What Does a Borderline ECG Mean?

A borderline ECG means the machine's automated analysis found something slightly outside its expected pattern, but not clearly abnormal. The word usually comes from the computer printout at the top of the tracing, before a clinician has reviewed it. Many borderline findings turn out to be normal variations once a clinician looks at the full picture.

This guide explains how to read the label. It cannot tell you what your own ECG shows; only a clinician who knows your history and symptoms can do that.

A borderline label does not mean you can ignore symptoms. Call your local emergency number straight away if you have chest pain or pressure that feels tight or squeezing, lasts more than a few minutes or comes and goes. Do not drive yourself to hospital.

Also get emergency help for:

• Chest discomfort spreading to the arm, shoulder, neck, jaw or back
• Shortness of breath, sweating, nausea or feeling light-headed
• Unusual tiredness with nausea or vomiting, which can be heart attack symptoms, particularly in women
• Fainting, collapse or pale, blue or grey skin or lips

Most ECG machines measure the waves automatically and print a short statement such as "normal ECG", "otherwise normal ECG", "borderline ECG" or "abnormal ECG". This is a screening summary. The computer does not know why the test was done, what symptoms you have or what your earlier tracings looked like.

A clinician then reads the tracing itself. One emergency department study reported that around 60% of triage ECGs at its hospital were labelled "borderline" or "abnormal" by the computer, and its authors said their findings were not meant to encourage skipping a physician's interpretation. In practice, the clinician's written conclusion is the one to rely on, and it may differ from the printout.

It is common for a printout to say "borderline" while the clinician's report says normal or within normal limits. This usually means the reader looked at the measurement the computer flagged and judged it acceptable for you. It is reasonable to ask which finding was flagged and why it was not a concern, so you can mention it if another ECG is taken in future.

Keep a copy of the report. If you have an ECG later, perhaps before surgery or at a new practice, the earlier tracing helps the next reader see that the finding is long-standing rather than new.

Wording varies between machines and software, but borderline statements often describe a measurement close to a cut-off or a pattern that can be normal in some people. Examples that may appear on a report include:

• Nonspecific or borderline ST-T wave or T wave changes
• Sinus bradycardia (a slow but regular rhythm) or sinus tachycardia (a fast regular rhythm)
• Left or right axis deviation, describing the main direction of the heart's electrical signal
• Incomplete right bundle branch block or other minor conduction delays
• Borderline intervals, such as a QT or PR interval near the upper limit
• Possible chamber enlargement, which an ECG can only suggest and an echocardiogram can measure
• Early repolarisation, a common variant often seen in young and active people

An ECG is a snapshot over a few seconds. Heart rate, breathing, body position, recent food, medicines and blood salt levels can all shift the waves slightly. Some medicines can also affect the accuracy of results. A measurement that lands just over a threshold on one day may be just under it on another.

Healthy hearts also differ. Some patterns flagged by software can be normal variants, for example in fit or younger people. That is why a borderline label is weighed against your age, fitness, symptoms and previous ECGs, not read on its own.

Not by itself. MedlinePlus notes that ECG results cannot diagnose a heart condition on their own, and that other tests may be needed before a diagnosis is made. A borderline statement is even less definite than an abnormal one: it flags something worth a second look rather than a confirmed problem.

At the same time, the label should not simply be dismissed if it has not been reviewed. Ask whether a clinician has read the tracing and what they concluded. If the ECG was done because of symptoms, the symptoms and the clinician's assessment guide what happens next, not the single word printed by the machine.

Many people with a borderline ECG and no symptoms need no further tests. Your clinician may suggest more if the finding is new, if you have symptoms, or if you have risk factors or a family history of heart disease.

A repeat ECG can check whether a finding persists or was linked to how the recording was taken. An echocardiogram uses ultrasound to show the heart's structure, pumping and valves, so it can answer questions an ECG can only hint at, such as whether a chamber is enlarged. A Holter or event monitor records the heart rhythm for longer if symptoms come and go, and a stress test looks at the heart during exertion.

Ask for a copy of the report and the tracing if possible. These questions can help:

• Which finding made the computer call this borderline, and do you agree with it?
• Is this new compared with my previous ECGs?
• Could my medicines, heart rate or the recording itself explain it?
• Does this change anything given my symptoms, age and family history?
• Do I need a repeat ECG, an echocardiogram or a heart monitor, and what would it show?
• Which symptoms should make me seek urgent care?

SameCase lets patients and verified doctors share de-identified cases. Looking at how others with similar borderline ECG reports were followed up can help you prepare questions and understand the terms on your printout. Similar cases cannot tell you what your ECG means, and they do not replace your own clinician's reading.