Q. I just finished watching the lectures for today and I had a question about the part you talk about what happens to the heart after an MI. You talked about if someone dies from an MI and an autopsy was performed you would not see any signs until at least 4 hours after death. However, is this true for all the way up to weeks 3-8? To better clarify, do people who die from an MI still develop a scar 3-8 weeks after passing or is this just for people who survive a MI? That would be crazy if our bodies still did this after we passed.
A. These are great questions! There are a several things to unpack here:
- What does heart tissue look like immediately after a myocardial infarction?
- How does that appearance change as the tissue heals?
- If the patient dies a few hours (or days, or months) after an MI, what does the tissue look like at autopsy?
The big-picture take-home point from this part of the lecture is that it takes a while to see abnormalities in the heart after an MI. So if you have an MI at noon, the infarcted region of the heart will look totally normal until at least 4 pm. And then, it will begin to start showing abnormalities (the myocytes will become more red, and then they’ll shrink a bit and start to look wavy, and then after about 12 hours neutrophils will start to show up, etc.).
Normally, of course, you don’t take biopsies of the heart in a person after they’ve had an MI! So we’ve only learned about the way things look at certain times by doing autopsies on patients who have died after an MI.
And in real life, the only time that we really care about the microscopic appearance of the heart after MI is at an autopsy. In that setting, it can be super helpful, because you can find out first of all whether the patient actually had an MI – and secondly, you can estimate how long ago that MI happened.
So back to our patient who had an MI at noon. If that patient dies at 2 pm, and you do an autopsy, the heart tissue will appear totally normal under the microscope. If the patient dies at 8 pm, though, the heart tissue will probably show evidence that there was an MI (it might be subtle – but you should be able to see something). And if the patient dies a couple months later, then you’ll see a fibrous scar in the region of the MI.
To get back to your questions…I think what you’re asking is: Does the heart tissue continue to develop changes (like scarring, or neutrophil infiltrate, etc.) after death? And the answer is no – when a person dies, the tissue is “frozen” at that point. So whatever process was taking place in the heart at the time of death (neutrophils infiltrating the tissue, macrophages chewing up debris, fibrous tissue starting to form…), that process stops as soon as the patient dies. And no matter when you do the autopsy, you’ll see the heart as it was at the time of death.
There’s one caveat to all of that, which is that very quickly after the patient dies, the body tissues start degenerating/breaking down. The process can be slowed by cold temperatures (which is why bodies are kept in a refrigerated state until the autopsy can be performed) – but even so, the longer you wait to do the autopsy, the “worse” the tissue will look under the microscope. It just sort of becomes mushy, and you lose cellular definition (the nuclei and cell outlines fade away), and eventually it’s really hard to see what’s going on.