The Utility of the 6-Minute Walk Test

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HEART FAILURE, FRAILTY, AND THE 6-MINUTE WALK 7THE AMERICAN JOURNAL OF GERIATRIC CARDIOLOGY 2008 VOL. 17 NO. 1

Approximately 5 million persons have conges-tive heart failure in the United States and 70%are older than 60 years.1 With the high prevalenceof hypertension and coronary artery disease andthe growing number of older adults, the burden ofheart failure (HF) will continue to increase. Frailty,defined as a poor physiologic reserve to deal withstress, is estimated to occur in 7% of the generalpopulation older than 65 years.2 The number of

frail older adults will likely also increase with theaging demographic. Targeting individuals whoare frail or at increased risk for becoming frail willallow earlier interventions aimed at both decreas-ing morbidity and hospitalizations and improvingquality of life (QOL). An association has beenfound between frailty and cardiovascular disease,

particularly HF.3,4 Understanding the physical limi-tations of HF patients in the context of the frailtysyndrome may enhance the development of interventions to improve physical function and slowphysical decline. The frailty phenotype has beenused to identify patients who are frail and is pre-dictive of falls, decreased mobility, performance inactivities of daily living (ADL), hospitalization, andmortality.2 This phenotype incorporates 5 mea-

sures for a composite score including grip strength,unexplained weight loss, self-reported exhaustion,walking speed, and physical activity level. It char-acterizes individuals as frail, intermediate frail, andnonfrail. The phenotype measures physical per-formance capability in several domains to identifyindividuals at risk for poor health outcomes.

Performance on the 6-minute walk test (6MWT)has been used to measure aerobic capacity/

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Rebecca S. Boxer, MD;1 Zhu Wang, PhD;2 Stephen J. Walsh, ScD;2 David Hager, MD;3 Anne M. Kenny, MD4

From the Department of Family Medicine and Internal Medicine, Divisions of Cardiology and Geriatrics, Case Western

Reserve University, Cleveland, OH;1 and the Center for Biostatistics,2 the Department of Internal Medicine, Division of

Cardiology,3 and the Center on Aging,4 University of Connecticut, Storrs, CT

Address for correspondence: Rebecca Boxer, MD, University Hospitals of Cleveland, Bolwell Suite 1200, BHC 5036,

11100 Euclid Avenue, Cleveland, OH 44106

E-mail: [email protected]

Manuscript received December 7, 2006; revised March 30, 2007; accepted April 16, 2007

Patients with heart failure (HF) are at increased risk for frailty, and identification is challeng-ing. The authors assessed the distance on the 6-minute walk test (6MWT) as a measure of frailtyin 60 older HF patients (ejection fraction 40%) compared with frailty phenotype (FP). Scoreswere dichotomized to frail (F) or nonfrail (NF), and the results of 6MWT were dichotomized tolow endurance (LE) or normal endurance (NE). FP and 6MWT results were in moderate agree-ment (=0.57, confidence interval [CI], 0.360.79; age-adjusted=0.54, 95% CI, 0.330.76);25% of participants were classified as F/LE, and 55% were classified as NF/NE. Discordancewas asymmetric (McNemar P=.006); 18% of participants were NF/LE. There were no differencesbetween the NF/LE and other groups in age, sex, body mass index, or physical activity level.Results in the NF/LE group differed from those in the NF/NE group by a slower 8-foot walkingspeed (P=.02), weaker grip strength (P=.056), and worse renal function (P=.01) and from those

in the F/LE group by faster 8-foot walking speed (P


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HEART FAILURE, FRAILTY, AND THE 6-MINUTE WALK8 THE AMERICAN JOURNAL OF GERIATRIC CARDIOLOGY 2008 VOL. 17 NO. 1

