Cardiac Pet Scan

Positron Emission Tomograpy (PET) technology is a relatively new medical application that has become vital in the diagnosis and treatment of cardiac disease. Cardiac disease is the leading killer of Americans and was responsible for 700,142 deaths in the United States of America during the year 2001. During that same year, the number of new cardiac disease diagnoses was approximately 23 million, which makes up 11.5% of the American population. Broken down into age groups, cardiac disease is:

• The third leading cause of death among individuals who are between the ages of 0 and 14.
• The fifth leading cause of death among individuals who are between the ages of 15 and 24.
• The second leading cause of death among individuals who are between the ages of 25 and 64.
• The leading cause of death among individuals who are over 65 years of age or older.

In 2001, cardiac disease resulted in 700,142 deaths, which makes it the leading cause of death in the United States of America. A catchall term that refers to diseases of the heart and the blood vessel system that is contained within the death, cardiac disease refers to both heart disease and cardiovascular disease. Heart disease refers to diseases of the heart and the blood vessel system that is contained within the heart while cardiovascular disease refers to diseases of the heart and diseases of the blood vessel system that is contained within the entire body. The blood vessel system referred to in cardiovascular disease contains such organs as the brains, legs, and lungs.

To understand the specific types of heart diseases and cardiovascular disease as well as the use of PET imaging in their treatment, it is important to understand the different categories of heart and cardiovascular diseases:

• Ischemic Heart Disease: This category refers to diseases caused by blood flow obstruction. The most common form of blood flow obstruction is atherosclerosis, which causes coronary artery disease, and refers to the buildup of fats and calcium on the interior walls of the coronary arteries. Angina pectoris and myocardial infarction (MI) can also result from obstructed arteries.
• Angina: This refers to the chest pain that occurs as a reaction to the heart’s receiving an inadequate blood supply during periods of increased demand. Angina is a reaction to the coronary arteries’ inability to perform their natural reaction to expand to deliver the required blood to the heart muscle.
• Myocardial Infarction (MI): Commonly known as a heart attack, MI occurs when the blood supply to the heart muscle is either severely reduced or stopped. Often caused by antherosclerotic arteries, MI results in the area of the heart muscle served by the affected artery to weaken and die. MI can also be a product of an unexplained temporary spasm of a coronary artery.
• Valvular Heart Disease: This category of heart disease refers to disorders affecting the four heart valves that assist the pumping of blood by opening and closing by allowing blood to flow through the heart in only one direction when it contracts. The most common form of valvular heart disease is mitral valve prolapse (MVP), which refers to a condition in which a partial two-way blood flow occurs as the valve between the left atrium and ventricle does not shut tightly. Another form of valvular heart disease include mitral valve stenosis, a condition that results from rheumatic fever and creates a narrowing of the mitral valve, which creates difficulty for blood to flow through this valve.
• Cardiomyopathy: This category refers to any disease of the heart muscle. Different forms of cardiomyopathy includes: idiopathic cardiomyopathy, a condition with no known cause; hypertrophic cardiomyopathy, a condition in which heart muscle tissue grows improperly; viral cardiomyopathy, a condition caused by certain viruses; ischemic cardiomyopathy, a condtion caused by the destruction of heart muscle by numerous tiny infarctions; and hypertensive cardiomyopathy, a condition that results from untreated high blood pressure.
• Congestive Heart Failure: This condition occurs when normal blood flow in not maintained due to a condition affecting the proper function of the heart muscle. Causes of congestive heart failure include: damaged heart muscle or valves, improper functioning by the nerves governing heartbeat, anemia (a disease referring to blood deficiency), pulmonary emboli (a disease referring to blockages of the pulmonary artery), rheumatic fever, infections, or thyroid disease.
• Bacterial Endocarditis: This condition refers to infections of the heart valves and heart lining and is present in individuals with: structural abnormalities of the heart, valve malfunctions, artificial valves, or are injection drug users.
• Arrhythmia: This category refers to irregular heartbeats caused by a malfunction in the electronic signals that stimulate heartbeat. Forms of arrhythmia include bradycardia, a condition in which heart rate is less than 60 beats per minute and can prevent the heart from pumping enough blood to the body. Tachycardia is the condition in which heart rate is more than 100 beats per minute and can lead to the reduction of the heart’s ability to pump properly as the ventricular chambers of the heart do not have the needed time to fill with blood.
• Noncoronary Cardiovascular Disease: This category refers to diseases affecting the circulatory system but not directly the heart, the two most common forms of this disease are hypertension and stroke.
• Hypertension: More commonly known as high blood pressure, this condition occurs when blood pressure readings consistently exceed 140/90. The average blood pressure reading for adults is 120/80. The first number in the reading refers to diastolic pressure (the force of blood flow when the heart beats) and the second number represents the pressure between heartbeats when the heart is at rest. This condition can cause such health problems as heart failure, stroke, and kidney failure.
• Stroke: A condition in which an artery or arteries that provide blood flow to the brain have burst or become clogged by a blood clot. When blood flow is restricted to the brain, it leads to the deprivation of oxygen that blow carries and causes nerve cells to die in this area.

