Dipyridamole Stress Radionuclide Imaging

Relevant Social Security Medical Listings

  • Listing 4.04 Ischemic Heart Disease (Adults)

Other Names

Persantine® Stress Test

Type

Objective/Radionuclide Imaging (Heart), Pharmacologic Stress (Heart), EKG (Resting)

Can SSA Purchase?

No, since the test requires injection of a drug (dipyridamole) that is not provided for in Social Security regulations. However, this is an important test and results should always be considered as part of the evidence of record when provided by a treating doctor.

Purpose

Diagnose and evaluate severity of decreased blood flow to heart muscle (myocardial ischemia) secondary to the obstruction of coronary arteries.

General

Dipyridamole stress testing is a type of pharmacologic stress testing in which physical exercise is not performed, but the heart put under stress by means of a drug. Dipyridamole inhibits the cellular reuptake of the coronary artery vasodilator adenosine that is naturally present in the heart; consequently, adenosine concentrations are higher on the adenosine receptors of blood vessels when dipyridamole is present, the blood vessels dilate, and blood flow increases in the intramyocardial arteries.[1] Dipyridamole increases coronary artery blood flow by a factor of 3 – 5 times, but perfusion pressure of blood is less beyond areas of coronary artery narrowing.

Radionuclides are radioactive isotopes; certain radionuclides such as thallium201 accumulate temporarily in the heart when injected intravenously. Radionuclides emit radiation that can be detected by a scanner placed over the patient’s chest. Thallium201 emits x-rays. Detectors count the amount and pattern of radiation received from the radionuclide in the patient’s heart to form an image that represents blood flow in the myocardium. Technetium99m is another radionuclide used with dipyridamole for pharmacologic stress imaging and emits gamma rays.

Isometric hand-grip can be used to enhance the myocardial workload and thus increase the likelihood of inducing ischemia caused by coronary disease during dipyridamole infusion.

Contraindications

Other than those concerning ability to ambulate, the contraindications to testing are similar or identical to those for Treadmill Stress Testing (TST, TMST).

Technique

Patients are told to not eat for at least 3 hours before testing, and avoid caffeine (e.g., coffee tea, or other caffeinated beverages) for at least 24 hours before testing. Xanthine drugs such as aminophylline should be discontinued at least 24 hours prior to testing, since they antagonize the effects of dipyridamole.

Dipyridamole is infused intravenously at a rate of 0.56 milligram (mg)/kilogram (kg) of patient body weight over period of 4 minutes. After an additional 3 minutes, a 2 to 3 millicurie (mCi) dose of the radionuclide thallium201 is given intravenously. Ten minutes later the first perfusion images (scan) are made, and the final scan is done 2 – 3 hours later.

The patient’s symptoms, EKG, and other vital signs are monitored continuously; apart from the radionuclide images, the EKG could show ST segment depression indicative of ischemia, arrhythmias, or other abnormalities. Aminophylline is given after testing to reverse the effects of the dipyridamole.

Complications

Significant side-effects are possible: chest pain secondary to cardiac ischemia (angina pectoris), constriction of pulmonary bronchi (bronchospasm), low blood pressure (hypotension), nausea, and arrhythmias. However, the procedure is considered to be generally safe. Aminophylline quickly reverses the effect of dipyridamole, and is kept available for that purpose if needed.

Interpretation

See Myocardial Perfusion Stress Imaging, §4.38, for a discussion of radionuclide imaging.

The interpretation of radionuclide images is the same whether the stress is induced by exercise as on a treadmill or a bicycle ergometer, or induced by a pharmacologic agent such as dipyridamole.

Exception:  This test is not sensitive enough to reliably detect severe coronary artery disease in transplanted hearts.

Comments

There is an additional possible refinement to the above imaging techniques called SPECT (single photon emission computed tomography); SPECT offers improved sensitivity for detecting disease in single coronary arteries. For example, the imaging radionuclide technique could be dipyridamole thallium201 or dipyridamole thallium201 SPECT, dipyridamole technetium99m or dipyridamole technetium99m SPECT. Unlike planar radionuclide imaging, SPECT is a tomographic technique that allows three dimensional reconstruction of the target organ or area of study by combining a series of planar images of the same area from different angles.

Examples

Example 1

Dipyridamole Technetium99m SPECT Stress Test

Clinical History: The patient is a 56 year old white female who presents for pre-operative evaluation.

Technique: One hour after the intravenous administration of 9.7 mCi [millicuries] of technetium99m sestamibi (Cardiolite®), multiple images of the heart were obtained in multiple projections. The patient was then given intravenous infusion of dipyridamole at a rate of 0.14 mg/kg per minute over a period of 4 minutes. Seven minutes after the initiation of this injection, 24.8 mCi of technetium99m Cardiolite® was given and after delay of one hour repeat images of the heart were performed. The patient was given 75 mg of intravenous aminophylline after complaining of flushing, nausea, and headache. These symptoms resolved with aminophylline.

Findings: The resting heart rate and blood pressure were noted to be 72 beats per minute and 135/61 mm Hg. There was an appropriate response to the aminophylline. Stressed heart rate and blood pressure being 89 beats per minute and systolic pressure 163 mm Hg. The resting EKG was normal and no changes were noted with the dipyridamole. Review of the stress and rest images reveals no reversible defects suggesting myocardial ischemia.

Impression: Normal dipyridamole stress test without reversible defects suggesting myocardial ischemia.[2]

Example 2

Dipyridamole Thallium201 Stress Test

Patient:  Female, age 63

Indications for Stress Test:  Weakness, fatigue, chest pain

Medications:  Procardia, Diabeta, Xanax

Blood Pressure:  Resting – 123/60  Maximal – 127/57

Heart Rate:  Resting – 62/min  Maximal – 74/min

Symptoms:  None.

Dysrhythmia:  None.

Ischemic EKG changes:  No

Impression:  Negative adequate stress test (EKG)

Dipyridamole thallium myocardial perfusion study: 4 millicuries of thallium201 were administered after administration of the dipyridamole dosage for pharmacologic stress. After the appropriate delay in an additional millicurie of thallium201 was utilized for equilibrium phase imaging.

Study demonstrates normal distribution of the radionuclide. No areas of ischemia or infarction are identified.

Impression:  Normal dipyridamole thallium study.

Footnotes

  1. Intramyocardial arteries are small arteries within the myocardium or heart muscle. They are to be distinguished from the large epicardial arteries that lie on the surface of the such as the left anterior descending, right coronary, circumflex arteries, etc., from which the intramyocardial arteries derive their origin.
  2. If the patient had areas of defective radionuclide uptake on scanning after administration of the dipyridamole which then reverse to normal uptake when the dipyridamole is stopped, then myocardial ischemia would have been present and most likely caused by coronary artery disease.