endurance in both healthy older adults and inpatients with cardiac, pulmonary, and peripheralvascular disease. It is predictive of morbidity andmortality outcomes and correlates with ADL andQOL.5 Multiple studies have found that individu-als walking 3 alcoholic drinks per day; useof androgen, estrogen, dehydroepiandrosterone,or hormone receptor antagonists in the preced-ing year; or the presence of advanced liver dis-ease, renal disease requiring dialysis, Parkinsonsdisease, an inability to ambulate, or a myocardialinfarction within 3 months before the study. Afterinformed consent was obtained, patients medical

histories were reviewed, including the cause ofHF and comorbidities. To determine the stabil-ity of HF, the hospitalizations and the need forintravenous diuretics in the UCHC Heart FailureCenter in the 6 months before the study visitwere recorded. In addition, serum for N-terminalpro-brain natriuretic peptide (NT-proBNP) andNew York Heart Association (NYHA) class weredetermined at the study visit. The frailty pheno-type was determined and 6MWT was performed.

Creatinine clearance was determined by theCockroft-Gault equation. The frailty phenotypeevaluation was adapted from Fried and col-leagues2 and included self-reported weight loss of10 lb in the preceding year, grip strength mea-sured by hand-held Jamar dynamometer, sense

of exhaustion as evaluated by 2 questions fromthe Center for Epidemiologic Studies-DepressionScale,9 walking speed on an 8-foot walk, and levelof physical activity reported in kcal/wk from thePhysical Activity Scale for the Elderly (PASE).10The results of the tests were dichotomized toidentify nonfrail (NF) as those with 02/5 charac-teristics, or frail (F) with 3/5 characteristics.

Protocol for 6MWT was as previously pub-lished.11 Participants were permitted to use a walk-er or cane if needed while the observer recordedsymptoms such as chest pain, shortness of breath,and leg pain. Participants were categorized into 2

groups according to the performance on the test.Those walking 300 m were classified as havinglow endurance (LE), and those walking 300 mwere classified as normal endurance (NE).

statta Mtho. Kappa statistic (), along with95% confidence intervals (CIs), was calculated toassess the agreement of the frailty phenotype andresults of 6MWT. Age adjustment was performed;age was dichotomized older and younger than75 years for this analysis. McNemars chi-squaretest was conducted to test for symmetry. Whensymmetry is not present, discordant groups may

be identified. In this study, one discordant groupwas identified and further analysis compared thegroups with similar results on frailty score and6MWT performance (F/LE and NF/NE) and thediscordant group (NF/LE). Analysis of variance was used to determine whether statistically sig-nificant differences existed between F/LE, NF/LE,and NF/NE demographics, outcome measures,and comorbidities. When statistical significanceexisted, pairwise t tests or Wilcoxon rank tests wereconducted to determine whether statistical signifi-cance existed in any pair of 2 groups, by adjusting

multiple comparisons with the Bonferroni correc-tion. Proportions in contingency tables were com-pared by Fisher exact test for HF status, comor-bidities, total daily dose of angiotensin-convertingenzyme (ACE) inhibitors, angiotensin receptorblockers, b-blockers, and loop diuretics. P values


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ResUlTsOne hundred sixty-nine patients (68 women and101 men) with HF volunteered for the study.Eighty-six were eligible, and 60 (43 men; meanage, 779 years/17 women; mean age, 7812 years) participated. The NYHA classificationsdetermined at the study visit were as follows: classI, 1% (n=1); class II, 57% (n=34); class III, 37%(n=22); and class IV, 5% (n=3). Mean EF was298%. By the frailty phenotype criteria, 44 (73%)

were classified as NF, and 16 (27%) were F. Basedon 6MWT performance, 26 (43%) walked 300 m,and 34 (57%) walked >300 m.

