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Six-minute Walk Distance Predicts 30-Day Readmission in Hospitalized Heart Failure Patients
Archives of Medical Research 41 (2010) 363e368
ORIGINAL ARTICLE
Six-minute Walk Distance Predicts 30-Day Readmission in Hospitalized Heart Failure Patients Naga V.A. Kommuri,a Monica L. Johnson,b and Todd M. Koellingb a
Department of Internal Medicine, DMC-Sinai-Grace Hospital, Detroit, Michigan Division of Cardiovascular Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
b
Received for publication March 12, 2010; accepted July 9, 2010 (ARCMED-D-10-00121).
Background and Aims. Identification of patients with heart failure (HF) at high risk of hospital readmission is critical to refine processes for reducing readmission rates. We hypothesized that patients with higher 6-min walk (6MW) distance at the time of hospital discharge are at low risk for early readmission. Methods. We prospectively enrolled 265 patients admitted with HF and left ventricular systolic dysfunction. 6MW testing was administered prior to discharge. Multivariate logistic regression analysis was performed to determine the relationship between 6MW distance and 30-day readmission, stratifying by #400 m and O400 m. Results. Two hundred ten patients underwent 6MW testing prior to discharge. Patients with 6MW O400 m had a 30-day readmission rate of 15.9%, whereas patients with 6MW #400 m had a 30-day readmission rate of 30.3% ( p 5 0.016). Patients requiring readmission within 30 days had a median 6MW of 30 m, whereas patients not requiring readmission at 30 days walked 338 m ( p 5 0.012). 6MW distance predicted freedom from readmission at 30 days (OR: 0.435, 95% CI 0.21e0.9, p 5 0.025). Other independent predictors of 30-day readmission included history of gout (0.117, 0.021e0.637, p 5 0.013), use of angiotensin-converting enzyme inhibitor or accepted alternative (0.372, 0.169e0.820, p 5 0.014) and blood urea nitrogen level (1.019, 1.003e1.035, p 5 0.020). Conclusions. Low 6MW distance predicts early hospital readmission in patients with HF. Programs seeking to produce systems that are effective in reducing early hospital readmission may desire to incorporate 6MW testing during HF hospital care. Ó 2010 IMSS. Published by Elsevier Inc. Key Words: Heart failure, Patient readmission, Risk factors, Exercise testing.
Introduction Many clinical prediction models in the field of heart failure (HF) have been developed to understand risk factors for mortality (1e8). Recently, the Centers for Medicare and Medicaid Services (CMS) in the United States have initiated an effort to measure and make public 30-day readmission rates for heart failure in acute care hospitals (9). To facilitate the development of novel interventions designed to reduce readmission rates, methods of identifying highrisk patients are needed. However, clinical determinants
Address reprint requests to: Todd M. Koelling, MD, 1500 E. Medical Center Drive, CVC Room 2167, SPC 5853, Ann Arbor, MI 48109, USA; Phone: (734) 936-5265; FAX: (734) 615-3326; E-mail: [email protected]
of early hospital readmission (within 30 days) are not fully understood. The recently published risk stratification model employed by CMS provides limited discriminatory information, with a c-statistic of only 0.60 (10e13). Strategies to reduce readmission rates would ideally involve identification of patients at high risk for early readmission. Strategies that utilize physiological performance data may better identify the patients at high risk of readmission. The 6-min walk (6MW) test has been commonly used as a clinical endpoint in studies of HF patients and proved to be of great value in predicting the mortality and long-term morbidity in HF (14e16). The administration of this test has been standardized and has been adopted as a part of clinical practice in the care of pulmonary arterial hypertension and other clinical scenarios (17). However, its role in
0188-4409/$ - see front matter. Copyright Ó 2010 IMSS. Published by Elsevier Inc. doi: 10.1016/j.arcmed.2010.07.005
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predicting short-term hospital readmission has not been previously studied. We hypothesized those patients with higher 6MW distance at the time of hospital discharges are at low risk for early hospital readmission.
