There is a growing body of evidence to support myocardial perfusion imaging as a clinically effective and cost-effective method of managing patients with actual or suspected cardiac disease. It is becoming increasingly used as the investigation of choice for several clinical indications. The British Nuclear Cardiology Society was founded in 1981 to promote the use of this branch of science in the United Kingdom.
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Myocardial perfusion scintigraphy imaging
- Myocardial perfusion scintigraphy (MPS) with single photon emission computed tomography (SPECT) uses a radio-pharmaceutical that is taken up into heart muscle in proportion to localised blood flow and stays in myocardial cells whilst scan is performed. Most use either thallium-201 or technetium-99m in proprietary compounds. One study found that the procedure was not used to its full potential in the investigation of cardiac disease in elderly patients.
- Stress test, eg treadmill, bicycle, IV adenosine or IV dobutamine.
- Thallium or technetium then injected.
- Image of myocardial perfusion then taken immediately and again over four hours after stress.
- NICE-released guidance in 2003 recommended that MPS with SPECT should be used in the following circumstances:
- As a first-line diagnostic tool for the exclusion of coronary artery disease in patients for whom exercise stress testing poses problems in interpreting or where sensitivity is poor. This may include women, patients with cardiac conduction defects (eg left bundle branch block) and for people who have difficulty using a treadmill for whatever reason.
- As part of an investigation strategy in patients with a lower risk of coronary artery disease (based on risk factor calculations) in the prediction of likely future cardiac events, as a less invasive alternative to coronary angiography.
- In patients with established coronary artery disease with persistent symptoms after a myocardial infarction or after a reperfusion intervention.
- Infarction causes matched perfusion defects during stress and at rest. Reversible ischaemia shows defects during stress which re-perfuse at rest.
- Severity, extent and number of reversible defects are a good prognostic indicator. A normal study implies a risk of an adverse cardiac event of less than 0.5% per annum.
- Less sensitive in multiple small vessel coronary disease, eg diabetes mellitus.
- Infarct-avid imaging:
- Can be used in the diagnosis of myocardial infarction.
- Commonly uses technetium-99m-stannous-pyrophosphate that concentrate in damaged myocardial cells for 'hot-spot' scanning.
- Scans are best performed 24-96 hours after myocardial infarction. Alternatively, can use cold-spot scanning where non-viable heart muscle does not take up the radio-pharmaceutical.
- Unfortunately, because of the delay this method is of no value in identifying patients suitable for thrombolytic therapy.
Radionuclide ventriculography - multiple gated acquisition (MUGA) scans
- Scintigraphy can be used to estimate ventricular ejection fraction as an indicator of left and right ventricular function.
- In first-pass method, technetium-99m-pertechnate is injected as an IV bolus and its passage through the heart recorded every second. The change in radioactivity recorded with time is related to the ejection fraction.
- With the gated cardiac blood pool method, the patient's own red blood cells are labelled with technetium-99m-pertechnate. Regional wall motion studies can also be performed with this method.
- Can assess both left ventricular and right ventricular function after myocardial infarction.
- Left ventricular ejection fraction measurement.
- Monitor anthracycline cardiotoxicity.
- Radio-labelled technetium red cells are injected followed by imaging.
- Combination with stress test allows assessment of cardiac reserve.
- Monitor treatment response in cardiac failure and cardiomyopathy.
- Useful for serial measurements during anthracycline therapy.
- Reliable in unechogenic subjects. Otherwise the procedure carries a high radiation dose and echocardiography is preferable for most patients.
- Cardiac dysrhythmias may interfere with results.
- One study found that this method contributed to a significant improvement in risk stratification and secondary prevention strategy in patients with known coronary artery disease.
- Cardiac MRI is non-invasive, has high spatial resolution and avoids use of potentially nephrotoxic contrast agents or radiation.
