Effectiveness of the 6-Minute Walk Test as a Predictive Measure on Hospital Readmission and Mortality in Individuals With Heart Failure: A Systematic Review of the Literature : Journal of Acute Care Physical Therapy

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REVIEW ARTICLE

Effectiveness of the 6-Minute Walk Test as a Predictive Measure on Hospital Readmission and Mortality in Individuals With Heart Failure

A Systematic Review of the Literature

Carballada, Cynthia; Mihalik, Mackenzie; Newman-Caro, Alyssa; Walter, Alysha

Author Information
Journal of Acute Care Physical Therapy 14(1):p 33-44, January 2023. | DOI: 10.1097/JAT.0000000000000195
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Abstract

Heart failure (HF) is a clinical condition in which the heart loses its ability to pump blood effectively and efficiently to meet the demands of the rest of the body. Typically, HF is caused by underlying abnormalities within the myocardium known as cardiac muscle dysfunction. HF is tied to diseases of the myocardium, pericardium, endocardium, abnormalities of the heart valves (stenosis, regurgitation), coronary vessels, toxins, uncontrolled hypertension, pulmonary vascular diseases, metabolic disorders, abnormalities of the heart rhythm/conduction, or some combination of the above.1 It affects approximately 6.2 million adults in the United States. According to the American Heart Association,2 this number is projected to increase by 46% by 2030.3 It is the leading cause of hospitalization in adults older than 65 years, with over 960 000 newly diagnosed cases each year.4 In acutely decompensated HF, the hallmark signs leading to hospitalization or unplanned medical care include increased congestion, increased ventricular filling pressure, fatigue, dyspnea, edema (both pulmonary and peripheral), weight gain, and chest pain.1

HF can be classified as either structural or functional. Structural HF includes left-sided, right-sided, or biventricular dysfunction. Left-sided HF is secondary to some form of left ventricle pathology leading to reduced cardiac output and a build-up of fluid within the left ventricle. This ultimately leads to pulmonary congestion and pulmonary edema in addition to fluid retention. Left-sided HF is marked by 2 hallmark signs, including dyspnea and cough. Right-sided HF is the result of pathology or injury to the right ventricle. This pathology is typically caused by conditions that cause elevated pressures within the pulmonary arterial system. Right-sided HF causes reductions in right ventricular cardiac output, leading to venous congestion. The hallmark signs of right-sided HF are jugular venous distension, peripheral edema, ascites, and pleural effusion. Patients with biventricular HF in which both ventricles fail experience pulmonary and peripheral signs and symptoms of fluid overload such as dyspnea, cough, jugular venous distension, and peripheral edema.1

Functional HF is tied to systolic or diastolic dysfunction of the left ventricle. Systolic dysfunction is referred to as HF with reduced ejection fraction (HFrEF), whereas diastolic dysfunction is known as HF with preserved ejection fraction (HFpEF). HFrEF is classified by decreased myocardial contractility, leading to reductions in ejection fraction, stroke volume, and cardiac output. Patients experiencing systolic HF typically present with left ventricular ejection fraction (LVEF) less than 40%. HFpEF is classified by compromised diastolic function of the ventricles. With this form of HF, the ventricles cannot fill adequately during the diastolic phase. This poor ventricular filling decreases the stroke volume and cardiac output. However, with HFpEF, LVEF is unaltered and remains between 55% and 75%.1 Patient symptoms at rest and with activity are used by medical practitioners to classify patients according to the New York Heart Association (NYHA) functional classification for HF.5 This classification system includes 4 stages, with stage I being the least severe and stage IV being the most.

The medical management of HF typically includes medications, surgery, and lifestyle changes, including smoking cessation, diet changes, exercise participation, and weight maintenance. While it is plausible for patients to produce meaningful and beneficial change secondary to lifestyle modifications and increased physical activity, the presentation of HF often leads to decreased exercise tolerance and the exacerbation of symptoms.6

The 6-minute walk test (6MWT) is a simple, inexpensive, widely used, and well-tolerated outcome measure for assessing functional capacity. The 6MWT requires no specialized equipment or specifically trained individuals to administer the test. The purpose of this test is to assess the submaximal level of activity of an individual while ambulating on a flat surface for 6 minutes.7,8 It can be an especially useful tool to measure the functional status of individuals with multiple comorbidities or patients who cannot endure more complex exercise tests, such as individuals with HF.7 The distance walked during the 6MWT is a useful prognostic marker of death or hospital readmission in patients with HF.9

