EKG's and heart disease

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.

Comments (6) -

  • David

    4/16/2007 10:32:00 AM |

    Sorry to insert this here since it only relates indirectly to the topic at hand, but I would be interested in your reaction to the following news item courtesy of TheStreet.com (TIA):

    "AGIX - based on further analysis, the company believes the new class of drug, called AGI-1067, may be able to treat other indications."
    "Although the formal primary composite endpoint in ARISE was not met, we believe that the trial generated strong evidence that the use of AGI-1067 will produce tangible clinical benefits for patients with coronary artery disease," said Marc Pfeffer, professor of medicine at Harvard Medical School and one of the principal investigators, said in a statement.
    AGI-1067 is a drug with both anti-inflammatory and anti-oxidant activity that the company is developing to prevent serious cardiovascular events in people at risk of heart disease.
    The drug is the first of a new class of medicines called vascular protectants, which work by blocking the inflammatory process in atherosclerosis, which is the buildup of fat, cholesterol and other substances in the inner lining of an artery.
    The trial, which involved 6,144 high-risk patients in four countries with unstable angina, or chest pain, who had suffered a heart attack.
    The trial met some predefined secondary goals such as reducing by 19% the risk of cardiovascular death, heart attack and stroke related to the build up of fatty plaque in the arteries.
    Surprisingly, the drug also showed a beneficial effect on diabetes, yes - diabetes, reducing the risk of getting diabetes by 64% compared to a placebo.
    Diabetes patients are at high risk of heart disease.
    To repeat = "reducing the risk of getting diabetes by 64%". That's tremendous!
    Chief Medical Officer Robert Scott said, "This gives us an opportunity to access both those markets."
    Whether that will require additional clinical studies isn't clear.
    AstraZeneca had agreed to pay AtheroGenics as much
    as $1 billion for exclusive rights to the drug. Analysts had expected the drug to reach annual sales in excess of $1 billion if successfully launched.
    AtheroGenics Chief Financial Officer Mark Colonnese said the company had the financial strength to bring the drug to market alone if necessary.
    The company said that it will show the large data set to the Food and Drug Administration but that the results would require confirmation.
    imo - If the FDA carefully looks again at the study, that same FDA might decide to give
    a fast track to the Phase III trial."

  • Dr. Davis

    4/17/2007 6:29:00 PM |

    Sounds interesting. However, it sounds like it's still in the proprietary stage in which the manufacturer still keeps a lot of the particular close to the vest. We can only wait for more details on what this is, how it works, and whether it offers real benefits in real people, and at what price (monetary and otherwise).

    Dr. Davis

  • Michelle C

    10/26/2007 7:24:00 PM |

    Will all "old" heart attacks show up on EKG?  In other words, if the EKG is completely normal, can the existence of an "old" heart attack be ruled out?


  • Dr. Davis

    10/27/2007 1:25:00 AM |

    Hi, Michelle-

    No. Ekg's are kind of like judging a used car by its finish--it might look good on the surface, but beneath . . .

  • kokil

    3/2/2010 7:18:38 AM |

    Dr. Davis,

    I am curious to know if ECG results or a treadmill test results can vary for a asthamatic patient vs. him actually having a problem in his heart? Please suggest if in your experience ECG or treadmill test results have experienced a change for other reasons than blockages in the arteries.


  • buy jeans

    11/3/2010 12:25:14 PM |

    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.