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Lower functional capacity is associated with higher cardiovascular risk in Brazilian patients with intermittent claudication
Vol. XXXIII No. 1
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Lower functional capacity is associated with higher cardiovascular risk in Brazilian patients with intermittent claudication Rita de Cassia Gengo e Silva, RN, PhD, Vanessa Ferreira Amorim de Melo, RN, Nelson Wolosker, MD, PhD, and Fernanda Marciano Consolim-Colombo, MD, PhD
The purpose of this study was to examine the association between cardiovascular risk estimated by the Framingham Risk Score and functional capacity in patients with peripheral artery disease using a 6-minute walk test. Fifty-six participants with intermittent claudication were recruited. The Framingham Risk Score was calculated and used to split the participants into two groups: Group A (mild and moderate risk) and group B (severe risk). The ankle-brachial index (ABI) was calculated for each leg using a handheld Doppler probe. Walking ability was verified by a 6-minute walk test. Descriptive statistics were used to describe the sample’s demographic and clinical characteristics. To compare clinical data between the two groups, a t test or Mann-Whitney test was used as appropriate according to the type of variable being analyzed. The Pearson coefficient was used to verify the association between cardiovascular risk and functional capacity. Group A had 19 participants (60.5 6.3 years; 36.8% male) and group B had 37 participants (63.4 8.7 years; 73% male). No differences were observed when comparing the ABI between both groups. The total distances covered by the men in group A were shorter compared with those of group B (331.4 + 51.5 vs 257.9 + 84.0; P = .02). The cardiovascular risk score was negative and was significantly correlated with total distances for men (r = 0.53; P = .001) and with painfree distances for women (r = 0.46; P = .03). Functional capacity, evaluated through a 6-minute walk test, seems to be associated with 10-year total mortality risk. (J Vasc Nurs 2015;33:21-25)
Lower extremity peripheral artery disease (PAD) affects men and women worldwide and is expected to increase owing to unhealthy lifestyle habits, aging, and an increased survival of people with chronic diseases. Recent statistical analyses of cardiovascular diseases estimated that PAD affects 8.5 million Americans $40 years of age and that cardiovascular disease is more prevalent among elderly people, non-Hispanic blacks, and women.1 ‘‘The Hearts of Brazil,’’ an epidemiologic study of the prevalence of cardiovascular risk factors in a random population sample from 72 Brazilian urban centers, showed that the prevalence of PAD in the Brazilian population is 10.5%.2 A populationbased prospective study on ageing, The Bambuı Health and Ageing Study, enrolled 1,485 elderly participants (>60 years) living in the town of Bambuı (Minas Gerais, Brazil). In this study, From the School of Nursing; Heart Institute (InCor), Medical School; Claudication Unit, Vascular and Endovascular Surgery Department, Medical School; Laboratory of Human Clinical Investigation of Hypertension Unit, Heart Institute (InCor), Medical School, University of Sao Paulo, Sao Paulo, Brazil. Corresponding author: Rita de Cassia Gengo e Silva, RN, PhD, Av Dr Eneas de Carvalho Aguiar, 419 – 3rd floor, Cerqueira Cesar, Sao Paulo/SP, Brazil, 05403-000 (E-mail: rcgsilva@ig. com.br). 1062-0303/$36.00 Copyright Ó 2015 by the Society for Vascular Nursing, Inc. http://dx.doi.org/10.1016/j.jvn.2014.08.001
2.5% of the participants met the criteria for probable intermittent claudication; that is, the interviewee reported pain in the calf during walking that was not present when standing or sitting, lasted #10 minutes, and disappeared with pace reduction or interruption of gait.3 More recent data from DATASUS, the Brazilian Health Ministry database, showed that atherosclerosis and other peripheral vascular diseases accounted for 20,565 hospitalizations in public hospitals in Brazil with an approximate cost of $24 million in 2012.4 Risk factors for PAD are similar to those that have been described for coronary heart disease (CHD).1,5 However, both diabetes and smoking are stronger risk factors for PAD than for CHD.3 Patients with PAD are at an increased risk of cardiovascular events. The results of the Atherosclerosis Risk In Communities (ARIC) study6 showed that 964 fatal or nonfatal CHD events occurred over a median follow-up period of 13.1 years. Moreover, CHD risk increased exponentially with decreasing ankle-brachial index (ABI). The ABI is the ratio of systolic pressure at the ankle to that in the arm. It is used for screening for and diagnosing PAD and to determine the severity of the disease. An ABI value of <0.90 is indicative of significant flow-limiting atherosclerotic disease in the lower extremity.5 It has been associated with an increased risk of coronary and cerebrovascular disease and with the presence of cardiovascular risk factors. In a meta-analysis, researchers observed that an ABI of #0.90 was associated with approximately two times greater 10-year total mortality, cardiovascular mortality, and major coronary event rates compared with the overall rate in each Framingham category. Furthermore, the risk of cardiovascular events was higher in patients with PAD
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compared with those without PAD, and the hazard ratio remained high for men and women, even after adjusting for the Framingham Risk Score.7 Patients with low ABI experience mobility loss and are less engaged in physical activities, including leisure activities.8 Studies have shown that the ABI is inversely related to physical activity and that people with low ABI are often less physically active.9,10 Recently, authors have investigated the relationship between the intensity of physical activity and cardiovascular disease risk with ABI status. They observed that individuals with a low ABI spent less time engaging in moderate-to-vigorous physical activity compared with those with a normal ABI and that total accelerometer counts were inversely related to Framingham Risk Score.11 Patients with PAD are at high risk of coronary events, and those with low ABI are less able to engage in physical activities. The purpose of this study was to examine the association between cardiovascular risk estimated by the Framingham Risk Score and functional capacity in patients with PAD using a 6-minute walk test.
