ASSESSING A DEGREE OF VASCULAR BLOCKAGE OR RISK OF ISCHEMIA

• US 20110082350A1
• Filed: 10/05/2009
• Published: 04/07/2011
• Est. Priority Date: 10/05/2009
• Status: Abandoned Application

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Koh, Steve
• Application Number:
  US12/573,735
• Publication Number:
  US 20110082350A1
• Time in Patent Office: Days
• US Class Current: 600/301
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/222 combined with detection or measurement of physiological parameters, e.g. heart rate
• CPC Class Codes: A61B 5/4884 inducing physiological or psychological stress, e.g. applications for stress testing

Abstract

A system and method for determining a patient'"'"'s degree of cardiac vascular blockage or, equivalently, a patient'"'"'s risk of cardiac ischemia, based on the time interval between the onset of exercise activity and the onset of an episode of cardiac ischemia. In one embodiment, an implantable cardiac device may obtain an EGM and possibly other measures of patient physiologic activity. These measures are used to determine when the patient has initiated exercise activity. Analysis of the EGM then detects an elevated or depressed ST segment, which typically indicates an episode of cardiac ischemia. The time interval between the onset of exercise and the onset of ischemia is a metric reflecting the patient'"'"'s degree of vascular blockage or, equivalently, the patient'"'"'s risk of ischemia. Other metrics may be derived, such as a substantially workload-level invariant measure determined as the product of the exercise workload level and the ischemia onset time interval.

Claims

1. A method for assessing a degree of cardiac vascular blockage in a patient comprising:

(a) determining an onset of patient exercise activity;

(b) determining an onset of myocardial ischemia; and

(c) determining a time interval between the onset of the patient exercise activity and the onset of myocardial ischemia,

wherein a shorter time interval indicates a greater degree of vascular blockage and a longer time interval indicates a lesser degree of vascular blockage.

2. The method of claim 1, wherein step (a) further comprises at least one of:

determining that a measure of patient metabolic activity has crossed a metabolic activity threshold;

determining that a measure of patient movement has crossed a patient movement threshold;

determining that a measure of external activity has crossed an external activity threshold;

or

determining that a measure of a duration of exercise activity has crossed an activity duration threshold.

3. The method of claim 2, wherein determining that the measure of patient metabolic activity has crossed the metabolic activity threshold comprises measuring at least one of a patient heart rate, a patient blood pressure, a patient respiration rate, or a patient blood oxygen concentration level.

4. The method of claim 2, wherein determining that a measure of patient metabolic activity has crossed a metabolic activity threshold further comprises measuring the patient metabolic activity via an implanted physiologic measuring device.

5. The method of claim 2, wherein determining that a measure of patient acceleration has crossed an acceleration threshold further comprises measuring the patient acceleration via an implanted accelerometer.

6. The method of claim 1, wherein step (b) further comprises:

obtaining at least one of an electrocardiogram (ECG) or an electrogram (EGM) of the patient during the patient exercise activity; and

determining the onset of myocardial ischemia by determining an onset of at least one of;

an elevation of an ST segment in the ECG or EGM of the patient;

a depression of the ST segment in the ECG or EGM of the patient;

a change of slope of the ST segment in the ECG or EGM of the patient;

or

a variation of shape of the ST segment in the ECG or EGM of the patient.

7. The method of claim 1, further comprising calculating a representative patient ischemia value, wherein the representative patient ischemia value is a product of the time interval and a level of patient workload;

wherein the level of patient workload is indicative of the level of patient exercise activity corresponding to the determination of the time interval; and

wherein if a first representative patient ischemia value for a patient and a second representative patient ischemia value for the patient have a substantially equal value, the substantial equality of the first and second values indicates a substantially similar level of ischemia for the patient.

8. The method of claim 1, further comprising determining a plurality of time intervals for the patient, wherein the plurality of time intervals are determined over a period of time, wherein the period of time is comprised of a plurality of days.

