The 6-minute walk test (6MWT) is a functional performance measure commonly used in the assessment of patients with heart failure (HF) and is often used to complement cardiopulmonary exercise (CPX) testing. Heart rate recovery (HRR) has recently been recommended as an additional CPX measurement, because it has been found to be a strong prognostic marker of increased mortality in patients with HF and is easily obtained. We are unaware of any previous investigation that has examined the characteristics of HRR after CPX testing compared to the 6MWT.
Six-minute walk and CPX tests were randomly performed in 258 patients with HF (216 with HF with reduced ejection fraction, 42 with HF with preserved ejection fraction), after which HRR was measured. HRR was defined as the difference between heart rate at peak exercise and 1 minute after test termination. The 6MWT was performed using standardized methods, and symptom-limited CPX testing was performed on a bicycle ergometer using individualized ramp protocols designed to obtain exercise durations of 8 to 10 minutes. The cool-down periods after the 6MWTs and CPX tests were passive and active (for ≥1 minute), respectively. Approval by the institutional review board was obtained before the study was initiated, and all patients provided written informed consent to participate in the study.
SPSS version 19.0 (SPSS, Inc., Chicago, Illinois) was used to analyze descriptive statistics of HRR after the 6MWTs and CPX tests and included the calculation of frequency, mean, median, mode, SEM, variance, skewness, kurtosis, range, minimum, and maximum.
Table 1 lists the descriptive statistics for HRR after the 6MWTs and CPX tests for the entire cohort and for patients with HF with reduced ejection fraction and those with HF with preserved ejection fraction. All descriptive statistics of HRR after the 6MWT were similar to the descriptive statistics of HRR after CPX testing. The mean, median, mode, and range of HRR were slightly greater after CPX testing. However, the maximum HRR after the 6MWTs and CPX tests were identical (21 beats). The minimum HRR and HRR variance were slightly greater after the 6MWT compared to CPX testing. The percentage of patients with HRR ≤12 beats was 55% after the 6MWT and 38% after CPX testing. The skewness and kurtosis values of HRR for the 6MWT and CPX testing were relatively normal. However, slightly negative skew was observed for HRR after CPX testing, and slightly greater negative kurtosis was observed for HRR after the 6MWT.
| Variable | Entire Cohort (n = 258) | HFrEF (n = 216) | HFpEF (n = 42) | |||
|---|---|---|---|---|---|---|
| 6MWT | CPX Test | 6MWT | CPX Test | 6MWT | CPX Test | |
| Mean | 12.22 | 13.58 | 12.38 | 13.74 | 11.43 | 12.76 |
| SEM | 0.19 | 0.18 | 0.21 | 0.20 | 0.48 | 0.49 |
| Median | 12.00 | 14.00 | 12.00 | 14.00 | 11.00 | 12.50 |
| Mode | 14.00 | 16.00 | 14.00 | 16.00 | 10.00 | 12.00 |
| SD | 3.11 | 2.95 | 3.08 | 2.89 | 3.13 | 3.15 |
| Variance | 9.65 | 8.73 | 9.52 | 8.38 | 9.81 | 9.94 |
| Skewness | 0.09 | −0.16 | 0.02 | −0.11 | 0.51 | −0.26 |
| SE of skewness | 0.15 | 0.15 | 0.17 | 0.17 | 0.36 | 0.36 |
| Kurtosis | −0.61 | −0.18 | −0.68 | −0.69 | 0.29 | 1.78 |
| SE of kurtosis | 0.30 | 0.30 | 0.33 | 0.33 | 0.72 | 0.72 |
| Range | 16.00 | 18.00 | 15.00 | 13.00 | 15.00 | 18.00 |
| Minimum | 5.00 | 3.00 | 6.00 | 7.00 | 5.00 | 3.00 |
| Maximum | 21.00 | 21.00 | 21.00 | 20.00 | 20.00 | 21.00 |
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