What Causes a Borderline ECG?

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  • Written By: Mary McMahon
  • Edited By: Nancy Fann-Im
  • Last Modified Date: 03 August 2018
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There can be a number of causes for a borderline electrocardiogram (ECG), a study of electrical activity in the heart. When an ECG is borderline, it means that some anomalies are present and the doctor needs to evaluate the patient to determine whether they are of significance. Patients should not panic if they have a borderline ECG result because there can be many reasons for this, and it is not necessarily dangerous.

In a borderline ECG, some of the readings do not look quite right, but they are not pushed into the margin where they are an immediate cause for concern. Sometimes, this occurs simply because a patient was stressed out or worried. Many patients are nervous before an ECG, and this can cause small variations in their heart rates that may appear on the test. The doctor might discard the results if the patient appeared especially worried, and request a new test to see if more accurate values can be obtained.

Another reason for a borderline ECG is improper procedure during the test. Sometimes the electrodes are not placed correctly or there is something wrong with the machine and the reading is off. Patients with large breasts or significant deposits of fat in their chests are more likely to have a borderline ECG because it is harder to place the electrodes. The technician may spot the problem if she has access to a real-time readout, and may halt the test to reposition and get a better reading.


A borderline ECG can also occur when a patient does have a genuine anomaly, but it is minor. The test will show small variations in the heart rhythm and function, but they are not significant enough to be a cause for concern. If a patient has a borderline ECG, the doctor might recommend testing again in the future to monitor the issue. Otherwise, the doctor may simply note the finding in the patient's chart so it will be available for future reference.

Patients should be aware that ECG equipment often marks up the printout with notations like “borderline” on the basis of stored algorithms. The equipment is sometimes wrong, because it does not account for patient history and other factors. A doctor can review the test result and determine whether it is significant. If it is, he will recommend some additional testing to learn more about the patient's situation. When it is not, the doctor will assure the patient that it is not anything he needs to worry about.


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Post 5

My test ECG indicated borderline, as well and more scary, possible septal infarct. My doctor said nothing, but after I looked it up, I am alarmed.

Post 3

@feruze-- Do you have any uncommon symptoms like pain in the chest area, arms or difficulty breathing?

I think if your doctor wants more tests done, you should definitely get it checked out. I think doctors also look for symptoms of coronary heart disease when there is a borderline ECG test to continue looking into it. Even if you don't have symptoms, I think it's worth having it done. I don't mean to worry you but I've heard of people who have had a stroke or heart attack without any symptoms whatsoever.

You should probably get a second interpretation with your ECG results from another doctor or have the test repeated if you don't trust your current doctor about this.

Post 2

@alisha-- I just had an ECG and it came out borderline as well but my doctor is sending me to a specialist to get more tests done.

Do you think this is unnecessary then? Or maybe he saw something else that he didn't tell me about?

Maybe I should get another ECG interpretation from another doctor. I don't really want to go to a specialist for more tests if this is unnecessary as I'm going to have to pay quite a lot for it.

Post 1

I have had several ECGs taken until now, and I've noticed that doctors don't generally mention a borderline ECG when they don't suspect that anything is wrong. I can't blame them because I think patients (including myself sometimes) tend to get hyped up about test results because we take them too seriously and assume that they always work perfectly.

A friend of mine had the same experience where she had an ECG taken with borderline results that the doctor didn't even mention. She saw the results later and was really upset that the doctor hadn't discussed this with her. Apparently he said that all is well and that she doesn't have a cause for worry.

I tried to

assure her that this is normal and happens a lot. After all, doctors have a lot of experience with ECG machines and they know when something is really off versus the machine not working right or the patient being especially stressed that day. I'd prefer my doctor to not tell me about that rather than have me worry for no reason because I don't know what's going on.

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