CORRESPONDENCE: RESEARCH CORRESPONDENCE
Diabetes Lowers Six-Minute Walk Test Performance in Heart Failure
Lee Ingle, PhD*,
Priya Reddy, MRCP,
Andrew L. Clark, MD and
John G.F. Cleland, MD, FACC
* Division of Academic Medicine, Department of Cardiology, Castle Hill Hospital, University of Hull, Castle Road, Cottingham, Hull, HU16 5JQ, United Kingdom (Email: l.ingle{at}hull.ac.uk).
To the Editor: Tibb et al. (1) have recently observed that patients with diabetes mellitus and left ventricular systolic dysfunction (LVSD) have a lower peak oxygen uptake  VO2 than patients with LVSD alone. Peak oxygen uptake provides important information on risk stratification and can be used to guide management (2). However, tests involve cycling- or walking-based protocols of increasing speed, gradient, or resistance, are not well tolerated in some patients with LVSD. Equipment for measuring metabolic gas exchange is expensive and cumbersome, and availability of trained staff is limited. The six-minute walk test (6-MWT) is an alternative and widely used method of assessing functional capacity; it is simple and cost effective to perform, it is safe because patients are self-paced during exertion, and previous reports suggest it is a reliable test provided it is well standardized in patients with heart failure (3). However, to our knowledge the impact of diabetes mellitus on 6-MWT performance has not been investigated previously.
Patients were recruited from a local community heart failure clinic; inclusion criteria were: stable medical therapy and evidence of LVSD, defined as a left ventricular ejection fraction (LVEF) of <40%. Exclusion criteria were: inability to walk without assistance from another person (not including mobility aids), chronic obstructive pulmonary disease (COPD) of at least moderate severity (1-s forced expiratory volume <70% of predicted, exertional angina, systolic blood pressure >160 mm Hg or diastolic blood pressure >90 mm Hg, participation in an exercise training program, and active tobacco use. Severe renal dysfunction was defined as an estimated glomerular filtration rate of <30 ml·min·1.73 m2). The Hull and East Riding Ethics Committee approved the study, and all patients provided informed consent for participation. Patients who met the inclusion/exclusion criteria underwent clinical history and physical examination, together with electrocardiogram, echocardiogram, and routine blood samples. Glycosylated hemoglobin was measured in all patients. The 6-MWT was conducted following a standardized protocol after usual medication (4). A flat obstacle-free corridor, with chairs placed at either end, was used. Patients were instructed to walk as far as possible, turning 180° every 15 m in the allotted time.
The 6-MWT performance was compared in diabetics and nondiabetics using the independent-samples t test. To explore the relation between 6-MWT and potential predictor variables, candidate variables were assessed using univariate and multivariable regression. For the final statistical model, the goodness-of-fit was assessed by calculating the explained variance and by plotting the residuals. A multivariable building process was used to identify the "best set" of predictor variables using routinely collected data, including diabetic state, hemoglobin, N-terminal portion of pro-brain natriuretic peptide (NT-proBNP), hypertension, ischemic heart disease (IHD), severe renal impairment, atrial fibrillation (AF), LVEF, and glycosylated hemoglobin.
We recruited our patients using the same process as Tibb et al. (1). We first identified 256 patients with chronic heart failure (CHF) and diabetes among the 756 patients with LVEF of <40% in our clinic. We then matched these patients for age and sex to the remaining 500 nondiabetic patients. Patients were case-matched to the nearest single decimal place. We found age and gender matches for 88 patients, who were selected as our patient cohort. The 6-MWT performance was lower in diabetic (238 ± 124 m) than in nondiabetic patients (296 ± 131 m) (p = 0.005) (Fig. 1). Diabetic state remained an independent predictor of impaired 6-MWT performance after controlling for hemoglobin, NT-proBNP, hypertension, IHD, severe renal impairment, AF, LVEF, and glycosylated hemoglobin. Ischemic heart disease was more prevalent in our diabetic patients than in nondiabetics (Table 1). Glycosylated hemoglobin was also higher in the diabetic patients (p = 0.001). Stature, body mass index (BMI), hemoglobin, NT-proBNP, COPD, hypertension, renal impairment, AF, and CHF medication were similar in both groups.