Hospital readmission and mortality rates for individuals with HF have been continuously increasing. Hospital readmission rates have been reported to be as high as 20% within 30 days and up to 50% within 6 months. Individuals with HF account for 26.9% of the total readmission rates among medical and surgical conditions and have the highest rate of hospital readmissions in 30 days. Often, readmissions are secondary to patient-reported symptoms, such as shortness of breath and fatigue and medication and dietary noncompliance. Strategies to address the increased hospital readmission rates for individuals with HF include education on proper self-management of HF as well as proper prescription of exercise and management by a physical therapist (PT) and other members of the interdisciplinary team.1

The role of PTs in managing individuals with HF is to be an advocate for an increase in physical activity. According to the recent clinical practice guideline (CPG),1 which focuses on care for patients with HF in the outpatient setting, PTs are responsible for making appropriate nutrition referrals, performing medication reconciliation, and assisting with preventive behaviors. Physical therapists are also the experts who provide appropriate and effective exercise prescriptions, including aerobic exercise training, high-intensity interval exercise training, resistance training, or any combination of the 3.1 While this CPG is extremely pertinent to the outpatient PT, it does not address the need for education and performance of outcome measures, as well as data collection that is vital in the acute care setting. Due to the increasing number of HF hospitalizations, acute care PTs have the unique ability to assess a patient's functional abilities and track progress, beginning with their most critical presentation during hospitalization. Outcome measures are vital for all areas of physical therapy practice, specifically to help support clinical decision-making in the acute care setting.10 In the acute care setting, many outcome assessments are available. However, we lack a standardized protocol specific for patients with HF during hospitalization. Although outcome measures are readily available, recent studies have found that only 50% of PTs report using outcome measures, with acute care PTs 7 times less likely to perform outcome assessments than therapists practicing in the outpatient setting.10

Due to the current lack of research regarding guidelines for the acute care PT caring for patients with HF, this study aims to assess whether the 6MWT could be a useful addition for acute care therapists to perform to track change and gather information regarding the risk of future hospitalization. This systematic review aims to investigate the effect that distance walked during the 6MWT has on determining the risk of hospital readmission and mortality for individuals with HF.

METHODS

Protocol and Registration

This protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on April 4, 2021.11 The registration number is CRD42021240949.

Literature Search Strategy

Three authors performed a comprehensive search of PubMed, CINAHL, and MEDLINE for 1 month (A.B., C.C., and M.M.). The search strategy was run from February 1, 2021, through February 28, 2021. Medical Subject Headings (MeSH) headings and keywords used in the search included heart failure, congestive heart failure, left-sided heart failure, 6-minute walk test, walk test, outcome measures (OM), exercise tests, and patient readmission (Appendix 1). Citation reference searching was also used for pulling additional articles that matched our search, were analyzed in depth, and included in their full-text form. The search was limited to the English language.

Inclusion and Exclusion Criteria

The types of studies included in the search were prospective studies, retrospective studies, prognostic studies, randomized controlled trials, observational studies, and cohort studies. Studies were included if they contained all of the following: (1) had a clear definition of the 6MWT as the primary outcome measure, (2) patients were 18 years or older, (3) patients were diagnosed with HF by a cardiologist, (4) subjects had an NYHA functional classification level I-IV, and (5) the study included a follow-up period to examine hospital readmission of at least 30 days.

Studies were excluded if any of the following were present: (1) patients had significant diagnoses other than HF, (2) pediatric cases (younger than 18 years), (3) study was not written in English, (4) study demonstrated a high level of bias according to the Quality in Prognostic Studies (QUIPS) assessment tool, (5) the study was published prior to 2000, (6) the study included patients who were hospitalized due to a planned surgery, (7) subjects were experiencing other limiting musculoskeletal factors that would hinder 6MWT results, and (8) studies were editorials or systematic reviews.