Subjects and Methods This study was performed at the University of Michigan Hospital and was approved by the Medical School Institutional Review board. Details of the recruitment were described in detail in an earlier publication (18). Data were collected from the medical records of the study group patients. Detailed evaluation of the subgroup included demographics, clinical characteristics, and compliance with medications and diet. Laboratory values were collected at the time of admission as well as at discharge. Information regarding compliance with medications and diet was extracted from the medical record. The study coordinator examined the admission note and problem summary list for evidence of noncompliance. Evidence of noncompliance was coded as either present or absent. 6MW Test Six-min walk test was administered on enrolled patients at the time of discharge. After informed consent the test was administered under the supervision of skilled personnel according to the standard protocol as described by the American Thoracic Society (17). A 30.5 m (100 ft) long hospital corridor course was used and was marked by colored tape at each end. Patients were instructed to ambulate end to end at their normal pace covering as much distance as possible in 6 min. A clinical nurse coordinator recorded the distance walked and timed the test. Patients were encouraged in a standardized fashion (using standard phrases, i.e., “you are doing well; keep up the good work”, etc.) at 1-min intervals. Patients were instructed to stop the test if they were symptomatic and offered a chair to take a rest but were encouraged to walk once symptoms resolved. The total distance walked in the 6 min was measured to the nearest meter. The test was administered only once on each patient at the time of discharge. Patients who were bed bound were assigned a 6MW distance of zero. Statistical Analyses All analyses were performed with SPSS v. 15.0 statistical software. The prespecified primary end point of the study was readmission to the hospital for any cause during the 30-day follow-up period. Comparisons of categorical variables were performed by c2 tests. Comparisons of continuous variables were performed using the Wilcoxon rank-sum tests. 6MW test results for the study patients were grouped as #400 m and O400 m. A p value of !0.05 was considered statistically significant. Multivariate logistic regression analysis was performed to determine the relationship between
6MW distance and 30-day readmission, controlling for age, gender, clinical characteristics, medications and laboratory values.
Results Of the 666 patients screened for participation in the study, 29 refused participation and 372 were excluded because they met the exclusion criteria set forth for the study protocol (Figure 1). The most common reasons for nonenrollment included evaluation for cardiac surgery (80), noncardiac illness likely to increase mortality or hospitalization risk (62), inpatient cardiac transplantation evaluation (48), dementia or psychiatric illness (46). Fifty five of the 265 consented patients in the study were excluded from the analysis because they were discharged on the weekend when study personnel were unable to perform the discharge 6MW test. Thus, the study population was comprised of a total of 210 patients. Comparisons of the baseline characteristics of the study groups (6MW #400 m, n 5 122, and O400 m, n 5 88) are shown in Table 1. Patients who walked O400 m were similar to those walking #400 m in age, gender and most comorbidities. However, those walking O400 m were more likely to be smokers and less likely to have gout and chronic kidney disease. Patients who walked #400 m had similar physical examination, laboratory measurements and medication usage as compared to those who walked O400 m (Table 2). Patients walking O400 m were more likely to be treated with angiotensin-coverting enzyme (ACE) inhibitors, angiotensin II receptor blockers (ARB) or the combination of hydralazine and nitrates and showed a trend for being more likely to be treated with a beta blocker. The clinical outcomes of the two patient groups are shown in Table 3. Patients who walked O400 m were less likely to be admitted within 30 days for any cause (15.9% vs. 30.3%, p 5 0.016) and also for exacerbation of heart failure (3.4 vs. 14.8%, p 5 0.007) when compared to the patients in #400 m group. There were no significant differences in readmission end points at the 180day follow-up period. There were no differences in the groups with respect to 30- or 180-day all-cause mortality. Patients able to walk O400 m at the time of discharge showed a trend for having less hospitalization days or died during the 180-day follow-up period. The results of multivariable regression analysis used to adjust for baseline differences in the two study groups (Table 4) shows that 6MW distance O400 m remained a strong predictor of remaining free of readmission or mortality at 30 days (OR: 0.435, 95% CI 0.21e0.9, p 5 0.025). Other variables found to independently predict this clinical outcome included the presence of gout, use of ACE, ARB or the combination of hydralazine and a nitrate medication and blood urea nitrogen. Patients requiring readmission within 30 days (n 5 51) had a median (IQR) 6MW of 30 m (0e420), whereas
Six-min Walk and Short-term Readmission
365
Figure 1. Study group screening.
patients not requiring readmission at 30 days (n 5 159) had a 6MW distance of 338 m (0e700), p 5 0.012. Of those patients with 6MW distance #400 m, 80 were those assigned a distance of 0 because of their inability to walk. Comparing these patients to the 42 patients with walk distances #400 m, we found that these groups had few differences with respect to demographics, comorbidities, physical examination findings, laboratories and medications. Patients who walked were less likely to be smokers but more likely to be noncompliant with diet, have chronic kidney disease, higher blood urea nitrogen and were more likely to have been admitted to hospital in the prior 12 months. There were no significant differences in the 30- or 180-day clinical outcomes between patients who walked when compared to patients who did not walk. To further examine the role of 6MW distance in predicting short-term clinical outcomes, we excluded patients who were unable to walk from the analysis and repeated the multivariable regression analysis. Including only those patients who walked (n 5 130), 6MW distance O400 m remained a significant predictor of remaining free of readmission for any cause at 30 days (ORe0.367, 95% CI: 0.148e0.909, p 5 0.03).