METHODS
Patient recruitment and estimation of cardiovascular risk Patients were recruited from the intermittent claudication clinic at the Hospital of the University of S~ao Paulo. The inclusion criteria were 18 to 80 years of age, both genders, and ABI of <0.90. All participants provided informed consent. Patients were excluded if they needed to use assistive devices for ambulation. Clinical information was obtained by reviewing medical records or interviewing and examining patients. Participants were considered current smokers if they reported that they were currently using tobacco. Clinical information regarding comorbidities, results of laboratory tests, and medications were obtained from medical records. Blood pressure measurements were taken according to the VI Diretrizes Brasileiras de Hipertens~ao12 (Brazilian Guidelines on Hypertension) with an oscillometric device (Omron HEM 741C, Omron Healthcare Inc., China) immediately before measuring the ABI. These data were used to estimate global cardiovascular risk. The Framingham Risk Score estimates global cardiovascular risk, which reflects 10-year total mortality risk. It is accurate and has a good discriminatory capacity. This score takes into account the clinical data of patients (risk factor). For each risk, a score is assigned, and then a total score is calculated. Absolute cardiovascular risk corresponds with a specific total score, which represents the percentage of risk that the patient has a cardiovascular event within 10 years. The global cardiovascular risk is classified as low, moderate, or severe according to absolute risk: <10%, 10% to 20%, and >20%, respectively.13,14 Absolute risk was used to classify participants into two groups: Group A, mild and moderate cardiovascular risk (n = 19; 60.5 6.3 years; 36.8% male), and group B, severe cardiovascular risk (n = 37; 63.4 8.7 years; 73.0% male). Table 1 provides the general characteristics of the participants. This study was approved by the Ethics Committee of the Clinical Hospital, Medical School, University of Sao Paulo. All subjects completed a consent form that was approved by that committee.
MARCH 2015
ABI measurements Participants rested in the supine position for 5 minutes before measuring ABI. An appropriately sized blood pressure cuff was placed over both the left and right brachial arteries and above each malleolus. The cuff was rapidly inflated to 20 mmHg above the audible systolic pressure. Using a handheld Doppler probe (Medmega, SP, Brazil), we measured the systolic blood pressure in each artery following a standardized sequence: The left brachial artery, the left dorsalis pedis artery, the left posterior tibial artery, the right dorsalis pedis artery, the right posterior tibial artery, and the right brachial artery. The cuff was deflated at an approximate rate of 2 mm/s. The ABI was calculated for each leg and was the ratio of the highest systolic blood pressure in the leg to the highest systolic blood pressure in the arm. The lower ABI between the two legs was used.
Walking ability Walking ability was used as a measure of functional capacity. The 6-minute walk test was used for this purpose. Participants were instructed to walk up and down a 20-m corridor for 6 minutes after being instructed to cover as much distance as possible, according to their tolerance, and to describe all symptoms during the walk. Total and pain-free distances were recorded.
Data analysis Descriptive statistics were used to describe the sample’s demographic and clinical characteristics. The statistical program SPSS 12.0 was used to analyze the data regarding cardiovascular risk and functional capacity. To compare clinical data between the two groups the t test or Mann-Whitney test were used as appropriate according to the type of variable being analyzed. The Pearson coefficient was used to verify the association between cardiovascular risk and functional capacity. That association was classified as weak (0-0.39), moderate (0.40-0.69), or strong (>0.70).
RESULTS We studied 19 patients with mild to moderate cardiovascular risk (group A) and 37 patients with severe cardiovascular risk (group B) for a total of 56 patients.
Framingham Risk Score As shown in Table 1, the frequency of male participants was higher in group B compared with group A, although both groups were similar regarding the mean age of the subjects. The frequency of current smokers was significantly higher in group A (P = .018). The prevalence of participants with diabetes was higher in group B. Total cholesterol serum levels were similar between the two groups; however, group A had higher levels of high-density lipoprotein cholesterol. The mean systolic blood pressure values were >140 mmHg in both groups, but were higher in group B, even though 78.4% of the participants in group B were taking antihypertensive medication. In group A, 63.1% of participants were treated for hypertension. Table 2 shows the estimated absolute risk of infarction and death within 10 years. The mean average risk for all participants in group A and B were 13.2 2.6% and 13.3 5.2, respectively.