There was moderate agreement between 6MWTresults and frailty phenotype (=0.57; 95% CI,0.370.77). No difference was found when adjustedfor age (=0.54; 95% CI, 0.330.76). Of the 26patients who walked 300 m, 15 were classified as F(F/LE) and 11 were classified as NF (NF/LE). Of the34 patients who walked >300 m, 33 were classifiedas NF (NF/NE), and only 1 participant who walked>300 m was classified as F (F/NE). In evaluation of

symmetry in the distribution of groups, asymmetryor discordance was found (McNemar,P=.006). TheF/LE and NF/NE groups were found to be as expect-ed but the NF/LE and F/NE groups are discordant.Since only 1 participant was in the F/NE group, thisindividual was excluded from analysis. Descriptiveinformation on groups is outlined in Table I.

Significant differences were found among allgroups in the overall frailty score (P


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agreement. These 2 assessment tools each serve toevaluate submaximal exercise, which mirrors ordi-nary activity. The 6MWT assesses aerobic capac-ity and endurance, and the frailty phenotypeis a multi-domain measure of physical function.Despite the different classifications of these tests,we hypothesized that these tests would categorizeindividuals similarly, in that frail patients wouldhave lower endurance than nonfrail patients. Thetests did have moderate agreement in identifyingthe same group of individuals, which suggests anoverlap in the tests abilities to identify at-risk indi-

viduals for poor health outcomes. The combinationof these 2 tests allowed identification of a thirdgroup of individuals who had lower endurance onthe 6MWT and were nonfrail. These patients hada mean frailty score of 1.5, which according to thefrailty phenotype definition2 categorizes them asintermediate frail. This frailty score was significant-ly higher than in the NF/NE group (1.5 comparedwith 0.8 [P=.05]) and significantly lower than theF/LE (1.5 compared with 3.4 [P


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shown to be good markers of general health andpredictive of disability and mortality.1517,19 At pres-ent, there are no studies to our knowledge thathave evaluated the 6MWT as a prognostic indica-tor exclusively in older adults. In this study, wedemonstrate that the 6MWT with a cutoff of 300

m has good agreement with another assessment ofglobal function, the frailty phenotype.The frailty phenotype was developed more spe-

cifically to include multiple physiologic domainsof an individuals overall function in an attemptto identify loss of reserve.2 The operational defini-tion of frailty has not been compared extensively toother physical performance measures or markers offrailty, although a relationship has been drawn withphysiologic changes represented by an increase ininflammatory mediators and clotting factors.4

Physical frailty and the 6MWT performance werenot affected by measures of HF severity: NYHA

class, brain natriuretic peptide level, or frequency ofhospitalization and outpatient intravenous diuretictherapy. The overall frailty score, walking speed,physical activity, and hand grip, plus the mean ageand creatinine clearance all identified the intermedi-ate group defined as the NF/LE group. Previously,hand grip and walking speed have been identifiedas indicators of functional decline.2022 Hand gripstrength and walking speed are dichotomized todefine their place in the frailty definition, but ascontinuous, independent variables, they identify agroup that may be transitioning from nonfrail tofrail. The relationship of renal function with physical

function is still being defined but has been associatedwith frailty23 and identified as a predictor of mortal-ity in HF patients.2426

A significant portion of the study group was identified as intermediate frail or NF/LE.Interventions targeted at improving lower extrem-ity strength and endurance may prevent declineto frailty and may be especially important in theintermediate group of patients with HF. A gradu-ated exercise program has improved walkingspeed in frail older adults,27 and exercise has beenshown to improve strength and decrease disability

even in the oldest old.

28

Exercise has successfullybeen used in HF patients to improve exercise tol-erance and duration.29 Exercise in HF patients ispresently the focus of a large ongoing multicentertrial to evaluate the effect of exercise on mortality,hospitalizations, and quality of life, and a similarprogram may be adapted to older HF patients.30

This study was limited by its cross-sectionaldesign. We were unable to assess outcomes accord-ing to the frailty phenotype/endurance classifi-

cation. Thus, we were only able to hypothesizeabout the importance of the intermediate group.Confirmation of a progression of participants inthe NF/LE group to the F/LE group or of prevention of progression with an intervention willrequire evaluation of this HF population in a lon-

gitudinal study. The generalizability of the studyis impacted by our exclusion of those with HF andpreserved systolic function, which is highly preva-lent in the older adult population. In addition,we had low power to detect a difference betweengroups due to the small sample size.

cOnclUsiOnsThe 6MWT is used widely in studies of HFpatients. Based on these findings, the 6MWT maybe useful in identifying individuals with the syn-drome of frailty or those who are in transition tofrailty. This may provide a new perspective when

evaluating older HF patients in a variety of stud-ies. Reframing the 6MWT as a frailty measure willfacilitate broader use of interventions to opposethe development of frailty.

