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Adenosine single-photon emission computed tomography (SPECT) thallium-201 (Tl-201) imaging is a noninvasive myocardial perfusion imaging (MPI) test using thallium as a radioisotope.[1] The underlying principle of the test is that when the myocardium is under stress, the diseased ventricle receives less blood flow than the normal heart muscle. The SPECT scan performed after the stress event reveals the distribution of thallium and the relative blood flow to the different parts of the ventricle. Images are also obtained at rest and compared. Thallium is injected and taken up by the myocardial cells so that the initial distribution of the tracer reflects viable myocardium. Images are then taken during stress (induced by adenosine) and at rest to reflect myocardial perfusion and viability. SPECT Tl-201 is used mainly for myocardial viability assessment when positron emission tomography (PET) or magnetic resonance imaging is not feasible. The American Society of Nuclear Cardiology recommends against using adenosine SPECT Tl-201/technetium 99m (Tc-99m), dual-isotope (rest-stress) imaging for detecting myocardial ischemia, as this protocol exposes patients to greater amounts of radiation (up to 23 mSv) than other isotopes.[2] Tl-201 is a potassium analog, a radioactive isotope of thallium with a half-life of 73 hours. Tl-201 is uptaken by myocardial cells and detects an area with hypoperfusion and myocardial infarction as a cold spot.[3] This isotope has many other medical applications, including renal medullary imaging and tumor detection.[4] In clinical practice, Tc-99m agents (Tc-99m Sestamibi and Tc-99m Tetrofosmin) are more commonly employed during SPECT imaging for myocardial ischemia detection due to lower radiation exposure (4.2–6.3 mSv) than Tl-201.[5]

Most of the side effects of this test are related to the use of pharmacological vasodilators and are often self-limited. However, these drugs have correlations with severe side effects such as myocardial infarction.[17][18] All patients should be informed that MPI risks exposure to significant radiation more than computed tomography. Radiocontrast has a small risk of an allergic reaction. The common side effects of vasodilator testing with adenosine include the following: Flushing Headache Chest discomfort Dyspnea Gastrointestinal discomfort Lightheadedness or dizziness Arrhythmias, importantly atrioventricular block Paresthesia Hypotension Nervousness Aminophylline (50 to 250 mg) or caffeine should be used to reverse pharmacological vasodilator effects if a patient develops severe side effects, including hypotension with systolic pressures less than 80 mm Hg, 2nd or 3rd-degree atrioventricular block, arrhythmia, wheezing, severe chest pain with ST-segment depression, or signs of poor perfusion.[19][20]

Healthcare workers in clinical practice should be familiar with the SPECT thallium imaging study, which assesses CAD and guides revascularization based on ischemia. This modality also serves as a method for evaluating myocardial viability when other tests are unavailable. A nuclear cardiologist usually performs the test with a team of nurses and radiology technicians. A nurse is tasked to monitor the patient during the test and is responsible for ensuring that resuscitative equipment is present in the suite before the test is started. A pharmacist specializing in nuclear medicine should assist with proper dosing. Vital signs and oxygenation must be recorded every few minutes at all times during the test. The team should be apprised immediately if abnormalities are detected. A team approach is vital to prevent complications from the SPECT thallium test. The team must run the test in a coordinated manner, with effective communication between team members. All reports should be reviewed preliminarily, and the referring physician should be promptly informed if any high-risk findings are identified.

Adequate preparation is essential. The nurse must confirm that the patient has not consumed caffeinated beverages or colas at least 12 hours before the procedure and has not taken theophylline 24 hours before the test. All medications the patient is taking should be documented, along with any prior allergies or history of adverse reactions. Intravenous access must be established, and the laboratory should be well-equipped to ensure the test runs smoothly.

The patient should be on continuous ECG monitoring during adenosine infusion and the recovery period. Vital signs should be monitored at baseline and at regular intervals during the test. Any ECG changes during the test should be noted and communicated. The nursing team should be prepared with the necessary medications and equipment to manage arrhythmias or cardiac arrest. Aminophylline and antiemetic medications should also be readily available. The recovery monitoring should end once the patient returns to baseline hemodynamically and is comfortable. Necessary home instructions should be provided to avoid radiation exposure to people around the patient, especially children and pregnant women.