Technetium Pyrophosphate Scanning

Technetium pyrophosphate scanning (also called hot spot myocardial imaging or infarct avid imaging) is used to detect a recent myocardial infarction (MI) and to determine its extent. This test uses an I.V. tracer isotope (technetium-99m [ 99mTc] pyrophosphate). This isotope accumulates in damaged myocardial tissue (possibly by combining with calcium in the damaged myocardial cells), where it forms a hot spot on a scan made with a scintillation camera. Such hot spots first appear within 12 hours of infarction, are most apparent after 48 to 72 hours, and usually disappear after 1 week. Hot spots that persist longer than 1 week usually suggest ongoing myocardial damage.

Purpose

• To confirm recent MI in patients suffering from obscure cardiac pain or when electrocardiography or serum enzyme studies don't provide sufficient information
• To help define the size and location of an MI
• To aid in determining the prognosis after acute MI

Patient preparation

• Explain to the patient that this test helps assess if the heart muscle is injured.
• Inform the patient that he needn't restrict food or fluids. Tell him who will perform the 30- to 60-minute test and where.
• Inform him that he'll receive a tracer isotope I.V. 2 or 3 hours before the procedure and that multiple images of his heart will be made.
• Reassure him that the injection causes only transient discomfort, that the scan itself is painless, and that the test involves less exposure to radiation than a chest X-ray.
• Instruct him to remain quiet and motionless while he's being scanned.
• Make sure the patient or a responsible family member has signed a consent form.

Procedure and posttest care

• Usually, 20 millicuries of 99mTc pyrophosphate are injected into the antecubital vein.
• After 2 or 3 hours, the patient is placed in a supine position and electrocardiography electrodes are attached for continuous monitoring during the test.
• Generally, scans are taken with the patient in several positions, including anterior, left anterior oblique, right anterior oblique, and left lateral. Each scan takes 10 minutes.

Normal findings

A normal technetium scan shows no isotope in the myocardium.

Abnormal findings

The isotope is taken up by the sternum and ribs, and their activity is compared with the heart's' 2+, 3+, and 4+ activity (equal to or greater' than bone) indicates a positive myocardial scan. The technetium scan can reveal areas of isotope accumulation, or hot spots, in damaged myocardium, Particularly 48 to 72 hours after onset of acute MI; however, hot spots are apparent as early as 12 hours after acute MI: In most patients with MI, hot spots disappear after 1 week; in some, they persist for several months if necrosis continues in the area of infarction.

Knowing where the infarct is makes it possible to anticipate complications and to plan patient care. About one-fourth of patients with unstable angina pectoris show hot spots due to subclinical myocardial necrosis, and may require coronary arteriography and bypass grafting.

Interfering factors

• Isotope accumulation (in about 10% of patients, may result from ventricular aneurysm associated with dystrophic calcification, pulmonary neoplasm, recent cardioversion, or valvular heart disease due to severe calcification)