Makindo Medical Notes

If you want to find a way to discriminate well perfused from poorly perfused myocardium you must induce an area of ischaemia so there is a large difference between perfusion and therefore ischaemic between 2 areas. This can then be exploited as above.

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• All these tests play on the fact that any increase in myocardial oxygen demand results in an area where demand outstrips blood supply so there is a detectable difference in perfusion between rest and exercise scans when there is a significant usually greater than 70% cross-sectional lumen fixed coronary stenosis impeding flow.
• Ischaemic areas will appear "cold" on nuclear scans or there will be relative wall motion abnormalities on stress echo.
• Exercise stress test using ST depression as an objective measure of impaired myocardial perfusion
• Dobutamine stress echo - using dobutamine to increase myocardial oxygen demand and then looking for regional wall motion defects suggesting poor perfusion
• Technetium study - studies the radioactivity over the heart following injection of a radioactive isotope. Myocardial O₂ demand may be increased using dobutamine or exercise
• THALLIUM, MIBI or SESTAMIBI or MYOVIEW scan - thallium is injected and its presence in the myocardium can be measured as it is radioactive and its distribution is a good guide to perfusion Thallium distributes much in the same way as potassium. Redistribution of thallium sometime after exercise to areas that appeared "cold" on exercise suggests reversible ischaemia. Technetium scans provide better images but are similar in other respects to thallium.
• Using Adenosine or dipyridamole increases blood flow similar to exercise and can be used to give a pharmacological challenge for those unable to exercise much as dobutamine does.
• Coronary angiography - direct 2D representation of coronary blood flow using radio-opaque contrast injected into the coronary arteries
• MUGA scan assesses LV function