Study Selection

Studies were independently reviewed by 2 authors (C.C. and M.M.). No discrepancies occurred, and no tie-breakers were needed. Had a tie-breaker been required, the third author would have reviewed the studies and provided additional feedback. Interrater agreement was measured using the unweighted kappa (κ), a test used with nominal data to assess the relationship between variables12 was calculated with a 95% confidence interval (CI) during the agreement for all of the following levels of screening: title, abstract, and full text (see the Figure).

F1
FIGURE.:
PRISMA Flow Diagram.

Quality Analysis

Each full-text study that met inclusion criteria underwent an independent review by 2 authors (A.B. and M.M.). The QUIPS tool was used to assess the level of bias and was completed by 3 authors (C.C., M.M., and A.B.). No discrepancies were found among the authors. The QUIPS was developed to measure the level of bias in prognostic studies.13 It consists of items categorized into 6 domains. Each section is judged on a scale including a low, moderate, or high risk of bias.13 Additionally, the AMSTAR 2 was used to appraise the confidence in this systematic review critically. Eleven applicable items from the checklist were considered.14

The 6-Minute Walk Test

The 6MWT is a submaximal exercise test used to assess the subject's aerobic capacity. Subjects' vital signs and Borg rating of perceived exertion (RPE) are taken before and after the test administration. Subjects are asked to walk in a hallway or open area with a long, consistent surface measuring at least 12 m. A clear pathway should be set, and a turnaround point of at least 49 inches wide needs to be set with clear markings. Both the patient and the person administering the test are encouraged not to speak during the administration of this test. The administrator should only speak when providing updates every minute or when providing necessary instructions. Patients should speak if they feel the test needs to be stopped, to report their RPE or any other symptom such as dizziness. If the patient needs the test to be stopped prior to the end of the 6 minutes, the test will be concluded, and the distance ambulated is recorded.8 Two common methods for detecting the clinical significance and meaningful change are the minimal detectable change (MDC) and the minimum clinically important difference (MCID). In a systematic review by Shoemaker et al,15 the MCID and the MDC were triangulated in the 6MWT in individuals with HF. The MDC, calculated at a CI of 95% for the 6MWT, was 32.4 m and the MCID was 30.1 m. Thus, changes of about 30 to 32 m likely represent a change that exceeds the measurement error of the 6MWT and a change that is perceptible to the individual subject. In addition, the intraclass correlation coefficient for the 6MWT reflected in this article was 0.99, calculated at a 95% CI, demonstrating excellent test-retest reliability.15

Data Extraction

Studies were independently assessed by 2 authors (A.B. and C.C.). The following items were extracted from each study: (1) the number of participants, (2) age/gender demographics, (3) inclusion/exclusion criteria, (4) study design, (5) HF stages (NYHA), (6) HF diagnosis, (7) follow-up period, (8) LVEF, (9) administered outcome measures, (10) 6MWT results and setting in which the study took place, (11) statistical analysis, (12) effect size, (13) setting the study took place, and (14) and readmission rate data. Refer to Table 1, which highlights the descriptive data for the included articles.

