Myocardial Perfusion Scintigraphy
Coronary heart disease (CHD) is a leading cause of death and morbidity in Europe, and its treatment takes up a significant percentage of national healthcare resources. New imaging technologies have increased immediate investigation expenses, but they also have the potential to lower overall costs due to their increased diagnostic and prognostic accuracy. This allows for a more informed therapeutic selection, which can result in an improved clinical outcome.
Myocardial perfusion scintigraphy (MPS) is a well-established imaging technology that is already used in the management of coronary artery disease (CAD) and is recommended by several professional organizations. Its most important uses are in the diagnosis of coronary artery disease, prognosis, revascularization selection, and evaluation of acute coronary syndromes (ACS), and it is especially useful in certain patient subgroups.
The only generally available method of direct evaluation of myocardial perfusion is myocardial perfusion scintigraphy (MPS). At maximal stress, modest doses of a radioactive tracer are injected intravenously, followed by gamma-camera imaging of the heart. Thallium-201 and two technetium-labeled tracers (sestamibi and tetrofosmin) are the three commercially available tracers. All three are disseminated throughout the myocardium in proportion to regional flow, and there is no evidence that one agent is superior to the others in terms of perfusion. The technetium-labeled tracers allow for the acquisition of ECG-gated perfusion signals and the assessment of perfusion and function in a single study.
Myocardial Perfusion Scans
MPS was established in the 1970s and has been used in clinical cardiology more frequently since the 1980s. Single-photon emission tomographic imaging (SPET), pharmacological stress, and ECG-gated imaging are some of the technological advancements that have driven this recent growth.
The procedure includes injecting small amounts of a radioactive tracer into the veins, usually during a phase of cardiovascular stress. Thallium-201 thallous chloride (thallium), technetium-99m 2-methoxy-isobutyl-isonitrile (MIBI), and technetium-99m 1,2-bis[bis(2-ethoxyethyl) phosphine] ethane (tetrofosmin) are the three commercially available tracers. Because cardiac myocytes remove them so quickly, their initial myocardial distribution reflects a combination of myocyte distribution and perfusion. Myocardial viability and perfusion can be measured independently by comparing pictures taken after stress and rest injections of tracer (or after thallium redistribution).
Patients who cannot reach maximal cardiovascular stress on a treadmill can be investigated using pharmacological stress, which uses a vasodilator like adenosine or a beta sympathetic agonist like dobutamine. This is an especially significant aspect of the technique that is applicable to between one-third and half of the patients.
The recommended imaging approach is SPET, which involves rotating the camera around the patient for 10-20 minutes and reconstructing the resulting series of planar projection images into a three-dimensional stack of tomographic slices into the myocardium. To produce a semi-quantitative assessment of regional tracer uptake, the tomograms are shown on a color scale, and a comparison with databases of normal appearances provides an objective assessment of the presence, depth, and degree of abnormalities. Although the stress and rest images are usually 3-4 hours apart, the total patient contact time for stress, injection, and image acquisition is about 45 minutes.
The lack of clinically significant infarction or coronary stenosis is demonstrated by homogeneous myocardial uptake of the tracer, which reflects normal myocardium and perfusion. A reversible defect (a deficit in the stress images that returns to normal in the rest images) shows an inducible perfusion defect and usually corresponds to substantial coronary stenosis. A fixed defect in both stress and rest imaging suggests an area where viable myocardium has been lost, such as after myocardial infarction. The technique is useful for diagnosing CHD, grading its severity, which is related to prognosis, and evaluating global and regional cardiac function using ECG-gated moving pictures since the site, extent, and depth of these defects are easily assessed.
Myocardial Perfusion Scintigraphy Indications
SPECT has been demonstrated to be more cost-effective than any other diagnostic method and more accurate than exercise ECG in diagnosing myocardial ischemia in patients who present with acute, stable angina (chest pain). In the case of Kawasaki disease, special indications include determining the hemodynamic relevance of abnormal coronary arteries, muscle bridging, and coronary aneurysms.
The blocked blood arteries and the mass of infarcted and viable myocardium, as well as inferior and posterior abnormalities and small patches of infarction, can all be seen.
SPECT has been shown to be a powerful tool for predicting the probability of future cardiac events in patients with established coronary artery disease.
After a myocardial infarction, stress images in SPECT may help establish the degree of inducible ischemia or viable myocardium responsive to revascularization in a given coronary artery distribution.
Myocardial Perfusion Scintigraphy Contraindications
The following are absolute contraindications to dynamic exercise:
- Exercise stress can be considered 1-3 days after chest pain in patients with non-ST-segment elevation acute coronary syndrome (NSTEMI) or unstable angina, depending on clinically determined risk. Myocardial infarction (MI) with ST-segment elevation within the past four days.
- Recent history of life-threatening arrhythmias.
- Left main coronary artery stenosis that is probably to be hemodynamically serious.