Discussion In this study of 265 patients hospitalized with HF and left ventricular systolic dysfunction, all-cause readmission to
the hospital was found to be strongly associated with 6MW distance at the time of discharge. After controlling for clinical characteristics, laboratory values and demographics, the distance walked in 6 min at the time of discharge continued to be a powerful predictor for the risk of readmission or death for any cause at 30 days. Patients who were able to walk O400 m in 6 min prior to discharge were 57% less likely to experience death or readmission within 30 days than patients who walked 400 meters or less. Although 6-min walk testing has been used to assess the risk of mortality in ambulatory patients with HF in previous studies, this is the first study that demonstrates that the test may be useful to assess the risk of short-term readmission in hospitalized HF patients (14e16). HF accounts for a significant burden on health care funds and is one of the diagnostic-related groups with the highest rate of readmission within 30 days (19,20). Prior studies have demonstrated that readmission rates for HF range from 10e19% at 2 weeks and 27% to 47% within 3 to 6 months (21e23). Eighty percent of expenditures on HF patients occur in the hospital setting, and interventions that are effective in reducing the risk of readmission hold the potential to result in cost savings to the health system (24). Studies have demonstrated the benefits of patienttargeted education at the time of discharge, either alone or in combination with post-discharge care strategies (18,21,25e29). These interventions have demonstrated reductions in rehospitalization rates after discharge and
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Table 1. Demographics and comorbidities of study population
Variable Age (years) Gender (% female) Peripheral vascular disease (%) Current smoker (%) History of coronary disease (%) History of hypertension (%) History of CABG (%) History of PCI (%) Implantable cardiac defibrillator (%) Diabetes mellitus (%) Hypothyroidism (%) Gout (%) Anemia (%) CKD (%) Nonhemorrhagic stroke (%) TIA (%) COPD (%) Asthma (%) Number of hospitalizations in past 12 months Noncompliance with medication (%) Noncompliance with diet (%) Days since last hospitalization
6MW #400 m, n 5 122
6MW O400 m, n 5 88
Median (IQR) Or n (percent)
Median (IQR) Or n (percent)
68 50 25 12 83 93 51 35 27 48 23 21 20 6 16 6 34 16 2 18 23 110
(56e76) (40.9) (20.5) (9.8) (68) (76.2) (41.8) (28.6) (22.1) (39.3) (18.9) (17.2) (16.4) (4.9) (13.1) (4.9) (27.9) (13.1) (1e4) (14.7) (18.8) (43e400)
65 35 13 17 57 66 35 21 15 35 13 4 22 0 7 3 20 12 2 10 11 150
(56e72) (39.7) (14.8) (19.3) (64.8) (75) (39.8) (23.9) (17) (39.8) (14.8) (4.5) (25) (8) (3.4) (22.7) (13.6) (1e3) (11.4) (12.5) (42e896)
p value 0.175 0.860 0.288 0.049 0.621 0.838 0.768 0.415 0.363 0.950 0.439 0.005 0.124 0.035 0.237 0.594 0.400 0.913 0.059 0.462 0.208 0.237
PCI, percutaneous coronary intervention; CABG, coronary artery bypass grafting; CKD, chronic kidney disease; TIA, transient ischemic attack; COPD, chronic obstructive pulmonary disease.
have also been shown to be associated with overall cost savings (18,27,28). Prospective identification of patients at high risk for readmission to the hospital holds the potential of making these types of interventions even more cost effective.
While hyperuricemia has been found by others to be a significant predictor of mortality in HF, our study demonstrated that patients with a history of gout were less likely to be readmitted or die within 30 days of hospital discharge (2,30,31). Gout was more likely to be found in patients who
Table 2. Physical examination, laboratory measurements and medications at baseline
Variable Heart rate Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) LVEF QRS interval (msec) Fatigue score Sodium Blood urea nitrogen Creatinine Alanine aminotransferase Hemoglobin (g/dL) White blood cell count Platelet count Total cholesterol ACE, ARB or hydralazine-nitrate combination, n (%) Beta blocker, n (%) Spironolactone, n (%) Loop diuretic, n (%) Thiazide diuretic, n (%)
6MW #400 m, n 5 122
6MW O400 m, n 5 88
Median (IQR) or n (%)
Median (IQR) or n (%)
84 130 70 28 120 30 138 28 1.3 29 12.2 8 217 160 94 83 50 103 12
(72e96) (108e148) (60e84) (20e35) (96e152) (10e50) (135e141) (20e48) (1.1e1.8) (20e48) (10.7e13.6) (6.1e9.6) (180e259) (135e193) (77) (68) (41) (84.4) (9.8)
83 130 72 25 123 32 139 22 1.3 34 12.8 7.5 212 158 79 70 39 73 12
(66e94) (111e146) (61e86) (20e33) (100e158) (10e50) (136e141) (17e40) (1.0e1.7) (23e46) (11.1e13.9) (6.1e9.3) (171e266) (139e193) (89.8) (79.5) (44.3) (83) (13.6)
LVEF, left ventricular ejection fraction; ACE, angiotensin-converting enzyme; ARB, angiotensin II receptor blocker.
