Heart disease has been the leading cause of death in the United States since the 1920s, although the number of deaths has been steadily declining since 1960 (Figure 1-3).18 Heart disease includes coronary heart disease (CHD), arrhythmia (irregular heart beat), congestive heart failure (ineffective heart contractions), heart infections, and congenital heart defects (birth defects).19,20 The term cardiovascular disease (CVD) is commonly used in place of heart disease, but it is a broader term that includes hypertension (high blood pressure) and stroke.20
More than 1 in 3 adults in the United States have one or more CVDs (approximately 83.6 million people).20 Older adults are affected at a higher rate than those younger than 40 years. Seventy percent of those aged 60 to 79 years have at least one CVD. The most common CVD is hypertension. An estimated 77.9 million (30%) Americans have high blood pressure. The second most common condition is CHD, with 15.4 million (approximately 6%) living with the disease.21 However, CHD has the highest rate of death. It has accounted for 49% of CVD deaths in 2009.20 There are significant differences in mortality between genders and races. Females develop CVD an average of 7 to 10 years later than males22 and survive for longer.23 However, Blacks have a higher mortality rate than Whites.24
Optimal function of the cardiovascular system depends on the health of the heart muscle, the lungs, the blood vessels, and the blood. If one segment of the system is not healthy, the others must work harder to make up for the deficit. The risk factors that are common to all CVDs have a negative impact on the function of the heart, lungs, blood, and blood vessels. These include a lack of regular physical activity, cigarette smoking, obesity, family history of CVD, diabetes mellitus, and high cholesterol.20 The links between cardiovascular risk factors and the development of the disease are strong. For example, blood vessels become rigid and inflexible due to the development of plague within their walls. Excess cholesterol in the blood stream starts the process by which those plagues form. The thicker, less flexible vessel walls then contribute to hypertension. The
Deaths from heart disease 1900 to 2010. (Reprinted with permission from National Heart, Lung, and Blood Institute. Diease statistics. http://www.nhlbi.nih.gov/about/documents/factbook/2012/chapter4#4_1. Accessed October 14, 2015.) role of physical activity in reducing cholesterol and blood pressure is discussed in Chapter 2. The study of how a disease begins and the steps it takes as it progresses is called etiology. When disease processes are well understood from years of research, the risk factors are closely tied to their etiologies.
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CVD originates with physical changes to blood vessels, whether in the heart (coronary arteries), brain (stroke), or arms and legs (peripheral artery disease). The opening through which blood flows is called the lumen. Healthy blood vessels have a smooth layer of epithelial cells that line the lumen. When there are high levels of low-density lipoproteins (LDLs) in the blood, some of the LDL molecules cross the lining into the area just above the muscle layer of the vessel wall called the intima. The LDLs irritate the endothelium and trigger an inflammatory response that brings white blood cells (monocytes) to the intima (Figure 1-4).25 The LDLs are treated as foreign invaders by the monocytes. Once a monocyte engulfs the LDL molecule, it transforms into a foam cell that hardens over time. This progress is continual so that a build-up of hardened foam cells creates atherosclerotic plaques inside the walls of arteries. Initially, the artery remodels and pushes the plaque outward away from the lumen. This allows the vessel to maintain its normal diameter. The surface of the lumen changes because of the plaque below becoming thinner.26 This fibrous cap is weaker and less flexible than the undamaged epithelium and is more likely to rupture.
When a rupture occurs, an even greater inflammatory response occurs, and the site is packed with platelets and macrophages trying to seal the break in the intima. This clot is called a thrombus and can slow or block blood flow through the artery. Rather than completely occluding an artery, a thrombus will heal as a scar on the inside of the lumen and slowly encroach on blood flow. The cells that get oxygen and nutrients from that blood vessel will die if they cannot get adequate blood flow. When those cells are heart muscle cells, the damage makes it harder for the heart to contract normally. If enough cells die, the heart will not be able to produce normal contractions, and the risk of a heart attack is high.27 Over time, if the plaque buildup in the vessel walls gets to be great, the artery will not be able to remodel the external wall of the vessel anymore, and the diameter of the lumen will shrink (see Figure 1-4) and restrict blood flow.26
Treatment for atherosclerosis includes medications for hypertension (beta blockers) and high cholesterol (statins). Changes in diet and physical activity are also suggested. Increasing
Figure 1-4. Atherosclerosis. (Reprinted with permission from Hao W, Friedman A. The LDL-HDL profile determines the risk of atherosclerosis: a mathematical model. PLoS One. 2014;9(3):e90497.) physical activity can reduce blood pressure,14 heart rate,14 and chronic inflammation.28 Dietary recommendations include reducing the intake of saturated fats and salt.29 If a coronary artery is nearly blocked by plaque or occluded, surgery is typically done. An angioplasty is a procedure in which a narrow tube with a balloon is placed in the artery and the balloon is expanded to push the plaque against the wall of the artery so that a larger opening is made.30 A stent is a small mechanical device that can be inserted into the artery to hold it open. A coronary bypass is another surgical option in which a section of healthy blood vessel is taken from another part of the body and connected to the heart so that the blood flow to the heart can be improved. Fortunately, the number of Americans having surgery for heart disease has been declining. Between 2007 and 2008, there were approximately 216,500 surgeries performed, down from 239,145 in 2005 and 2006.31
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