About Nuclear Cardiology
“The Role of Nuclear Cardiology in Heart Disease?”
Heart disease is the leading cause of death in the western world. Each year in the U.S.A, more than 500,000 men and women die from coronary artery disease. During the past two decades, major strides have been made in the diagnosis and treatment of heart disease. Nuclear Cardiology has played a pivotal role in establishing the diagnosis of heart disease and in the assessment of disease extent and the prediction of outcomes in the setting of coronary artery disease.
What is Coronary Artery Disease?
Coronary artery disease results from the narrowing of the blood vessels that supply the heart. The blood vessels become narrow when fatty deposits build up inside the arterial wall. This is the process of atherosclerosis. When the arteries become clogged, the blood flow to the heart muscle is impaired and a heart attack can occur.
Nuclear cardiology studies use noninvasive techniques to assess myocardial blood flow, evaluate the pumping function of the heart as well as visualize the size and location of a heart attack. Among the techniques of nuclear cardiology, myocardial perfusion imaging is the most widely used.
Myocardial Perfusion Imaging
Myocardial perfusion images are combined with exercise to assess the blood flow to the heart muscle. Exercise can be in the form of walking on the treadmill or riding a stationary bicycle. A “chemical” stress test using the drug dipyridamole, adenosine, regadenoson, or dobutamine can be performed in patients who are not able to exercise maximally, providing similar information about the heart’s blood flow.
A small amount of an imaging agent is injected into the blood stream during rest and during exercise or chemical stress. A scanning device (gamma camera) is used to measure the uptake by the heart of the imaging material during (exercise or chemical stress) and at rest. If there is significant blockage of a coronary artery, the heart muscle may not get enough of a blood supply in the setting of exercise or during chemical stress. This decrease in blood flow will be detected by the images.
Myocardial perfusion studies can thus identify areas of the heart muscle that have an inadequate blood supply as well as the areas of heart muscle that are scarred from a heart attack. In addition to the localization of the coronary artery with atherosclerosis, myocardial perfusion studies quantify the extent of the heart muscle with a limited blood flow and can also provide information about the pumping function of the heart. Thus, it is superior to routine exercise stress testing and provides the necessary information to help identify which patients are at an increased risk for a heart attack and may be candidates for invasive procedures such as coronary angiography, angioplasty and heart surgery.
Evaluation of Cardiac Function with Radionuclide Ventriculography
Radionuclide ventriculography is a noninvasive study, which provides information about the pumping function of the heart. In patients with coronary artery disease, and in those who have had a heart attack, the assessment of the pumping function of the heart (also known as the ejection fraction) is essential in the prediction of both long term and short-term survival. A small dose of an imaging agent is injected into the blood stream and pictures of the four chambers of the heart are taken using a special camera (gamma camera). These techniques can also provide information about the function of the valves of the heart, the integrity of all the cardiac chambers and can be used to monitor the effect of different drugs on the heart muscle (in patients with cancer who are treated with chemotherapy). The evaluation of cardiac function with radionuclide ventriculography is accurate and noninvasive and continues to play a critical role in predicting outcomes in patients with heart disease.
Assessment of Myocardial Injury, Infarction and Infection
The basic cellular component of the heart muscle may be irreversibly affected in the setting of a limited blood supply and or inflammation. Nuclear cardiology techniques can be used to determine which areas of the heart muscle have been damaged by infection or by a heart attack. These techniques can also be used to monitor the status of the heart muscle in the patient after cardiac transplantation.
Imaging of the Nervous System of the Heart
The heart has its own nervous system, which is crucial for the proper functioning of the heart muscle. When there is damage to the heart muscle, the nervous system of the heart can be impaired leading to abnormal function of the electrical system of the heart. An abnormal heart rate and disarray of the normal cardiac rhythm can manifest this abnormality. Imaging agents are injected into the blood stream and then the nervous system of the heart can be imaged using a gamma camera. The information acquired from these noninvasive studies can be used in the management of patients with heart disease, especially heart failure.
Positron Emission Tomography (PET)
PET studies are noninvasive and are used to provide information about both the blood supply to the heart muscle and the metabolic activity of the heart. These studies can outline the heart muscle that is not getting adequate blood flow because of the blockage in the arteries of the heart. These studies can also show the heart muscle that has been scarred from past heart attacks, and also what has been damaged but has the potential to recover if a bypass surgery or an angioplasty is performed on the patient. This ability to distinguish irreversibly damaged heart muscle from damaged heart muscle with a potential to recover its function after bypass surgery or angioplasty is a major strength of PET imaging. PET studies can also be used to evaluate the nervous system of the heart. These studies can also help in making determinations about candidacy for bypass surgery or angioplasty. With the wider availability of PET imaging cameras, the use of PET imaging has increased significantly in the last few years.
Nuclear cardiology studies continue to play an increasingly important role in the new millennium, in the noninvasive diagnosis of coronary artery disease, the assessment of the pumping function of the heart and in the prediction of outcomes in patients with heart disease.