p value 0.253 0.686 0.251 0.566 0.452 0.373 0.485 0.126 0.503 0.170 0.240 0.539 0.581 0.529 0.017 0.064 0.623 0.775 0.393
Six-min Walk and Short-term Readmission
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Table 3. Clinical outcomes
Variable Readmission or death from any cause at 30 days (%) Readmission for heart failure or death from any cause at 30 days Readmission or death from any cause at 180 days (%) Readmission for heart failure or death from any cause at 180 days (%) Death from any cause at 30 days (%) Death from any cause at 180 days (%) Days hospitalized or death at 180 days
were not able to walk O400 m. Whereas patients with acute gout exacerbation would be expected to have limitations in their ability to walk, none of the patients in this study demonstrated to have limited 6MW distance due to this reason. The association between history of gout and lower risk of 30-day event is contrary to what would be expected, given the prior literature showing that hyperuricemia has been demonstrated to be a predictor of poor prognosis in HF. One possible explanation is that this is a chance finding due to the small number of patients with gout in this study sample. Functional assessment of HF patients is commonly used to determine candidacy for therapies and for prognostic evaluation. The NYHA classification is used routinely to determine candidacy for defibrillator placement or cardiac resynchronization therapy (31). Demers et al. reported that the 6MW test was found to be very reliable in the RESOLVD study but only correlated moderately with NYHA functional classification and measures of quality of life (32). More objective methods of assessing functional limitations have traditionally been used to assess HF patients for risk of adverse events. Cardiopulmonary exercise testing is employed by many programs in the assessment of mortality risk when determining candidacy for heart transplantation (1). 6MW testing has also been shown to be helpful in the assessment of mortality risk in patients with HF (14e16, 33). The SOLVD investigators showed that a lower 6MW distance was a significant predictor of mortality and long-term morbidity (15). Subsequent investigators have redemonstrated the association between 6MW distance and mortality in patients with systolic HF (14,16). Shah et al. previously demonstrated that 6MW distance
6MW #400 m, n 5 122
6MW O400 m, n 5 88
n (%)
n (%)
37 18 77 33 5 14 5
(30.3) (14.8) (63.1) (27) (4.1) (11.5) (0e20)
14 3 47 20 1 6 2.5
p value
(15.9) (3.4) (53.4) (22.7) (1.1) (6.8) (0e12)
0.016 0.007 0.158 0.477 0.204 0.257 0.069
serves as a potent predictor of 1 year mortality and hospitalization in a randomized trial of patients with HF and left ventricular systolic dysfunction (34). More recently, Alahdab et al. reported that 6MW distance was highly predictive of 40-month mortality and 18-month rehospitalization in African-American patients treated for acute decompensated HF irrespective of left ventricular ejection fraction (35). Yamokoski et al. reported that a prognostic model including 6MW distance was useful for prediction of death but not of rehospitalization (13). However, none of these studies has examined the relationship between 6MW distance and short-term (30 day) readmission and/or death. Given that early readmission has become an end point used for public reporting, predictors of this specific end point deserve renewed attention. HF patients with left ventricular systolic dysfunction hospitalized for the treatment of HF who are unable to walk O400 m in 6MW testing are at high risk for early hospital admission. The 6MW test is a safe and inexpensive clinical tool that can be applied in the hospital setting to identify patients who are more likely to be readmitted to the hospital. Further study is needed to determine if using this test routinely during inpatient care of HF patients can lead to more efficient application of strategies designed to lower readmission rates in this population. Study Limitations This study was performed in a single center and testing was performed by the same study coordinator for all patients. Whether these results can be generalized to other hospitals or would be similar using other personnel is unknown. The study sample
Table 4. Multivariable regression analysis for determinants of readmission or death from any cause at 30 days
Gout ACE, ARB or hydralazine-nitrate combination Blood urea nitrogen 6MW distance O400 m
Beta (SEM)
Wald
p value
2.147 0.989 0.018 0.833
6.156 6.011 5.379 5.03
0.013 0.014 0.020 0.025
(0.865) (0.403) (0.008) (0.371)
OR (95% CI) 0.117 0.372 1.019 0.435
(0.021e0.637) (0.169e0.82) (1.003e1.035) (0.21e0.9)
Variables removed by backward selection: age, current smoking, hepatic dysfunction, chronic kidney disease, anemia, alanine aminotransferase, beta blocker.
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was relatively small, limiting the statistical power of subgroup analyses. This sample was limited to patients with LVEF #40%, and thus extrapolating these results to HF patients with relatively preserved systolic function is not possible. Acknowledgments Funding Agency: Quality Care Research Fund from the Academic Medicine and Managed Care Forum. Financial Disclosure: None necessary.
