One of our associates had a mild heart attack over the weekend. He’s doing fine, thank you, and the prognosis is good. He will require a procedure of some sort, the exact type is yet to be determined.
Here’s the thing though: The cardiologist examined the data from an EKG and told our associate that he’d experienced the attack within the previous four days! I admititedly know nothing about EKG’s, but I would LOVE to know just how this doctor was able to tell approximately when the attack occurred by examining the data. Certainly an EKG is nothing like a seismograph. Or is it? Of course not! Inquiring minds want to know. Is there a doctor in the house?
I don’t think that’s strange at all.
About 4 years ago, I was diagnosed with type 2 diabetes. My doctor looked at the pattern of hair vs. baldness on my legs, and determined that I’d been diabetic for 7 years.
I know that, when a cardiologist examines an EKG, there are all sorts of little subtleties that the rest of us wouldn’t even notice. And if they took more than one EKG, they can extrapolate the data over time.
They have their ways of knowing.
I’ll chime in until a doctor answers 
There are tell-tale signs of damage from a heart attack that are visible on an EKG. These subside over a period of days, enabling a doctor to guess how long it’s been. It’s helpful to have some background on the patient, and knowledge about what drugs they’re taking, also.
Arjuna34
The EKG pattern following a heart attack often (but not always) follows a predictable pattern.
Basically, the electrical properties of the heart muscle change when its been damaged and this shows up on the EKG (in fact, that’s what an EKG is - a recording of the electrical depolarization and repolarization pattern of the heart muscle).
In any case, following damage to the heart muscle, there is a typical pattern of polarization changes. For those interested in such things, the main information is found in the so-called ST segment and T wave.
One site about EKG’s that looks interesting is this one.
Sorry, I should have said explicitly that the pattern of changes is temporal as well as in the changing shape of the waves themselves.
Let’s not make this a lesson in cardiac anatomy, electrophysiology, or vector analysis, OK?
Briefly, the EKG, or for nitpickers out there, the ECG, records variations in the net direction of electricity flowing through the heart with each beat.
A heart attack, or myocardial infarction, results in the death of heart muscle cells. This causes the loss of some electrical current, and a change in the net vector during the phase of the heartbeat when electricity would normally pass through the dead area. These changes take several days to develop after a heart, and are usually permanent. Heart muscle that is not working well, however, is less effective at conducting electricity than normal tissue, and this causes different kinds of changes that typically are only seen for a few days after a heart attack.
So, if you’re seeing someone who has both types of changes at the same time, they probably had their heart attack more than 24 hours ago, but less than 3-4 days ago.
Another possibility is that the doctor combined information from blood tests with information from the ECG. When heart muscle cells die, protein contained inside the cell leaks through the dissolving cell membrane into the bloodstream. High levels of certain proteins indicate a recent heart attack. The 4 day time frame in your associate’s case would be compatible with this.
The process of diagnosing a heart attack (known in the General Medicine lingo as simply a “rule out”) is to admit the patient, get an EKG, and check enzyme levels in the blood over the next 24 hours. The EKG can show a characteristic pattern, but doesn’t always; it’s especially difficult if you don’t have an old one to compare it to. The enzymes tell the story more than anything.
There are several enzyme changes that occur with a heart attack, but the mose useful is creatinine kinase, or CK-MB. An increase in serum CK-MB is fairly sensitive and specific for an MI, and the increase is detectable within six hours of the MI and lasts until 3-4 days later. Another enzyme is troponin, which (IIRC) is not as sensitive or specific as CK-MB but rises at the same time and stays elevated for 5-7 days.
I’d guess that your friend’s EKG showed an ST-segment elevation and his troponin level was elevated, but his CK-MB was normal. Other enzyme tests plus more minute changes in the EKG (which I admit I don’t have a good grasp of yet) could pin it down even further.
Glad your friend is doing well.
Dr. J
I believe that troponin is both more sensitive and more specific than CK-MB. Several recent references are here, here and here.