Inverse association between cardiorespiratory fitness estimated by a 1-km moderate treadmill walk and mortality in hypertensive patients with cardiovascular disease

Background: Poor cardiorespiratory fitness (CRF) has often been associated with incidence and severity of hypertension (HTN). Cardiopulmonary exercise testing is the "gold standard" for CRF determination (i.e. VO2peak). However, because of physical, financial and time limitations, direct VO2peak determination is often not routinely assessed in clinical settings. A moderate 1-km treadmill-walking test (1k-TWT) has been demonstrated to be a valid and simple tool for CRF estimation in an outpatient setting. Aim: To examine the association between VO2peak estimated during a 1k-TWT and all-cause mortality in a cohort of patients with HTN and known cardiovascular disease (CVD). Methods: 711 patients aged 30 to 85 (mean 62 ± 10 years) underwent 1k-TWT, and were followed for all-cause mortality for up to 10 years. The 1k-TWT was individualized at a moderate perceptually-regulated exercise intensity (11-13 on the 6-20 Borg scale). Age, body mass index, heart rate, and time to complete the 1-km treadmill walk were entered into the equations originally validated for VO2peak estimation. Subjects were stratified into quartiles according to baseline VO2peak and mortality risks were calculated. Results: During a median follow-up of 9.6 years, survival decreased in a graded fashion from the highest VO2peak quartile to the lowest quartile. A total of 106 deaths from any cause occurred, and resulted 48 for the first (27% of the sample), 33 for the second (19% of the sample), 18 for the third (10% of the sample), and 7 for the fourth quartile (4% of the sample). Age, body mass index, left ventricular ejection fraction, smoking status, fasting glucose, total cholesterol, family history for CVD, history of previous coronary artery by-pass graft and acute myocardial infarction, and use of statins and diuretics were significantly associated with survival. Compared to the lowest quartile (average VO2peak 18.0 mL/kg/min, n = 178), the full-adjusted hazard ratios (95% confidence intervals) were 0.80 (0.41 to 1.57, P = 0.40) for the second quartile (average VO2peak 21.8 mL/kg/min, n = 178), 0.29 (0.11 to 0.77, P = 0.01) for the third quartile (average VO2peak 24.5 mL/kg/min, n = 177), and 0.05 (0.01 to 0.44, P = 0.007, n = 178) for the fourth quartile (average VO2peak 29.2 mL/kg/min, n = 178), P for trend <0.0001. Conclusions: Peak oxygen uptake estimated by a moderate and perceptually regulated 1k-TWT is a strong and independent predictor of all-cause mortality in patients with HTN and known CVD. Assessing VO2peak by the 1k-TWT can be a useful, simple and low cost tool to stratify and follow-up hypertensive patients with CVD through cardiac rehabilitation and secondary prevention programmes.