Introduction to How Heart Disease Works

blocked artery
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Heart disease is the leading cause of death in the United States. Learn about heart disease, risk factors for heart disease, angina and heart attacks.

Heart disease is the leading cause of death in the U.S. At some point in your life, either you or one of your loved ones will be forced to make decisions about some aspect of heart disease. Knowing something about the anatomy and functioning of the heart, in particular how angina and heart attacks work, will enable you to make informed decisions about your health.

Heart disease can strike suddenly and require you to make decisions quickly. Being informed prior to an emergency is a valuable asset to you and your family.

In this article we will discuss various heart diseases and how they can lead to a heart attack, or even a stroke. We will also look at how heart attacks are treated and what you should do to prevent heart disease.

The basics Coronary Artery Disease (CAD), Coronary Heart Disease (CHD), Ischemic Heart Disease (IHD) and Arteriosclerotic Cardiovascular Disease (ASCVD) are all different names for the same disease. This disease is caused by atherosclerosis, which is a buildup of fatty deposits (atheroma) in the coronary arteries. See the figure below:

Coronary arteries supply blood to the heart muscle. When a blockage occurs in one of these arteries, blood flow to the heart muscle is decreased. This becomes most evident during exertion. During exertion, the heart muscle is working harder and needs more oxygen-enriched blood than usual. By preventing the much needed increase in blood flow, the blockage deprives the heart muscle of oxygen thereby causing the heart muscle to hurt. This chest pain is called angina or Angina Pectoris. When the heart muscle goes without sufficient oxygen, the muscle is said to be ischemic. If cell death occurs it is called infarction. Since a heart attack is cell death of heart muscle (myocardium), it is called a Myocardial Infarction (MI). The condition that causes CAD, angina and heart attacks is called atherosclerosis.

Arteriosclerosis is a more general term for hardening of the arteries. Atherosclerosis is a type of arteriosclerosis that causes a buildup of fatty material (referred to as atheromas and plaques) along the inner lining of arteries. Depending on where these blockages occur, they can cause a number of different outcomes:

  • If the blockage occurs in a coronary artery, it causes chest pain (angina).
  • If the blockage is complete, it can cause a heart attack (Myocardial Infarction or MI).
  • If the blockage occurs in one of the arteries near the brain, a stroke can occur.
  • If a blockage occurs in a leg artery, it causes Peripheral Vascular Disease (PVD) and can cause pain while walking called intermittent claudication.
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­Atherosclerosis takes many years, even decades to develop and the condition can easily go unnoticed. Sometimes symptoms such as angina will gradually indicate the condition. However, it can also become evident in a sudden and severe way, in the form of a heart attack.

Let's take a look at some of the risk factors for atherosclerosis. Some of these factors are things you can control. By being proactive, you could reduce your risk.



Atherosclerosis: Are You at Risk?

There are many risk factors that increase the likelihood of developing atherosclerosis and CAD. These include:

  • hypertension (high blood pressure)
  • diabetes
  • elevated cholesterol
  • smoking
  • sedentary lifestyle
  • stress
  • obesity
  • male sex
  • family history of heart disease
  • older age

Obviously, some of these risk factors can be changed or controlled (on your own or with the help of your physician) and some cannot. And, some of these risk factors have an effect on each other. For example, many people can lower their blood pressure by simply giving up smoking. Also losing weight can help:

  • control blood sugar in diabetes
  • lower blood pressure
  • lower cholesterol

Age, Sex, Family history
You cannot control your age, family history, or gender. However, you can use these risk factors as impetous to take control of those risk factors you can change. Because heart disease is more common as we age, it is even more important to pay attention to your weight, blood sugar, cholesterol levels, blood pressure and exercise regimen. Men, in general, are at increased risk for coronary artery disease. When women reach menopause and the protective effect of the estrogen hormone is lost, the risk among genders becomes equalized. Keep in mind that while estrogen replacement may reduce a woman's risk of heart disease, there's a slightly increased risk of some cancers. Also, CAD is more common if you have a close relative (mother, father, sibling) who has had CAD at an early age.