View larger version (14K):
[in this window]
[in a new window]
|
Figure 1 Six-minute walk test (6-MWT) performance in diabetic and nondiabetic patients with left ventricular systolic dysfunction. Median, interquartile range, and outliers are shown. *Significant difference in 6-MWT performance between diabetics and nondiabetics (p = 0.005).
|
|
To our knowledge, our study is the first to show that patients with diabetes mellitus and LVSD are likely to have impaired 6-MWT performance compared with patients with LVSD alone. We acknowledge the retrospective nature of the study is a limitation. These data extend previous findings that have examined VO2 only in patients with CHF and diabetes mellitus (1,5,6). Whereas VO2 is a strong prognostic indicator (7), maximal exercise testing cannot be tolerated by some patients with symptomatic heart failure. The relative exercise intensity required to perform the 6-MWT is lower, and it is simple and cost effective to perform. Our findings relate to a larger and more controlled patient population than previous investigations. Others have shown VO2 was significantly lower in diabetic than in nondiabetic patients (1,6). Tibb et al. (1) recruited slightly fewer patients with diabetes (n = 78). We recruited older patients with a higher BMI, glycosylated hemoglobin, and prevalence of AF. Conversely, our patients had a lower prevalence of hypertension and less aggressive diabetic and heart failure therapy.
We acknowledge that IHD was more prevalent in our diabetic patients than in nondiabetics. To determine if IHD had influenced our results we rematched patients to account for prevalence of ischemia. We included only patients with IHD, and matched 50 diabetic patients (6-MWT = 231 ± 139 m) and 50 CHF patients (6-MWT= 283 ± 126 m) (p = 0.001). The mean difference in 6-MWT performance was 52 m. We reran the multivariable analysis, and diabetic state remained an independent determinant of poorer walking performance in patients with LVSD. Ischemic heart disease was not included in the model and did not affect 6-MWT performance.
To determine if our conclusions were similar if we adjusted the analysis in the complete patient cohort (n = 256), we reanalyzed the data, adjusting for diabetic state, hemoglobin, NT-proBNP, hypertension, IHD, severe renal impairment, AF, LVEF, and glycosylated hemoglobin. We found that diabetic state remained an independent determinant of poorer walking performance in patients with LVSD. Our conclusions are not altered if we adjusted for confounders in all of our diabetic patients.
Although 6-MWT performance is compromised in patients with LVSD compared with aged-matched controls (8), the addition of diabetes mellitus to LVSD is likely to further reduce patients’ functional status. In summary, diabetic patients with LVSD have a poorer 6-MWT performance than patients with LVSD alone. Diabetic state is an independent determinant of poorer walking performance in patients with LVSD.
 |
References
|
|---|
1. Tibb AS, Ennezat PV, Chen JA, et al. Diabetes lowers aerobic capacity in heart failure J Am Coll Cardiol 2005;46:930-931.[Free Full Text]2. Schalcher C, Rickli H, Brehm M. Prolonged oxygen uptake kinetics during low-intensity exercise are related to poor prognosis in patients with mild-to-moderate congestive heart failure Chest 2003;124:580-586.[Abstract/Free Full Text] 3. Ingle L, Shelton RJ, Rigby AS, Nabb S, Clark AL, Cleland JGF. The reproducibility and sensitivity of the 6-minute walk test in elderly patients with chronic heart failure Eur Heart J 2005;26:1742-1751.[Abstract/Free Full Text] 4. ATS statementguidelines for the six-minute walk test. Am J Respir Crit Care Med 2002;166:1111-1117. 5. Guazzi M, Brambilla R, Pontone G, Agostoni P, Guazzi MD. Effect of noninsulin-dependent diabetes mellitus on pulmonary function and exercise tolerance in chronic congestive heart failure Am J Cardiol 2002;89:191-197.[CrossRef][Web of Science][Medline] 6. Guazzi M, Tumminello G, Matturri M, Guazzi MD. Insulin ameliorates exercise ventilatory efficiency and oxygen uptake in patients with heart failure-type 2 diabetes comorbidity J Am Coll Cardiol 2003;42:1044-1050.[Abstract/Free Full Text] 7. Stelken AM, Younis LT, Jennison SH, et al. Prognostic value of cardiopulmonary exercise testing using percent achieved of predicted peak oxygen uptake for patients with ischemic and dilated cardiomyopathy J Am Coll Cardiol 1996;27:345-352.[Abstract] 8. Ingle L, Rigby AS, Nabb S, Jones PK, Clark AL, Cleland JGF. Clinical determinants of poor six-minute walk test performance in patients with left ventricular systolic dysfunction and no major structural heart disease Eur J Heart Fail 2005Oct 30 [epub ahead of print]..
This article has been cited by other articles:
|
|
|
|
 
M. R. MacDonald, M. C. Petrie, N. M. Hawkins, J. R. Petrie, M. Fisher, R. McKelvie, D. Aguilar, H. Krum, and J. J.V. McMurray
Diabetes, left ventricular systolic dysfunction, and chronic heart failure
Eur. Heart J.,
May 2, 2008;
29(10):
1224 - 1240.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
Top
References