The 6-minute walk test in chronic heart failure

Functional level in patients with chronic heart failure (CHF) can be evaluated inexpensively and easily using the 6-minute walk test.^1,2 This test, which employs a form and intensity of exercise that is well known to patients with CHF, can also predict morbidity and mortality.³ In addition, the test can be used to assess the impact of resynchronization therapy.⁴

One of the goals of heart failure treatment is to improve patients’ symptoms.⁵ Because the association between patients’ perceptions of heart failure symptoms and results objective from tests are not known, we evaluated the relationship between the 6-minute walk test and patients’ perceptions of symptoms in a cohort of elderly patients.

Patients and methods

All patients were 60 years of age or older and were classified with New York Heart Association (NYHA) functional class II to IV heart failure symptoms. They also had a left ventricular ejection fraction of 40% or lower. Patients were given the EuroHeart Failure Survey (see Box), which consists of 6 questions regarding perception of heart failure symptoms during physical work, with the answers rated on a scale of 1 (unimpaired) to 6 (very impaired).⁶ Patients were then given the 6-minute walk test according to established procedures.⁷

After 1 year, the 6-minute walk test was given to patients a second time, and the severity of their symptoms was again assessed. Based on symptom changes since the start of the study, participants were categorized into 3 groups: those with no change in symptoms, with a score at baseline of ± 3 points on the EuroHeart Failure Survey (group 1); those whose symptoms had increased, as shown by a score of >= 4 points on the survey (group 2); and those whose symptoms had improved, as shown by a score of 4 points (group 3). Analysis of variance was used to establish group differences at the start of the study. To establish the differences in symptoms between baseline and 1 year, the chi-square test was used. A P value of < .05 was considered statistically significant.

The EuroHeart Failure Survey

Patients answered each of the 6 questions of the EuroHeart Failure Survey with 1 of the following responses: (1) not at all, (2) very little, (3) a little, (4) some, (5) a lot, (6) very much.

The 6 questions were:

In the last month, how much did the following affect you:

1. Breathlessness limiting daily activities?

2. Fatigue limiting daily activities?

3. Inability to engage in normal daily activities due to health?

4. Inability to engage in hobbies/sports due to health?

5. Inability to work due to health?

6. Chest pain during normal activity?

Results

A total of 1013 patients re&shy;mained from the original sample of 1077 patients after 64 patients died. There were no differences in results on the 6-minute walk test between groups 1 and 3 (P = .09). A difference was shown, however, between group 2 and the other 2 groups at baseline (P = .03).

For all patients, there was a significant relationship between the change in symptom severity and change in results on the 6-minute walk test (r = -0.59; P = .001; Figure). As shown in the Table, the mean distance in the 6-minute walk test decreased to 195 ± 130 m from 279 ± 127 m, in 516 patients in group 2 after 1 year. For these pa&shy;tients, there was an inverse relationship between changes in symptom severity and changes in the 6-minute walk test (r = -0.53; P = .001). For patients in group 3, there was also an inverse relationship between changes in symptom severity and changes in the 6-minute walk test (r = -0.55; P = .001).

Discussion

For elderly patients with left ventricular systolic dysfunction who died before 1 year, the distance on the 6-minute walk test (208 ± 103 m) was markedly less than that of other patients, but the severity of their symptoms was similar. Patients who walked less than 300 m on the 6-minute walk test have been shown to have higher mortality rates, according to prior studies.^7,8 This corroborates the results of our study. Performance on the 6-minute walk test at baseline may also be a better predictor of mortality than symptom severity at baseline. In our study, although there was high sensitivity between changes in symptom severity and changes in the 6-minute walk test at the start of the study and at the 1-year follow-up, there was no relationship between the severity of symptoms at the start of the study and results on the 6-minute walk test. After 1 year, only 7% of patients had unchanged symptoms.

The patient’s own assessment of heart failure symptoms has not been previously studied, as far as we know. No correlation has been shown be&shy;tween the 6-minute walk test and general quality-of-life (QOL) measures in previous studies.^9,10 In 1 study, no relationship was shown between QOL and functional ability in patients with NYHA functional class I and II symptoms among patients with dilated cardiomyopathy.¹¹ Results equivalent to ours were shown in a study of 205 patients with heart failure.¹⁰ According to the results of our study, the 6-minute walk test correlated with changes in self-perceived heart failure symptoms for patients with NYHA functional class II to IV. A significant but frequently overlooked clinical parameter is the sensitivity of a test to symptom changes.¹² In addition to emotional and pathophysiological changes, many other variables play a role in these changes.¹¹ An increase in symptoms usually occurs with depression, which is common in patients with CHF.¹³ Further research is needed to determine how well self-reported depression is predicted by objective tests of functional ability. We cannot assert that the 6-minute walk test and symptom severity were influenced by this factor because we did not assess depression in our patients after 1 year. Additional research should concentrate on establishing the predictive power of changes in symptom severity and changes in the 6-minute walk test in CHF patients.

It is hard to contrast the results of our study with those of other studies because not many other studies have evaluated changes in QOL and symptoms without some form of intervention. In 1 study, after a follow-up period of 3 to 8 weeks, there were no changes in QOL among 53% of elderly patients with CHF,¹⁴ which is a significantly greater proportion of patients than in our study. This study is not comparable with our study, however, because the sample size was smaller than ours, a different measurement of QOL was used, the duration of follow-up was shorter, a different analysis was used, and changes in symptoms were not evaluated.

Conclusions

As far as we know, our study is the first to report changes in symptoms over a 12-month period in a large cohort of patients with CHF. Results showed that performance on the 6-minute walk test is sensitive to self-perceived changes in symptoms of heart failure among CHF patients.