Heart Disease

According to the American Heart Association, more than 81 million Americans have some form of heart and vascular disease and approximately 800,000 die from the disease each year.

Many heart conditions are related to the presence of atherosclerosis in the heart arteries (also called coronary artery disease or CAD). In CAD—a leading cause of death in America today—plaque builds up on the walls of arteries in the heart, narrowing the vessels and making it harder for blood to flow through.

Plaque on the inner surface of  the coronary artery can erode or rupture causing a blood clot to form, which can stop the blood flow, causing heart muscle damage we call a heart attack.

The presence of plaque in arteries of the brain can lead to stroke and in arteries of the legs to claudication or pain in the legs with exertion.

Heart disease also includes heart rhythm problems (arrhythmias), valve problems, infections, weakening of the heart muscle (cardiomyopathy), and defects that are present at birth (congenital). In heart failure, sometimes called congestive heart failure, the heart does not pump blood as well as it should and the body's need for blood and oxygen is not met.

Molecular Imaging and Heart Disease

Unlike conventional imaging studies that produce primarily structural pictures, nuclear medicine and molecular imaging visualize how the body is functioning and what’s happening at the cellular and molecular levels. Cardiovascular nuclear and molecular diagnostic imaging studies enable physicians to assess the function and physiological processes of the heart, providing extremely useful information for the diagnosis, risk assessment and management of heart disease patients.

Cardiovascular nuclear medicine and molecular imaging studies are able to identify biochemical and cellular changes that occur in the earliest, most treatable stages of heart disease. These early changes provide diagnostic clues and guidance for lifestyle, medical and revascularization interventions to optimize patient outcomes.

Like the heart itself, heart disease is complex and specific to each individual. Information provided by cardiac nuclear and molecular imaging is increasingly allowing physicians to personalize treatment.

In the research laboratory, nuclear medicine and molecular imaging are also improving our understanding of cardiovascular disease and facilitating the development of new and more effective medications.

How Does Molecular Imaging Help People with Heart Disease?

Molecular and functional imaging is increasingly playing a pivotal role in evaluating and managing patients with cardiovascular disease — as well as identifying and stratifying patient risk for the disease.

Imaging techniques are being developed to allow for a more “personalized” approach to the management of cardiac disease, including identifying early molecular and cellular events associated with heart disease to assist in early detection.

Today, PET and increasingly, SPECT, are routinely used to image the heart. Each year, more than five million nuclear cardiology tests are performed in the United States.

The most frequently used nuclear imaging procedure is myocardial perfusion imaging (MPI), which provides accurate diagnostic and prognostic information about patients with suspected or known heart disease.

Radiation Concern

Although nuclear cardiology tests are extremely useful in the early diagnosis and treatment of heart disease, the studies involve small doses of radiation.

A typical effective dose for a same-day MPI study is 10 mSv. To put this in perspective, consider that the average person receives 3 mSv of radiation exposure just by living in the United States. Natural radiation exposure comes from the earth in rocks and soil and from outer space in the form of cosmic rays. A small amount of radioactive material even exists naturally in our bodies.

Before performing any diagnostic test, physicians should ensure the appropriateness of the test. Nuclear medicine specialists use the ALARA principle (As Low As Reasonably Achievable) to carefully select a protocol  that will provide an accurate test with the least amount of radiation exposure to the patient. Appropriate Use Criteria (AUC) and guidelines have been developed and endorsed by SNM, the American Society of Nuclear Cardiology and other professional societies. These criteria and guidelines are based on a large body of scientific evidence including studies on thousands of patients.

The physician and patient should also weigh the proven clinical benefits and theoretical risks of the any diagnostic exam. For the nuclear cardiology studies, this should include a careful evaluation of a patient’s:

  • risk status
  • clinical characteristics
  • CAD risk factors
  • prior history of CAD
  • heart (specifically left ventricular) function.

Given that heart disease is the number one cause of death for Americans, the potential for death or disability as a result of heart disease is much greater than the radiation risk associated with nuclear cardiology tests such as the MPI. In most cases, the benefit of MPI testing far outweighs the study’s small potential risk of radiation exposure.

Research

Molecular imaging is already playing an important role in the diagnosis, management and risk stratification of patients with heart disease. However, we have only seen the beginning of a new and ever expanding frontier using targeted molecular imaging.

Molecular imaging approaches not only complement existing imaging technology, but will also permit the early detection of disease — before changes in physiological function or anatomical structure occur. Molecular imaging will enhance the development and application of truly personalized treatment. Molecular imaging will affect clinical care indirectly by facilitating faster and better drug development and improving the basic understanding of cardiovascular disease.

There are many new and emerging molecular imaging technologies that may help patients with heart disease. In addition to using myocardial perfusion imaging and nuclear functional studies, physicians are using new radiotracers such as  I-123-metaiodobenzylguanidine (MIBG) with SPECT and carbon-11-meta-hydroxyephedrine or carbon-11-mHED with PET to:

  • assess the potential for sudden cardiac death and other cardiac events in patients who have suffered a heart attack or who have chronic heart failure
  • improve the selection of patients who receive automatic internal cardiac defibrillators (AICDs)
  • identify the development of congestive heart failure.

Physicians are also using activation levels of an enzyme called matrix metalloproteinases (MMP), which can be imaged with PET, to determine help determine left ventricular remodeling (changes in the size, shape, and function of the heart after injury).

Other molecular imaging procedures and technologies under development include:

  • fusion imaging, also called co-registration or hybrid imaging, which allows information from two different studies to be viewed on one image.
  • the use of imaging biomarkers
  • the use of cardiovascular molecular imaging to monitor genetic or stem cell therapy
  • nanomedicine, including the use of laser-activated nanoparticles to destroy atherosclerotic plaque and adult stem cells to rejuvenate arteries.