defibrillator system is predicted by a fixed increment in relation to the energy level determined to be the upper limit of vulnerability.

16 more elements

Dependencies are inferred from the claim text.

Description12,235 words

Summary5,974 words

#Not applicable.

#1. Field of the Invention

Brief description of the drawings8 figures

#FIG. 1 is an anterior sectional view of a human heart in relative anatomical position, depicting the relative positioning of intravascular electrode catheters and an ICD according to the present invention.

#FIG. 2 is a schematic block diagram depicting a suitable arrangement for an ICD according to the present invention.

#FIG. 3A. is an actual recording of ECG lead II, an intracardiac electrogram (EGM), and its first time derivative (EGM dV/dt).

Detailed description5,978 words

#Referring to FIG. 1, an embodiment of the present invention is depicted as an ICD system 10 comprising an implantable electrical pulse generating housing 12, an electrical connector pin housing 14, an implantable intravascular discharge catheter 16 electrically connected to pin housing 14 via a pin connector 18, and an implantable intravascular pacing/sensing catheter 20 electrically connected to pin housing 14 via a pin connector 22. Discharge catheter 16 carries proximal defibrillation discharge electrode 24 and distal defibrillation discharge electrode 26 and is configured to position proximal electrode 24 within right atrium 28 and position distal electrode 26 within right ventricle 30. Alternatively, these two electrodes may be on different catheters. Pacing/sensing catheter 20, carries two sets of pacing/sensing electrodes, a proximal electrode set 32 positioned within the right atrium 28 and a distal electrode set 34 positioned within the right ventricle 30. Alternatively, electrode sets 32 and 34 may be on different catheters or on the catheter that carries either or both defibrillation discharge electrodes 24 and 26. As another alternative, separate electrode pairs may be used for right-ventricular pacing and sensing. The catheters, discharge electrodes and pacing/sensing electrodes may be of any implantable design known to the art (including intracardiac, epicardial, intravascular, subcutaneous or submuscular designs). At least one defibrillation electrode must be intravascular or epicardial, with a preferred embodiment using a pacing electrode and defibrillation electrode near the right ventricular apex. Positioning of implanted pacing electrodes is preferred to be near the right ventricular apex or left ventricle, but is also not critical so long as pacer capture is reliable. This invention also permits determination of ULV without any surface electrodes.

#Because DFTs vary with electrode placement and lead configuration, as well as with the responsiveness of a particular patient's heart, the ULV is determined after the electrodes and leads have been placed at their permanent positions. In this manner, the DFT corresponds to the patient and particular arrangement of the defibrillation electrodes used.

#Referring to FIG. 2, an embodiment of an upper limit of vulnerability (ULV) subsystem 50 according to the present invention is depicted in one possible configuration in electrical connection with a shock subsystem 52. ULV subsystem 50 and shock subsystem 52 are component subsystems of ICD 10 of FIG. 1 and are contained within housing 12 and electrically connected. ULV subsystem 50 includes a test-shock driver for T-wave shocks 54, a test/treatment controller 56, a timing circuit 58, a sensing, storing, and analyzing circuit 60, a pacing circuit 62 (in a preferred embodiment), and a memory unit 64. Shock subsystem 52 may be of any design known to the art, but preferably is programmable to deliver either monophasic or biphasic shocks, having variable tilt, and controllable through a step wise range of energy outputs from at least 5 J to at least 30 J. Shock subsystem 52 is preferably connected to the test shock driver 54, memory 64 and controller 56 of the ULV subsystem 50. Shock subsystem 52 is used to deliver test shocks as well as defibrillation shocks. The pacing circuit 62 is not necessary for embodiments of the method and system which are operative in a native rhythm.

Defibrillation shock strength determination technology

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Defibrillation shock strength determination technology

Life of this patent

Life of this patent

Abstract

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Claims135

Description12,235 words

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Classification4 codes

Life of this patent

Description12,235 words