Cardiovascular diseases, both coronary and carotid disease, are the leading causes of death among women in the United States. Although the prevalence and magnitude of heart disease in women have been recognized for a decade, early diagnosis continues to be complicated by several factors, including lack of "typical" symptoms in women. Carotid artery disease also requires early identification to prevent adverse outcomes such as a stroke. Women represent more than half of the stroke victims nationwide. Therefore, screening for early recognition and diagnosis of cardiovascular diseases and risks may improve outcomes for women. This research focused on the potential use of ankle-brachial index (ABI) measurement as a noninvasive screening tool for early diagnosis of cardiovascular diseases and risks in women, specifically carotid disease and coronary disease.
Use of ABI
The ABI is the ratio value of the systolic pressure in either the dorsalis pedis or posterior tibial artery and the systolic pressure in the brachial artery. This noninvasive test is used routinely in vascular surgery patients for preoperative and postoperative evaluation. When performed correctly, the ABI has 97% sensitivity and 100% specificity for peripheral arterial disease when compared with invasive arteriogram.1 Researchers are beginning to explore the use of ABI in both general and specifically defined populations, such as hemodialysis and diabetic patients, in an effort to identify peripheral arterial disease earlier in the disease process.
Cardiac Disease and ABI
Several study results indicate the existence of a strong link between an ABI value of less than 0.90 mm Hg and cardiac disease.2-5 In one prospective study, ABI measurements taken at the time of cardiac angiography and compared with the angiographic results demonstrated that patients with ABI values less than 0.90 mm Hg were more likely to have multivessel coronary artery disease.2 Results of a retrospective study of patients who were previously diagnosed with coronary artery disease by angiography provide a description of a significant relationship between an ABI of less than 0.90 mm Hg and diagnosis of 2- or 3-vessel coronary artery disease.3 Conclusions from another study indicate that 40% of patients who were hospitalized with a diagnosis of coronary artery disease also had an ABI of less than 0.90 mm Hg.4 A recent study revealed that ABI values of less than 0.90 mm Hg are significantly associated with the degree of subclinical atherosclerosis in the coronary and carotid arteries as measured by coronary artery calcium scores and carotid intima-media thickness.5
Additional studies corroborate the connection between peripheral arterial disease and cardiac events as evidenced by an increased occurrence of cardiovascular events and risk factors in persons with a low ABI (defined as ABI <0.90 mm Hg).6 An ABI of less than 0.90 mm Hg measured at the time of cardiac angiography is an independent predictor of cardiovascular events during a 2- to 15-month follow-up period.7 Research demonstrates that patients with a low ABI are at 6 to 7 times higher risk for experiencing a myocardial infarction.6,8,9 An ABI of less than 0.90 mm Hg is also a strong independent predictor of all-cause cardiovascular mortality.9,10
Research investigations substantiate a connection between peripheral arterial disease, as defined by a low ABI, and the presence of coronary artery disease, as well as increased risk of coronary events.2,4,5,7,8,10 However, women have been underrepresented in most of these studies. Therefore, 1 goal of this study was to focus solely on women and the connection between ABI values and cardiac disease.
Carotid Disease and ABI
Studies are beginning to reveal a linkage between low ABI values and carotid artery disease and cerebrovascular events.5,8,11,12 A study using the Framingham data demonstrated a significant relationship between low ABI values and risk of stroke in both men and women with a mean age of 80 years.8 Research also revealed changes in carotid artery morphology and increased carotid atherosclerosis in patients with ABI values less than 0.90 mm Hg.5 In a recent investigation, an abnormal ABI was found in one third of patients hospitalized with acute coronary or cerebrovascular events; low ABI served as a predictor of an adverse 1-year outcome.13
Strokes are more prevalent among women than men; women represent 61% of strokes reported in 2004 in the United States. Based on the high incidence of stroke and poor outcomes among women, there is a need for research focused specifically on women. Therefore, a secondary goal of this study was to examine the association between low ABI values and the presence of carotid artery stenosis in women.
Cardiovascular Risk Factors and ABI
Atherosclerotic risk factors are not adequately recognized or treated in patients with peripheral vascular disease.14 Multiple studies describe a strong correlation between an ABI of less than 0.90 mm Hg (which is diagnostic of peripheral arterial) and the presence of the following risk factors: hypertension, hyperlipidemia, smoking, diabetes, and increased uric acid levels.3,4,15 Research also indicates that patients with peripheral arterial disease fail to perceive their own risk for coronary and stroke events as a major threat.16 Because of the continued prevalence of cardiovascular disease and risks in women, this study explored the correlation of a low ABI value with known cardiovascular risk factors in women.
The specific aim of this retrospective, descriptive correlational study was to identify the relationships between a low ABI value (<0.90 mm Hg) and coronary heart disease, carotid artery disease, and cardiovascular risk factors in women. Several research hypotheses guided our examination of these relationships. Specific hypotheses were the following: (1) A low ABI value is correlated with the presence of cardiac disease in women. (2) A low ABI value is correlated with carotid disease in women. (3) A low ABI value is correlated with claudication in women. (4) A low ABI value is correlated with diabetes, hypercholesterolemia, physical activity, and body mass index in women.
