The Process of Atherosclerosis

Many diseases can affect the heart, but the most common one is atherosclerosis. The word was first introduced in 1904 and is derived from two Greek words: athera, meaning “porridge” or “gruel”; and scleros, meaning “hard.”

One of the earliest signs of atherosclerosis is called the “fatty streak.” These lesions are made up of specialized white blood cells that have eaten up (phagocytized) cholesterol. In the developed world, the process of atherosclerosis begins in childhood.

We are still unraveling what happens as plaque builds up in arteries; for reasons that are not totally understood, veins do not build up plaque. We do know that anything that injures the artery, such as smoking, makes it more apt to develop plaque.

Arteries are made up of three layers. The thin, innermost layer, called the intima, or endothelium, forms the main protective barrier against harmful agents that may travel in the blood, such as carbon monoxide and other poisons given off by cigarette smoke. The next layer, the media, is made up mainly of smooth
muscle cells that can contract and relax, allowing the artery to constrict in response to something like hemorrhage or to dilate in response to anything that increases the demand for blood, such as exercise. The outermost layer is called the adventitia, and it is made up mainly of connective tissue, which gives
support to the artery.

Multiple agents can injure the innermost wall of the artery, among them high levels of LDL cholesterol, high blood pressure, high levels of blood sugar as is seen in diabetes, and many of the toxins in cigarette smoke. When LDL cholesterol enters the blood vessel wall, it sets off an inflammatory reaction.

Inflammation is the body’s attempt to seal off an area of injury, remove it, and begin the process of
healing the damage. Key to the inflammatory process is a special kind of white blood cell called a monocyte. When monocytes sense inflammation, they rush to the site and turn themselves into macrophages (literally “big eaters,” from the Greek words macros for “large” and phagein for “eat”), which gobble up the LDL cholesterol particles and, in the process, become what are called foam cells. Over time, with recurrent injury to the vessel wall, these foam cells accumulate, smooth muscle cells and fibrous tissue cells migrate into the intima in an attempt to wall off the injury, and the resultant plaque can start to narrow the arterial lumen, obstructing the blood flow. The plaque becomes covered by a fibrous cap, a covering of scar tissue that walls off the plaque and its contents from the bloodstream.

If a coronary artery develops so much plaque that not enough blood reaches the heart muscle, ischemia results. Heart muscle that is starved for oxygen is said to be ischemic, and people who have ischemic heart muscle often experience the symptom we call angina pectoris. It is predictably brought on by exercise or emotional stress and goes away in a few minutes with rest, relaxation, or a medicine called nitroglycerin.

But it is not just the extent to which plaque buildup interferes with blood flow that is important. Also crucial is how stable or unstable the plaque is. An unstable plaque is one with more liquid fat, a thinner fibrous cap, and more inflammatory cells. When an unstable plaque ruptures, the contents of the plaque come into contact with the bloodstream. The body tries to wall off this injury by forming a clot. If the clot totally blocks blood flow through that artery, the tissue downstream of the clot dies unless blood flow is restored promptly. If this occurs in the heart, a heart attack (myocardial infarction) results. If this occurs in the brain, a stroke results. In fact, most heart attacks are caused not by plaques that narrow the artery to a great extent but by unstable plaques that block the opening in the range of 10 percent to 40 percent.

Atherosclerotic cardiovascular disease is quintessentially a lifestyle disease. But as we’ve grown addicted to calorically dense, nutritionally deficient fast food, overweight if not obese (two-thirds of Americans), and far too often too busy or too lazy to exercise, we prefer to believe that a pill will take care of the damage we inflict on our bodies.

 

 

 

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