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Myocardial Perfusion

Myocardial perfusion is the passage of blood through the blood vessels to the heart. Coronary artery disease results from a narrowing or blockage of the vessels that feed the heart muscles. As plaque or calcifications build up on the inside of the arteries, blood flow to the heart muscle is reduced.

Screening is an important way to detect coronary artery disease because the symptoms may not be noticeable or may be very mild. People who have high blood pressure, are not physically active, have high blood cholesterol, smoke or have a history of smoking, or are obese are at a greater risk for developing coronary artery disease. Finding coronary artery disease early is important, because it can lead to a heart attack.

Diagnosis

Physicians diagnose coronary artery disease based on medical and family histories, risk factors and the results of a physical exam and diagnostic tests and procedures. No single test can diagnose coronary artery disease so your physician may perform several tests. These include blood tests, X-ray, electrocardiogram, echocardiography, coronary angiography, single photon emission computed tomography (SPECT), or positron emission tomography/computed tomography (PET/CT).

An electrocardiogram (EKG) is a simple test that detects and records the electrical activity of your heart, how fast it is beating and whether it has a regular rhythm. It also shows the strength and timing of electrical signals as they pass through each part of your heart. Certain electrical patterns that the EKG detects can suggest whether coronary artery disease is likely. An EKG also can show signs of a previous or current heart attack.

Echocardiography uses sound waves to create a moving picture of your heart. And provides information about the size and shape of your heart and how well your heart chambers and valves are working.

A chest X-ray takes a picture of the organs and structures inside the chest, including your heart, lungs, and blood vessels.

A coronary angiogram is a procedure that uses X-ray imaging to examine the blood vessels or chambers of the heart. A long, thin, flexible plastic tube (catheter) is inserted into a blood vessel in your upper thigh or arm. The tip of the tube is positioned either in the heart or at the beginning of the arteries supplying the heart, and a dye that is visible by X-ray is injected. The X-ray pictures that are obtained are called angiograms and offer a detailed look inside your blood vessels.

Blood tests check the levels of certain fats, cholesterol, sugar, and proteins in your blood. Abnormal levels may show that you have risk factors for coronary artery disease.

Stress testing is an exercise procedure to make your heart work hard and beat fast while heart tests are performed. If you can't exercise, you're given medicine to speed up your heart rate. A PET or PET/CT myocardial perfusion imaging test can help the physician detect restricted blood flow. In less severe cases of coronary artery disease, the deficit in blood flow may only be seen after exercise or stress. In more severe heart disease, the blood flow abnormality can be seen at rest as well.

PET/CT myocardial perfusion imaging utilizes a radioactive drug, either 82Rubidium or 13N Ammonia, that shows the physician the normal or abnormal patterns of blood flow to the left ventricle of the heart. The muscle tissue around the left ventricle pumps blood to the rest of the body and adequate muscle tone is needed to perform this function well. If blood flow to this heart muscle is restricted by a blockage, then the myocardial perfusion images will show a blood flow deficit.

The PET/CT myocardial perfusion test shows how well blood flows to the heart muscle and is performed while the heart is at rest, but may also be done during exercise or other stress by using a drug that increases blood flow to the heart, mimicking exercise.

Treatment

The results of the PET/CT scan will help the physician determine the best course of treatment and could include medical treatment with drugs such as cholesterol lowering medications, coronary interventions such as angioplasty or coronary stent implantation, or coronary artery bypass surgery.

Angioplasty or coronary stent implantation is the technique of mechanically widening a narrowed or obstructed blood vessel. Coronary stents containing tightly folded balloons are passed into the narrowed locations and then inflated to a fixed size using water pressure. The balloon is then removed leaving the stent in place, pressed into the newly opened artery wall.

Coronary artery bypass surgery is a type of heart surgery. It's sometimes called CABG ("cabbage"). The surgery reroutes, or "bypasses," blood around clogged arteries to improve blood flow and oxygen to the heart.

Normal during both exercise and rest portion of the test, then blood flow through the coronary arteries is normal.

Normal during rest but is reduced in part of the heart during exercise, then part of the heart is not getting enough blood when it is working harder than normal, which may be due to a blockage.

Reduced in a part of the heart during both exercise and rest, then the blood flow to that part of the heart is restricted at all times.

The results of the PET/CT scan will help the physician determine the best course of treatment.

Follow-up

Myocardial perfusion imaging can be used to assess whether the treatment was successful. The physician can measure changes in myocardial perfusion or blood flow to the heart with PET/CT imaging, before and after treatment. The highly sensitive PET/CT scan can be used by physicians to re-evaluate blood flow after bypass surgery or angioplasty, can provide measurements of the progression of coronary artery disease over time, and can provide information to help the physician assess improvement in coronary heart perfusion with therapies, such as lipid lowering treatment.

Myocardial Perfusion Utilization

PET/CT imaging provides a way to assess the severity of heart disease and measure its impact on heart function. Clinical studies show an important role for PET/CT in screening for coronary heart disease, assessing flow rates and flow reserves, and distinguishing viable from nonviable heart tissue. Advancements in quantification software give the clinician the ability to easily calculate blood flow values at peak stress and rest as well as obtain the coronary flow reserve estimate. Studies have evaluated the impact of estimating flow values and flow reserve in combination for assessing coronary artery disease and identifying triple vessel ischemia.1

Myocardial perfusion imaging indications

  1. Identifying ischemic disease, or reduced blood supply to the heart
  2. Detecting coronary artery disease even before clinical symptoms show
  3. Determining the extent of coronary artery disease before and after treatment
  4. Demonstrating whether a surgery to reverse the effects of a blockage will improve the function of the heart

Source: Parkash et al. Potential Utility of Rubidium 82 PET Quantification in Patients with 3-Vessel Coronary Artery Disease. J Nucl Cardiol 2004; 11:440-49