Hypertension
Hypertension (elevated blood pressure)is a risk factor for CAD. Hypertension can also lead to strokes, kidney disease, and aneurysms. Also, hypertension causes the heart to work harder and can lead to Congestive Heart Failure. Your blood pressure (BP) has two numbers. In a blood pressure reading, the upper number is called the systolic blood pressure. A systolic BP less than 140 is considered normal. The lower number is called the diastolic BP. A diastolic BP less than 90 is considered normal. Blood pressure that is slightly higher than this is called mild hypertension and can sometimes be reduced by weight loss, cessation of smoking, and decreased salt intake. However, medications may sometimes be necessary. There are six classes of medications to treat hypertension. These are:

  • Diuretics - Also known as "water pills" these medications -- such as hydrochlorothiazide and furosemide -- excrete extra water and salt to lower blood pressure.
  • Anti-Adrenergic drugs - Commonly called alpha and beta blockers, include medications such as Prazosin, Terazosin, Doxazosin, and Propranolol, Metoprolol and Atenolol. These block a part of the nervous system that increases blood pressure.
  • Vasodilators - Medications such as Hydralazine and Minoxidil work by relaxing blood vessels to lower blood pressure.
  • ACE (angiotensin converting enzyme) inhibitors - These medications work by dilating (enlarging) blood vessels by preventing the production of angiotensin which is a vasoconstrictor (blood vessel constrictor). Some commonly prescribed ACE inhibitors are Captopril, Enalapril, Lisinopril and Benazepril.
  • Angiotensin receptor antagonists - Medications such as Losartan and Valsartan are similar to ACE inhibitors and block the effects of angiotensin instead of preventing its production.
  • Calcium channel blockers - Because they block the calcium flow into cells which is needed to constrict blood vessels, medications such as Diltiazem, Verapamil, and Nifedipine work by dilating blood vessels.

Smoking
Smoking leads to CAD as well as many other illnesses such as COPD (chronic obstructive pulmonary disease which includes emphysema, asthma and chronic bronchitis). It also causes lung cancer, strokes and many other illnesses. Smoking may increase atherosclerosis as well. The nicotine in cigarettes causes constriction in blood vessels which causes an increase in blood pressure thereby causing the heart to work harder. Furthermore, nicotine may constrict coronary arteries and reduce blood flow to the heart muscle.

There are many ways to stop smoking. Usually it is best to quit completely either by yourself or with the help of support groups, along with the use of nicotine gum or a nicotine patch.

Elevated cholesterol
There is a definite relationship with elevated cholesterol and CAD. Cholesterol is transported in the blood by lipoproteins. Two of these lipoproteins are low density lipoprotein (LDL) and high density lipoprotein (HDL). An elevated level of LDL (the bad cholesterol) is associated with an increased risk of CAD. An elevated level of HDL (the good cholesterol) is associated with a decreased risk of CAD. Cholesterol levels can be lowered by eating a diet low in meat, eggs and dairy products. However, most of the cholesterol in the blood is produced in the liver. If a low fat diet does not sufficiently reduce your cholesterol, then your physician can prescribe medications to do so. There are four classes of medications that lower cholesterol:

  • Bile acid binding resin medications, such as cholestyramine and cholestipol, bind bile salts and prevent their reabsorption so that the body uses its cholesterol to keep making more bile salts.
  • Nicotinic acid (Niacin) decreases the production of LDL.
  • HMG-CoA reductase inhibitors decrease cholesterol synthesis. These medications include Lovastatin, Pravastatin, Simvastatin and Atorvastatin.
  • Fibric acid derivatives such as Gemfibrozil increase HDL and decrease triglyceride levels.

Obesity
Obesity is defined as being 20% over maximum desirable weight for your height. The Body Mass Index (BMI) is the most widely used formula for determining obesity: (weight/height2). A BMI of 20-25 is considered good, over 27 is considered overweight, and over 30 is considered obese. To calculate your BMI, visit this Web site. Obesity increases the risk of heart disease by increasing other risk factors such as high blood pressure, diabetes, and lowering HDL (good cholesterol).