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TABLE 1 DEMOGRAPHIC AND CLINICAL CHARACTERISTICS OF PARTICIPANTS
Characteristic Age, mean (y) Sex (male) Current smoker (%) Associated disease Diabetes mellitus (%) Glucose (mg/dL) Hyperlipidemia (%) Cholesterol (mg/dL) HDL cholesterol (mg/dL) LDL cholesterol (mg/dL) Arterial hypertension (%) Systolic BP (mmHg) Diastolic BP (mmHg) Coronary disease (%) Cerebrovascular disease (%) ABI
Group A, Mild and Moderate Risk (n = 19)
Group B, Severe Risk (n = 37)
P Value
60.5 6.3 36.8% 10.5
63.4 8.7 73.0% 40.5
.121 .010 .018
26.3 106.9 38.2 73.7 180.4 36.8 51.4 11.2 101.7 32.9 78.9 140.3 19.9 86.0 13.9 26.3 0.0 0.61 0.13
70.3 133.5 50.0 59.5 180.1 51.2 45.8 14.1 98.3 32.2 78.4 159.0 24.8 87.5 14.0 59.5 5.4 0.59 0.14
.002 .002 .577 .521 .041 .749 .496 .005 .690 .022 .504 .659
ABI = ankle-brachial index; BP = blood pressure; HDL = high-density lipoprotein; LDL = low-density lipoprotein. Values are means SD or relative frequency (%) where indicated.
TABLE 2
TABLE 3
FRAMINGHAM RISK SCORE BY GROUP AND GENDER (MEAN ± STANDARD DEVIATION)
DISTANCES (METERS) COVERED DURING THE 6-MINUTE WALK TEST
Participants
Group A, Mild and Moderate Risk (n = 19)
Group B, Severe Risk (n = 37)
All Women Men
13.2 2.6 13.3 3.2 13.1 1.5
13.3 5.2 21.7 2.1 20.2 2.4
However, the risk score was higher for both men and women in group B.
ABI measurements All participants had low ABI values. No differences were observed when comparing the ABI results between both groups (Table 1). ABI values were similar among men with mild/moderate and severe cardiovascular risk (0.63 0 .11 vs 0.57 0 .18, respectively; P > .05), and among women with mild/moderate and severe cardiovascular risk (0.57 0 .16 vs 0.60 0 .13, respectively; P > .05).
Group A (n = 19)
Group B (n = 37)
P-Value
294.5 61.5 220.3 97.1
251.1 84,5 182.0 93.3
.08 .213
272.9 58.0 217.1 96.8
233.0 86.3 134.0 75.5
.138 .06
331.4 51.5 225.7 105.2
257.9 84.0 199.8 94.2
.02 .443
Participants All Total Pain free Women Total Pain free Men Total Pain free
Walking ability Participants with severe cardiovascular risk walked shorter distances than the participants with mild or moderate cardiovascular risk. However, only for men were the total distances
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MARCH 2015
Figure 1. Association between distances covered in the 6-minute walk test and Framingham Risk Score.
covered by participants with severe cardiovascular risk significantly lower than for those with mild or moderate cardiovascular risk. Results of the 6-minute walk test are shown in Table 3.
Association between cardiovascular risk and functional capacity Total and pain-free distances covered in the 6-minute walk test were weakly, but significantly, associated with cardiovascular risk score among all participants (Figure 1). For women, a negative, moderate, and significant correlation between cardiovascular risk score and pain-free distance was observed (r = 0.46; P = .03), but there was no correlation between cardiovascular risk score and total distance (r = 0.30; P = .18). For men, the inverse result was observed; the cardiovascular risk score was negative, moderate and significantly correlated with total distance (r = 0.53; P = .001), but was not correlated with pain-free distance (r = 0.19; P = .26).
