Cardioprotection and antihypertensive therapy
The key importance addressing the associated coronary risk factors (The Framingham experience)
Hypertension in the United States has apparently been dropping in recent decades, even as obesity has risen. This assertion may appear contradictory given the strong association between obesity and body weight, but it would seem that a decline in the use of salt may be a factor. The prevalence of a condition that causes such a dramatic increase in cardiovascular mortality, however, remains unacceptably high.
About 20% of the adult population under 74 years old has hypertension, defined as at least 140 mm Hg systolic blood pressure and at least 90 mm Hg diastolic blood pressure. Of Americans in their fifties, 44% are hypertensive, while the proportion climbs to two-thirds of those in their seventies. At all ages, the prevalence of hypertension is much greater in blacks than in whites. Almost 75% of black Americans aged 60-74 are affected by chronic hypertension.
Treatment to continues to lag at unacceptable levels. While the number of undiagnosed hypertensives has fallen since the 1970s, when almost half were unaware of their condition compared with only about a third by the late 1980s, only 21% of hypertensive Americans have their blood pressure maintained at under 140/90 mm Hg by medication. Twenty-seven percent receive treatment but remain insufficiently controlled, while 17% are diagnosed but receive no treatment whatsoever.
Evidence that reducing hypertension through medication does not radically reduce cardiovascular mortality has led some sceptics to cast doubt on the strength of the link between blood pressure and atherosclerosis. Yet this link has been established again and again in studies of arterial disease, particularly the Framingham study, which showed that hypertension almost quadrupled the risk of stroke in men and almost tripled it in women, doubled the risk of peripheral arterial disease in men and almost quadrupled it in women, quadrupled the risk of cardiac failure in men and tripled it in women, and – most signifcantly in terms of overall mortality – doubled the risk of coronary artery disease in both sexes.
Atherogenesis is the name given to the process by which atherosclerosis is stimulated and accelerated. Most cholesterol is of course atherogenic, as are abnormally high levels of lipids (fatty acids and fat-soluble substances) and of fibrinogens (clotting proteins in blood plasma). Equally atherogenic are dysfunctions of glucose metabolism through which the body breaks down and uses carbohydrate energy. In their more extreme forms, these dysfunctions of glucose intolerance and insulin resistance (the failure of insulin to process glucose at normal levels) become diabetes. Yet they begin to accelerate the deterioration of arteries well before becoming so serious.
Hypertension is intimately linked with these conditions in a variety of ways. Firstly, it is often associated with them in “clusters”. For example, insulin resistance and hypertension are quite likely to occur in the same individual, partly (but only partly) because they often share the common denominator of overweight. Hypertensive women are twice as likely to be obese as normotensive women, yet are more than three times as likely to have diabetes. Hypertensives are also likelier to have high total cholesterol and low levels of beneficial high-density lipoprotein cholesterol, as well as a number of other atherogenic conditions known to contribute to heart disease. This phenomenon is known as risk factor clustering.
Furthermore, hypertension not only makes other atherogenic conditions more likely to occur, it also increases their effect when they do. Cholesterol, to take one example, does more damage when the blood it floats in is under high pressure. Not all of the circulatory system of the body is under uniform pressure. Pressure is much lower in the veins and arterioles than in the large arteries, and atherogenesis does not generally occur in these low-pressure spots, but in the areas where pressures are highest. Given that high pressure spots within an individual are clearly more susceptible to atherogenesis, it’s hard not to conclude that individuals with higher overall blood pressure are also more susceptible. That conclusion is supported by statistical evidence.
The strongest association between hypertension and another potent coronary risk factor is left ventricular hypertrophy, or the abnormal enlargement of the lower left chamber of the heart, the chamber that receives arterial blood and pumps it into the aorta. Hypertensive men and women are respectively eight and nine times more likely to manifest this condition than their peers with normal blood pressure, and left ventricular hypertrophy is one of the most potent indicators of future stroke, cardiac failure and coronary heart disease.
The detection of left ventricular hypertrophy (a condition which can improve) is just one of the many weighty reasons for recommending regular electrocardiogram testing in hypertensive individuals. The detection of silent myocardial infarctions (heart attacks of which the patient is not aware) is another.
Cardiologists have become aware in recent years of a growing web of interconnection between risk factors once considered independent or only loosely associated. Hypertension, insulin resistance, low levels of high-density lipoprotein (beneficial) cholesterol, high levels of other cholesterols, of fibrinogens, of lipids, of insulin and of blood sugars are all intimately joined together in a pathology, still only partly understood, of athereosclerosis and cardiovascular disease.
For that reason, treatment of hypertension can no longer afford to concentrate only on the reduction of blood pressure, but must look at other risk factors and try to reduce clustering. Sixty percent of all hypertensive victims of a cardiovascular event have only mild hypertension; in most of those cases, it is the presence of other risk factors combined with hypertension that tips the balance. Diagnosis and treatment of hypertension should be accelerated and diversified to look at the wider risk profile, not only because this condition affects so many people, but also because effective treatments to reduce it already exist.
Comment from Cardiologist: The number-one identified predisposing factor for the development of hypertension is: get fat. The attributable risk we calculated in Framingham for people who started off normotensive and developed hypertension under observation was as high as 70%; in other words, we can attribute 70% of hypertension to people getting fat. High salt and low potassium intake, not enough exercise, insulin resistance and glucose intolerance, and excess alcohol consumption are also contributing factors.
This post has been viewed 3043 times.
Comments are closed.