Diabetes Mellitus
Diabetes Mellitus increases the risk of heart disease because it elevates cholesterol levels and increases atherosclerosis. Furthermore, people with diabetes are often overweight thereby exacerbating their diabetes and increasing the risk of heart disease. There are two types of Diabetes, Type I (insulin dependent) and Type II (non-insulin dependent). In Type I diabetes, very little or no insulin is produced by the pancreas so this condition is treated with insulin. In Type II diabetes, insulin is still being produced by the pancreas but the body is resistant to it. Type II diabetes can be treated by weight loss, a modified diet and an exercise regimen. If these methods are unsuccessful, medications called Oral Hypoglycemics are used. By increasing the secretion of insulin by the pancreas, these medications usually work. However, if these fail, insulin may be necessary.

Stress
High levels of stress and having what is known as a "Type A personality" may be risk factors for heart disease. Stress can cause your heart to work harder by increasing your blood pressure and pulse. Learning to calm down, slow down, and relax can help ease the effects of stress. It can also be beneficial to avoid caffeine and nicotine, and incorporate some type of exercise regimen into your daily routine.

Sedentary Lifestyle
Having a sedentary lifestyle leads to being overweight which can then lead to diabetes and elevated blood pressure -- both are risk factors for CAD. Exercise may lower LDL and increase HDL. It also strengthens the heart and increases its efficiency as well as the efficiency of the body's use of oxygen. People who exercise generally have a slower pulse and this puts less strain on the heart.

In the following sections, we'll look closely at angina and heart attack, two conditions that can result from atherosclerosis.

Angina

When Coronary Artery Disease (CAD) causes chest pain, it is called Angina Pectoris. Approximately 6.2 million people in the U.S. have been diagnosed with Angina Pectoris. It is usually described as a heaviness, pressure, squeezing, or aching in the substernal (front, central area) of the chest. Anginal pains can radiate to the left shoulder or down the left arm, back, neck, jaw and only occasionally down the right arm. It occurs with exertion and resolves with rest. Usually it lasts only a few minutes. Sometimes an onset can occur during a heavy meal, cold weather or increased emotional stress. Angina should not be worsened by deep breaths, bending over, pressing on the chest, or twisting in certain positions. Sometimes it can be confused with indigestion.

While the physical examination of someone with angina is often normal, sometimes the signs of other diseases that are risk factors for CAD can be detected during the exam.

Certain laboratory tests will be abnormal during a heart attack (CPK, CPK-MB, Troponin, Myoglobin) when heart muscle cells die. However, these tests will be normal during angina because the lack of oxygen to the cells is temporary and cell death does not occur. Your physician may want to check your total cholesterol level as well as HDL and LDL levels. Also your blood sugar or fasting blood sugar should be checked to see if diabetes is present.

EKG
ST segment (the line between the QRS complex and the T wave) depression and T wave changes (usually inversion) are the hallmarks of ischemia. However, an EKG in someone with a history of CAD and angina often has a "normal" reading. If an EKG is done during an episode of angina, sometimes the typical ST segment depression can be seen.

Stress Test
Because a resting EKG often results in a "normal" reading for a person with angina, your physician may need to have a stress test to evaluate the presence of CAD. As described earlier, if the characteristic ST segment depression occurs during stress testing, especially if typical chest pain occurs, the test is considered "positive".