17. 18.
19.
20. 21.
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ORIGINAL ARTICLE
Six-minute Walk Distance Predicts 30-Day Readmission in Hospitalized Heart Failure Patients Naga V.A. Kommuri,a Monica L. Johnson,b and Todd M. Koellingb a
Department of Internal Medicine, DMC-Sinai-Grace Hospital, Detroit, Michigan Division of Cardiovascular Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
b
Received for publication March 12, 2010; accepted July 9, 2010 (ARCMED-D-10-00121).
Background and Aims. Identification of patients with heart failure (HF) at high risk of hospital readmission is critical to refine processes for reducing readmission rates. We hypothesized that patients with higher 6-min walk (6MW) distance at the time of hospital discharge are at low risk for early readmission. Methods. We prospectively enrolled 265 patients admitted with HF and left ventricular systolic dysfunction. 6MW testing was administered prior to discharge. Multivariate logistic regression analysis was performed to determine the relationship between 6MW distance and 30-day readmission, stratifying by #400 m and O400 m. Results. Two hundred ten patients underwent 6MW testing prior to discharge. Patients with 6MW O400 m had a 30-day readmission rate of 15.9%, whereas patients with 6MW #400 m had a 30-day readmission rate of 30.3% ( p 5 0.016). Patients requiring readmission within 30 days had a median 6MW of 30 m, whereas patients not requiring readmission at 30 days walked 338 m ( p 5 0.012). 6MW distance predicted freedom from readmission at 30 days (OR: 0.435, 95% CI 0.21e0.9, p 5 0.025). Other independent predictors of 30-day readmission included history of gout (0.117, 0.021e0.637, p 5 0.013), use of angiotensin-converting enzyme inhibitor or accepted alternative (0.372, 0.169e0.820, p 5 0.014) and blood urea nitrogen level (1.019, 1.003e1.035, p 5 0.020). Conclusions. Low 6MW distance predicts early hospital readmission in patients with HF. Programs seeking to produce systems that are effective in reducing early hospital readmission may desire to incorporate 6MW testing during HF hospital care. Ó 2010 IMSS. Published by Elsevier Inc. Key Words: Heart failure, Patient readmission, Risk factors, Exercise testing.
Introduction Many clinical prediction models in the field of heart failure (HF) have been developed to understand risk factors for mortality (1e8). Recently, the Centers for Medicare and Medicaid Services (CMS) in the United States have initiated an effort to measure and make public 30-day readmission rates for heart failure in acute care hospitals (9). To facilitate the development of novel interventions designed to reduce readmission rates, methods of identifying highrisk patients are needed. However, clinical determinants
Address reprint requests to: Todd M. Koelling, MD, 1500 E. Medical Center Drive, CVC Room 2167, SPC 5853, Ann Arbor, MI 48109, USA; Phone: (734) 936-5265; FAX: (734) 615-3326; E-mail: [email protected]
of early hospital readmission (within 30 days) are not fully understood. The recently published risk stratification model employed by CMS provides limited discriminatory information, with a c-statistic of only 0.60 (10e13). Strategies to reduce readmission rates would ideally involve identification of patients at high risk for early readmission. Strategies that utilize physiological performance data may better identify the patients at high risk of readmission. The 6-min walk (6MW) test has been commonly used as a clinical endpoint in studies of HF patients and proved to be of great value in predicting the mortality and long-term morbidity in HF (14e16). The administration of this test has been standardized and has been adopted as a part of clinical practice in the care of pulmonary arterial hypertension and other clinical scenarios (17). However, its role in
0188-4409/$ - see front matter. Copyright Ó 2010 IMSS. Published by Elsevier Inc. doi: 10.1016/j.arcmed.2010.07.005
364
Kommuri et al./ Archives of Medical Research 41 (2010) 363e368
predicting short-term hospital readmission has not been previously studied. We hypothesized those patients with higher 6MW distance at the time of hospital discharges are at low risk for early hospital readmission.