A convenience sample of 810 women who had participated in a self-referred cardiovascular screening program in a community-based health education and screening center was used for this retrospective study. Each woman had voluntarily participated and paid an out-of-pocket fee for the screening. Demographic and health history information and physiologic measurements were obtained and recorded at the time of the screening. A coronary risk profile by Wellsource had been completed by individuals at the time of their screening.
Presence of cardiac disease was measured using the self-reported response on a question on the coronary risk profile regarding a history of cardiac disease. Ankle-brachial index values had been calculated from the results of a sphygmomanometer and a handheld Doppler measurement of both the left and right lower extremities. Carotid disease was defined as the presence of carotid artery plaque determined through bilateral carotid ultrasound at the time of the screening. Additional risk factors recorded at the time of screening included fasting blood glucose, lipid profile, and height and weight, which were used to calculate body mass index.
Data from a demographic questionnaire, the coronary risk profile, and recorded physiologic measurements had previously been entered into a computer database by personnel at the community screening center. These data were accessed and de-identified through a numbering system prior to statistical analysis for this retrospective study. Hypotheses were tested using χ2 and independent t test.
The demographic characteristics and health history of the 810 women were compiled. Mean ± SD age was 59.55 ± 12.0 years. Most women in this study were white (94.5%). Only 5.4% were current smokers, much lower than expected based on state and national statistics (see Figure). More than half (60%) reported exercising on a weekly basis. Frequency of specific medical diagnoses reported by women is shown in the Table.
Only 5.7% of the women who underwent cardiovascular screening had an ABI of less than 0.90 mm Hg. Most (74.2%) had a body mass index greater than 25, defined as overweight, known to be a cardiac risk for women. Less than half of the women had physiologic measurements within the reference range. The percentages with physiologic measurements within recommended ranges were the following: 31.6% with a systolic blood pressure less than or equal to 130 mm Hg; 43.6% with diastolic blood pressure less than or equal to 80 mm Hg; 41.2% with a fasting glucose less than 100 mg/dL; and 43.2% with total cholesterol less than 200 mg/dL.
Analysis revealed a statistically significant relationship between an ABI of less than 0.90 mm Hg and the presence of moderate to severe carotid artery stenosis determined by ultrasound (χ2= 5.90, P = .015). An ABI of less than 0.90 mm Hg was not found to be significantly related to self-reported cardiac disease (χ2 = 0.83, P = .36), diabetes (χ2 = 1.82, P = .18), hypercholesterolemia (χ2 = 0.01, P = .93), claudication (χ2 = 2.06, P = .15), physical activity (χ2 = 1.17, P = .88), or body mass index (t = 1.12, P = .27) in the women in this study.
The strong relationship between an ABI of less than 0.90 mm Hg and the presence of moderate to severe carotid artery stenosis supported our hypothesis. When the degree of carotid stenosis was rated by an ultrastenographer and listed as mild, moderate, or severe, only 1.6% of the women in this study had moderate to severe carotid artery stenosis. However, the correlation between carotid stenosis and an ABI of less than 0.90 mm Hg was significant. This finding confirms the correlation between ABI values and stroke risk found in previous studies and strengthens the growing evidence that atherosclerosis is a generalized process occurring in multiple sites simultaneously. These results suggest that ABI measurements may be used as a noninvasive screening tool for carotid artery disease risk, which may lead to early recognition of disease and a reduction in the number of strokes among women.
The percentage (5.7%) of women with low ABI values in this study was much lower than the 18% to 29% reported in a previous clinical research of patients in a primary care setting.15 Even though the sample is large (N = 810), the power for analysis was low because of the small number of women with an ABI of less than 0.90 mm Hg. The lack of a statistically significant correlation between low ABI measurements (<0.90 mm Hg) and coronary artery disease in this study may be a reflection of the imprecise measurement of atherosclerotic process in the coronary system. The presence of coronary artery disease was not determined by physiologic testing, but rather by self-report. Furthermore, the questionnaire item regarding cardiac disease did not specify coronary artery disease but included valvular heart disease and dysrhythmias.
The potential use of ABI as a screening tool for coronary artery disease will require additional investigation using a more precise physiologic measurement such as cardiac catheterization or stress echocardiogram or a precise question designed to distinguish coronary artery disease from other cardiac diagnoses.
The study was limited by the enrollment of a relatively healthy group of women who had elected to pay for and undergo voluntary cardiovascular screening. The percentage of women who reported smoking was low, and the number of cardiovascular risk factors was relatively low in the women in this study. Thus, the sample was not an accurate reflection of the larger population of women seen in primary care settings.
The results of this study suggest a need for further study of the usefulness of the use of ABI as a screening tool for generalized atherosclerosis in women. Future research should focus on the use of ABI in women with documented cardiovascular risk factors at baseline and in disparate and minority populations who do not have the means to pay for elective screening. Additional studies should continue to investigate potential correlations between ABI and coronary disease in a diverse group of women. Further translational research is also needed to continue building our known of the relationship between ABI values and carotid artery disease in women.
The author acknowledges the following Mountain States Health Alliance Screening Center personnel for their help in this study: Lori Hamiton, RN; Denise Highsmith, RN; Susan Ordway; and ETSU statistician Debbie Pfortmiller.
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Keywords:© 2007 Lippincott Williams & Wilkins, Inc.
ankle-brachial index; cardiovascular screening; carotid disease; coronary artery disease; women