Cardiac Catheterization
A cardiac catheterization test can be used to determine if CAD is present, how severe it is and determine if a coronary artery bypass graft is needed. It can definitely exclude CAD if it is not present. This test is performed for many reasons. It is especially important if:

  • angina symptoms continue, even though your condition is being treated by a physician
  • severe ischemia is present on a stress test and symptoms suggestive of CAD are present, but the doctor is not able to determine the diagnosis with other tests
  • multiple hospital admissions for chest pain occur in which heart attack is ruled out but the presence of CAD has not been determined

During a cardiac catheterization, blockages are treated as a balloon is blown up inside the coronary arteries, thereby opening the passage. This procedure is called Percutaneous Transluminal Coronary Angioplasty (PTCA) or just plain angioplasty. Here is an example of how an angioplasty works:

angioplasty diagram

The most important factors that determine the course and outcome of Coronary Artery Disease (CAD) are the functional ability of the Left Ventricle and the number, location and severity of the blockages. Although it obviously can lead to heart attacks and death, many people lead long productive lives despite CAD.

The treatment of CAD consists of the prescription of medications, controlling risk factors, treating aggravating conditions and sometimes angioplasty or coronary artery bypass surgery. Conditions that aggravate CAD include anemia, lung disease, hypertension, obesity and hyperthyroidism; treating these problems can help with CAD. The treatment of risk factors helps to slow down the progression of CAD as well as prevent CAD.

Some medications that are used to treat angina include:

  • Nitrates - Nitrates are medications that come in many forms such as sublingual (under the tongue) pills or spray, nitrate pills (Isosorbide), and nitroglycerin patches. These medications work by dilating the veins and therefore decreasing the oxygen requirements of the heart. They also dilate the coronary arteries and consequently increase blood flow to the heart muscle. Sublingual nitroglycerin is used during an episode of angina. One tablet or a single spray under the tongue can be used every five minutes up to three times. A burning feeling is usually felt under the tongue and frequently a headache occurs. Anginal chest pain usually resolves within a few minutes. Nitrate pills and patches can also be used for angina. These medications tend to have less effectiveness over time due to tolerance. Therefore, a medication free period of 8 to 12 hours per day is recommended.

  • Beta-Blockers - Beta-Blockers decrease the heart rate and the force of the heart's contraction by blocking the effects of the sympathetic nervous system on the heart. This class of medications reduces heart attacks and decreases mortality in patients who have had heart attacks. Medications in this class include Propranolol, Metoprolol, and Atenolol. These medications are extremely useful but sometimes have side effects that may limit their use in some people.

  • Aspirin - Platelets are necessary for clotting. Aspirin is an anti-platelet medication that prevents platelets from clotting and clumping on blood vessel walls. If this were to occur in a coronary artery, a heart attack could result. The exact dose of Aspirin is not clear, but usually a baby aspirin, one-half of an adult aspirin, or one adult aspirin is given per day. Aspirin may have side effects such as stomach upset or bleeding, or allergies. People who are allergic to aspirin can take another anti-platelet medication called Ticlopidine.

Unstable Angina
Often a person with angina has pain with a predictable amount of exertion. This is called stable angina. Unstable angina exists when the angina worsens. Unstable angina is defined as more frequent episodes of anginal chest pain with less exertion, anginal chest pain at rest, or new onset of severe angina. This usually means a worsening of the Coronary Artery Disease (CAD), with a larger obstruction. This condition can quickly lead to a heart attack and is especially true if unstable angina is associated with certain EKG changes. Persons with unstable angina are hospitalized to treat the unstable angina and to determine if a heart attack has occurred.

Nitrates (such as nitroglycerin) are used to relieve chest pain. This can be given sublingually or intravenously (through the vein). Heparin, a potent anti-clotting drug, is used to prevent the worsening obstruction in the coronary artery from becoming complete. Recently, new anti-clotting medications have been introduced called IIb/IIIa inhibitors (Abciximab or Tirofiban) that are used in unstable angina. In addition, patients are started on aspirin and often a beta-blocker as well. If these medications are insufficient, then a cardiac catheterization can be performed to determine the location and severity of any blockages. Often an angioplasty can be performed at the same time. Sometimes an angioplasy is not possible, then a coronary artery bypass graft may be necessary.

In the next section, we'll discuss heart attacks.

Heart Attack

Heart Attack

A Heart Attack (Myocardial Infarction, or MI) occurs when a coronary artery is completely obstructed and no blood flows past the obstruction. As a result, that part of the heart muscle dies. This obstruction is caused by a clot and occurs in an artery that previously had an atherosclerotic plaque.