TABLE 1. - Descriptive Data of Included Articles
Study Study Design Age/Gender Acute/Chronic HF Sample Size Ethnicity Setting of Care for 6MWT Definition of HF Sensitivity/Specificity of Test HF Stage (Participants) BNP/NT-proBNP LVEF, %
Rostagno et al16 Comparative prognostic study 29-70 y old (mean age 57.3); 119 M, 95 F Both 214 Did not specify Hospital (25-m corridor) Did not specify Did not report NYHA class I (44), class II (102), class 3-4 (69) Did not report Class 1 = 52.5 ± 12.8
Class 2 = 42.7 ± 15.1
Class 3 = 33.1 ± 14.2
Teramatsu et al23 Single centered retrospective cohort study Age: 74 ± 11 for readmission and 71 ± 10 for nonreadmission; 60 M, 56 F Acute 116 Did not specify Hospital “Heart failure (HF) is a common disease with a high prevalence; moreover, the number of patients with HF is expected to increase in the future” Did not report 2 NYHA class I, 8 class II, 12 class III, 0 class IV Did not report Readmitted: 41.2± 16.6
Nonreadmitted: 45.6 ± 12.4
Wegrzynowska-Teodorczyk et al17 Prospective longitudinal observational study Mean age of 60; M Both 243 Did not specify Hospital corridor (30-m distance) “A marked reduction in the capacity to undertake physical activity is one of the principal symptoms of heart failure” Did not report 35 NYHA class I, 107 class II, 90 class III, 10 class IV NT-proBNP = survived: 708 pg/mL; died 3119 pg/mL Survived: 31% (9)
Died: 27% (8)
McCabe et al18 Secondary analysis Aged 18-85 y; F Both 71 19 Caucasian, 52 African American Hospital Did not specify Did not report 26 NYHA class II, 44 NYHA class III 974.5 (840.4 SD) pg/mL <40%
Howie-Esquivel et al19 Prospective cohort design Mean age of 59.6, 27-100 y; 29 M, 15 F Acute 44 22 Caucasian, 13 African American, 5 Hispanic, 4 Latino Hospital Did not specify Did not report NYHA class III 13 hospitalized, 7 not hospitalized
NYHA class IV 9 hospitalized, 9 not hospitalized
Did not report <40%
Arslan et al9 Prognostic clinical investigation Mean age 62 y ± 10; 6 F, 37 M Chronic 43 Did not specify Outpatient “The cause of heart failure was idiopathic dilated cardiomyopathy in 26 patients and ischemic cardiomyopathy in 17 patients” Did not report 26 patients NYHA stage II and 17 NYHA stage III Did not report All participants ≤40%; 0.35 ± 0.06
Tabata et al24 Prognostic clinical study Average age 68.5 ± 11.8 y; 162 M, 90 F Chronic 252 Did not specify Hospital Did not specify The 6MWT cut-off score of 390 m, with a sensitivity of 0.75 and a specificity of 0.77 43 NYHA class III; 209 NYHA class IV BNP: 958 ± 655 pg/mL readmitted patients; 1009 ±963 pg/mL nonreadmitted patients Mean: 35.4% ± 12.8%
Curtis et al21 Prognostic clinical study Mean age 64.5 y; 26.2% F, 73.8% M Chronic 541 14.6% African American Outpatient Did not specify Did not report 13.9 NYHA class I, 55.1 class II, 31.1 class III/IV Did not report Mean: 34.7 (13.3)
Shah et al22 Prognostic clinical study Ages between 58 and 71 y; 290 M, 48 F Chronic 440 56 African American, 365 Caucasian, 19 Other Hospital (65-ft corridor) Did not specify Did not report. 185 patients NYHA class IIIB, 255 NYHA class IV Did not report EF ≤25%; 17 participants (14%-21%); 19 (14%-23%)
Alahdab et al20 Clinical Trial prospective Mean age 55.7 ± 12.9 y; 74 F; 126 M Chronic 198 198 African American Hospital (36-, 27-, 23-, 20-, or 15-m corridors) Did not specify Did not report 13 patients NYHA class I; 50 patients NYHA class II; 100 patients NYHA class III; 35 patients NYHA class IV Did not report 29% ± 40%

RESULTS

Search Results

The results of the initial search yielded a total of 272 titles. A hand search and gray literature review were conducted. After duplicate removal, 228 titles were screened for inclusion. Two authors (C.C. and M.M.) completed a title, abstract, and full-text review. The κ value for the title screen was 0.75 (CI 0.68-0.82) and demonstrates substantial reviewer agreement. Ten full-text articles were included in this systematic review, with a κ value for the full-text review being κ= 1 (CI 1-1), demonstrating 100% agreement. Refer to the Figure (PRISMA), which illustrates the details of the study selection process.

Study Demographics

A total of 2164 subjects with HF were included within the 10 articles. The studies included comparative prognostic studies,16 retrospective cohort studies,17 prospective longitudinal observational studies,17 secondary analyses,18 prospective cohort designs,19 prognostic clinical investigations,9 and prognostic clinical studies.20–23 Articles in this review included reports on acute HF,17,19 chronic HF,9,20–23 and both acute and chronic HF diagnoses.16–18 Only 2 of the research studies, Tabata et al24 and Teramatsu et al,23 assessed the effect of cardiac intervention programs for their subjects during hospitalization. The research included a cardiac rehabilitation program that administered the 6MWT at initial discharge for future analysis. The remaining studies obtained 6MWT data before discharge for an individual postacute hospitalization for HF.9,16–22 Each of the studies collected data to determine whether that subject was at risk for rehospitalization based on the 6MWT distance.