DISCUSSION This study aimed to verify the association between Framingham Risk Score and functional capacity. It is well known that patients with intermittent claudication tend to engage in less physical activities and to have a more sedentary life style owing to disease symptoms.8 A reduction in the activities of daily life may contribute to a reduction in functional capacity and an increase in cardiovascular risk. In our study, participants had modifiable and nonmodifiable risk factors for cardiovascular disease. Male sex, current smoking, and diabetes were more prevalent among participants with severe cardiovascular risk (group B). The distances covered by patients during the 6-minute walk test were lower than in other studies. Brazilian researchers found that patients with intermittent claudication and a mean ABI of 0.63 were able to walk 361 83 meters.15 Although our study did not investigate the reasons behind the shorter distances covered by our patients, we believe that these participants perform little or no physical activity during their daily lives. Researchers have evaluated associations between physical activity during daily life and corridor-based functional performance measures in persons with PAD. They found that corridor-based functional performance measures reflect usual physical activity levels and certain aspects of typical walking during daily life.16 Our results showed that PAD severity was similar among all participants (ABI was low and similar between both groups) and
that the majority of participants had severe cardiovascular risk. A meta-analysis showed that ABI provided independent risk information compared with the Framingham Risk Score and that low ABI (<0.90) approximately doubled the risk of total mortality, cardiovascular mortality, and major coronary events across all Framingham risk categories.17 In the present study, coronary disease was more prevalent among patients with severe cardiovascular risk. This finding may be attributed to the observed risk factors, which were more common in group B, to the progression of atherosclerotic disease, and to a more sedentary life style (not measured). The results of the Multi-Ethnic Study of Atherosclerosis suggested that sedentary behavior can increase the progression of coronary disease once it is present and that any type of activity is better than sedentary behavior for patients with early coronary artery disease.18 Compared with participants with mild and moderate cardiovascular risk, those with severe cardiovascular risk were able to cover shorter distances during the 6-minute walk test, although a significant difference was only observed for the total distances covered by men. Previous studies demonstrated that self-reported ability to walk using the Walking Impaired Questionnaire (WIQ) was associated with or predicted cardiovascular mortality. In the Peripheral Arteriopathy and Cardiovascular Events (PACE) study, the authors demonstrated that WIQ scores were associated with an higher incidence of cardiovascular events and were correlated with poorer prognosis.19 More recently, researchers showed that PAD patients in the lowest baseline quartile of the WIQ stair-climbing score had higher all-cause mortality and higher CVD mortality compared with those with the highest baseline WIQ stair-climbing score, independent of ABI and other covariates.20 Interestingly, in another study authors demonstrated that the WIQ stair-climbing score, distance, and speed score were negatively correlated with the rate of all-cause mortality in PAD patients; furthermore, those who experienced $20.0-point declines in the WIQ distance score had higher cardiovascular mortality.21 This study is important for nurses and has implications for nursing practice. Patients with intermittent claudication are less likely to engage in physical activities. A sedentary life style could worsen the walking ability of patients with intermittent claudication. Nurses should help these patients to understand the importance of engaging in a physical activity program, encourage them to do so, and monitor their adherence to their assigned physical activity program. Patients who have a lower walking ability probably have a higher cardiovascular risk.
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Our study did have limitations. First, we had a small sample size, and we had more participants in group B than in group A. The patient distribution between the groups was probably not equivalent because participants were consecutively enrolled in the study, and our hospital is a tertiary care facility. Another limitation of our study is related to laboratory data, which were obtained from medical records. Although we only reviewed the results of tests performed within 6 months of the study, it is possible that some test results may have changed before the time of the study. In conclusion, in this study, participants had similar PAD severity and were able to walk similar distances during the 6-minute walk test. Interestingly, participants who had lower functional capacity were at a greater risk for cardiovascular events within 10 years.
REFERENCES 1. Go AS, Mozaffarian D, Roger VL, et al. Heart disease and stroke statistics—2013 update. A report from the American Heart Association. Circulation 2013;127:e6-245. 2. Makdisse M, Pereira AC, Brasil DP, et al. Prevalence and risk factors associated with peripheral arterial disease in the hearts of Brazil project. Arq Bras Cardiol 2008;91:402-14. 3. Passos VMA, Barreto SM, Guerra HL, et al. The Bambuı health and aging study (BHAS). Prevalence of intermittent claudication in the aged population of the community of Bambuı and its associated factors. Arq Bras Cardiol 2001;77:458-62. 4. Brazilian Ministry of Health. DATASUS. Available at: http://tabnet.datasus.gov.br/cgi/tabcgi.exe?sih/cnv/niuf.def. Accessed January 7, 2014. 5. Hirsch AT, Haskal ZJ, Hertzer NR, et al. ACC/AHA 2005 practice guidelines for the management of patients with peripheral arterial disease (lower extremity, renal, mesenteric, and abdominal aortic): a collaborative report from the American Association for Vascular Surgery/Society for Vascular Surgery, Society for Cardiovascular Angiography and Interventions, Society for Vascular Medicine and Biology, Society of Interventional Radiology, and the ACC/AHA Task Force on Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients With Peripheral Arterial Disease). Circulation 2006;113:e463-654. 6. Weatherley BD, Nelson JJ, Heiss G. The association of the ankle-brachial index with incident coronary heart disease: the Atherosclerosis Risk In Communities (ARIC) study, 1987–2001. BMC Cardiovasc Disord 2007;7:3. 7. Fowkes FG, Murray GD, Butcher I, et al. Ankle Brachial Index Collaboration. Ankle Brachial Index combined with Framingham Risk Score to predict cardiovascular events and mortality: a meta-analysis. JAMA 2008;300:197-208. 8. Gardner AW, Clancy RJ. The relationship between anklebrachial index and leisure-time physical activity in patients with intermittent claudication. Angiology 2006;57:539-45.
