# US 6,026,320 A · Heart rate variability as an indicator of exercise capacity

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- Number: US 6,026,320 A
- Document ID: US6026320A
- Status: Granted
- Kind: A
- Application number: 09/093,118
- Filed: 1998-06-08
- Granted: 2000-02-15
- Earliest claimed: 1998-06-08
- Assignees: Cardiac Pacemakers, Inc.
- Inventors: Gerrard M. Carlson; Veerichetty A. Kadhiresan; Julio C. Spinelli
- Web page: https://patentgrep.com/patent/US6026320A

## CPC

- A61N 1/365: controlled by a physiological parameter, e.g. heart potential {(evoked response A61N1/371)}
- A61N 1/3627: {for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy}
- A61N 1/36592: {controlled by the heart rate variability}
- A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B)

## Abstract

Based upon patient studies indices a high degree of correlation was found between HRV and VO2.sub.max, i.e., the patient's exercise capacity. Based on this finding, a pacing therapy optimization protocol for treating patients with CHF has been devised. The protocol involves first pacing the patient's heart with a pacemaker programmed to operate in a first mode for a predetermined time period and then collecting electrogram data from which a HRV index is derived. The mode is then changed and the steps repeated until all possible modes have been utilized. At that time, a determination is made as to which of the modes is associated with the largest HRV index and the pacemaker is then programmed to function in that mode. Alternatively, the method of the present invention can be applied to changes in drug therapy instead of or in combination with pacing therapy.

## Claims

### Claim 1

A method for indirectly assessing a patient's maximum oxygen uptake (VO2.sub.max), comprising the steps of:
(a) sensing and recording RR intervals obtained from ECG waveforms from the patient over a predetermined period;
(b) determining from the recording, the average length of RR intervals in said waveforms during a plurality of time segments of predetermined length in said predetermined period;
(c) calculating the absolute value of the time difference between successive RR intervals determined in step (b);
(d) plotting as a two-dimensional histogram array the RR intervals as a function of said absolute value of the time difference; and
(e) measuring a feature of the two-dimensional histogram.

### Claim 2 (depends on 1)

The method of claim 1 wherein the feature measured comprises an area on the plot occupied by the two-dimensional histogram.

### Claim 3

A method of optimizing a mode of therapy applied to a patient, comprising the steps of:
(a) measuring and recording ECG waveforms over a predetermined time interval at a first point in time;
(b) computing from said ECG waveforms the absolute value of the difference in the length of successive RR intervals;
(c) plotting a two-dimensional histogram of the values computed in step (b) vs. RR intervals;
(d) measuring the area subtended by the plot of step (c) as an indicator of a patient's exercise capacity;
(e) subsequently changing the mode of therapy applied to the patient;
(f) repeating steps (a) through (d) at a later time;
(g) comparing the area measured in step (d) at the first point in time to the area measured in step (d) at the later time to assess which area is the greater; and
(h) adjusting the mode of therapy to increase the patient's exercise capacity.

### Claim 4 (depends on 3)

The method of claim 3 wherein the mode of therapy applied to the patient comprises electrical cardiac stimulation.

### Claim 5 (depends on 3)

The method of claim 3 wherein the mode of therapy applied to the patient comprises drug application.