Cardiorespiratory requirements of the 6-min walk test in older patients with left ventricular systolic dysfunction and no major structural heart disease

Prolonged heart rate recovery time after 6-minute walk test is an independent risk factor for cardiac events in heart failure: A prospective cohort study

OBJECTIVES

To determine whether the time for peak exercise heart rate to return to resting heart rate after the 6-minute walk test (6MWT) can predict cardiac events in patients with heart failure (HF) within 2 years.

DESIGN

Prospective cohort study.

SETTING

HF outpatient facility at a tertiary teaching hospital.

PARTICIPANTS

Seventy-six patients with HF, New York Heart Association functional classification II and III, and left ventricular ejection fraction <50%.

MAIN OUTCOME MEASURES

Patients used a heart rate monitor to measure the time for peak exercise heart rate to return to resting heart rate after the 6MWT. Data were analysed using Polar Pro-Trainer 5 software (Kempele, Finland). Patients were followed for >2 years for cardiac events (hospitalisations and death).

RESULTS

Thirty-four patients had cardiac events during the 2-year follow-up period. However, there was a significant difference in the time to return to resting heart rate between the groups with and without cardiac events {with 3.6 (SD 1.1) vs without 2.8 (SD 1.1) minutes; mean difference of 0.79 (95% confidence interval (CI) of the difference 0.28 to 1.28; P=0.003}. No significant differences between patients with and without cardiac events were found for mean walking distance, mean heart rate recovery at 1minute and mean heart rate recovery at 2minutes. The receiver operating curve discriminated between patients with and without cardiac events (área under the curve 0.71, 95% CI 0.61 to 0.81; P<0.001). Using logistic regression analysis, prolonged time to return to resting heart rate (≥3minutes) independently increased the risk for cardiac events 6.9-fold (95% CI 2.34 to 20.12; P<0.001). The Kaplan-Meier curve showed more cardiac events in patients with prolonged time to return to resting heart rate (P=0.028).

CONCLUSIONS

Prolonged time to return to resting heart rate (≥3minutes) after the 6MWT was an independent predictor of cardiac events in patients with HF.

Prognostic value of 6-minute walk test and cardiopulmonary exercise test in acute heart failure (from the ESCAPE trial)

Introduction

We aim to study the utility of 6-minute walk distance (6MWD) and cardiopulmonary exercise testing (CPET) in patients with acute systolic heart failure (HF) in predicting post-discharge outcomes.

Methods

The ESCAPE trial data was utilized to examine the prognostic role of 6MWD and CPET in predicting 6-month all-cause mortality and rehospitalization in acute HF.

Results

The average 6MWD recorded in 271 and 292 patients on admission and discharge was 597 and 765 ft., respectively. Compared with non-survivors, survivors had significantly higher 6MWD on admission (624 vs. 463 ft., P = 0.006) and discharge (789 vs. 636 ft., P = 0.006). Admission and discharge 6MWD had an AUC of 0.629 (P = 0.0047) and 0.628 (P = 0.0093) in predicting mortality. The combination of optimal 6MWD cutoff values of >288 ft. on admission and > 320 ft. on discharge was associated with significantly lower mortality (11.1% vs. 28.3%, OR 0.316, P = 0.002). When dividing the sample into quartiles of increasing walking distance, patients in the 1st quartile had significantly higher mortality on admission (OR 3.59, 95% CI 1.396-9.282, P = 0.008) and discharge (OR 3.66, 95% CI 1.357-9.839, P = 0.01) compared with 4th quartile. P-value for the trend in mortality across quartiles of 6MWD on admission and discharge was 0.016 and 0.047, respectively. Cox proportional hazard analysis revealed that admission (HR 0.632, 95% CI 0.449-0.890, P = 0.009) and discharge 6MWD (HR 0.657, 95% CI 0.467-0.926, P = 0.016) were independent mortality determinants after adjustment for age, creatinine, sodium, systolic blood pressure and NYHA class, all on admission. CPET-derived variables did not predict either outcomes.

Conclusion

6MWD is an independent mortality determinant in advanced systolic HF.