- Has an important part in diagnosing congenital heart disease as well as disorders of the pericardium, cardiac tumours, atrial or ventricular thrombus, pericardial thickening, myocardial hypertrophy and valvular disease.
- May also be used to image the coronary vessels and disease of the aorta, including aortic dissection.
- Is contraindicated for many prosthetic valves and for patients with cardiac pacemakers.
- The slowness of scanners available at most centres limits its usefulness but the introduction of new faster techniques will allow breath-hold and real time scans.
- The role of cardiac MRI is very likely to continue to increase for assessing cardiac structure and function as well as detecting coronary artery disease and the assessment of those patients who may need angioplasty.
- One study found that MRI might be more sensitive than scintigraphy in detecting small areas of myocardial necrosis.
- MRI is considered to be the gold-standard imaging modality for the assessment of aetiology, myocardial anatomy, regional and global function and viability in patients with ischaemic heart failure. In patients with non-ischaemic heart failure it also allows assessment of fibrosis, infiltration and iron overload.
- Various enhancements have recently been developed including cine MRI. Stress perfusion MRI is superior to stress perfusion single-photon emission computed tomography in patients with multivessel coronary artery disease. MRI is not as widely used as other modalities in the investigation of cardiac disease because it is technically difficult but education and training should eventually rectify this.
Computed tomography (CT)
- Mainly used to demonstrate aortic dissection, pericardial thickening and fluid, cardiac tumours and coronary calcification. CT with IV contrast is the most reliable and practical technique for the investigation of aortic dissection.
- Spiral CT is the investigation of choice for pulmonary embolism.
- With latest spiral CT, scanners can acquire whole volume of heart in a single breath-hold but still needs 0.3 sec for a single slice so needs ECG gating and IV contrast with very fast electron-beam scanner to image the heart.
Further reading & references
- British Nuclear Cardiology Society, Information 2010.
- Perrone-Filardi P, Costanzo P, Dellegrottaglie S, et al; Prognostic role of myocardial single photon emission computed tomography in the J Nucl Cardiol. 2009 Dec 24.
- Yao SS, Rozanski A; Principal uses of myocardial perfusion scintigraphy in the management of patients with known or suspected coronary artery disease. Prog Cardiovasc Dis. 2001 Jan-Feb;43(4):281-302.
- Angina and myocardial infarction - myocardial perfusion scintigraphy, NICE Technology Appraisal (2003)
- Nott L; Thallium Scintigraphy Nuclear Cardiology Seminars
- Khaw BA; The current role of infarct avid imaging. Semin Nucl Med. 1999 Jul;29(3):259-70.
- Society of Nuclear Medicine; Procedure Guideline for Gated Equilibrium Radionuclide Ventriculography 2002.
- Hashimoto A, Nakata T, Wakabayashi T, et al; Incremental prognostic value of stress/rest gated perfusion SPECT in patients Circ J. 2009 Dec;73(12):2288-93. Epub 2009 Oct 2.
- Nott L; Diagnostic Imaging Modalities Seminars in Nuclear Cardiology
- Constantine G, Shan K, Flamm SD, et al; Role of MRI in clinical cardiology. Lancet. 2004 Jun 26;363(9427):2162-71.
- Monte GU, Drager LF, Souza FS, et al; Magnetic resonance vs technetium-99m pyrophosphate scintigraphy in the detection Arq Bras Cardiol. 2008 Aug;91(2):113-8.
- Karamitsos TD, Francis JM, Myerson S, et al; The role of cardiovascular magnetic resonance imaging in heart failure. J Am Coll Cardiol. 2009 Oct 6;54(15):1407-24.
- Ishida M, Kato S, Sakuma H; Cardiac MRI in ischemic heart disease. Circ J. 2009 Sep;73(9):1577-88. Epub 2009 Aug 10.
|Original Author: Dr Colin Tidy||Current Version: Dr Laurence Knott|
|Last Checked: 20/04/2011||Document ID: 2525 Version: 22||© EMIS|
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