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9. McDermott MM, Guralnik JM, Tian L, et al. Associations of borderline and low normal ankle-brachial index values with functional decline at 5-year follow-up: The WALCS (Walking and Leg Circulation Study). J Am Coll Cardiol 2009;53:1056-62. 10. McDermott MM, Greenland P, Liu K, et al. The ankle brachial index is associated with leg function and physical activity: The Walking and Leg Circulation Study. Ann Intern Med 2002;136:873-83. 11. Hawkins MS, Gabriel KP, Conroy MB, et al. Physical activity intensity and cardiovascular risk by ankle–brachial index. Vasc Med 2013;18(2):79-84. 12. Sociedade Brasileira de Cardiologia/Sociedade Brasileira de Hipertens~ao/Sociedade Brasileira de Nefrologia. VI Diretrizes Brasileiras de Hipertens~ao. Arq Bras Cardiol 2010; 95(Suppl. 1):1-51. 13. Petterle WC, Polanczyk CA. Avaliac¸~ao crıtica dos escores de risco. Revista da Sociedade de Cardiologia do Estado do Rio Grande do Sul 2011;23:1-6. 14. D’Agostino RB, Vasan RS, Pencina MJ, et al. General cardiovascular risk profile for use in primary care. The Framingham Heart Study. Circulation 2008;117:743-53. 15. Franc¸a MA, Lima TM, Santana FS, et al. Relationship between the performance of 6-minute walk test and treadmill test in patients with intermittent claudication of lower limbs. J Vasc Bras 2012;11(4):263-8. 16. McDermott MM, Ades PA, Dyer A, et al. Corridor-based functional performance measures correlate better with physical activity during daily life than treadmill measures in persons with peripheral arterial disease. J Vasc Surg 2008;48: 1231-7. 17. Ankle Brachial Index Collaboration. Ankle brachial index combined with Framingham Risk Score to predict cardiovascular events and mortality: a meta-analysis. JAMA 2008; 300(2):197-208. 18. Delaney JAC, Jensky NE, Criqui MH, et al. The association between physical activity and both incident coronary artery calcification and ankle brachial index progression: The Multi-Ethnic Study of Atherosclerosis. Atherosclerosis 2013;230:278-83. 19. Schiano V, Brevetti G, Sirico G, et al. Functional status measured by walking impairment questionnaire and cardiovascular risk prediction in peripheral arterial disease: results of the Peripheral Arteriopathy and Cardiovascular Events (PACE) study. Vasc Med 2006;11:147-54. 20. Jain A, Liu K, Ferrucci L, et al. The Walking Impairment Questionnaire stair-climbing score predicts mortality in men and women with peripheral arterial disease. J Vasc Surg 2012;55(6):1662-73. 21. Jain A, Liu K, Ferrucci L, et al. Declining walking impairment questionnaire scores are associated with subsequent increased mortality in peripheral artery disease. J Am Coll Cardiol 2013;61(17):1820-9.
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Lower functional capacity is associated with higher cardiovascular risk in Brazilian patients with intermittent claudication Rita de Cassia Gengo e Silva, RN, PhD, Vanessa Ferreira Amorim de Melo, RN, Nelson Wolosker, MD, PhD, and Fernanda Marciano Consolim-Colombo, MD, PhD
The purpose of this study was to examine the association between cardiovascular risk estimated by the Framingham Risk Score and functional capacity in patients with peripheral artery disease using a 6-minute walk test. Fifty-six participants with intermittent claudication were recruited. The Framingham Risk Score was calculated and used to split the participants into two groups: Group A (mild and moderate risk) and group B (severe risk). The ankle-brachial index (ABI) was calculated for each leg using a handheld Doppler probe. Walking ability was verified by a 6-minute walk test. Descriptive statistics were used to describe the sample’s demographic and clinical characteristics. To compare clinical data between the two groups, a t test or Mann-Whitney test was used as appropriate according to the type of variable being analyzed. The Pearson coefficient was used to verify the association between cardiovascular risk and functional capacity. Group A had 19 participants (60.5 6.3 years; 36.8% male) and group B had 37 participants (63.4 8.7 years; 73% male). No differences were observed when comparing the ABI between both groups. The total distances covered by the men in group A were shorter compared with those of group B (331.4 + 51.5 vs 257.9 + 84.0; P = .02). The cardiovascular risk score was negative and was significantly correlated with total distances for men (r = 0.53; P = .001) and with painfree distances for women (r = 0.46; P = .03). Functional capacity, evaluated through a 6-minute walk test, seems to be associated with 10-year total mortality risk. (J Vasc Nurs 2015;33:21-25)
Lower extremity peripheral artery disease (PAD) affects men and women worldwide and is expected to increase owing to unhealthy lifestyle habits, aging, and an increased survival of people with chronic diseases. Recent statistical analyses of cardiovascular diseases estimated that PAD affects 8.5 million Americans $40 years of age and that cardiovascular disease is more prevalent among elderly people, non-Hispanic blacks, and women.1 ‘‘The Hearts of Brazil,’’ an epidemiologic study of the prevalence of cardiovascular risk factors in a random population sample from 72 Brazilian urban centers, showed that the prevalence of PAD in the Brazilian population is 10.5%.2 A populationbased prospective study on ageing, The Bambuı Health and Ageing Study, enrolled 1,485 elderly participants (>60 years) living in the town of Bambuı (Minas Gerais, Brazil). In this study, From the School of Nursing; Heart Institute (InCor), Medical School; Claudication Unit, Vascular and Endovascular Surgery Department, Medical School; Laboratory of Human Clinical Investigation of Hypertension Unit, Heart Institute (InCor), Medical School, University of Sao Paulo, Sao Paulo, Brazil. Corresponding author: Rita de Cassia Gengo e Silva, RN, PhD, Av Dr Eneas de Carvalho Aguiar, 419 – 3rd floor, Cerqueira Cesar, Sao Paulo/SP, Brazil, 05403-000 (E-mail: rcgsilva@ig. com.br). 1062-0303/$36.00 Copyright Ó 2015 by the Society for Vascular Nursing, Inc. http://dx.doi.org/10.1016/j.jvn.2014.08.001
