How helpful are EKG's for detecting hidden heart disease?
I pose this question because several patients asked this question just this week. It's also a frequent point of confusion and misperception.
Your EKG is nothing more than an expression of the surface electrical activity emitted by heart muscle activity. Multiple (12) leads are attached to the body simply to provide various "views" of this electical activity. EKG, or sometimes "ECG", is short for "electrocardiogram".
What modifies this surface electrical activity? Anything that modifies the electrical activity within the heart itself, or interferes with the detection of the activity. An old heart attack modifies the patterns of electrical conduction in the heart and that can change your EKG. An ongoing heart heart attack likewise. High blood pressure commonly creates changes in the EKG, as does lung disease. A bellyache can change your EKG, as can a stroke. (These non-heart-related phenomena probably are often due to changes in autonomic, or "automatic," nervous system activity.) The heart generates electrical activity in a predictable sequence that generates the heart beat, or "rhythm". EKG's are useful for monitoring heart rhythm, also.
Does having plaque in your coronary arteries have any effect on the EKG? None whatsoever , unless plaque rupture caused heart attack or is about to cause heart attack. So, you can have a horrendous CT heart scan score of, say, 3000, yet maintain a perfectly normal EKG, as long as the heart muscle is normal.
Then why bother with these iffy tests? They are indeed useful to diagnose the cause of active symptoms. For instance, go to the ER with chest pain and an EKG could show changes suggesting that the chest pain is a heart attack. EKG's are also useful for future comparison. Any change in EKG can suggest certain things, like new heart rhythm disturbances unrelated to coronary plaque.
Think of your EKG as just like buying a used car. Say I'm trying to sell you my 1999 Buick Century. It looks pretty good from the outside and I tell you that it has 70,000 miles and runs well. You ask to open the hood, look in the interior and take it out for a drive. I tell you no, you can't do that.
Would you buy the car? Of course you wouldn't. You were permitted only a very superficial examination of the car. You have no idea what's going on inside. Just because the paint job looks brand new doesn't mean the engine and transmission are good.
The same with your EKG: It's a superficial look at one aspect of this used car called your heart. If the EKG is normal, that's good, just like a good exterior on the Buick. But you cannot assume that the heart is otherwise normal.
View the EKG as a simple, superficial test that can only provide minimal reassurance, no matter how often you have it done.