Dipyridamole-Thallium Scan (Dip-Thall) is a myocardial perfusion study: it looks at blood supply to the heart muscle while under the relative stress of dipyridamole, which causes the coronary arteries to slightly and temporarily constrict (become narrower). Thallium is the radio-isotope used to “light up” the blood cells.
How the Test is Performed
Patients are required to abstain from any foods, drinks or medications which contain caffeine or theophylline, for 24 hours prior to the Dipyridamole-Thallium Scan. Rather than exercise stress, the heart is stressed by the injection of Dipyridamole into a vein, so-called pharmacologic stress. A radio-isotope (radiotracer) such as Thallium is then injected into a vein via an intravenous cannula. This substance is taken up by heart muscle according to the amount of blood supply to that area of heart muscle, and shows up on an image as a “concentration map”. Sometimes additional images are taken when the heart is not being stressed, these can then be compared to the stressed images to see if there is an area of “reversible ischaemia”. This may help to differentiate coronary artery disease from areas of permanently damaged heart muscle, as with a heart attack (myocardial infarction).
Medical Conditions and Symptoms
A Dipyridamole-Thallium Scan (Dip-Thall) may be requested by a General Practitioner (GP), Emergency Physician or Cardiologist, in cases of chest pain where the cause is not certain.
It therefore has similar use to an Exercise Stress Test, the advantage being that the patient is not required to exercise for a Dipyridamole-Thallium Scan, which may be useful in people with severe arthritis or lung disease who are not able to reach a high level of exercise.
Symptoms of shortness of breath on exertion, waking up in the night with severe breathing difficulty (paroxysmal nocturnal dyspnoea or PND), or ankle swelling may all be due to heart failure, where the heart’s ability to pump is impaired. Heart failure (left ventricular failure = LVF, congestive cardiac failure = CCF) is sometimes due to ischaemic heart disease, also known as coronary artery disease. IHD (ischaemic heart disease) may cause chest pain (angina) or symptoms of heart failure.
A Dipyridamole-Thallium Scan (Dip-Thall) may also be used to monitor the effects of treatment in a patient known to have ischaemic heart disease (angina).
Test Results Explained
Dipyridamole-Thallium Scan (Dip-Thall) results may show:
- Normal perfusion study – normal blood supply to all areas of the heart muscle
- Reversible perfusion defect – decreased blood flow to an area of heart muscle, due to inadequate blood supply from a particular coronary artery (blood vessel around the heart)
- Fixed perfusion defect – decreased blood flow to an area of heart muscle, due to permanently damaged muscle (essentially a scar in the heart muscle)
- General Practitioner (GP)
- Emergency Physician
- General Physician
- Occupational Health Physician
- Intravenous Cannulation
- Pre-operative Anaesthetic assessment
- Percutaneous Coronary Intervention (PCI)(=PTCA: Percutaneous Coronary Angioplasty - with or without coronary stent placement)
- Coronary Artery Bypass Grafting (CABG)
- Exercise Stress Test (EST)
- Electrocardiogram (ECG)
- Echocardiogram (Echo)
- Chest X-Ray (CXR)
- Lipid Profile (Cholesterol Test)
- Glucose Tolerance Test
Also Known As
- (Nuclear) Myocardial Perfusion Imaging (MPI)