All 4 functional classifications of HF based on the NYHA functional classification system were represented in the 10 studies. The most frequent stage studied was stage III. One study included participants in NYHA stages I to III,17 while the remaining were NYHA stages II and III,9,18,20 NYHA stages II to IV,19 stages III to IV,22,23 or all 4 stages.16,17,21 All 10 studies used the 6MWT as the primary outcome measure, with 3 studies including additional assessments such as a cardiopulmonary stress test or the Heart Failure Symptom Survey.16–18 Rostagno et al16 used the cardiopulmonary exercise test, which included a phased treadmill stress test following a modified Bruce protocol. McCabe et al18 used the Heart Failure Symptom Survey, and Teramatsu et al23 incorporated data on the level of strength impairments and physical function, including knee extensor strength, grip strength, 30-second chair stand test, 1-leg standing test, functional reach test, and the Barthel index. Studies included a range of hospital readmission dates up to 1 year. Other pertinent study characteristics are included in Table 1.

Study Quality

Each article included in this review had a prognostic study design; therefore, the QUIPS tool was used to assess each study for risk of bias. Each article was independently assessed by 3 authors (C.C., M.M., and A.B.) for bias. Four of the 10 articles had a low level of bias throughout the 6 domains.9,16,17,23 The other 6 studies had moderate bias levels within the confounding factor category, which assesses whether an extraneous variable influences the effects of an outcome; the other 5 domains were rated as low level of bias.18–23 The κ value for our QUIPS agreement was 1 (CI 1-1), demonstrating 100% agreement. Table 2 illustrates these findings. According to the AMSTAR 2, the overall confidence in our systematic review is high. This indicates that this systematic review provides an accurate report of findings that aligned with our research questions, looking at the effect of the 6MWT and the effectiveness in determining the risk of readmission in patients with HF.14

TABLE 2. - QUIPS Assessment Tool for Risk of Biasa
Author Biases Overall Score
Study Participation Study Attrition Prognostic Factor Outcome Measurement Study Confounding Statistical Analysis and Reporting
Alahdab et al20 Low Low Low Low Moderate Low Low
Arslan et al9 Low Low Low Low Low Low Low
Curtis et al21 Low Low Low Low Moderate Low Low
Howie-Esquivel et al19 Low Low Low Low Moderate Low Low
McCabe et al18 Low Low Low Low Moderate Low Low
Rostagno et al16 Low Low Low Low Low Low Low
Shah et al22 Low Low Low Low Moderate Low Low
Tabata et al24 Low Low Low Low Moderate Low Low
Teramatsu et al23 Low Low Low Low Low Low Low
Wegrzynowska-Teodorczyk17 Low Low Low Low Low Low Low
aKey: Low/moderate/high level of bias in each section.

Overview of Studies

6-Minute Walk Distance

The purpose of 6 of the 10 articles was to determine whether the 6MWT predicted hospital readmission or mortality of subjects after admission to hospital with an acute HF diagnosis.17–20,23,24 These studies mostly generalized the timing of hospital readmission. Table 3 depicts the different cut-off scores for each article related to the duration of the studies' follow-up period. The duration of the studies ranged from 30 days to 40 months.

TABLE 3. - Cut-off Distance Scores Predicting Future Hospitalization and Mortality
Study Cut-off Distance NYHA Class (I-IV) Duration of Study/Follow-up Period
McCabe et al18 <948 ft (288 m) 26 NYHA class II
44 NYHA class III
1 mo
Howie-Esquivel et al19 <300 m 20 NYHA class III
18 NYHA class IV
3 mo
Shah et al22 <218 m 185 NYHA class IIIB
255 NYHA class IV
12 mo
Teramatsu et al23 <382.5 m 2 NYHA class I
8 NYHA class II
12 NYHA class III
0 NYHA class IV
12 mo
Arslan et al9 <300 m 26 NYHA class II
17 NYHA stage III
12-24 mo
Curtis et al21 <200 m 13.9 NYHA class I
55.1 NYHA class II
31.1 NYHA class III/IV
32 mo
Rostagno et al16 <300 m 44 NYHA class I
102 NYHA class II
69 NYHA class III-IV
34 mo
Wegrzynowska-Teodorczyk et al17 <468 m 35 NYHA class I
107 NYHA class II
90 NYHA class III
10 NYHA class IV
36 mo
Tabata et al24 <390 43 NYHA class III
209 NYHA class IV
36 mo
Alahdab et al20 <200 m 13 NYHA class I
50 NYHA class II
100 NYHA class III
35 NYHA class IV
40 mo
NYHA, New York Heart Association.