Cardiac disease can occur for a variety of reasons. Despite the myriad number of factors that can contribute to the onset of cardiac disease which are uncontrollable, such as aging and family health history, there are also a number of risk factors associated with cardiac disease that can be avoided. Such risk factors include:

• Smoking: Individuals that smoke increase their susceptibility to developing heart disease and/or cardiovascular disease. Smoking contributes to heart disease in a number of ways that includes: causing blood thickening that leads to clots, raising the level of carbon monoxide in the blood, and also depriving the heart and other tissues of oxygen. Additionally, nicotine in tobacco causes the heart to work harder as it raises blood pressure as well as constricts the coronary arteries.
• High Blood Pressure: Individuals with high blood pressure increase their susceptibility to developing heart disease and/or cardiovascular disease as high blood pressure causes the heart to work harder. Ways to control high blood pressure include improving diet to reduce weight levels and partaking in physical in regular physical exercise.
• High Blood Cholesterol: Individuals with high blood cholesterol levels increase their susceptibility to developing heart disease and/or cardiovascular disease as high blood cholesterol as high levels of low density lipoprotein (LDL) leaves deposits on the interior wall of the arteries and contributes to atherosclerosis. Ways to control high blood cholesterol levels include improving diet to reduce saturated fat and high cholesterol consumption and partaking in regular physical exercise.

As it produces no symptoms, cardiac disease is a difficult disease to detect in its early stages. Overt symptoms are not produced in its early stages and cardiac disease is a disease that takes many years to develop. Often referred to as a silent killer, there are some symptoms that is indicative of the possibility of cardiac disease and these symptoms include:

• Chest or arm discomfort during activity
• Unexplained feeling of fatigue
• Shortness of breath
• Feelings of dizziness or nausea
• Abnormal heart beats (palpitations)

In most cases, individuals are alerted to their cardiac disease through a heart attack or a stroke. The American Heart Association lists these warning signs of a stroke:

• Sudden numbness, particularly on only one side, of the face, arm, or leg
• Sudden confusion particularly trouble speaking or understanding
• Sudden trouble in seeing either in one or both eyes
• Sudden loss of balance or coordination
• Sudden feeling of dizziness
• Sudden appearance of a severe headache with no known cause

Symptoms of a heart attack include:

• Chest discomfort that lasts longer than a few minutes or comes and goes in succession
• The spreading of pain from the chest to one or both arms, back, jaw, or stomach
• The presence of cold sweats and the feeling of nausea

One of the most effective treatments used in the various medical stages of treating cardiac disease is Positron Emission Tomography. PET scans of the heart is a highly effective imaging tool that is used to diagnose cardiac disease. It is particularly useful in detecting coronary heart disease, a condition in which the coronary arteries (the small blood vessels that supply blood and oxygen to the heart) are narrowed due to the buildup of fatty material and atherosclerosis (plaque). Due to the narrowing of the coronary arteries, blood flow to the heart is either slowed and can even stop. The early detection of coronary heart disease and other forms of cardiac disease is vital as the early treatment of heart disease can prevent heart attack and/or stroke.