Subjects and Methods This study was performed at the University of Michigan Hospital and was approved by the Medical School Institutional Review board. Details of the recruitment were described in detail in an earlier publication (18). Data were collected from the medical records of the study group patients. Detailed evaluation of the subgroup included demographics, clinical characteristics, and compliance with medications and diet. Laboratory values were collected at the time of admission as well as at discharge. Information regarding compliance with medications and diet was extracted from the medical record. The study coordinator examined the admission note and problem summary list for evidence of noncompliance. Evidence of noncompliance was coded as either present or absent. 6MW Test Six-min walk test was administered on enrolled patients at the time of discharge. After informed consent the test was administered under the supervision of skilled personnel according to the standard protocol as described by the American Thoracic Society (17). A 30.5 m (100 ft) long hospital corridor course was used and was marked by colored tape at each end. Patients were instructed to ambulate end to end at their normal pace covering as much distance as possible in 6 min. A clinical nurse coordinator recorded the distance walked and timed the test. Patients were encouraged in a standardized fashion (using standard phrases, i.e., “you are doing well; keep up the good work”, etc.) at 1-min intervals. Patients were instructed to stop the test if they were symptomatic and offered a chair to take a rest but were encouraged to walk once symptoms resolved. The total distance walked in the 6 min was measured to the nearest meter. The test was administered only once on each patient at the time of discharge. Patients who were bed bound were assigned a 6MW distance of zero. Statistical Analyses All analyses were performed with SPSS v. 15.0 statistical software. The prespecified primary end point of the study was readmission to the hospital for any cause during the 30-day follow-up period. Comparisons of categorical variables were performed by c2 tests. Comparisons of continuous variables were performed using the Wilcoxon rank-sum tests. 6MW test results for the study patients were grouped as #400 m and O400 m. A p value of !0.05 was considered statistically significant. Multivariate logistic regression analysis was performed to determine the relationship between
6MW distance and 30-day readmission, controlling for age, gender, clinical characteristics, medications and laboratory values.
Results Of the 666 patients screened for participation in the study, 29 refused participation and 372 were excluded because they met the exclusion criteria set forth for the study protocol (Figure 1). The most common reasons for nonenrollment included evaluation for cardiac surgery (80), noncardiac illness likely to increase mortality or hospitalization risk (62), inpatient cardiac transplantation evaluation (48), dementia or psychiatric illness (46). Fifty five of the 265 consented patients in the study were excluded from the analysis because they were discharged on the weekend when study personnel were unable to perform the discharge 6MW test. Thus, the study population was comprised of a total of 210 patients. Comparisons of the baseline characteristics of the study groups (6MW #400 m, n 5 122, and O400 m, n 5 88) are shown in Table 1. Patients who walked O400 m were similar to those walking #400 m in age, gender and most comorbidities. However, those walking O400 m were more likely to be smokers and less likely to have gout and chronic kidney disease. Patients who walked #400 m had similar physical examination, laboratory measurements and medication usage as compared to those who walked O400 m (Table 2). Patients walking O400 m were more likely to be treated with angiotensin-coverting enzyme (ACE) inhibitors, angiotensin II receptor blockers (ARB) or the combination of hydralazine and nitrates and showed a trend for being more likely to be treated with a beta blocker. The clinical outcomes of the two patient groups are shown in Table 3. Patients who walked O400 m were less likely to be admitted within 30 days for any cause (15.9% vs. 30.3%, p 5 0.016) and also for exacerbation of heart failure (3.4 vs. 14.8%, p 5 0.007) when compared to the patients in #400 m group. There were no significant differences in readmission end points at the 180day follow-up period. There were no differences in the groups with respect to 30- or 180-day all-cause mortality. Patients able to walk O400 m at the time of discharge showed a trend for having less hospitalization days or died during the 180-day follow-up period. The results of multivariable regression analysis used to adjust for baseline differences in the two study groups (Table 4) shows that 6MW distance O400 m remained a strong predictor of remaining free of readmission or mortality at 30 days (OR: 0.435, 95% CI 0.21e0.9, p 5 0.025). Other variables found to independently predict this clinical outcome included the presence of gout, use of ACE, ARB or the combination of hydralazine and a nitrate medication and blood urea nitrogen. Patients requiring readmission within 30 days (n 5 51) had a median (IQR) 6MW of 30 m (0e420), whereas
Six-min Walk and Short-term Readmission
365
Figure 1. Study group screening.
patients not requiring readmission at 30 days (n 5 159) had a 6MW distance of 338 m (0e700), p 5 0.012. Of those patients with 6MW distance #400 m, 80 were those assigned a distance of 0 because of their inability to walk. Comparing these patients to the 42 patients with walk distances #400 m, we found that these groups had few differences with respect to demographics, comorbidities, physical examination findings, laboratories and medications. Patients who walked were less likely to be smokers but more likely to be noncompliant with diet, have chronic kidney disease, higher blood urea nitrogen and were more likely to have been admitted to hospital in the prior 12 months. There were no significant differences in the 30- or 180-day clinical outcomes between patients who walked when compared to patients who did not walk. To further examine the role of 6MW distance in predicting short-term clinical outcomes, we excluded patients who were unable to walk from the analysis and repeated the multivariable regression analysis. Including only those patients who walked (n 5 130), 6MW distance O400 m remained a significant predictor of remaining free of readmission for any cause at 30 days (ORe0.367, 95% CI: 0.148e0.909, p 5 0.03).