9. The method of claim 8, further comprising at least one of storing the plurality of time intervals, storing a subset of the plurality of time intervals, or calculating and storing a set of representative patient ischemia values, wherein each representative patient ischemia value is indicative of at least one of a patient time interval or a plurality of patient time intervals.

10. The method of claim 9, further comprising analyzing the plurality of stored values to determine at least one of a patient trend of cardiac vascular blockage over the period of time, a patient risk of ischemia, or a patient risk of myocardial infarction.

11. A method for assessing a degree of risk of cardiac ischemia in a patient comprising:

(a) determining an onset of patient exercise activity;

(b) obtaining a measure of patient cardiac electrical activity during the patient exercise activity;

(c) analyzing the measure of patient cardiac electrical activity to determine an onset of myocardial ischemia; and

(d) determining a time interval between the onset of the patient exercise activity and the onset of myocardial ischemia;

wherein a shorter time interval indicates a greater risk of cardiac ischemia and a longer time interval indicates a lesser risk of cardiac ischemia.

12. The method of claim 11, wherein step (a) further comprises determining that a measure of patient activity has crossed a respective activity threshold, wherein the measure of patient activity comprises at least one of a patient heart rate, a patient blood pressure, a patient respiration rate, a patient blood oxygen concentration level, or a patient acceleration;

and

wherein the measure of patient activity is made via at least one of an implanted physiologic measuring device or an implanted accelerometer.

13. The method of claim 12, further comprising determining that the measure of patient activity has crossed an activity duration threshold.

14. The method of claim 11, further comprising:

obtaining at least one of an electrogram (EGM) of the patient or an electrocardiogram (ECG) of the patient; and

determining the onset of myocardial ischemia by determining an onset of at least one of;

an elevation of an ST segment in the ECG or EGM of the patient;

a depression of the ST segment in the ECG or EGM of the patient;

a change of slope of the ST segment in the ECG or EGM of the patient;

or

a variation of shape of the ST segment in the ECG or EGM of the patient.

15. The method of claim 11, further comprising determining the onset of myocardial ischemia via an analysis of data obtained from an intra-ventricular pressure transducer.

16. The method of claim 11, further comprising calculating a representative patient ischemia value, wherein the representative patient ischemia value is a product of the time interval and a level of patient workload;

wherein the level of patient workload is indicative of the level of patient exercise activity corresponding to the determination of the time interval; and

wherein if a first representative patient ischemia value for a patient and a second representative patient ischemia value for the patient have a substantially equal value, the substantial equality of the first and second values indicates a substantially similar level of ischemia for the patient.

17. A system for assessing a degree of cardiac vascular blockage in a patient comprising:

means for determining an onset of patient exercise activity;

means for determining an onset of myocardial ischemia; and

means for determining a time interval between the onset of the patient exercise activity and the onset of myocardial ischemia; and

wherein a shorter time interval indicates a greater degree of vascular blockage and a longer time interval indicates a lesser degree of vascular blockage.

18. The system of claim 17, wherein the means for determining the onset of patient exercise activity comprises at least one of an implanted physiologic measuring device or an implanted accelerometer.

19. The system of claim 17, wherein the means for determining the onset of myocardial ischemia comprises an implanted physiologic measuring device, said implanted physiologic measuring device comprising a means of measuring a patient EGM;

wherein the onset of an episode of myocardial ischemia is determined by at least one of;

an elevation of an ST segment of the patient EGM;

a depression of the ST segment of the patient EGM;

a change of slope of the ST segment of the patient EGM;

or

a variation of a shape of the ST segment of the patient EGM.

20. The system of claim 17, wherein the means for determining a time interval between the onset of the patient exercise activity and the onset of myocardial ischemia comprises at least one of a microprocessor of an implanted physiologic measuring device, an external microprocessor, an external computer, a timing circuit, or means of storing timing data.