Studies Cardiovascular Disease (CVD) Essay
Studies Cardiovascular Disease (CVD)
Cardiovascular disease (CVD) has long been considered a disorder which principally affects men in our society; consideration of the occurrence of heart attacks in females, for example, has been largely an afterthought. In the past few years, however, it has become increasingly obvious that this is not a problem limited to males, but that it occurs with great frequency in women. We now know that CVD is the cause of death more than any condition in women over the age of 50, including cancer (1) and in fact is responsible for more than a third of all deaths in women (2). It is estimated that 370,000 women in the United States die from heart disease each year. However, our knowledge base regarding CVD in African American (AA) women has not kept pace with the accumulation of data on white females.
Thus, there is a deficit of information about this subgroup and the prevalence of CVD despite the fact that black women have more risk factors for CVD than do white women (3). The purpose of this paper is to review the subject of CVD in African American women and to focus upon four principal CVD categories: Coronary artery disease (CAD), hypertension, stroke, and congestive heart failure (CHF).The impact of gender and race on each of these entities will be examined in comparison to white women, and a determination will be made as to whether a different approach to the management of these disorders should be made based on ethnicity and sex.
Coronary Artery Disease
It has long been held that men have much more of a problem with CAD than women do; the belief has been that men are more susceptible to the disease, whereas women enjoy the benefits of hormonal protection. Gender differences in the occurrence of heart attacks have been noted, especially in the younger years of adult life. However, as each decade passes, the gap between prevalence rates for males and females progressively narrows to the point where there is essentially no difference by the seventh and eighth decades (4). Thus, although heart attack rates in women lag behind that for men by approximately ten years in the early years of adult life, equivalency is achieved later. Clinical features of CAD have also been shown to differ substantially between men and women. The Framingham Study (5) demonstrated that CAD presented much more frequently as myocardial infarction in men than in women (49 vs. 29 percent), but women developed angina pectoris more frequently than men (47 vs. 26 percent). Risk factors for CAD such as dyslipidemia, hypertension, cigarette smoking, diabetes mellitus, family history, obesity, and sedentary lifestyle have about the same incidence in men and women. However, the effect that certain risk factors have is more adverse in women. For instance, the risk of developing CAD is much greater in diabetic women. Another risk factor with substantially greater impact on females is hypertriglyceridemia (6). African American women are especially affected by CAD in a negative manner.
They have a higher mortality and morbidity than African American men and white women under the age of 55. In the age group 25-44, African American women have 2.5 times the coronary heart disease mortality risk of white women. The mortality rate from CAD for black women is about 69 percent higher than that for white women (7). Overall, in 1995, the CAD death rate for African American males was 133.1 per 1000 compared to 124.4 per 1000 for white males, or 7 percent higher for black males. Comparative rates for black and white women were 81.6 and 60.3 per 1000, respectively, indicating a 35 percent higher mortality rate for black women over white women. A study at West Virginia University stated that, compared to the overall national death rate from CVD in women of 401 per 100,000, the rate for black women in New York City was the highest among all major racial groups at 587 per 100,000. Rates for white and Hispanic women were 559 and 320 per 100,000, respectively. Mississippi had the highest black female CVD death rate in the nation at 686 per 100,000.
The heart attack event rate is more than twice as high for black women than for white women in the age group 65-74 years (8), indicating that the impact of having a higher number of risk factors over time is more deleterious in black women. Despite a lower coronary artery disease prevalence in black women based on angiographic studies, mortality rates are higher in this group than in white women. This inverse relationship between angiographic evidence of CAD and CAD mortality represents what may be termed the paradox of CAD in African American women (9). Post-infarction mortality is also higher than that for black men and white men and women (10). It should be emphasized that first myocardial infarction occurs at an earlier age with an earlier death in African American women. Certain risk factors are indeed more frequently seen in African American as compared to white women. There is a significantly higher incidence of hypertension and stroke in black women with myocardial infarction (11), and other risk factors which occur more frequently in this group include physical inactivity, higher mean body mass index (BMI) (12), and greater consumption of cholesterol and saturated fat (13).