- Left ventricular dysfunction with complaints at rest; history of fatal arrhythmias; serious dynamic or fixed left ventricular outflow tract obstruction (aortic stenosis and obstructive hypertrophic cardiomyopathy).
- Severe hypertension (systolic blood pressure higher than 220 mm Hg and/or diastolic blood pressure higher than 120 mmHg).
- Recent pulmonary embolism, thrombophlebitis, deep vein thrombosis; and active endocarditis, myocarditis, or pericarditis.
The following are some relative contraindications of dynamic exercise:
- LBBB, bifascicular block, and ventricular paced beats (because dynamic exercise results in perfusion abnormalities of the septum and adjacent walls in the absence of obstructive coronary disease).
- Inability or lack of desire to engage in dynamic exercise
- An acceptable workload (85% of the maximum expected heart rate) was not achieved during a recent exercise ECG.
The following are absolute contraindications to vasodilator stress:
- Acute coronary syndrome that occurred recently is a contraindication. Stress with vasodilators can be evaluated 1-3 days after chest discomfort has been managed, depending on clinical risk.
- Hypotension (systolic blood pressure less than 90 mmHg), suspected or recognized severe bronchoconstriction, second-and third-degree atrioventricular (AV) block in the absence of a functioning pacemaker, sick sinus syndrome in the absence of a functioning pacemaker, xanthine intake in the previous 12 hours, or dipyridamole use in the previous 24 hours are all contraindications.
The following are some of the relative contraindications of vasodilator stress:
- Bradycardia of less than 40 beats per minute: Initial dynamic exercises usually raise the rate enough to allow the infusion to begin.
- Recent ischemia or infarction of the brain
- Hypokalemia, left bundle branch block, bifascicular block, and paced rhythm, for the same cause as for dynamic exercise (contraindications of dobutamine stress).
Myocardial Perfusion Scintigraphy Preparation
- There is no need to fast. On the day of the exam, light meals are recommended.
- If the exam is in the afternoon, a light, readily digestible lunch should be consumed two hours before the exam.
- For at least 12 hours before the exam, avoid caffeine-containing food and beverages (e.g., coffee, chocolates, mate tea, black tea, green tea, Coca-Cola, Guarana, chocolate cake, coffee candy, etc.), the use of medications, and alcoholic beverages.
- When showering, scrub the chest carefully with soap and avoid using any type of moisturizer. If needed, doctors will perform trichotomy (hair removal) in the chest for males to improve electrode placement. They do not recommend wearing a bra with metal elements if you are a woman.
- Bring sportswear, shorts or shorts, sneakers or shoes with rubber soles, and a face towel to the evaluation. To conduct the physical exertion test, these clothes are required. Doctors also advocate using a top to do the test, both physically and pharmacologically, for females.
- On the day before, avoid moderate to vigorous physical activity.
- Patients who have experienced chest pain or shortness of breath the previous day should avoid this test.
- 2 hours before the exam, stop smoking.
- Snags, medals, prostheses, bras with metal pieces, coins, electrodes, and other metallic and dense things in the upper chest should be removed.
- It is critical to get adequate rest the night before.
- Bring the findings of recent heart exams, including catheterization, exercise testing, and echocardiography, as well as blood tests (cholesterol with its fractions and triglycerides).
- The day before, you must confirm your presence.
- The exam lasts between 4 to 6 hours on average, although it is recommended that you plan the entire day for it.
- Some drugs should be stopped before the examination; consult your doctor for a detail.
- Always tell your doctor the names of all medications you're taking, and no prescription should be stopped without his or her advice.
- It is suggested that the patient bring his or her regular prescriptions to take following the test (even those that have been stopped).
- This test is not suggested for women who are pregnant or nursing.
Myocardial Perfusion Studies
Maximum dynamic exercise or pharmacological stress using one of the vasodilator drugs (adenosine or dipyridamole) or dobutamine, a beta-agonist, are the two options for stress. Most patients undergoing pharmacological stress are treated with vasodilators; dobutamine is usually reserved for asthma patients who cannot take adenosine or dipyridamole:
- Maximum possible dynamic exercise is physiological and gives important prognostic hemodynamic information.
- Pharmacological stress is more efficient, needs less patient cooperation, and is especially effective in patients with limited exercise tolerance or who already have exercise ECG data.
All but a small proportion of patients can be stressed using one of these strategies, with extreme hypotension (systolic blood pressure 90 mmHg) posing the biggest issue.
Caffeine has been proven to reduce the response to vasodilator stress, hence patients undergoing pharmacological stress testing should avoid caffeine for at least 12 hours prior to the treatment. Dipyridamole (persantin) should be discontinued for 12 hours since it can cause an overreaction to vasodilator stress. Other cardioactive drugs can normally be used without a pause.
