« Angina | Main | Dementia »
Coronary Heart Disease
Coronary heart disease (CHD), also called coronary artery disease (CAD) and atherosclerotic heart disease, is the end result of the accumulation of atheromatous plaques within the walls of the arteries that supply the myocardium (the muscle of the heart). While the symptoms and signs of coronary heart disease are noted in the advanced state of disease, most individuals with coronary heart disease would have evidence of disease decades before the first symptoms arise. After decades of progression, some of these atheromatous plaques may rupture and (along with the activation of the blood clotting system) start limiting blood flow to the heart muscle. Current views are that an inflammatory process of the lining of the arteries, though poorly understood in specifics, promotes the disease progression.
Atherosclerotic heart disease can be thought of as a wide spectrum of disease of the heart. At one end of the spectrum is the asymptomatic individual with atheromatous streaks within the walls of the coronary arteries (the arteries of the heart). These streaks represent the early stage of atherosclerotic heart disease and do not obstruct the flow of blood. A coronary angiogram performed during this stage of disease may not show any evidence of coronary artery disease, because the lumen of the coronary artery has not decreased in caliber.
Over a period of many years, these streaks increase in thickness. While the atheromatous plaques initially expand into the walls of the arteries, eventually they will expand into the lumen of the vessel. As the plaques expand into the lumen of the vessel, they can affect the flow of blood through the arteries. While it was originally believed that the growth of atheromatous plaques was a slow, gradual process, some recent evidence suggests that the gradual buildup of plaque may be complemented by small plaque ruptures which cause the sudden increase in the plaque burden due to accumulation of thrombus material.
Atheromatous plaques that cause obstruction of less than 70 percent of the diameter of the vessel rarely cause symptoms of obstructive coronary artery disease. As the plaques grow in thickness and obstruct more than 70 percent of the diameter of the vessel, the individual develops symptoms of obstructive coronary artery disease. At this stage of the disease process, the patient can be said to have ischemic heart disease. The symptoms of ischemic heart disease are often first noted during times of increased workload of the heart. For instance, the first symptoms include exertional angina or decreased exercise tolerance.
As the degree of coronary artery disease progresses, there may be near-complete obstruction of the lumen of the coronary artery, severely restricting the flow of oxygen-carrying blood to the myocardium. Individuals with this degree of coronary heart disease typically have suffered from one or more myocardial infarctions (heart attacks), and may have signs and symptoms of chronic coronary ischemia, including symptoms of angina at rest and flash pulmonary edema.
A distinction should be made between myocardial ischemia and myocardial infarction. Ischemia means that the amount of oxygen supplied to the tissue is inadequate to supply the needs of the tissue. When the myocardium becomes ischemic, it does not function optimally. When large areas of the myocardium becomes ischemic, there can be impairment in the relaxation and contraction of the myocardium. If the blood flow to the tissue is improved, myocardial ischemia can be reversed. Infarction means that the tissue has undergone irreversible death due to lack of sufficient oxygen-rich blood.
It is interesting to note that an individual may develop a rupture of an atheromatous plaque at any stage of the spectrum of coronary heart disease. The acute rupture of a plaque may lead to an acute myocardial infarction (heart attack). It is unclear at present which plaques in an individual are more likely to rupture in the future and cause a heart attack.
Pathophysiology of Coronary Heart Disease
Limitation of blood flow to the heart causes ischemia (cell starvation secondary to a lack of oxygen) of the myocardial cells. When myocardial cells die from lack of oxygen, this is called a myocardial infarction (commonly called a heart attack). It leads to heart muscle damage, heart muscle death and later scarring without heart muscle regrowth.
Myocardial infarction usually results from the sudden occlusion of a coronary artery when a plaque ruptures, activating the clotting system and atheroma-clot interaction fills the lumen of the artery to the point of sudden closure. The typical narrowing of the lumen of the heart artery before sudden closure is typically 20%, according to clinical research completed in the late 1990s and using IVUS examinations within 6 months prior to a heart attack. High grade stenoses exceeding 75% blockage, such as detected by stress testing, were found to be responsible for only 14% of acute heart attacks. The events leading up to plaque rupture are only partially understood. Myocardial infarction is also caused, far less commonly, by spasm of the artery wall occluding the lumen, a condition also associated with atheromatous plaque and CHD.