Cigarette smoking and obesity represent risks which have been documented to increase cardiovascular disease in black women. Smoking negates the advantage against CAD induced by estrogen in pre-menopausal women (14). Diabetes mellitus is of particular concern in black women as a risk factor; the death rate among diabetic blacks is 2.5 times higher than in diabetic whites (15), and black women have a higher prevalence of this disease. Diabetes completely eliminates the pre-menopausal protection that women have against CAD, and this would appear to be more of a problem for African American women. Access to preventive medical attention for CAD has been noted to be deficient for African American women. A classic example is the study performed by Schulman et al (16). Eight actors were used, of whom 4 were black, 4 were white, 4 were male, 4 were female, and the age range was from younger to older. All had videotaped interviews which were presented to more than 700 predominately white male primary care physicians attending a medical conference.
The doctors were asked which patients they would be likely to refer for cardiac catheterization, based on a suggestive CAD profile which all of the patients possessed. Univariate analysis of the physicians’ responses revealed that both men (90.6 percent) and whites (90.6 percent) were more likely to be referred for cardiac catheterization than women (84.7 percent) and blacks (84.7 percent). A race-gender analysis also showed that black women in particular were referred for this diagnostic procedure 40 percent less often than white men. This study has been interpreted as demonstrating racial and gender bias against African American women by white male physicians regarding referral for a critical cardiovascular procedure designed to detect CAD.
The use of hormone or estrogen replacement therapy (HRT or ERT) has been investigated intensively in the past several years regarding their possible reduction of CVD risk in post-menopausal women. Several clinical trials including PEPI, ERA, and HERS have been performed, producing results which do not show a clear CAD mortality benefit derived from hormone use in post-menopausal women with CAD. There is still a possibility that they may be advantageous for primary prevention, and the ongoing Women’s Health Initiative should provide useful information when it is concluded. There is no indication that black women respond differently than white women to HRT/ERT regarding the impact on CVD risk.
Pre-menopausal women who are hypertensive have a CAD mortality risk which is ten times greater than normal (17). In the United States there are more hypertensive women than there are men with high blood pressure (18), and the prevalence of hypertension is greater among African American women than among white women. Specifically, the prevalence of hypertension in blacks twenty years of age or older is in excess of that for the population of the nation as a whole. The percentages are 35 for black males and 34.2 for black females, compared to 24.4 for white males and 19.3 for white females (19). Hypertension is the most important risk factor for stroke and is easily the most modifiable one. In addition, it is the largest contributor to CVD morbidity and mortality in blacks. Comparative death rates for hypertension per 100,000 population are 29.6 for black males (355 percent higher than for white males), and 21.7 for black females (352 percent higher than for white females).
The third National Health and Nutrition Examination Survey (NHANES III) also found that blacks have a higher prevalence of severe or stage III hypertension compared to non-blacks (20). Several differences in the pathogenesis of hypertension have been documented to exist between blacks and whites (21). African Americans are characterized by low-renin hypertension accompanied by salt sensitivity, e.g., poor toleration of salt-loading, and greater volume expansion as a consequence. These characteristics tend to make blacks less responsive to drugs which impact on the renin-angiotensin-aldosterone system (RAAS) such as angiotensin-converting enzyme (ACE) inhibitors and beta-blockers in the treatment of hypertension, and relatively more responsive to medications which decrease plasma volume, such as diuretics. Their salt sensitivity also renders them more susceptible to the hypertensive effects of a high-salt diet. It is estimated that over 70 percent of African Americans have low-renin hypertension as compared to about half of whites.
Although more than 90 percent of blacks have essential, or primary, hypertension, the discovery of a high renin level in a black patient, for instance, an elderly African American female, is so unusual that it strongly suggests a secondary cause for the blood pressure elevation. Black patients also tend to be more responsive to dihydropyridine calcium-channel blockers (CCBs) and alpha-1 blockers. However, there are some mitigating factors. For instance, although ACE inhibitors and beta-blockers may not be as effective as other drugs when used as monotherapy in blacks, they do have an antihypertensive result similar to that seen in whites when these drugs are administered in combination with diuretics. In addition, many black patients who do not respond to monotherapy treatment with these drugs used in conventional doses may respond to higher doses, although there is a risk of more side-effects. ACE inhibitors are also indicated in the treatment of congestive heart failure and for the deadly combination of hypertension and diabetes, especially if proteinuria is present. Other pathophysiological characteristics which are different between hypertensive blacks and whites are altered vascular reactivity, increased sodium retention, increased potassium excretion, and decreased kallikrein excretion seen in blacks, as well as more nephrosclerosis.