Acknowledgments and disclosures: This work has been supportedby the General Clinical Research Center (MO1-RR06192). Wewish to thank the staff at the University of Connecticut GeneralClinical Research Center includingPaula Gendreau, RN, fordata collection andDavid Lazuk and Alison Kleppinger fordata management. We also thank the UCONN Heart FailureCenter staff includingMary Beth Barry, APRN, and LauraKearney, RN, for patient recruitment and data collection andfor the support of the UCONN Division of Geriatrics. Drs Boxer,

Kenny, and Hager were directly involved with the study concept, design, interpretation of data, and manuscript preparation. Dr Boxer was responsible for recruitment and data acquisi-tion. Drs Walsh and Wang were responsible for statistical plan and analysis. Dr Kenny has been supported with fellowships from the Brookdale Foundation and the Paul Beeson FacultyScholar Program. None of the sponsors were involved in design,methods, participant recruitment, data collection or analysis, orpreparation of this paper.

RefeRences

1 Centers for Disease Control and Prevention.MMWR MorbMortal Wkly Rep. 1998;48:633637.

2 Fried LP, Tangen CM, Walston J, et al. Frailty in olderadults: evidence for a phenotype.J Gerontol A Biol Sci Med

Sci. 2001;56:M146M156.3 Newman AB, Gottdiener JS, McBurnie MA, et al, for the

Cardiovascular Health Study Research Group. Associationsof subclinical cardiovascular disease with frailty.J GerontolA Biol Sci Med Sci. 2001;56:M158M166.

4 Walston J, McBurnie MA, Newman AB, et al. Frailtyand activation of the inflammation and coagulation sys-tems with and without co-morbidities. Arch Intern Med.2002;162:23332341.

5 Enright PL, McBurnie MA, Bittner V, et al. CardiovascularHealth Study. The 6-min walk test: a quick measure of


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functional status in elderly adults. Chest. 2003;123:387398.6 Bittner V, Weiner DH, Yusuf S, et al. Prediction of mortality

and morbidity with a 6-minute walk test in patients withleft ventricular dysfunction. SOLVD Investigators. JAMA.1993;270:17021707.

7 Shah MR, Hasselblad V, Gheorghiade M, et al. Prognosticusefulness of the six-minute walk in patients with advancedcongestive heart failure secondary to ischemic or nonisch-emic cardiomyopathy.Am J Cardiol. 2001;88:987993.

8 Rostagno C, Galanti G, Romano M, et al. Prognostic valueof 6-minute walk corridor testing in women with mild tomoderate heart failure.Ital Heart J. 2002;3:109113.

9 Orme JG, Reis J, Herz EJ. Factorial and discriminant valid-ity of the Center for Epidemiological Studies Depression(CES-D) scale.J Clin Psychol. 1986;42:2833.

10 Washburn RA, Smith KW, Jette AM, et al. The Physical Activity Scale for the Elderly (PASE): development andevaluation.J Clin Epidemiol. 1993;46:153162.

11 Guyatt GH, Sullivan MJ, Thompson PJ, et al. The 6-minute walk: a new measure of exercise capacity in patients withchronic heart failure. Can Med Assoc J. 1985;132:919923.