According to the American Heart Association, more than one million heart attacks occur per year in the U.S.

Some people think that every episode of chest pain or angina is actually a heart attack. This is not correct; angina is reversible and does not cause death of the heart muscle cells. Some people think that when you have a heart attack your heart stops beating. Although heart attacks can lead to this, the proper term for when the heart stops beating is cardiac arrest.

Chest pain is obviously the most common symptom of an MI. The chest pain of an MI is similar to that of angina but is usually more severe and lasts longer. Typically, it is described as tightness, squeezing, pressure, aching or heaviness. The pain is located in the substernal (front and center) part of the chest and can radiate to the left arm, back, neck or jaw. Associated symptoms include shortness of breath, nausea, vomiting, profuse sweating and sometimes a feeling of impending doom.

To confirm the diagnosis of an MI, an EKG and blood tests are performed.

  • EKG
    During an MI, the EKG goes through a series of abnormalities. The initial abnormality is called a hyperacute T wave. This is a T wave that is taller and more pointed than the normal T wave. The abnormality lasts for a very short time, and then elevation of the ST segment occurs. This is the hallmark abnormality of an acute MI. It occurs when the heart muscle is being injured by a lack of blood flow and oxygen and is also called a current of injury. This is followed by T wave inversions. Over time, when the heart muscle cells actually die, these abnormalities are replaced with Q waves. However, not everyone with an MI has an abnormal EKG. In fact the initial EKG may not show ST elevation in up to 40% of patients having an MI. When a Q wave develops after an MI, it is called a Q-wave MI and usually corresponds to a transmural MI (entire thickness of the heart muscle wall has died). When a Q wave does not develop after an MI, it is called a non-Q-wave MI and usually corresponds to non transmural heart muscle death or a subendocardial MI(heart muscle just under the inner lining of the heart has died). An EKG can not only tell a physician if an MI is present but can also show the approximate location of the heart attack and often which artery is involved. When the EKG abnormalities mentioned above occur in certain of the 12 EKG leads, then the MI can be localized to a certain region of the heart. For example, see the table below:

EKG leadsLocation of MICoronary Artery
II, III, aVFInferior MIRight Coronary Artery
V1-V4Anterior or Anteroseptal MILeft Anterior Descending Artery
V5-V6, I,aVLLateral MILeft Circumflex Artery
ST depression in V1, V2Posterior MILeft Circumflex Artery or Right Coronary Artery

Note: there are many anatomic variations that may alter the exact artery involved in any particular person.

  • Lab tests
    Certain blood tests read as "abnormal" after an MI has occurred because when heart muscle cells die, the chemicals in these cells are released into the blood. This does not occur instantly and usually takes several hours and it is why your doctor cannot always tell you if you are having an MI on the spot. Because results can take some time to develop, you may need to be admitted to the hospital to have a series of EKGs and blood tests to catch the abnormalities when they happen in order to determine if an MI has occurred.

    These chemicals are called markers of MI and include CPK, CPK-MB, Troponin, and Myoglobin. Some of these markers occur in other cells and can limit their usefulness in diagnosing an MI.

Lab TestBegins to risePeakDurationFound in
CPK4-8 hours
-
48-72 hoursHeart, Brain, Skeletal Muscle
CPK-MB3-4 hours12-24 hours48 hoursHeart
Myoglobin1-2 hours4-6 hours24 hoursHeart, Skeletal Muscle
Troponin3-6 hours12-24 hours1 weekHeart


Treatment of MI

Initially a patient is placed on a cardiac monitor because of the risk of cardiac arrhythmias which can occur during an MI. Ventricular fibrillation is one such arrhythmia and is a frequent cause of death in patients with MI who do not survive to reach the hospital. Approximately 250,000 people die per year of a heart attack before reaching a hospital. Ventricular fibrillation causes death in a few minutes if untreated. Patient's are also placed on oxygen and intravenous lines are started. The chest pain of a heart attack is treated with Nitroglycerin (either sublingually or intravenously). Morphine is given if nitroglycerin is unable to relieve the pain. An aspirin should be given at this time as well. Beta-blockers and ACE inhibitors are given after MI's because they both are known to reduce mortality after an MI.