Howie-Esquivel et al19 focused primarily on comparing gender with HF and found that women and men were equally at an increased risk of mortality if they walked a distance less than 300 m. The period in which the 6MWT was conducted varied between performing at initial hospital admission16,21,22 or directly before discharge.18,19,23 Four studies did not specify when the outcome measure was performed.9,17,20,23 Two studies included a formal cardiac rehabilitation program during an inpatient stay.23,24 The 6MWT was administered at initial discharge and was used to make comparisons between readmitted and nonreadmitted groups.23,24

Significant Results

All 10 articles defined a P value of < .05 indicating clinical significance. Statistically significant results were reported in 7 of the 10 articles9,16–18,22–24 in reference to the distance walked during the 6MWT, hospital readmission, and mortality rates. Statistically significant data were not reported in the remaining 3 studies19–21 regarding rehospitalization and mortality with respect to distance ambulated with the 6MWT. McCabe et al18 researched length of hospital stays and occurrence of hospitalization based on 6MWT results. They noted that an adjusted risk of a 30-day readmission was decreased by 16% for each additional 100 ft walked by the patient in each concurrent 6MWT. Conversely, for each day added to a length of stay, the risk of 30-day readmission increased by 17%. Tabata et al24 was the only study that reported the sensitivity and specificity of their 6MWT cut-off scores. They reported a 6MWT cut-off score of 390 m, with a sensitivity of 0.75 and a specificity of 0.77.

Regarding genders, most of the articles had both male and female participants, but more men than women were assessed. For example, percentages of women included in each study are as follows: 0%,17 34.1%,19 20%,22 44.4%,16 14%,9 36.1%,20 35.7%,24 42.3%,18 26.2%,21 and 50%.23 This leads to a lack of generalizability of data. Only McCabe et al18 reported on only women with HF participating in the 6MWT. Tabata et al24 found that gender had no significant effect. Alahdab et al20 observed differences in statistics between male and female participants. They used the multivariate cox regression analyses for stratifying gender; once this was done, they found that men who ambulate less than 200 m have a higher mortality rate. Compared with women, the statistical significance was lost.

DISCUSSION

This review aimed to identify and evaluate the prognostic value of the 6MWT, specifically its ability to predict hospital readmission and mortality for individuals with HF. The authors of the studies included in this review examined the relationship between overall distance walked during the 6MWT compared with the prevalence of hospital readmission over the course of 30 days to 3 years for individuals with HF. Based on the 10 studies that met the inclusion criteria for this review, evidence supports that distance walked during the 6MWT can help predict the likelihood of future hospitalization and mortality of individuals with HF.

All 10 studies included in this review reported a cut-off distance used in determining future outcomes in subjects diagnosed with NYHA class I-IV HF, ranging from 200 to 468 m. However, statistically significant data regarding a cut-off distance that can predict future hospitalization or mortality were reported in only 7 articles.9,16–18,22,24 A general trend was that an individual with a higher NYHA class, indicating increased HF severity, walked a lesser distance than lower classes.17 Therefore, patients with higher NYHA class HF were also found to have a higher risk of rehospitalization or mortality. Regardless of the setting of care where the 6MWT took place, for example, whether in an outpatient setting or during hospitalization, a common theme that emerged during the 6MWT is that if the distance ambulated was less than 300 m, then the risk of rehospitalization or mortality increased. This finding was found to be statistically significant in 7 of the 10 articles and was also not impacted by the length of the study and follow-up period, which ranged from 30 days to 40 months.9,16–18,22,24

