I was sitting here just thinking about nuclear scans, and realised something. A perfusion scan, which is the most common, is one which checks blood supply to areas of heart muscle. Once intervention has occurred, such as stenting or bypass, this image should look pretty good. These scans take around 20 minutes and is certainly the type I've had twice. However, it hit me that this type of scan doesn't reveal heart muscle damage. Blood will still flow through dead areas of tissue and the scan would never know the tissue was in fact dead. A nuclear viability scan on the other hand works in a different way. First a scan is done using radioactive ammonia to show up the blood vessels, much in the same way as the perfusion scan. Then a radioactive glucose is injected which is metabolised by the cells in the body, including heart cells. After enough time has elapsed for the metabolism to establish, another scan is taken which shows the areas of tissue that have absorbed the glucose. This scan takes just over an hour.
Have I got this wrong? My cardiologist said I have no tissue death by looking at a perfusion scan, but surely that's nonsense? isnt it?
My understanding is that blood will not always pass through damaged heart muscle, even after intervention. I have asked that question and was told that dead cells no longer have the ability to absorb blood, the small vessels no longer exist once the cells die and there is no way for oxygen (or the tracer) to pass from blood to cell.
I have not read that anywhere, it's what a Cardiologist told me. Maybe someone with more knowledge will respond.
That's what I was told too. What I can't seem to establish is what happens to the blood vessels themselves. Let's give a simple scenario....
A patient has a heart attack, angiography reveals a total blockage to an area of the heart muscle. The blockage is stented then blood can flow again. But would it? Would the blood vessels still act as conduits of some kind, or be permanently collapsed? If the blood vessels still allow blood to flow then a perfusion scan would show good vascularisation, if they do not, then it would show as dead. Either way, a viability scan would reveal dead tissue.
I think my confusion comes from a comment my cardiologist made, which is a kind of contradiction "If I stent the LAD and the tissue is dead, it would be a waste of time because the Oxygen isn't needed". This seems to point to the idea that the blood vessels survive much longer. I believe heart tissue has a life of about 40 mins when starved, but I have no idea how long blood vessels can last. This begs another question too doesn't it?
When an emergency procedure is called for on a patient, some of the collateral vessels, if developed, are too small to be seen on angiography. Mine showed clearly on a perfusion scan, but nothing showed on angiography which is why they thought the heart muscle was probably dead. How do they make the decision whether to stent or not when they don't see the whole picture? The call could be enough to create tissue damage or save it.
Wow, three years later and still so many questions but ones I should have thought of in the beginning I suppose.
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