Thrombolytics
Streptokinase, TPA (Tissue Plasminogen Activator), and Reteplase are thrombolytic medications that dissolve blood clots in the coronary artery that causes the MI. These medications clearly decrease death from heart attacks. It is crucial that this medication be given quickly, as soon as an MI is diagnosed. If this medication is delayed, the cell death is permanent and cannot be reversed even if blood flow is restored by dissolving the clot. There is a common saying in medicine that "time is muscle" which means that the longer the heart muscle is without blood flow before thrombolytic medications can dissolve the clot, the more heart muscle dies. There is much controversy about which medication is the most effective. There are several contraindications to the use of these medications:

  • active internal bleeding
  • history of a stroke
  • cancer or aneurysm of the brain
  • recent brain or spinal surgery
  • known bleeding disorder
  • severe hypertension.

These medications have complications. Bleeding is the most common complication and usually occurs at I.V. sites. If the bleeding happens in the brain, it can cause a stroke and possibly death.

Angioplasty
Another treatment for MI is angioplasty. The obstruction is mechanically opened with a balloon during cardiac catheterization. Many cardiologists believe that this therapy has advantages over thrombolytics. However, an angioplasty must be performed within 60 minutes of the MI in a center that does a high volume of these procedures, to be most effective. Less than 20% of U.S. hospital have this capability.

Obviously, there are many complications of heart attacks. Some of the more common ones are:

  • Arrhythmias - variation from the normal heartbeat
  • premature ventricular beats
  • ventricular tachycardia
  • ventricular fibrillation
  • Accelerated idioventicular rhythm
  • AV node block
  • bradycardia
  • supraventricular tachycardia
  • Heart failure - The inability of the heart to pump out enough blood to meet the needs of the body. If 20-25% of the left ventricle becomes damaged from an MI, heart failure will result. Death usually results if over 40% of the heart is infarcted.
  • Cardiac rupture - The heart bursts open, rupture of papillary muscle (attaches to Mitral valve) or rupture of the Ventricular Septum (wall between right and left Ventricle)
  • Aneurysm of the left ventricle
  • Pericarditis
  • Blood clots
  • Repeat MI

Following a Miocardial Infarction (MI), several days of rest in the hospital are advised. A cardiac rehabilitation program should be a part of the recovery from an MI and includes an exercise program and education about heart disease and risk factors. A stress test is often performed at some point after an MI to assess the degree of ischemia and tolerance for exercise. If repeated episodes of chest pain and ischemia occur, you may need a cardiac catheterization to determine if an angioplasty or a coronary artery bypass graft is necessary.

Some medications that are given to post-MI patients include aspirin, beta-blockers, and ACE inhibitors.

After reading this article, one thing that you are probably thinking is this: "I don't want atherosclerosis!" One of the best parts about this disease is that there are things you can do to lower your risk factors. These include:

  • quitting smoking
  • reducing cholesterol levels
  • reducing blood pressure
  • losing weight
  • exercising

Hopefully this article has provided some insight into how the most common diseases of the heart work. Perhaps this can be an impetus to control the risk factors that can lead to heart disease. If you do develop CAD, then having a background knowledge will help immeasurably in your treatment.

For more information on heart disease and related topics, check out the links on the next page.

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About the Author
Dr. Carl Bianco, M.D. is an Emergency Physician practicing at Dorchester General Hospital in Cambridge, MD, located on the Eastern Shore of Maryland. Dr. Bianco attended Medical school at Georgetown University School of Medicine and he received his undergraduate degree from Georgetown University majoring in nursing and pre-med. He Completed an internship and residency in Emergency Medicine at Akron City Hospital in Akron, Ohio.