Despite a broad search strategy, only 10 articles met the inclusion criteria for this study. This review included individuals from various ethnic backgrounds, genders, and chronicity of HF. Inclusion criteria allowed for a diverse group of subjects, which included a globally accepted definition of HF and NYHA classifications to gather information about the utility of the 6MWT throughout the stages of HF. This review used the QUIPS tool to assess bias within each of the selected articles, which was one of the strengths of this study, evidenced by the majority of articles reporting “low bias” in each of the domains. This, in turn, would correlate to an overall “low bias” review when taking each article into account.13

A small percentage of data on women and subjects of different races were reported, which indicates a lack of generalizability of the data. For example, percentages of women included in each study ranged from 0% to 50%, while different races and ethnicities were only included in 5 articles18–22 and ranged from 14% to 100% of African Americans subjects, as well as 3.3% to 11.4% of subjects being of Hispanic/Latino, Asian/Pacific Islander, or other descent.16,19

Several limitations are present in the articles included in this review. Small sample sizes were a limitation of 3 articles.9,18,19 Multiple authors also reported a loss of subjects to follow-up, which created a smaller sample size. Two studies' authors reported a lack of information regarding the relationship of socioeconomic variables and the effect on the outcome of each subject.18,19 For example, Howie-Esquivel et al19 reported on subjects in an urban population with socioeconomically disadvantaged patients. Cost of medications, treatment, adherence to programs, and general access to health care are all impacted by socioeconomic status, which differs based on each situation.19 Many authors believed that living status, level of social support, and environmental factors would specifically impact hospital readmission and course of HF treatment.9,17,20–22,24

Specifically, the most notable limitation to this review was the inability to narrow the search into a more specified HF population. This is due to a lack of current research on the topic of 6MWT results predicting future hospitalizations for patients with HF. By allowing subjects with all NYHA classes, cut-off values could be skewed. Some articles had many individuals with a lower NYHA class,9,16–18 compared with other studies with a majority of higher NYHA class individuals.17–20,22,24 For studies including a majority of subjects with NYHA class III or IV, cut-off scores were more likely to be a lower distance (200 m,20 218 m,22 288 m,18 300 m,19 382.5 m,23 and 390 m24) to predict future hospitalizations. For example, Shah et al22 and Alahdab et al,20 who investigated subjects with a majority of subjects having class III and IV HF, 100%22 and 68.2%,20 respectively, had cut-off scores of less than 218 m22 and 200 m,20 compared with Wegrzynowska-Teodorczyk et al,17 who studied a majority of subjects with class I and II HF, reported less than 468 m as their cut-off score.

Results from this review align with the results of previous studies. Rubim et al,25 who looked at subjects with NYHA class II HF, found that a distance shorter than 520 m increases the 18-month cardiovascular mortality risk. Similarly, Cahalin et al26 found that a 6MWT of less than 300 m predicted an overall increased likelihood of death or hospitalization due to the increased possibility of needing mechanical circulatory support within 6 months of the test. Kommuri et al27 reported that subjects hospitalized with HF with a 6MWT distance of less than 400 m were 1.57 times more likely to be readmitted to hospital within 30 days of discharge. Finally, Boxer et al28 stated that “increasing the walking distance by 30 meters reduces the mortality risk of heart failure patients irrespective of their age and NYHA class.”

In relation to the practice of physical therapy, the results from the 10 studies included in this review showed that individuals with HF who have a cut-off score of less than 300 m are at greater risk for hospital readmission or mortality. With this data in mind, PTs practicing in the acute care setting are uniquely positioned to include the 6MWT in the management of this patient population. Outcome measures can provide PTs with vital information, specifically measurements of overall function, responsiveness, and normative value comparisons.10 This review suggests that the 6MWT is a standardized outcome measure that would be beneficial to include in the acute care PT's examination for individuals with HF due to its ability to predict hospital readmission and mortality.

The 6MWT is recommended by the APTA Neurologic Physical Therapy task force as an outcome measure that should be used for individuals post-stroke who can walk independently across the continuum of care, including the acute care setting.29 In 2016, Malamud and Ricard30 demonstrated the feasibility of using the 6MWT for 2 individuals with cystic fibrosis who were mechanically ventilated, ambulatory, and awaiting lung transplantation. Furthermore, Collins et al31 studied the safety and feasibility of implementing the 6MWT for 46 subjects with acute HF, specifically subjects with HFpEF, from their emergency department admission throughout their acute care hospitalization.