Clinical studies have shown that PET imaging is more accurate than other tests such as electrocardiogram (ECG) stress testing, single photon emission computed tomography (SPECT), and the angiogram in detecting coronary heart disease. Whereas these tests often produce “false positive” reports detailing the presence of coronary artery disease in a patient where none exists, PET has a 95% diagnostic accuracy rating in identifying coronary heart disease. This makes Positron Emission Tomography the most reliable noninvasive cardiac imaging technology available and PET imaging is often used in cases where a suspected “false positive” report has been given by these other tests.

Blood flow to the heart is measured through PET imaging, which makes PET imaging a highly useful procedure in cardiac disease diagnosis. A metabolic imaging test, PET imaging involves the administering of a radioactive tracer that is a combination of a radioisotope (a radioactive compound whose movements are detectable by a PET scanner) with a natural body compound. In cardiac disease diagnosis, the radioactive tracer used in the Positron Emission Tomography procedure is most commonly Fluorodeoxyglucose (FDG), which combines the natural body compound glucose with the radioisotope Fluorine-18. This radioactive tracer, or radiopharmaceutical, is used in cardiac disease detection as it measures the body’s metabolic reaction to FDG. In cases where the heart muscle is damaged or functioning in an improper fashion because it is ischemic (a condition that indicates lowered blood flow and the lacking of sufficient oxygen to sustain its function), its impaired metabolic action will be shown in the PET scan images.

The use of PET imaging in cardiac diseases takes two stages. During the first stage, Positron Emission Tomography utilizes the administration of FDG while the patient is in a state of rest. The images that are produced from this first PET scan will then be checked with a second PET scan in which the patient is administered with dipyridamole, a drug that produces an effect in the body similar to the effects of strenuous exercise. The effects of dipyridamole on PET imaging is that it allows the PET scan to produce images of the arteries in a state of stress. During the initial PET scan where a patient is at rest, regional myocardial perfusion (pumping of blood through the capillaries to the heart muscle) may be maintained despite severe cases of stenosis (the constriction of a blood vessel or valve in the heart). However, the second PET scan produces images of blood flow in the body while the body is in a period of stress and is able to detect instances of coronary heart disease. This is because coronary arteries exhibit a diminished capacity to increase blood flow compared to normal coronary arteries if it suffers from over 50% stenosis.

Following the PET scan for cardiac disease, the two images produced by the two stages of PET imaging are compared to examine blood flow through the heart muscle. The comparison between the two PET images aids in assessing whether coronary heart disease is present, and is performed under these criteria:

• Blood flow through the coronary arteries is normal if blood flow levels are normal during both the stimulated exercise and rest portions of PET tests.
• Blockage may be present in the coronary arteries if blood flow levels are normal during the rest portion of the PET test, but is reduced during the stimulated exercise PET test.
• Blood flow is restricted at all times if blood flow is reduced in a part of the heart during both the stimulated exercise and rest portions of PET tests.

Due to its comprehensive and accurate approach, PET imaging is used to reveal coronary artery disease by detecting impaired blood flow and this test is also used to rule out the presence of coronary artery disease in suspected cases.

Additionally, PET imaging is a highly effective imaging tool used in cardiac disease diagnosis as it produces images that are less likely to be distorted by conditions of the patient’s body, such as obesity or large breast. PET images are consistently of high quality that focuses on the patient’s biochemical structure rather than its anatomical structure. Due to this phenomenon, PET leads to more accurate diagnosis in cardiac disease cases.

Perhaps more important than detection, Positron Emission Tomography is greatly used during the staging phase of cardiac disease treatment. Staging commences after cardiac disease diagnosis and is used to determine the specifics of the heart disease. The staging component of cardiac disease is critical, as physicians depend on receiving the necessary information in this part of cardiac disease treatment in their recommendations of an appropriate future medical action.

