Your
Heart and How it Works
The normal heart is a strong, hard-working pump made of muscle tissue.
It's about the size of a person's fist.
The heart has four chambers. The upper two chambers are the right atrium and left atrium, and the lower two are the right ventricle and left ventricle. Blood is pumped through the chambers, aided by four heart valves. The valves open and close to let the blood flow in only one direction.
HEART ATTACKWhat is a heart attack?
A heart attack occurs when the blood supply to part of the heart muscle
itself -- the myocardium -- is severely reduced or stopped. The medical
term for heart attack is myocardial infarction. The reduction or stoppage
happens when one or more of the coronary arteries supplying blood to the
heart muscle is blocked. This is usually caused by the buildup of plaque
(deposits of fat-like substances), a process called atherosclerosis. The
plaque can eventually burst, tear or rupture, creating a "snag"
where a blood clot forms and blocks the artery. This leads to a heart
attack. A heart attack is also sometimes called a coronary thrombosis
or coronary occlusion.
If the blood supply is cut off for more than a few minutes, muscle cells
suffer permanent injury and die. This can kill or disable someone, depending
on how much heart muscle is damaged.
Sometimes a coronary artery temporarily contracts or goes into spasm.
When this happens the artery narrows and blood flow to part of the heart
muscle decreases or stops. We're not sure what causes a spasm. A spasm
can occur in normal-appearing blood vessels as well as in vessels partly
blocked by atherosclerosis. A severe spasm can cause a heart attack.
What causes a heart attack?
Atherosclerosis
Atherosclerosis is a gradual process in which plaques (collections) of cholesterol are deposited in the walls of arteries. Cholesterol plaques cause hardening of the arterial walls and narrowing of the inner channel (lumen) of the artery. Arteries that are narrowed by atherosclerosis cannot deliver enough blood to maintain normal function of the parts of the body they supply.
Smoking cigarettes, high blood pressure, elevated cholesterol, and diabetes mellitus can accelerate atherosclerosis and lead to the earlier onset of symptoms and complications, particularly in those people who have a family history of early atherosclerosis.
Coronary atherosclerosis (or coronary artery disease) refers to the atherosclerosis that causes hardening and narrowing of the coronary arteries. Diseases caused by the reduced blood supply to the heart muscle from coronary atherosclerosis are called coronary heart diseases (CHD). Coronary heart diseases include heart attacks, sudden unexpected death, chest pain (angina), abnormal heart rhythms, and heart failure due to weakening of the heart muscle.
Atherosclerosis and angina pectoris
Angina pectoris (also referred to as angina) is chest pain or pressure that occurs when the blood and oxygen supply to the heart muscle cannot keep up with the needs of the muscle. An insufficient supply of oxygen to the heart muscle causes angina.
Exertional angina usually feels like a pressure, heaviness, squeezing, or aching across the chest. This pain may travel to the neck, jaw, arms, back, or even the teeth, and may be accompanied by shortness of breath, nausea, or a cold sweat.
Angina also can occur at rest. Angina at rest more commonly indicates that a coronary artery has narrowed to such a critical degree that the heart is not receiving enough oxygen even at rest. Angina at rest infrequently may be due to spasm of a coronary artery (a condition called Prinzmetal's or variant angina). Unlike a heart attack, there is no permanent muscle damage with either exertional or rest angina.
Atherosclerosis and heart attack
Occasionally the surface of a cholesterol plaque in a coronary artery may rupture, and a blood clot forms on the surface of the plaque. The clot blocks the flow of blood through the artery and results in a heart attack. The cause of rupture that leads to the formation of a clot is largely unknown, but contributing factors may include cigarette smoking or other nicotine exposure, elevated LDL cholesterol, elevated levels of blood catecholamines (adrenaline), high blood pressure, and other mechanical and biochemical forces.
Some heart attacks are sudden and intense — the "movie heart attack," where no one doubts what's happening. But most heart attacks start slowly, with mild pain or discomfort. Often people affected aren't sure what's wrong and wait too long before getting help.
Warning signs and symptoms of a heart attack include:
§ Pressure, fullness or a squeezing pain in the center of your chest
that lasts for more than a few minutes
§ Pain extending beyond your chest to your shoulder, arm, back, or
even to your teeth and jaw
§ Increasing episodes of chest pain
§ Prolonged pain in the upper abdomen
§ Shortness of breath
§ Sweating
§ Impending sense of doom
§ Lightheadedness
§ Fainting
§ Nausea and vomiting
Risk
factors
Certain factors, called coronary risk factors, increase your risk of a
heart attack. These factors contribute to the unwanted buildup of deposits
(atherosclerosis) that narrows arteries throughout your body, including
arteries to your heart. Coronary risk factors include:
§ Tobacco smoke. Smoking and long-term exposure
to secondhand smoke damage the interior walls of arteries — including
arteries to your heart — allowing deposits of cholesterol to collect
and hamper blood flow. Smoking also increases the risk of deadly blood
clots forming and causing a heart attack.
§ High blood pressure. Blood pressure is determined
by the amount of blood your heart pumps and the amount of resistance to
blood flow in your arteries. Over time, high blood pressure can damage
arteries that feed your heart by accelerating atherosclerosis. High blood
pressure can be an inherited problem. The risk of high blood pressure
increases as you age.
§ High blood cholesterol or triglyceride levels.
Cholesterol is a major part of the deposits that can narrow arteries throughout
your body, including those that supply your heart. A high level of the
wrong kind of cholesterol in your blood increases your risk of a heart
attack.
§ Lack of physical activity. An inactive lifestyle
contributes to high blood cholesterol levels and obesity. Conversely,
people who get regular aerobic exercise have better cardiovascular fitness,
which decreases their overall risk of heart attack. Exercise is also beneficial
in lowering high blood pressure.
§ Obesity. Obesity raises the risk of heart disease
because it's associated with high blood cholesterol levels, high blood
pressure and diabetes.
§ Diabetes. Diabetes is the inability of your body
to produce or respond to insulin properly. Diabetes greatly increases
the risk of a heart attack by speeding up atherosclerosis and negatively
affecting blood cholesterol levels.
§ Stress. You may respond to stress in ways that
can increase your risk of a heart attack. If you're under stress, you
may overeat or smoke from nervous tension. Too much stress, as well as
anger, can also raise your blood pressure.
§ Alcohol. Consumed in moderation, alcohol helps
raise HDL levels — the "good" cholesterol — and
can have a protective effect against heart attack. On the other hand,
excessive drinking can raise your blood pressure and triglyceride levels,
increasing your risk of heart attack.
§ Family history of heart attack. . In addition,
families may contribute to coronary artery disease by practicing or promoting
poor health habits, such as smoking or eating high-fat diets.
§ Homocysteine, C-reactive protein and fibrinogen.
People who have higher blood levels of homocysteine, C-reactive protein
and fibrinogen appear to have an elevated risk of heart disease. These
factors have only recently been identified as players in increasing cardiovascular
disease risk