The long-term prognostic significance of 6-minute walk test distance in patients with chronic heart failure

Background. The 6-minute walk test (6-MWT) is used to assess patients with chronic heart failure (CHF). The prognostic significance of the 6-MWT distance during long-term followup (>5 years) is unclear. Methods. 1,667 patients (median [inter-quartile range, IQR]) (age 72 [65–77]; 75% males) with heart failure due to left ventricular systolic impairment undertook a 6-MWT as part of their baseline assessment and were followed up for 5 years. Results. At 5 years' followup, those patients who died (n = 959) were older at baseline and had a higher log NT pro-BNP than those who survived to 5 years (n = 708). 6-MWT distance was lower in those who died [163 (153) m versus 269 (160) m; P < 0.0001]. Median 6-MWT distance was 300 (150–376) m, and quartile ranges were <46 m, 46–240 m, 241–360 m, and >360 m. 6-MWT distance was a predictor of all-cause mortality (HR 0.97; 95% CI 0.96-0.97; Chi-square = 184.1; P < 0.0001). Independent predictors of all-cause mortality were decreasing 6-MWT distance, increasing age, increasing NYHA classification, increasing log NT pro-BNP, decreasing diastolic blood pressure, decreasing sodium, and increasing urea. Conclusion. The 6-MWT is an important independent predictor of all-cause mortality following long-term followup in patients with CHF.

Walking tests during the exercise training: specific use for the cardiac rehabilitation

Walk tests, principally the six-minute walk test (6mWT), constitute a safe, useful submaximal tool for exercise tolerance testing in cardiac rehabilitation (CR). The 6mWT result reflects functional status, walking autonomy and efficacy of CR on walking endurance, which is more pronounced in patients with low functional capacity (heart failure - cardiac surgery). The 6mWT result is a strong predictor of mortality. However, clinically significant changes and reliability are still subject to debate - probably because of the ambiguity in terms of the target speed (either comfortable or brisk walking). Of the other time-based walk tests, the 2-minute-walk test is the only one applicable during CR, reserved for patients with severe disabilities by its psychometric properties. Fixed-distance tests (principally the 200m fast walk test) and incremental shuttle walking, tests explore higher levels of effort and may represent a safe and inexpensive alternative to laboratory-based tests during CR. These walking tests may be useful for personalizing prescription of training programs. However, the minimum clinically significant difference has not yet been determined. Lastly, walking tests appear to be potential useful tools in promoting physical activity and behavioural changes at home. Thus, validation of other walk tests with better psychometric properties will be necessary.

Clinically meaningful change estimates for the six-minute walk test and daily activity in individuals with chronic heart failure

PURPOSE

The purpose of the present pilot study was to provide a preliminary estimate of the minimum detectable difference (MDD) and minimum clinically important difference (MCID) of the six-minute walk test (6MWT) and daily activity in outpatients with chronic heart failure (CHF).

METHODS

A convenience sample of 22 adults with stable New York Heart Association Functional Class II and III CHF performed two baseline 6MWTs separated by 30 minutes of rest. Subjects then wore a triaxial accelerometer for 7 days to monitor daily activity. After 7 weeks of usual care, subjects again wore the accelerometer for 7 days and then returned to the clinic to complete the Global Rating of Change Scale (GRS) with regard to their heart disease and perform another set of 6MWTs. For the 6MWT, the MDD was calculated using the two baseline 6MWT distances. For daily activity, the MDD was calculated using two methods: (1) day-to-day test-retest reliability during baseline monitoring, and (2) baseline to follow-up test-retest reliability in those who reported no change on the GRS. The MCID for the 6MWT and daily activity was calculated using the mean and 95% confidence interval (CI95%) for those subjects who reported 'improvement' on the GRS.

RESULTS

The MDD at the CI95% for the 6MWT was 32.4 meters. The MCID for the 6MWT was 30.1 (CI95% 20.8, 39.4) meters. The MDD for daily activity was 5,909 vector magnitude units (VMU·hr.(-1)) The MCID for daily activity was 1,337 VMU·hr.(-1) There was good alignment of the MDD and MCID for the 6MWT, suggesting that clinically meaningful change is approximately 32 meters. However, the calculated MCID was substantially less than measurement error as represented by the MDD, indicating that the MCID was underestimated in this sample or that daily activity may be robust to change in overall disease status.

The effect of carrying a portable respiratory gas analysis system on energy expenditure during incremental running

This study aimed to assess the effect of portable gas analysis system carriage on energy expenditure (EE) during incremental treadmill running. Eight males (Mean ± SD) age 25.0 ± 9.47 y, body mass 78.5 ± 8.39 kg, completed an experimental trial (PT) during which they wore the system in a chest harness and a control trial (CT) when the system was externally supported. Each protocol consisted of 4 min stages at speeds of 0, 4, 7, 10, 12, 14 km h(-1). Increments continued until volitional exhaustion. The EE was greater (3.95 and 7.02% at 7 and 14 km h(-1) respectively) during PT (p < 0.05) but no significant differences were observed during standing, walking or VO(2max.) (4.10 ± 0.53, and 4.28 ± 0.75 l min(-1) for CT and PT respectively), HR or RPE. Portable gas analysis systems therefore only increase EE when running sub-maximally, but VO(2max) is unaffected, suggesting that using portable gas analysis systems in field-based situations is appropriate for maximal aerobic capacity measurement, but the effects of prolonged use on EE remains unclear.