Discussion In this study of 265 patients hospitalized with HF and left ventricular systolic dysfunction, all-cause readmission to
the hospital was found to be strongly associated with 6MW distance at the time of discharge. After controlling for clinical characteristics, laboratory values and demographics, the distance walked in 6 min at the time of discharge continued to be a powerful predictor for the risk of readmission or death for any cause at 30 days. Patients who were able to walk O400 m in 6 min prior to discharge were 57% less likely to experience death or readmission within 30 days than patients who walked 400 meters or less. Although 6-min walk testing has been used to assess the risk of mortality in ambulatory patients with HF in previous studies, this is the first study that demonstrates that the test may be useful to assess the risk of short-term readmission in hospitalized HF patients (14e16). HF accounts for a significant burden on health care funds and is one of the diagnostic-related groups with the highest rate of readmission within 30 days (19,20). Prior studies have demonstrated that readmission rates for HF range from 10e19% at 2 weeks and 27% to 47% within 3 to 6 months (21e23). Eighty percent of expenditures on HF patients occur in the hospital setting, and interventions that are effective in reducing the risk of readmission hold the potential to result in cost savings to the health system (24). Studies have demonstrated the benefits of patienttargeted education at the time of discharge, either alone or in combination with post-discharge care strategies (18,21,25e29). These interventions have demonstrated reductions in rehospitalization rates after discharge and
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Table 1. Demographics and comorbidities of study population
Variable Age (years) Gender (% female) Peripheral vascular disease (%) Current smoker (%) History of coronary disease (%) History of hypertension (%) History of CABG (%) History of PCI (%) Implantable cardiac defibrillator (%) Diabetes mellitus (%) Hypothyroidism (%) Gout (%) Anemia (%) CKD (%) Nonhemorrhagic stroke (%) TIA (%) COPD (%) Asthma (%) Number of hospitalizations in past 12 months Noncompliance with medication (%) Noncompliance with diet (%) Days since last hospitalization
6MW #400 m, n 5 122
6MW O400 m, n 5 88
Median (IQR) Or n (percent)
Median (IQR) Or n (percent)
68 50 25 12 83 93 51 35 27 48 23 21 20 6 16 6 34 16 2 18 23 110
(56e76) (40.9) (20.5) (9.8) (68) (76.2) (41.8) (28.6) (22.1) (39.3) (18.9) (17.2) (16.4) (4.9) (13.1) (4.9) (27.9) (13.1) (1e4) (14.7) (18.8) (43e400)
65 35 13 17 57 66 35 21 15 35 13 4 22 0 7 3 20 12 2 10 11 150
(56e72) (39.7) (14.8) (19.3) (64.8) (75) (39.8) (23.9) (17) (39.8) (14.8) (4.5) (25) (8) (3.4) (22.7) (13.6) (1e3) (11.4) (12.5) (42e896)
p value 0.175 0.860 0.288 0.049 0.621 0.838 0.768 0.415 0.363 0.950 0.439 0.005 0.124 0.035 0.237 0.594 0.400 0.913 0.059 0.462 0.208 0.237
PCI, percutaneous coronary intervention; CABG, coronary artery bypass grafting; CKD, chronic kidney disease; TIA, transient ischemic attack; COPD, chronic obstructive pulmonary disease.
have also been shown to be associated with overall cost savings (18,27,28). Prospective identification of patients at high risk for readmission to the hospital holds the potential of making these types of interventions even more cost effective.
While hyperuricemia has been found by others to be a significant predictor of mortality in HF, our study demonstrated that patients with a history of gout were less likely to be readmitted or die within 30 days of hospital discharge (2,30,31). Gout was more likely to be found in patients who
Table 2. Physical examination, laboratory measurements and medications at baseline
Variable Heart rate Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) LVEF QRS interval (msec) Fatigue score Sodium Blood urea nitrogen Creatinine Alanine aminotransferase Hemoglobin (g/dL) White blood cell count Platelet count Total cholesterol ACE, ARB or hydralazine-nitrate combination, n (%) Beta blocker, n (%) Spironolactone, n (%) Loop diuretic, n (%) Thiazide diuretic, n (%)
6MW #400 m, n 5 122
6MW O400 m, n 5 88
Median (IQR) or n (%)
Median (IQR) or n (%)
84 130 70 28 120 30 138 28 1.3 29 12.2 8 217 160 94 83 50 103 12
(72e96) (108e148) (60e84) (20e35) (96e152) (10e50) (135e141) (20e48) (1.1e1.8) (20e48) (10.7e13.6) (6.1e9.6) (180e259) (135e193) (77) (68) (41) (84.4) (9.8)
83 130 72 25 123 32 139 22 1.3 34 12.8 7.5 212 158 79 70 39 73 12
(66e94) (111e146) (61e86) (20e33) (100e158) (10e50) (136e141) (17e40) (1.0e1.7) (23e46) (11.1e13.9) (6.1e9.3) (171e266) (139e193) (89.8) (79.5) (44.3) (83) (13.6)
LVEF, left ventricular ejection fraction; ACE, angiotensin-converting enzyme; ARB, angiotensin II receptor blocker.