Due to the wide variability in practice, adopting the 6MWT into practice would require a knowledge translation plan to address barriers to its use. Pattison et al32 suggested a recommendation to address these barriers in their research focused on using outcome measures to access walking capacity post-stroke across the continuum of care. Suggestions for increasing adoption could include using experienced PTs to champion practice and provide instruction in administering and scoring the test.32

The authors of this review would also like to suggest the benefit of using an outcome measure that considers patients' aerobic capacity and functional mobility beyond levels of impairment in bed mobility, functional transfers, gait, and stair negotiation for patients with cardiovascular and pulmonary impairment to help determine appropriate discharge destination.

By including the 6MWT, PTs can screen the aerobic capacity and movement system of individuals with HF. These results can then be communicated with the individual's primary health care provider or cardiologist to help identify individuals at risk of rehospitalization. PTs may also consider tracking initial and final 6MWT results to demonstrate whether physical therapy interventions improve 6MWT distance and, in turn, decrease the risk of rehospitalization in the HF population.10 In the acute care settings, PTs may also use this measure at discharge to help with discharge planning or support the recommendation of continued physical therapy services for an individual. Since patients can set their own pace during the 6MWT, results of previous studies have found it to be a useful tool to identify limitations in daily life and better represent overall function.18 With this in mind, points of education that could be provided after the 6MWT include how to best understand symptoms, to better identify patients' own limitations, the level of assistance needed with activities of daily living, energy conservation techniques, and safe exercises to remain active, as well as any necessary referrals to other disciplines (psychology, cardiac rehabilitation, occupational therapy, etc). We currently lack guidelines regarding the importance of conducting the 6MWT before discharge in this patient population. Based on the results of this systematic review, conducting a 6MWT prior to discharge for individuals admitted to hospital with HF would be useful to screen the risk of hospital readmission and mortality.

Recommendations for further research include research that could build upon existing data about the prognostic value of the 6MWT concerning hospitalization and mortality in the HF population. Future studies should focus on 6MWT results and cut-off values specifically for women and patients of different races and ethnicities with HF. Alahdab et al20 looked specifically at African Americans and reported a shorter cut-off distance. Further research could be conducted to study the history of HF in the African American population and why cut-off values may differ between races. Environmental factors such as level of support and sociodemographic variables for each individual should also be explored and reported in future research to understand each individual's unique circumstance. Research exploring the implementation of a standardized exercise program before and after discharge could also be useful to understand the effect of cardiac rehabilitation or separate protocols on the outcomes of this population. Previous studies have reported a need to develop an outcome measure protocol in the acute care setting specific to patient diagnosis.10 Therefore, the 6MWT would be a valuable addition to future standardized acute care outcome measure protocols due to its ability to predict rehospitalizations and mortality in subjects with HF.

CONCLUSION

The 6MWT is an effective and easily administered tool used to measure the possibility of rehospitalization and mortality in the HF population. Further research on a standardized protocol of the tool used in clinical practice would allow for greater knowledge on future implementation of guidelines regarding how to best care for these patients both during hospitalization and after discharge.

REFERENCES

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APPENDIX 1. PubMed Search Strategy

((((((((((“heart decomposition”[Text Word]) OR (“left sided heart failure”[Text Word])) OR (“right sided heart failure”[Text Word])) OR (“congestive heart failure”[Text Word])) OR (“cardiac failure”[Text Word])) OR (“heart failure”[Text Word])) OR (“chronic heart failure”[Text Word])) OR (“acute heart failure”[Text Word])) OR (heart failure[MeSH Terms])) AND (((((((“walk test”[Text Word]) OR (“6-minute walk test”[Text Word])) OR (“6-min walk test”[Text Word])) OR (“outcome measures”[Text Word])) OR (“outcome assessment, health care”[Text Word])) OR (walk test[MeSH Terms])) OR (outcome assessment health care[MeSH Terms]))) AND (((((“patient readmission”[Text Word]) OR (“hospital readmission”[Text Word])) OR (“length of stay”[Text Word])) OR (patient readmission[MeSH Terms])) OR (length of stay[MeSH Terms]))

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