2.5% of the participants met the criteria for probable intermittent claudication; that is, the interviewee reported pain in the calf during walking that was not present when standing or sitting, lasted #10 minutes, and disappeared with pace reduction or interruption of gait.3 More recent data from DATASUS, the Brazilian Health Ministry database, showed that atherosclerosis and other peripheral vascular diseases accounted for 20,565 hospitalizations in public hospitals in Brazil with an approximate cost of $24 million in 2012.4 Risk factors for PAD are similar to those that have been described for coronary heart disease (CHD).1,5 However, both diabetes and smoking are stronger risk factors for PAD than for CHD.3 Patients with PAD are at an increased risk of cardiovascular events. The results of the Atherosclerosis Risk In Communities (ARIC) study6 showed that 964 fatal or nonfatal CHD events occurred over a median follow-up period of 13.1 years. Moreover, CHD risk increased exponentially with decreasing ankle-brachial index (ABI). The ABI is the ratio of systolic pressure at the ankle to that in the arm. It is used for screening for and diagnosing PAD and to determine the severity of the disease. An ABI value of <0.90 is indicative of significant flow-limiting atherosclerotic disease in the lower extremity.5 It has been associated with an increased risk of coronary and cerebrovascular disease and with the presence of cardiovascular risk factors. In a meta-analysis, researchers observed that an ABI of #0.90 was associated with approximately two times greater 10-year total mortality, cardiovascular mortality, and major coronary event rates compared with the overall rate in each Framingham category. Furthermore, the risk of cardiovascular events was higher in patients with PAD
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compared with those without PAD, and the hazard ratio remained high for men and women, even after adjusting for the Framingham Risk Score.7 Patients with low ABI experience mobility loss and are less engaged in physical activities, including leisure activities.8 Studies have shown that the ABI is inversely related to physical activity and that people with low ABI are often less physically active.9,10 Recently, authors have investigated the relationship between the intensity of physical activity and cardiovascular disease risk with ABI status. They observed that individuals with a low ABI spent less time engaging in moderate-to-vigorous physical activity compared with those with a normal ABI and that total accelerometer counts were inversely related to Framingham Risk Score.11 Patients with PAD are at high risk of coronary events, and those with low ABI are less able to engage in physical activities. The purpose of this study was to examine the association between cardiovascular risk estimated by the Framingham Risk Score and functional capacity in patients with PAD using a 6-minute walk test.
METHODS
Patient recruitment and estimation of cardiovascular risk Patients were recruited from the intermittent claudication clinic at the Hospital of the University of S~ao Paulo. The inclusion criteria were 18 to 80 years of age, both genders, and ABI of <0.90. All participants provided informed consent. Patients were excluded if they needed to use assistive devices for ambulation. Clinical information was obtained by reviewing medical records or interviewing and examining patients. Participants were considered current smokers if they reported that they were currently using tobacco. Clinical information regarding comorbidities, results of laboratory tests, and medications were obtained from medical records. Blood pressure measurements were taken according to the VI Diretrizes Brasileiras de Hipertens~ao12 (Brazilian Guidelines on Hypertension) with an oscillometric device (Omron HEM 741C, Omron Healthcare Inc., China) immediately before measuring the ABI. These data were used to estimate global cardiovascular risk. The Framingham Risk Score estimates global cardiovascular risk, which reflects 10-year total mortality risk. It is accurate and has a good discriminatory capacity. This score takes into account the clinical data of patients (risk factor). For each risk, a score is assigned, and then a total score is calculated. Absolute cardiovascular risk corresponds with a specific total score, which represents the percentage of risk that the patient has a cardiovascular event within 10 years. The global cardiovascular risk is classified as low, moderate, or severe according to absolute risk: <10%, 10% to 20%, and >20%, respectively.13,14 Absolute risk was used to classify participants into two groups: Group A, mild and moderate cardiovascular risk (n = 19; 60.5 6.3 years; 36.8% male), and group B, severe cardiovascular risk (n = 37; 63.4 8.7 years; 73.0% male). Table 1 provides the general characteristics of the participants. This study was approved by the Ethics Committee of the Clinical Hospital, Medical School, University of Sao Paulo. All subjects completed a consent form that was approved by that committee.
