THALLIUM TESTING – Purpose, Thallium 201, Findings, Client Preparation, Procedure, After Care and Complication (NURSING PROCEDURE)
Thallium is a radioactive analog of potassium, which is readily taken up myocardial cells. After thallium 201 is given, almost 90% of it is extracted by the myocardium within seconds. For this to occur, two factors are essential: (i) adequate perfusion and (ii) cellular extraction efficiency. Since cellular ischemia does not seem to affect thallium uptake in myocardium, its lack of uptake is an indication of an infraction
PURPOSE
- Thallium imaging is used to assess coronary blood flow to determine areas of infarction and ischemia
- To diagnose CAD and assess revascularization following coronary artery bypass surgery
THALLIUM 201
- Thallium 201 is the most widely used isotope for myocardial perfusion due to its short (73 hours), half-life and low total body radiation dose
- Thallium 201 is a radioactive analogue of potassium, which is easily extracted by smooth skeletal and cardiac muscle fiber that possess the potassium active transport system
- A 80% of blood-borne thallium 201 is taken up on its first pass through the heart
- The amount of thallium 201 found in the myocardium after an intravenous injection depends on the regional myocardial perfusion and the efficiency of cellular extraction
FINDINGS
- Cold spots indicate and distinguish areas of infarction and ischemia. High concentration of thallium 201 is present in well-perfused cells, and a lower concentration remains in the blood, setting up a concentration gradient for the diffusion on thallium 201
- Infarcted or scarred myocardium does not extract any thallium 201 showing up as cold spots. If the defective area is ischemic, the cold spots fill in or become warm on the delayed images
CLIENT PREPARATION
- Ask female clients if they are pregnant or suspected pregnancy, because these studies involve radiation exposure
- Explain the purpose of the procedure to the client and tell him or what to expect during the procedure
- Explain that electrodes will be placed on the client and an intravenous line will be inserted for the administration of the radioisotope
- Generally, total exposure to radiation during these scan is less than or equal to that of one chest X-ray study
- Instruct the client to wear walking shoes if exercise on the treadmill or bicycle is anticipated
- Encourage the client to notify the nurse or technologist of any signs of ischemia (chest pain) during or after the procedure
- Keep the patient NPO for 4-6 hours before the test but may drink water
- An infusion is started for intravenous access
- Inform the client, of the need to go to the nuclear medicine department twice
- If a SPECT scan is planned, check if the client is claustrophobic
PROCEDURE
- Thallium or adenosine is given intravenously about a minute before the completion of the stress test
- After the completion of the stress test, the client is placed supine on the table and multiple scintigraphic images are taken
- The perfusion scanning is performed with a special camera that is capable of showing the source of emitted camera that is capable of showing the source of emitted low-energy photons on a screen
- Each photon detected by the camera is recorded on film and a computer screen over a half-hour period
- The computer refines and enhances the images and then provides qualitative information about the myocardial walls
- Two sets of images are taken 3 hours apart and compared
- Thallium can be given under a state of no physical demand, which is known as a resting thallium study, or it can be part of a stress test, in which case it is called exercise thallium imaging
- Exercise thallium imaging distinguishes ischemic sites from infarcted areas
- Thallium scans are repeated, once during stress testing and then 3-4 hours after thallium was given and the stress test was completed
- With the second imaging, if a cold spot disappears, it is recognized as an ischemic area
AFTER CARE
- Assess the client’s response
- Three to four hours later, the client returns for repeat films
COMPLICATIONS
- Dysrhythmias
- Myocardial ischemia
