Method and apparatus for detecting arrhythmias in a medical device

• US 7,742,812 B2
• Filed: 04/28/2006
• Issued: 06/22/2010
• Est. Priority Date: 03/29/2006
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Ghanem, Raja N., Stadler, Robert W., Zhang, Xusheng
• Primary Examiner(s): Layno; Carl H
• Assistant Examiner(s): Porter, Jr.; Gary A
• Application Number:
  US11/380,830
• Publication Number:
  US 20070239050A1
• Time in Patent Office: 1,516 Days
• Field of Search: 600/509, 607/2, 607/4, 607/5, 607/7, 607/9, 607/11, 607/14
• US Class Current: 607/4
• CPC Class Codes: A61B 5/287 Holders for multiple electrodes, e.g. electrode catheters for electrophysiological study [EPS]
• CPC Class Codes: A61B 5/341 Vectorcardiography [VCG]
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/364 Detecting abnormal ECG interval, e.g. extrasystoles, ectopic heartbeats
• CPC Class Codes: A61B 5/4836 Diagnosis combined with treatment in closed-loop systems or methods A61B5/0036 takes precedence
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/05 for implantation or insertion into the body, e.g. heart electrode A61N1/06 takes precedence
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal
• CPC Class Codes: Y10S 128/902 Biological signal amplifier

Abstract

A method of detecting a cardiac event that includes sensing cardiac signals from a plurality of electrodes, determining rates of change of the sensed cardiac signals, and determining a range of the sensed cardiac signals. The sensed cardiac signals are detected as being associated with the cardiac event in response to the determined rates of change and the determined range.

Claims

1. A method of detecting a cardiac event, comprising:

sensing cardiac signals from a plurality of electrodes, the plurality of electrodes forming a first sensing vector and a second sensing vector;

determining a first low slope content of the cardiac signals sensed by the first sensing vector after taking a first derivative of the cardiac signals sensed by the first sensing vector in each of a first plurality of sub-segments of a first predetermined sensing window, wherein the first low slope content is defined as a number of sample points representative of the first derivative of the cardiac signals of the first vector having an absolute value less than or equal to a first predetermined slope threshold;

determining a second low slope content of the cardiac signals sensed by the second sensing vector after taking a first derivative of the cardiac signals sensed by the second sensing vector in each of a second plurality of sub-segments of a second predetermined sensing window, wherein the second low slope content is defined as a number of sample points representative of the first derivative of the cardiac signals of the second vector having an absolute value less than or equal to a second predetermined slope threshold;

determining a first spectral width of the cardiac signals sensed by the first sensing vector defined by a difference between a mean frequency and a fundamental frequency of the cardiac signals sensed by the first sensing vector over the first predetermined sensing window;

determining a second spectral width of the cardiac signals sensed by the second sensing vector defined by a difference between a mean frequency and a fundamental frequency of the cardiac signals sensed by the second sensing vector over the second predetermined sensing window;

identifying each of the first sensing vector and the second sensing vector as being one of shockable and not shockable in response to the first low slope content, the second low slope content, the first spectral width and the second spectral width; and

delivering therapy in response to the identifying.

2. The method of claim 1, wherein the first predetermined slope threshold is defined, at least in part, as an average of a largest absolute slope of the cardiac signals sensed by the first sensing vector in each individual one of the first plurality of sub-segments;

and

the second predetermined slope threshold is defined, at least in part, by an average of a largest absolute slope of the cardiac signals sensed by the second sensing vector in each individual one of the second plurality of sub-segments.

3. The method of claim 2, wherein the largest absolute slope for each of the first plurality of sub-segments is defined as a maximum slope of the cardiac signal of the first predetermined window if a maximum slope of an individual sub-segment of the first plurality of sub-segments is less than a portion of the maximum slope of the cardiac signal of the first predetermined window, otherwise the largest absolute slope for the individual sub-segment of the first plurality of sub-segments is defined as a maximum slope of the sub-segment, and;

wherein the largest absolute slope for each of the second plurality of sub-segments is defined as a maximum slope of the cardiac signal of the second predetermined window if a maximum slope of an individual sub-segment of the second plurality of sub-segments is less than a portion of the maximum slope of the cardiac signal of the second predetermined window, otherwise the largest absolute slope for the individual sub-segment of the second plurality of sub-segments is defined as a maximum slope of the sub-segment.

4. The method of claim 1, wherein determining the first spectral width comprises determining a difference between an RR-cycle length and a mean spectral period corresponding to the cardiac signals sensed by the first sensing vector sensed over the first predetermined sensing window and wherein determining the second spectral width comprises determining a difference between an RR-cycle length and a mean spectral period corresponding to the cardiac signals sensed by the second sensing vector sensed over the second predetermined sensing window.

5. The method of claim 1, wherein the identifying step comprises:

identifying the first sensing vector as being shockable if the first low slope content is less than a first boundary and the first spectral width is less than a second boundary different from the first boundary; and

identifying the second sending vector as being shockable if the second low slope content is less than the first boundary and the second spectral width is less than the second boundary.

6. The method of claim 5, wherein the first boundary corresponds to at least one of the first low slope content being equal to −

0.0013×

the first spectral width+0.415 and the second low slope content being equal to −

0.0013×

the second spectral width+0.415, and the second boundary corresponds to at least one of the first spectral width and the second spectral width being equal to 200 Hz.

7. The method of claim 3, wherein the identifying step comprises:

identifying the first sensing vector as being shockable if a predetermined number of sample points of the first low slope content is less than a first boundary and the first spectral width is less than a second boundary different from the first boundary; and

identifying the second sending sensing vector as being shockable if a predetermined number of sample points of the second low slope content is less than a first boundary and the second spectral width is less than a second boundary.

8. The method of claim 7, wherein the first boundary corresponds to at least one of the first low slope content being equal to −

0.0013×

the first spectral width+0.415 and the second low slope content being equal to −

0.0013×

the second spectral width+0.415, and the second boundary corresponds to at least one of the first spectral width and the second spectral width being equal to 200 Hz.

9. A device for detecting a cardiac event, comprising:

means for sensing cardiac signals from a plurality of electrodes, the plurality of electrodes forming a first sensing vector and a second sensing vector;

means for determining a first low slope content of the cardiac signals sensed by the first sensing vector after taking a first derivative of the cardiac signals sensed by the first sensing vector in each of a first plurality of sub-segments of a first predetermined sensing window, wherein the first low slope content is defined as a number of sample points representative of the first derivative of the cardiac signals of the first vector having an absolute value less than or equal to a first predetermined slope threshold;

means for determining a second low slope content of the cardiac signals sensed by the second sensing vector after taking a first derivative of the cardiac signals sensed by the second sensing vector in each of a second plurality of sub-segments of a second predetermined sensing window, wherein the second low slope content is defined as a number of sample points representative of the first derivative of the cardiac signals of the second vector having an absolute value less than or equal to a second predetermined slope threshold;

means for determining a first spectral width of the cardiac signals sensed by the first sensing vector defined by a difference between a mean frequency and a fundamental frequency of the cardiac signals sensed by the first sensing vector over the first predetermined sensing window;

means for determining a second spectral width of the cardiac signals sensed by the second sensing vector defined by a difference between a mean frequency and a fundamental frequency of the cardiac signals sensed by the second sensing vector over the second predetermined sensing window;

means for identifying each of the first sensing vector and the second sensing vector as being one of shockable and not shockable in response to the first low slope content, the second low slope content, the first spectral width and the second spectral width; and

means for delivering therapy in response to the identifying.