Influence of step length on 6-minute walk test performance in patients with chronic heart failure

OBJECTIVE

To investigate the influence of gait parameters including step length and walking speed during performance of the 6-minute walking test (6MWT) in patients with chronic heart failure (CHF).

DESIGN

Observational study.

SETTING

Specialist heart failure clinic.

PARTICIPANTS

Patients with CHF and aged-matched, apparently healthy controls.

INTERVENTIONS

Each patient and control performed a 6MWT following a standardised protocol in a 15m corridor. The number of steps (defined as step from left foot to right foot) taken every 15m was counted, and reported as minute-by-minute changes in 6MWT performance. In addition, minute-by-minute changes in time taken to complete 15m and mean walking speed throughout the test were calculated.

MAIN OUTCOME MEASURES

Walking speed and step length.

RESULTS

Thirty patients with CHF {87% males; mean age 75 [standard deviation (SD) 8] years} and 10 healthy controls [80% males; mean age 77 (SD 11) years] undertook the 6MWT. For the CHF group, the mean distance walked was 309 (SD 48)m and the peak Borg score was 12 (SD 1). For the controls, the mean distance walked was 334 (SD 138)m and the peak Borg score was 12 (SD 1). Patients with CHF showed no significant minute-by-minute changes in step length or walking speed over the course of the 6MWT. In the first 5minutes, healthy controls had a longer step length and faster walking speed than patients with CHF [step length: mean difference in the first minute was 0.03m, 95% confidence interval (CI) of the difference 0.01 to 0.05m; P=0.02; walking speed: mean difference in the first minute 0.04m/second, 95% CI of the difference 0.02 to 0.07m/second; P=0.01]. A multiple linear regression analysis demonstrated that body mass index (P=0.02) was the most important predictor of 6MWT performance.

CONCLUSION

Patients with CHF have a shorter step length and walk more slowly than controls during the 6MWT. Altered gait mechanics may contribute to limited exercise capacity in patients with CHF.

Theoretical rationale and practical recommendations for cardiopulmonary exercise testing in patients with chronic heart failure

The syndrome of chronic heart failure (CHF) becomes increasingly prevalent in older patients, and while mortality rates are declining in most cardiovascular diseases, both prevalence and mortality in CHF remain high. The heart is unable to meet the demands of the skeletal musculature, and symptoms manifest as dyspnoea and signs of fatigue during exercise. The cardiopulmonary exercise test (CPET) can provoke symptoms which may be useful in improving the accuracy of diagnosis in CHF in a non-invasive setting. CPET also provides important information on the pathophysiology of exercise limitation, risk stratification and can establish exercise-training protocols. The information provided by the CPET allows suitable pharmacological or device-based adjustments to be considered in the management of CHF, which can be crucial in maintaining a patient's quality of life. This manuscript provides a useful insight into the theoretical rationale and practical recommendations for CPET in patients with CHF. Prior to CPET, it is important to consider the mode of exercise, as cycle ergometry or treadmill protocols will yield different outcomes in patients with CHF. We discuss how pre-CPET set-up procedures should be conducted and also the significance of electrocardiographic abnormalities found in CHF patients, and how these should be interpreted. The assessment of lung function is integral to the underlying pathophysiological basis of exercise limitation and we explain how this should be performed. CHF patients display the following abnormal exercise responses which can be identified by CPET: peak oxygen uptake ( [Formula: see text] peak), anaerobic threshold (AT), DeltaVO(2)/Delta work rate (WR), peak oxygen pulse, estimated peak stroke volume and predicted peak heart rate are reduced. The [Formula: see text] slope is abnormally high and the breathing reserve is normal or high. An immediate post-exercise increase in O(2) pulse is evident, and/or a regular oscillatory breathing pattern has been observed at lower exercise intensities in some CHF patients. Symptoms of breathlessness, fatigue, and/or leg pain occur earlier during CPET and may cause the CPET to be aborted early. We explain the significance of the 9-panelled array, and how it can help to determine the underlying pathophysiology of exercise intolerance in these patients.