p value 0.253 0.686 0.251 0.566 0.452 0.373 0.485 0.126 0.503 0.170 0.240 0.539 0.581 0.529 0.017 0.064 0.623 0.775 0.393
Six-min Walk and Short-term Readmission
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Table 3. Clinical outcomes
Variable Readmission or death from any cause at 30 days (%) Readmission for heart failure or death from any cause at 30 days Readmission or death from any cause at 180 days (%) Readmission for heart failure or death from any cause at 180 days (%) Death from any cause at 30 days (%) Death from any cause at 180 days (%) Days hospitalized or death at 180 days
were not able to walk O400 m. Whereas patients with acute gout exacerbation would be expected to have limitations in their ability to walk, none of the patients in this study demonstrated to have limited 6MW distance due to this reason. The association between history of gout and lower risk of 30-day event is contrary to what would be expected, given the prior literature showing that hyperuricemia has been demonstrated to be a predictor of poor prognosis in HF. One possible explanation is that this is a chance finding due to the small number of patients with gout in this study sample. Functional assessment of HF patients is commonly used to determine candidacy for therapies and for prognostic evaluation. The NYHA classification is used routinely to determine candidacy for defibrillator placement or cardiac resynchronization therapy (31). Demers et al. reported that the 6MW test was found to be very reliable in the RESOLVD study but only correlated moderately with NYHA functional classification and measures of quality of life (32). More objective methods of assessing functional limitations have traditionally been used to assess HF patients for risk of adverse events. Cardiopulmonary exercise testing is employed by many programs in the assessment of mortality risk when determining candidacy for heart transplantation (1). 6MW testing has also been shown to be helpful in the assessment of mortality risk in patients with HF (14e16, 33). The SOLVD investigators showed that a lower 6MW distance was a significant predictor of mortality and long-term morbidity (15). Subsequent investigators have redemonstrated the association between 6MW distance and mortality in patients with systolic HF (14,16). Shah et al. previously demonstrated that 6MW distance
6MW #400 m, n 5 122
6MW O400 m, n 5 88
n (%)
n (%)
37 18 77 33 5 14 5
(30.3) (14.8) (63.1) (27) (4.1) (11.5) (0e20)
14 3 47 20 1 6 2.5
p value
(15.9) (3.4) (53.4) (22.7) (1.1) (6.8) (0e12)
0.016 0.007 0.158 0.477 0.204 0.257 0.069
serves as a potent predictor of 1 year mortality and hospitalization in a randomized trial of patients with HF and left ventricular systolic dysfunction (34). More recently, Alahdab et al. reported that 6MW distance was highly predictive of 40-month mortality and 18-month rehospitalization in African-American patients treated for acute decompensated HF irrespective of left ventricular ejection fraction (35). Yamokoski et al. reported that a prognostic model including 6MW distance was useful for prediction of death but not of rehospitalization (13). However, none of these studies has examined the relationship between 6MW distance and short-term (30 day) readmission and/or death. Given that early readmission has become an end point used for public reporting, predictors of this specific end point deserve renewed attention. HF patients with left ventricular systolic dysfunction hospitalized for the treatment of HF who are unable to walk O400 m in 6MW testing are at high risk for early hospital admission. The 6MW test is a safe and inexpensive clinical tool that can be applied in the hospital setting to identify patients who are more likely to be readmitted to the hospital. Further study is needed to determine if using this test routinely during inpatient care of HF patients can lead to more efficient application of strategies designed to lower readmission rates in this population. Study Limitations This study was performed in a single center and testing was performed by the same study coordinator for all patients. Whether these results can be generalized to other hospitals or would be similar using other personnel is unknown. The study sample
Table 4. Multivariable regression analysis for determinants of readmission or death from any cause at 30 days
Gout ACE, ARB or hydralazine-nitrate combination Blood urea nitrogen 6MW distance O400 m
Beta (SEM)
Wald
p value
2.147 0.989 0.018 0.833
6.156 6.011 5.379 5.03
0.013 0.014 0.020 0.025
(0.865) (0.403) (0.008) (0.371)
OR (95% CI) 0.117 0.372 1.019 0.435
(0.021e0.637) (0.169e0.82) (1.003e1.035) (0.21e0.9)
Variables removed by backward selection: age, current smoking, hepatic dysfunction, chronic kidney disease, anemia, alanine aminotransferase, beta blocker.
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was relatively small, limiting the statistical power of subgroup analyses. This sample was limited to patients with LVEF #40%, and thus extrapolating these results to HF patients with relatively preserved systolic function is not possible. Acknowledgments Funding Agency: Quality Care Research Fund from the Academic Medicine and Managed Care Forum. Financial Disclosure: None necessary.
17. 18.
19.
20. 21.
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