Through PET imaging, a physician is able to determine the presence of a coronary artery disease more efficiently than other screening tests. With a diagnostic accuracy rating of 95%, PET scans prevents the likelihood of unnecessary medical treatment in cases where a “false positive” indicating the presence of coronary heart disease where there is none. Consequently, PET scans are often performed to confirm results given by an electrocardiogram (ECG) and/or single photon emission computed tomography (SPECT) that is suspected to be a “false positive.”

Additionally, Positron Emission Tomography is a valuable procedure that is used to determine whether bypass surgery or transplant is an appropriate medical action following diagnosis. This is because PET is the “gold standard” of imaging tests in determining the viability of heart tissue for revascularization (a surgical procedure that is used to open up blocked blood vessels to improve blood flow to the heart). In most instances, a thallium test is used to measure the presence of live tissue. In the thallium test, radioactive thallium is administered into the blood stream and produces images of the heart that traces blood flow to the heart. The images produced by the thallium test outline areas of the heart where there is severely restricted blood flow. These areas are considered to be dead tissue and are termed non-functional. A heart transplant is recommended based on the images produced by the thallium test in cases where there is an abundance of dead heart tissue.

However, PET imaging is a much more effective imaging tool in determining the presence of dead heart tissue. This is because PET scans are a metabolic imaging tool that not only measures blood flow but also cellular metabolism. In many cases, thallium testing will identify dead tissue that are actually alive but are considered “hibernating tissue.” Hibernating tissue refers to areas of the heart that appear to be dead when judged by blood flow but are actually deprived of oxygenated blood. Once it receives an adequate supply of oxygenated blood, the hibernating tissue can contribute again to muscle contraction. As PET imaging is able to detect the presence of hibernating tissue, it is a vital instrument used by physicians in the heart disease staging process. The use of PET often results in bypass surgery for patients that, if thallium tests alone were used, would have been recommended heart transplant.

Positron Emission Tomography is able to detect the presence of hibernating tissue and, therefore, is the most effective imaging tool in heart disease staging because it is a metabolic imaging tool. PET imaging involves the administering of a radioactive tracer that combines a radioisotope (a radioactive compound whose movements are detectable by a PET scanner) with a natural body compound. In cardiac disease staging, the radioactive tracer used in PET scanning is usually Fluorodeoxyglucose (FDG), which is a combination of the natural body compound glucose and the radioisotope Flourine-18. This radioactive tracer is effective in cardiac disease staging as it measures the heart’s metabolic reaction to FDG. Much like thallium testing, Positron Emission Tomography produces images that measure blood flow to the heart. However, in addition to measuring blood flow, PET scanning also measures glucose metabolism. Consequently, hibernating tissue that does not produce any signs in thallium testing appear in PET imaging as these cells also use glucose as an energy source. In this manner, PET scans are able to produce the most accurate reports of dead heart tissue as truly dead heart tissue do not demonstrate glucose metabolism.

Further medical action in treating cardiac disease is based on the information attained in both cardiac disease diagnosis and staging. A common treatment used to treat cardiac disease is bypass surgery, or as it is technically known as, coronary artery bypass graft (CABG). Bypass surgery involves the removal of a short piece of blood vessel from another part of the body to be used as a replacement of the clogged portion of the coronary artery. Another common cardiac disease treatment is angioplasty, which involves the enlargement of the artery opening that is in danger of being blocked. In angioplasty, a tiny balloon attached to the tip of a catheter is threaded up through an artery until it reaches the developing blockage. From there, the balloon is inflated to push the blockage aside and enlarge the artery opening. Other heart disease treatments include beta blockers, which are used to reduce blood fat (lipid) levels.

Regardless of the type of cardiac disease treatment, one of the most important components of cardiac disease treatment is the follow-up procedure that confirms heart health. Positron Emission Tomography is a useful procedure to measure changes in blood flow to confirm the effectiveness of the treatment. A highly sensitive non-invasive diagnostic imaging tool, PET imaging is used to reevaluate blood flow following bypass surgery and angioplasty.

Additionally, PET imaging is used to measure the progression of coronary heart disease and it is a useful measure used to measure the effectiveness of lipid lowering treatments.