This is blog 3 of 3 explaining the most common types of cardiac testing encountered when doing preop evaluations of patients at ambulatory surgery centers. I’ve already talked about two of the best cardiac tests: EKG and ECHO.
Although they go by slightly different names based on the type of radioactive dye used: Thallium, Myoview or Cardiolite, they all do largely the same thing: assess blood flow to the heart, i.e., test for the presence of ischemia (tissue that is not getting sufficient blood flow and oxygen) in the heart. The test involves injecting radioactive dye intravenously and then taking nuclear medicine images during physical exertion (usually on a treadmill) and at rest. By the way, for patients who can’t walk on a treadmill, there are pharmacologic ways to stress the heart. The rest images maybe done a few days later, if needed.
An old MI shows up as a “defect”, i.e., an area of the heart that doesn’t get any blood flow either during exercise or at rest. An area of ischemia, on the other hand, will show up as a “reversible defect”, i.e., an area that doesn’t get blood flow during exercise but does get blood flow at rest.
- What it is – it’s a radioactive image of the heart during exercise and at rest
- What it can tell you for sure – whether the patient has had a prior MI or has ischemia during exertion.
- What it can maybe tell you – it’s a fair indicator of pump function (ejection fraction)
- What it can’t tell you – valve function, heart rate or heart rhythm.
- What to look for – a reading that says “normal perfusion”
This is a great test for assessing blood flow to the heart, and, if normal, can give you a high degree of reassurance that the patient is not in jeopardy of having a perioperative MI. However, like so many things in life, the devil is in the details, and frequently this test will open up a proverbial “can of worms”. This happens when the test is “equivocal”, i.e., not definitively ruling in or out the presence of ischemia or an old MI. Like all xrays, there is a fair amount of interpreter subjectivity in reading nuclear medicine stress tests. This occurs when the test is a “maybe” for old MI or ischemia and the reader states that “it is either attenuation artifact or an inferior MI or ischemia”. Now what? Not too infrequently, patients with equivocal scans will end up getting a cardiac catheterization aka a “cardiac cath”.
So that’s it. The “Big 3” of cardiac testing explained. In coming blog articles, I will talk about interpreting cardiac caths, heart valve abnormalities and common sense preop testing from one anesthesiologist’s (me!) perspective. If you have questions, comments or suggestions for other topics, feel free to reply in the comments section and make sure to subscribe to our newsletter to stay in the know when it comes to hot topics in the ASC world. Now get out there and impress your nursing and anesthesia colleagues with how smart you are!!!!