MARCH 2015
ABI measurements Participants rested in the supine position for 5 minutes before measuring ABI. An appropriately sized blood pressure cuff was placed over both the left and right brachial arteries and above each malleolus. The cuff was rapidly inflated to 20 mmHg above the audible systolic pressure. Using a handheld Doppler probe (Medmega, SP, Brazil), we measured the systolic blood pressure in each artery following a standardized sequence: The left brachial artery, the left dorsalis pedis artery, the left posterior tibial artery, the right dorsalis pedis artery, the right posterior tibial artery, and the right brachial artery. The cuff was deflated at an approximate rate of 2 mm/s. The ABI was calculated for each leg and was the ratio of the highest systolic blood pressure in the leg to the highest systolic blood pressure in the arm. The lower ABI between the two legs was used.
Walking ability Walking ability was used as a measure of functional capacity. The 6-minute walk test was used for this purpose. Participants were instructed to walk up and down a 20-m corridor for 6 minutes after being instructed to cover as much distance as possible, according to their tolerance, and to describe all symptoms during the walk. Total and pain-free distances were recorded.
Data analysis Descriptive statistics were used to describe the sample’s demographic and clinical characteristics. The statistical program SPSS 12.0 was used to analyze the data regarding cardiovascular risk and functional capacity. To compare clinical data between the two groups the t test or Mann-Whitney test were used as appropriate according to the type of variable being analyzed. The Pearson coefficient was used to verify the association between cardiovascular risk and functional capacity. That association was classified as weak (0-0.39), moderate (0.40-0.69), or strong (>0.70).
RESULTS We studied 19 patients with mild to moderate cardiovascular risk (group A) and 37 patients with severe cardiovascular risk (group B) for a total of 56 patients.
Framingham Risk Score As shown in Table 1, the frequency of male participants was higher in group B compared with group A, although both groups were similar regarding the mean age of the subjects. The frequency of current smokers was significantly higher in group A (P = .018). The prevalence of participants with diabetes was higher in group B. Total cholesterol serum levels were similar between the two groups; however, group A had higher levels of high-density lipoprotein cholesterol. The mean systolic blood pressure values were >140 mmHg in both groups, but were higher in group B, even though 78.4% of the participants in group B were taking antihypertensive medication. In group A, 63.1% of participants were treated for hypertension. Table 2 shows the estimated absolute risk of infarction and death within 10 years. The mean average risk for all participants in group A and B were 13.2 2.6% and 13.3 5.2, respectively.
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TABLE 1 DEMOGRAPHIC AND CLINICAL CHARACTERISTICS OF PARTICIPANTS
Characteristic Age, mean (y) Sex (male) Current smoker (%) Associated disease Diabetes mellitus (%) Glucose (mg/dL) Hyperlipidemia (%) Cholesterol (mg/dL) HDL cholesterol (mg/dL) LDL cholesterol (mg/dL) Arterial hypertension (%) Systolic BP (mmHg) Diastolic BP (mmHg) Coronary disease (%) Cerebrovascular disease (%) ABI
Group A, Mild and Moderate Risk (n = 19)
Group B, Severe Risk (n = 37)
P Value
60.5 6.3 36.8% 10.5
63.4 8.7 73.0% 40.5
.121 .010 .018
26.3 106.9 38.2 73.7 180.4 36.8 51.4 11.2 101.7 32.9 78.9 140.3 19.9 86.0 13.9 26.3 0.0 0.61 0.13
70.3 133.5 50.0 59.5 180.1 51.2 45.8 14.1 98.3 32.2 78.4 159.0 24.8 87.5 14.0 59.5 5.4 0.59 0.14
.002 .002 .577 .521 .041 .749 .496 .005 .690 .022 .504 .659
ABI = ankle-brachial index; BP = blood pressure; HDL = high-density lipoprotein; LDL = low-density lipoprotein. Values are means SD or relative frequency (%) where indicated.
TABLE 2
TABLE 3
FRAMINGHAM RISK SCORE BY GROUP AND GENDER (MEAN ± STANDARD DEVIATION)
DISTANCES (METERS) COVERED DURING THE 6-MINUTE WALK TEST
Participants
Group A, Mild and Moderate Risk (n = 19)
Group B, Severe Risk (n = 37)
All Women Men
13.2 2.6 13.3 3.2 13.1 1.5
13.3 5.2 21.7 2.1 20.2 2.4
However, the risk score was higher for both men and women in group B.
ABI measurements All participants had low ABI values. No differences were observed when comparing the ABI results between both groups (Table 1). ABI values were similar among men with mild/moderate and severe cardiovascular risk (0.63 0 .11 vs 0.57 0 .18, respectively; P > .05), and among women with mild/moderate and severe cardiovascular risk (0.57 0 .16 vs 0.60 0 .13, respectively; P > .05).