Decreases in vasodilatory substances in blacks such as kinins, prostaglandins, and dopamine are also seen. Black hypertensives have also been noted to have increased intracellular sodium and calcium concentration, decreased membrane sodium transport, and decreased red-cell sodium-potassium transport activity. These changes are believed to render the African American patient more prone to vascular, renal and circulatory alterations which result in elevated blood pressure. Complications of hypertension have an earlier age of onset and a later age of detection in blacks than in their white counterparts. The principal complications are CAD, stroke, left ventricular hypertrophy, end-stage renal disease, and congestive heart failure. Because of these facts, it is important to treat hypertension in blacks more aggressively, e.g., early, thoroughly, and with multiple drugs as necessary. In addition, non-pharmacological measures such as diet, attention to obesity, increased physical exercise, and avoidance of excess alcohol intake are essential components of a well-rounded therapeutic approach to the black hypertensive.
Stroke is the third leading cause of death in the United States after coronary heart disease and cancer. There are about 500,000 strokes each year of which 150,000 are fatal. Stroke is also a major cause of physical impairment and the cost of acute and chronic care exceeds $30 billion a year in this country. A so-called “stroke belt” exists in the Southeastern part of the country, where almost 60 percent of the African American population resides (22). Although stroke is generally thought of as a disorder primarily affecting the elderly, it should be recognized that 28 percent of the victims are under age 65. African Americans have a stroke mortality which is twice that of whites (23). Age-adjusted stroke mortality rates are 76 percent higher among African American than among white men, and 54 percent higher among African American than white women (24). Although the rate of decline for stroke mortality has increased since the 1970s, there has been a recent slowdown in this decline.
This has been especially true for African Americans, in whom stroke mortality is actually increasing. Since it is very difficult to treat stroke once the process is initiated, much of the focus has been on primary prevention. Hypertension is the most powerful predictor of stroke and is found to be a factor in 70 percent of cases (25). Control of hypertension therefore represents the best strategy to prevent stroke, and in fact a meta-analysis showed that when all studies of the association between treatment to lower blood pressure and stroke were reviewed, there was a 42 percent reduction in the incidence of stroke and a 45 percent reduction in fatal stroke when the diastolic blood pressure was reduced by 5-6 mmHg (26).
In addition, the Systolic Hypertension in the Elderly Program (SHEP) demonstrated that a 36 percent decrease in stroke risk resulted from mean blood pressure reduction of 11/3.4 mmHg. This benefit was seen in all ages, races, and genders. These data and other information support the need for vigorous drug therapy of hypertension for the primary prevention of stroke. This is especially important for African American patients, particularly women.
Congestive Heart Failure
Congestive heart failure (CHF) is the only cardiovascular disease whose incidence is increasing. There are great differences between blacks and whites in the etiology of CHF. Hypertension is the principal precursor of CHF in African Americans, whereas ischemic heart disease more commonly precedes CHF in whites. Mortality due to heart failure is about 2.5 times higher in blacks than in whites less than 65 years of age. Additionally, in 1990 the age-adjusted death rate for CHF among patients older than 65 years of age was 143.9 for black men compared with 117.8 for white men, and 113.4 for black women compared with 97.5 for white women (27). In a study of racial differences in heart failure, Afzal et al (28) prospectively analyzed 163 consecutive patients admitted to Henry Ford Hospital in Detroit, Michigan with a diagnosis of CHF. They found that compared with whites, blacks were younger in age (mean age 63.8 vs. 70.8, p=0.0003), and had a higher prevalence of hypertension (86 vs. 66 percent, p=0.0004), left ventricular hypertrophy (24 vs. 8 percent, p=0.02), ejection fraction