Reliability of Stress Thallium Test

[nspower]

If a stress thallium test shows scar tissues does it mean, the scar is across complete thickness of that particular heart  muscle section. Could it be possible that the scared muscle tisssues on the surface, which is imaged, may actually have healthy tissues below them.

It is said that blood is locally distributed to heart muscles by smaller size arteries. Can the same section of muscle have blood supplied from two different sources and when one of the sources is blocked due to MI, some layer of same muscle continues to get blood, limiting the scaring to only that layer of muscle which is deprived of blood supply.

Since stress thallium test scan the thallium only on the surface can it be possible that (i) the healthy muscles shown on the image may actually have scarred tissues in lower layer and (ii) the upper layer which appear as scar in fact has healthy muscle tisues below it.

Thanks

[nspower]

Thanks All. Kenkeith's reply calrifies my doubts. When I compared my echo reports with my stress test, the echo report sometimes showed movement in the scarred part of heart whereas stress thallium report identified this area as dead, which raised a doubt in my mind whether there could be some live pockets across the thickness of muscles.

If some of the thickness of scarred area is still alive this means it is getting blood supply. So the question remains, can the scarred area which also has some alive tissues, have multiple source of blood supply, implying that the source of blood supply specifically to the scarred mass was disrrupted during MI whereas the tissues which are alive in the scarred region (either below or above the scarred tissues across thickness) continued to get the blood supply during MI. I am not sure if I have made myself clear?

My recent stress thallium report says "pockets of small ischemic area adjascent to scarred area". Can this be due to blockage of small arteries, locally. This comment was not there in last year's stress thallium report.

Can some one guide me to reference materials in this regard?

Thanks.

[ed34]

My reply wasnt aimed at you, I was just stating I was on the wrong track.
No apology necessary.

[erijon]

"I misunderstood the question, I thought it was asking if two different blood supplies went to the same tissue."

I was talking about myself from my first post where I stated I did not know the answer, did not try to imply you were worng................. sorry if it came across that way.

[ed34]

I misunderstood the question, I thought it was asking if two different blood supplies went to the same tissue.

[erijon]

There you go, that's the nice thing about the forum, what one person doesn't know, the next will!

[kenkeith]

QUOTE: "If a stress thallium test shows scar tissues does it mean, the scar is across complete thickness of that particular heart  muscle section. Could it be possible that the scared muscle tisssues on the surface, which is imaged, may actually have healthy tissues below them".
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>>>>Damaged heart cells does not necessarily mean the section is completely scarred as can be seen with an MRI.   "As part of a baseline MRI, the researchers used a technique developed at Hopkins to map and gauge the precise amount and distribution of scar tissue in the heart’s muscle wall. The amount of scar tissue was measured as a percentage of the thickness of the muscle wall, which is on average about 1 centimeter. Composed of dense, fibrous tissue, with little to no blood supply, scar tissue was clearly visible on the image, the researchers say. After MRI, each patient underwent a standard electrophysiological assessment with a catheter.

Statistical analysis showed that the five patients who tested positive had the characteristic scar pattern, ranging from 26 percent to 75 percent scar tissue, with MRI.
While MRI did not explain why the scar tissue forms, such scar patterns have been previously noted on autopsy studies of patients with heart disease. The researchers believe that previous inflammation, injury or excess stress on the heart wall may lead to this fibrosis and scar formation.

The risk with damaged heart cells is arrhythmia. Researchers at Johns Hopkins have found that people whose muscle wall thickness contained more than 25 percent scar tissue were approximately nine times more likely to test positive for a fast and dangerous heart rhythm known as ventricular arrhythmia.  

A therapeutic implication with MRI can be to identify the telltale scar pattern and that could potentially improve existing procedures to ablate, or burn off, regions of the heart muscle that trigger arrhythmia.  Yes, there are viable layers of a scar tissue section that are viable and have a blood supply source.  

[ed34]

"It is said that blood is locally distributed to heart muscles by smaller size arteries. Can the same section of muscle have blood supplied from two different sources and when one of the sources is blocked due to MI, some layer of same muscle continues to get blood, limiting the scaring to only that layer of muscle which is deprived of blood supply"

Hi nspower, I think you are describing a fantastic human design modification which would be brilliant if possible. Imagine having two different sources of blood supplying the same area of tissue. Blockages in arteries would stop one feed, still leaving the other as a backup. However, this is not what happens in the Heart, unfortunately. If it did, we would not have such as thing as Angina.

In reality, the whole body is effectively supplied by one artery, the aorta, which is like the trunk of a large tree. This breaks down into various other major arteries, which in turn also break down into smaller and smaller vessels. Just like looking at the branches on a tree. Eventually arteries become tiny vessels called arterioles which then become the minute capillaries which are so small and thin that gas molecules can pass through the walls for living cells to use. The capillaries bundle eventually bundle together, becoming veins and these get larger and larger running back to the heart, like an upside down tree.
If you put all vessels end to end, they will add up to more than 60,000 miles. This should give you an idea of how thin most of them are.
A single artery turns into many capillaries feeding an area of tissue, such as heart muscle and that will be from the surface to the lower layer. In thicker fleshy tissue, it is likely you will find capillaries from different arteries in different layers. So in the heart, when an artery blocks, many capillaries in one section will be cut off from their supply.
Imagine it like a single tap with hundreds of hose pipes connected. Turn off the tap, they all lose their supply.
In some individuals however, small vessels called collaterals grow across to supply the deprived area of tissue. These come from an artery still receiving a good supply of blood.
I'm not sure how the blood finds its way back to veins however.

[erijon]

My understanding is that scar tissue in the heart is not delineated by layers. Once the area of the heart is dead, I don't think it is only a surface issue, perhaps some one with more knowledge of that will post.

It sounds like you are asking about collaterals. These micro arteries can grow around a blockage in a main artery and continue to supply blood to the heart muscle beyond the blockage. Again, I have never heard about heart muscle being separated into layers with the surface being affected but the underlying area being disease free, If SPECT was used during your test it would  help confirm the area as dead scar tissue by looking at the wall motion to determine if it is normal and contracts with the rest of the heart muscle or if the motion is absence or impaired which would show permanent muscle damage or the possibility of cells that have been shocked into hibernation.

Hope this helps,

Jon