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

The six-minute walk test (6-MWT) is widely used to assess functional status in patients with chronic heart failure (CHF). The aims of the present study were: (1) to compare metabolic gas exchange during the 6-MWT in older patients with left ventricular systolic dysfunction (LVSD) and in breathless patients with no major structural heart disease (MSHD); (2) to determine the exercise intensity of the 6-MWT relative to peak oxygen uptake; (3) to establish the accuracy and reproducibility of the Metamax 3B ergospirometer during an incremental workload. Twenty four older patients with LVSD (19 male; age 76 ± 5 years; BMI 27 ± 4), and 18 patients with no MSHD (12 male; age 75 ± 8 years; BMI 27 ± 4) attended on consecutive days at the same time. Patients completed a 6-MWT with metabolic gas exchange measurements using the Metamax 3B portable ergospirometer, and an incremental cycle ergometry test using both the Metamax 3B and Oxycon Pro metabolic cart. Patients returned and performed a second 6-MWT and an incremental treadmill test, metabolic gas exchange was measured with the Metamax 3B. In patients with LVSD, the 6-MWT was performed at a higher fraction of maximal exercise capacity (p = 0.02). The 6-MWT was performed below the anaerobic threshold in patients with LVSD (83 %) and in patients with no MSHD (61 %). The Metamax 3B showed satisfactory to high accuracy at 10 W and 20 W in patients with LVSD (r = 0.77 - 0.97, p < 0.05), and no MSHD (r = 0.76 - 0.94, p < 0.05). Metabolic gas exchange variables measured during the 6-MWT showed satisfactory to high day-to-day reproducibility in patients with LVSD (ICC = 0.75 - 0.98), but a higher variability was evident in participants with no MSHD (ICC = 0.62 - 0.97). The Metamax 3B portable ergospirometer is an accurate and reproducible device during submaximal, fixed rate exercise in older patients with LVSD and no MSHD. In elderly patients with LVSD and no MSHD, the 6-MWT should not be considered a maximal test of exercise capacity but rather a test of submaximal exercise performance. Our study demonstrates that the 6-MWT takes place at a higher proportion of peak oxygen uptake in patients with LVSD compared to those with no MSHD, and may be one reason why fatigue is a more prominent symptom in these patients

Prognostic value of the VE/VCO2 slope calculated from different time intervals in patients with suspected heart failure

Background: Maximal exercises testing, whether involving cycling- or walking-based protocols, are often not well tolerated in patients with chronic heart failure (CHF). The peak oxygen consumption and the slope of the relation between ventilation (V E ) and carbon dioxide production (V CO2 ) are independent predictors of outcome and help risk stratification. The prognostic usefulness of submaximal exercise testing is not clear. The aim of the present study was to assess the prognostic value of the V E /V CO2 slope when derived from data acquired from submaximal exercise. Methods: 394 patients referred with breathlessness and suspected heart failure (74% male) (mean ± S.D.) age 60 ± 12 years; BMI 27 ± 5 performed a CPET to determine peak V O2 and the V E /V CO2 slope. The V E /V CO2 slope was calculated using least squares regression from data acquired from the first 25% of exercise (mean V E /V CO2 slope ± SD; 30.6 ± 5.7), 50% (29.6 ± 6.9), below the ventilatory compensation point (sub-VCP) (29.9 ± 6.8), and all data points (full slope) (32.1 ± 7.8). For each measure, patients were divided into quartiles and Kaplan-Meier curves were constructed to determine probability of death after 24 months. The prognostic value of the different classifications was assessed using the χ 2 statistic from the Mantel-Cox log-rank test. Results: During a mean follow-up period of 41 ± 19 months, 48 patients died. For the V E /V CO2 slope, the log-rank statistic was greatest for the full slope (χ 2 = 53.7; P = 0.0001), followed by the sub-VCP (χ 2 = 45.5; P = 0.0001), 50% (χ 2 = 41.9; P = 0.0001), and 25% (χ 2 = 26.0; P = 0.01). The pair-wise log-rank statistic between the fourth and third quartiles was also greatest using the full slope (χ 2 = 25.4; P = 0.001) followed in order by the sub-VCP (χ 2 = 20.1; P = 0.001), 50% (χ 2 = 19.7; P = 0.001), and 25% (χ 2 = 14.2; P = 0.05). Using the stratified slope measurements entered into a Cox regression analysis using a forward LR stepwise elimination procedure; only the full slope remained significant (P = 0.0001). Conclusions: The V E /V CO2 slope should be calculated from all data points to optimise prognostic sensitivity. Data acquired from the first 50% of exercise and below the VCP provide adequate prognostic surrogates in patients who may not be able to perform maximal exercise testing (i.e. in patients with a respiratory exchange ratio < 1.10). © 2006 Elsevier Ireland Ltd. All rights reserved