JMIR Publications

ABSTRACT

Background:

The New York Heart Association (NYHA) functional classification system has poor inter-rater reproducibility. A previously published pilot study showed a statistically significant difference between the daily step counts of heart failure (with reduced ejection fraction) patients classified as NYHA functional class II and III as measured by wrist-worn activity monitors. However, the study’s small sample size severely limits scientific confidence in the generalizability of this finding to a larger heart failure (HF) population.

Objective:

Validate the pilot study on a larger sample of patients with HF with reduced ejection fraction (HFrEF) and attempt to characterize the step count distribution to gain insight into a more objective method of assessing NYHA functional class.

Methods:

We repeated the analysis performed during the pilot study on an independently recorded dataset consisting of a total of 50 patients with HFrEF (35 NYHA II and 15 NYHA III) patients. Participants were monitored for step count with a Fitbit Flex for a period of two weeks in a free-living environment.

Results:

Comparing group medians, patients exhibiting NYHA class III symptoms had significantly lower recorded two-week mean daily total step count (3541 vs. 5729 [steps], P = .04), lower two-week maximum daily total step count (10792 vs. 5904 [steps], P = .03), lower two-week recorded mean daily mean step count (4.0 vs. 2.5 [steps/minute], P = .04,), and lower two-week mean and two-week maximum daily maximum per minute step count (88.1 vs. 96.1, & 111.0 vs. 123.0 [steps/minute], P = .02, & .004 respectively).

Conclusions:

Patients with NYHA II and III symptoms differed significantly by various aggregate measures of free-living step count including the 1) mean and 2) maximum daily total step count as well as, by the 3) mean of mean daily step count, and by the 4) mean and 5) maximum of the maximum daily per minute step counts. These findings affirm that the degree of exercise intolerance of NYHA II and III patients as a group is quantifiable in a replicable manner. This is a novel and promising finding that suggests the existence of a possible, completely objective measure of assessing HF functional class, something which would be a great boon in the continuing quest to improve patient outcomes for this burdensome and costly disease.