Group A (n = 19)
Group B (n = 37)
P-Value
294.5 61.5 220.3 97.1
251.1 84,5 182.0 93.3
.08 .213
272.9 58.0 217.1 96.8
233.0 86.3 134.0 75.5
.138 .06
331.4 51.5 225.7 105.2
257.9 84.0 199.8 94.2
.02 .443
Participants All Total Pain free Women Total Pain free Men Total Pain free
Walking ability Participants with severe cardiovascular risk walked shorter distances than the participants with mild or moderate cardiovascular risk. However, only for men were the total distances
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Figure 1. Association between distances covered in the 6-minute walk test and Framingham Risk Score.
covered by participants with severe cardiovascular risk significantly lower than for those with mild or moderate cardiovascular risk. Results of the 6-minute walk test are shown in Table 3.
Association between cardiovascular risk and functional capacity Total and pain-free distances covered in the 6-minute walk test were weakly, but significantly, associated with cardiovascular risk score among all participants (Figure 1). For women, a negative, moderate, and significant correlation between cardiovascular risk score and pain-free distance was observed (r = 0.46; P = .03), but there was no correlation between cardiovascular risk score and total distance (r = 0.30; P = .18). For men, the inverse result was observed; the cardiovascular risk score was negative, moderate and significantly correlated with total distance (r = 0.53; P = .001), but was not correlated with pain-free distance (r = 0.19; P = .26).
DISCUSSION This study aimed to verify the association between Framingham Risk Score and functional capacity. It is well known that patients with intermittent claudication tend to engage in less physical activities and to have a more sedentary life style owing to disease symptoms.8 A reduction in the activities of daily life may contribute to a reduction in functional capacity and an increase in cardiovascular risk. In our study, participants had modifiable and nonmodifiable risk factors for cardiovascular disease. Male sex, current smoking, and diabetes were more prevalent among participants with severe cardiovascular risk (group B). The distances covered by patients during the 6-minute walk test were lower than in other studies. Brazilian researchers found that patients with intermittent claudication and a mean ABI of 0.63 were able to walk 361 83 meters.15 Although our study did not investigate the reasons behind the shorter distances covered by our patients, we believe that these participants perform little or no physical activity during their daily lives. Researchers have evaluated associations between physical activity during daily life and corridor-based functional performance measures in persons with PAD. They found that corridor-based functional performance measures reflect usual physical activity levels and certain aspects of typical walking during daily life.16 Our results showed that PAD severity was similar among all participants (ABI was low and similar between both groups) and
that the majority of participants had severe cardiovascular risk. A meta-analysis showed that ABI provided independent risk information compared with the Framingham Risk Score and that low ABI (<0.90) approximately doubled the risk of total mortality, cardiovascular mortality, and major coronary events across all Framingham risk categories.17 In the present study, coronary disease was more prevalent among patients with severe cardiovascular risk. This finding may be attributed to the observed risk factors, which were more common in group B, to the progression of atherosclerotic disease, and to a more sedentary life style (not measured). The results of the Multi-Ethnic Study of Atherosclerosis suggested that sedentary behavior can increase the progression of coronary disease once it is present and that any type of activity is better than sedentary behavior for patients with early coronary artery disease.18 Compared with participants with mild and moderate cardiovascular risk, those with severe cardiovascular risk were able to cover shorter distances during the 6-minute walk test, although a significant difference was only observed for the total distances covered by men. Previous studies demonstrated that self-reported ability to walk using the Walking Impaired Questionnaire (WIQ) was associated with or predicted cardiovascular mortality. In the Peripheral Arteriopathy and Cardiovascular Events (PACE) study, the authors demonstrated that WIQ scores were associated with an higher incidence of cardiovascular events and were correlated with poorer prognosis.19 More recently, researchers showed that PAD patients in the lowest baseline quartile of the WIQ stair-climbing score had higher all-cause mortality and higher CVD mortality compared with those with the highest baseline WIQ stair-climbing score, independent of ABI and other covariates.20 Interestingly, in another study authors demonstrated that the WIQ stair-climbing score, distance, and speed score were negatively correlated with the rate of all-cause mortality in PAD patients; furthermore, those who experienced $20.0-point declines in the WIQ distance score had higher cardiovascular mortality.21 This study is important for nurses and has implications for nursing practice. Patients with intermittent claudication are less likely to engage in physical activities. A sedentary life style could worsen the walking ability of patients with intermittent claudication. Nurses should help these patients to understand the importance of engaging in a physical activity program, encourage them to do so, and monitor their adherence to their assigned physical activity program. Patients who have a lower walking ability probably have a higher cardiovascular risk.
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Our study did have limitations. First, we had a small sample size, and we had more participants in group B than in group A. The patient distribution between the groups was probably not equivalent because participants were consecutively enrolled in the study, and our hospital is a tertiary care facility. Another limitation of our study is related to laboratory data, which were obtained from medical records. Although we only reviewed the results of tests performed within 6 months of the study, it is possible that some test results may have changed before the time of the study. In conclusion, in this study, participants had similar PAD severity and were able to walk similar distances during the 6-minute walk test. Interestingly, participants who had lower functional capacity were at a greater risk for cardiovascular events within 10 years.
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