CHD is associated with smoking, obesity and hypertension. A family history of CHD is one of the strongest predictors of CHD. Screening for CHD includes evaluating homocysteine levels, high-density and low-density lipoprotein (cholesterol) levels and triglyceride levels.
Preventing Heart Disease Symptoms
Coronary heart disease is the most common form of heart disease in the Western world. Prevention centers on the modifiable risk factors, which include blood sugar, lipoprotein transport systems, obesity, homocysteine, hypertension, sedentary lifestyle, dietary choices, smoking, uric acid, and omega 3 oils. An increasingly growing number of other physiological markers and homeostatic mechanisms are currently under scientific investigation.
Individuals with CHD are advised to avoid fats that are readily oxidized (e.g., saturated fats and trans-fats), limit carbohydrates and processed sugars to reduce production of Low density lipoproteins while increasing High density lipoproteins, keeping blood pressure normal, exercise and stop smoking. These measures limit the progression of the disease. Recent studies have shown that dramatic reduction in LDL levels can cause mild regression of coronary heart disease.
Risk factor management is carried out during cardiac rehabilitation, a 4-phase process beginning in hospital after MI, angioplasty or heart surgery and continuing for a minimum of three months. Exercise is a main component of cardaic rehabiltation along with diet, smoking cessation and blood pressure and cholesterol management.
Preventative Heart Disease with Diet
Vegetarians have been shown to have a 24% reduced risk of dying of heart disease (source: Key TJ, Fraser GE, et al. 1999, Sep. Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am J Clin Nutr, 70:516S-524S). This is not surprising, as plant foods are low in saturated fat and have no cholesterol.
The most powerful cholesterol-lowing agents are soluble fiber, unsaturated fats, and phytochemicals, all of which are found almost exclusively in plant foods. In the seventeen studies conducted between 1978 and 2002, the average vegan’s cholesterol level was a mere 160 mg/dl, while the average non-vegetarian’s cholesterol was 202 mg/dl. (source: Norris, J. 2003, March. Making Sense of Nutritional Research.)
Physicians such as Dr. Dean Ornish and Dr. Caldwell Esselstyn have actually stopped and even reversed heart disease in patients by putting them on programs that include plant-based diets.
Despite the strong benefits of a vegetarian diet, it is likely that with a few changes to the typical vegetarian diet, the risks of heart disease could be reduced even further. Vegetarian diets are sometimes low in Vitamin B12, which can lead to increased homocystein levels--a risk factor for heart diease. Since vegetarians don't eat fish, some vegetarians don't have high intakes of Omega-3 fatty acids. There is strong evidence that higher intakes of Omega-3 fatty acids reduce the risk of heart disease. Both of these shortcomings can be easily overcome by taking a vitamin B12 supplement and increasing intake of omega-3 fatty acids via ground flax seeds or flax oil, walnuts, and canola oil. There is some evidence that flax may be even more beneficial than fish oil in its effectiveness in reducing C-reactive protein, an indicator of heart disease.
Cretan Mediterranean-Style diet
The Seven Country Study found that Cretan men had exceptionally low death rates from heart disease, despite moderate to high intake of fat. The Cretan diet is similar to other traditional Mediterranean diets: lots of olive oil and bread, abundant fruit and vegetables, a moderate amount of wine, and a small amount of animal products. However, the Cretan diet consisted of less fish and wine consumption than some other Mediterranean-style diets, such as the diet in Corfu, another region of Greece, which had higher death rates.
The Lyon Heart Study set out to mimic the Cretan diet, but adopted a pragmatic approach. Realizing that some of the people in the study would be reluctant to move from butter to olive oil, they used a margarine based on rapeseed (canola) oil. The dietary change also included 20% increases in fruit and bread and decreases in processed and red meat. On this diet, mortality from all causes was reduced by 70%. This study was so successful that the ethics committee decided to stop the study prematurely so that the results of the study could be made available to the public immediately.
Posted by Staff at May 16, 2005 8:55 PMblog comments powered by Disqus