12 Roul G, Germain P, Bareiss P. Does the 6-minute walk testpredict the prognosis in patients with NYHA class II or III

chronic heart failure?Am Heart J. 1998;136:449457.13 Cahalin LP, Mathier MA, Semigran MJ, et al. The

six-minute walk test predicts peak oxygen uptake andsurvival in patients with advanced heart failure. Chest.1996;110:325332.

14 Lord SR, Menz HB. Physiologic, psychologic, and healthpredictors of 6-minute walk performance in older people.Arch Phys Med Rehabil. 2002;83:907911.

15 Guralnik JM, Ferrucci L, Pieper CF, et al. Lower extrem-ity function and subsequent disability: consistency acrossstudies, predictive models, and value of gait speed alonecompared with the short physical performance battery. JGerontol A Biol Sci Med Sci. 2000;55:M221M231.

16 Markides KS, Black SA, Ostir GV, et al. Lower body func-tion and mortality in Mexican American elderly people.J

Gerontol A Biol Sci Med Sci. 2001;56:M243M247.17 Onder G, Penninx BW, Ferrucci L, et al. Measures of physi-

cal performance and risk for progressive and catastrophicdisability: results from the Womens Health and AgingStudy.J Gerontol A Biol Sci Med Sci. 2005;60:7479.

18 Studenski S, Perera S, Wallace D, et al. Physical perfor-mance measures in the clinical setting. J Am Geriatr Soc.2003;51:314322.

19 Newman AB, Haggerty CL, Kritchevsky SB, et al. HealthABC Collaborative Research Group. Walking performanceand cardiovascular response: associations with age andmorbidityThe Health, Aging and Body CompositionStudy.J Gerontol A Biol Sci Med Sci. 2003;58:715720.

20 Rantanen T, Guralnik JM, Foley D, et al. Midlife handgrip strength as a predictor of old age disability. JAMA.1999;281:558560.

21 Rantanen T, Volpato S, Ferrucci L, et al. Handgripstrength and cause-specific and total mortality in olderdisabled women: exploring the mechanism. J Am GeriatrSoc. 2003;51:636641.

22 Guralnik JM, Simonsick EM, Ferrucci L, et al. A shortphysical performance battery assessing lower extrem-ity function: association with self-reported disability andprediction of mortality and nursing home admission. JGerontol. 1994;49:M85M94.

23 Shlipak MG, Stehman-Breen C, Fried LF, et al. The pres-ence of frailty in elderly persons with chronic renal insuf-ficiency.Am J Kidney Dis. 2004;43:861867.

24 Bibbins-Domingo K, Lin F, Vittinghoff E, et al. Renalinsufficiency as an independent predictor of mortal-ity among women with heart failure. J Am Coll Cardiol.

2004;44:15931600.25 Smith GL, Shlipak MG, Havranek EP, et al. Race and renal

impairment in heart failure: mortality in blacks versuswhites. Circulation. 2005;111:12701277.

26 Dries DL, Exner DV, Domanski MJ, et al. The prognosticimplications of renal insufficiency in asymptomatic andsymptomatic patients with left ventricular systolic dysfunc-tion.J Am Coll Cardiol. 2000;35:681689.

27 Binder EF, Schechtman KB, Ehsani AA, et al. Effects ofexercise training on frailty in community-dwelling olderadults: results of a randomized, controlled trial. J AmGeriatr Soc. 2002;50:19211928.

28 Fiatarone MA, ONeill EF, Ryan ND, et al. Exercise train-ing and nutritional supplementation for physical frailty invery elderly people. N Engl J Med. 1994;330:17691775.

29 Pia IL, Apstein CS, Balady GJ, et al. Exercise and heartfailure: a statement from the American Heart AssociationCommittee on Exercise, Rehabilitation, and Prevention.Circulation. 2003;107:12101225.

30 Exercise training program to improve clinical outcomesin individuals with congestive heart failure. ClinicalTrials.gov. http://www.clinicaltrials.gov/ct/show/NCT00047437.Accessed August 20, 2005.

The Utility of the 6-Minute Walk Test

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