Over the course of 10-20 minutes, patients are scanned supine with their arms lifted over their heads while the camera moves around their chest. To avoid attenuation in the lateral projections and to get the camera as close to the chest wall as possible, the arms must be lifted. Images are taken three to four hours after the heart has been exercised. While research may take many hours to complete, the total patient contact time for stress, injection, and imaging is less than one hour. As a semi-quantitative evaluation of regional tracer intake, reconstructed images are exhibited using a color scale.
Myocardial Perfusion Scintigraphy Results
The following are the results of MPS:
- The lack of substantial coronary stenosis is indicated by homogeneous myocardial uptake of tracer, indicating normal perfusion.
- A reversible defect (a stress image defect that normalizes in rest images) implies an inducible perfusion defect and usually correlates with a functionally significant coronary stenosis.
- A fixed defect in both stress and rest images usually suggests an infarction region.
- Anteroseptal abnormalities are commonly associated with disease of the left anterior descending artery.
- Left circumflex disease is diagnosed by lateral wall abnormalities.
Myocardial Perfusion Scintigraphy in Coronary Artery Disease
In persons with stable chest discomfort and limited exercise tolerance, as well as women and those with an irregular resting ECG, MPS is indicated as the first test.
Many centers, on the other hand, utilize a staged approach to investigation, with exercise ECG as the first test and MPS, with its increased costs and associated radiation load, reserved for people with a moderate risk of coronary disease following exercise testing.
Based on a pooled analysis of 79 trials (>8,000 patients), the average sensitivity and specificity for MPS are 86% and 75%, respectively. However, MPS delivers significantly more than a simple diagnosis. Because of its potential to predict future coronary events, it can be utilized as a gatekeeper for coronary angiography while also driving the need for eventual revascularization, a cost-effective and safe method in terms of clinical outcome.
Myocardial Perfusion Scintigraphy Prognosis
For predicting cardiac events, MPS has a high negative predictive value. Patients with a normal perfusion study have a risk of major coronary events of less than 1% per year, which is similar to the incidence in the general population without signs of coronary disease. In the absence of persistent symptoms, further evaluation can be deferred, whether or not the modest coronary disease is present. Patients with moderate to significantly abnormal MPS, on the other hand, had a high average event rate (6% per year) and would likely benefit from coronary angiography. The following are the most essential factors in estimating the likelihood of future events:
- The severity and degree of inducible ischemia.
- Thallium uptake in the lungs.
- Ventricular dilatation caused by stress.
- Ejection fraction of the left ventricle.
In general, left ventricular dysfunction markers indicate cardiac death, whereas inducible ischemia predicts acute coronary syndromes. Even after clinical examination, exercise ECG, and coronary angiography, MPS provides incremental prognostic value.
Myocardial Perfusion Scintigraphy after Angiography
In a subset of individuals, MPS is used to guide therapy after coronary angiography. For example, there could be a moderately severe coronary stenosis with atypical symptoms, a catheter tip spasm could cause confusion in interpretation, or a vessel could be difficult to visualize on its whole. MPS can be utilized to guide percutaneous or surgical intervention in multivessel disease.
Myocardial Perfusion Scintigraphy and Coronary Intervention
The recent development of ECG-gated MPS allows information on myocardial perfusion and function to be obtained from a single test, making MPS a helpful technique for risk-stratifying patients before major non-cardiac surgery. MPS can determine the necessity for revascularization in individuals with ischemic left ventricular dysfunction by assessing the presence and severity of inducible ischemia as well as viable but dormant myocardium. In individuals with recurrent angina, MPS can also be used to assess the success of coronary interventions and detect inducible ischemia. If the clinical situation allows, withhold MPS until about two months after the percutaneous intervention, as perfusion abnormalities may take longer to resolve even after successful intervention (for unknown causes).
Myocardial Perfusion Scintigraphy Activity
Despite the overwhelming evidence that MPS should be regularly integrated into diagnostic and therapeutic strategies, some centers still employ it infrequently. A lack of awareness of published instructions, poor local service, or long local wait times are all possibilities. All three challenges have been addressed in recent initiatives:
- The evidence for MPS has been detailed in a number of articles.
- Procedure guidelines have been created to assist centers with the fundamentals of service delivery.
- MPS reporting requirements have been improved with the help of teaching aids.
For centers intending to start or develop a nuclear cardiology service, published information on the clinical and business aspects of putting up service is available.
In heart problems, myocardial perfusion scanning is important for making diagnostic and therapeutic decisions. These are a series of non-invasive imaging tests that can be used to evaluate blood flow to parts of the heart by doctors. Obtaining data on myocardial perfusion and metabolite uptake is important for selecting the best medical treatment or intervention for improving one's cardiac health. These tests are useful for a variety of diagnostic and prognostic reasons in a variety of clinical settings, including evaluating angina symptoms, ruling out acute coronary syndrome as the main reason for chest pain, evaluating therapeutic outcomes after interventions, and determining whether the cardiac muscle is viable or scarred.