An ST depression is a possible outcome of an electrocardiogram (ECG) test. It can indicate health conditions such as hypokalemia, myocardial ischemia, or a side effect of medications.

Doctors may decide to order an ECG when evaluating a person’s heart. This is a test that measures the electrical activity in a person’s heart. It can help a doctor diagnose and monitor a large number of conditions, including:

  • blocked blood vessels
  • thickening of the heart’s walls
  • arrhythmia
  • heart failure
  • heart attack

This article explains what an ST depression is and what may cause it. The article also outlines some possible treatments for specific causes of ST depression.

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ST depression is a term that refers to the position of the ST segment in a person’s ECG results.

ECG results appear on a graph as a waveform with spikes that correspond to the electrical activity in the heart. According to the American Heart Association (AHA), the points on this graph represent different waves of electrical activity. There are three main waves that make up this graph.

These three waves are:

  • P wave: This wave shows the electrical activity occurring in the atria. These are the two upper chambers of the heart.
  • QRS complex: This shows the electrical activity in the ventricles — the two lower chambers of the heart — that stimulates them to contract.
  • T wave: This shows the electrical activity involved in the heart’s ventricular repolarization. This means it shows the electrical reset of the heart as it prepares for the next cardiac cycle.

The ST segment appears in the ECG results. It corresponds to the area visible at the end of the QRS complex and the beginning of the T wave.

A 2021 article notes that if the ST segment appears abnormally low and sits below the baseline, then a person is said to have ST depression. ST depression has associations with a number of medical conditions, so it can have a variety of causes.

Clinically speaking, the ST segment represents the period in the cardiac cycle when the muscular layer of the heart contracts to expel blood from the ventricles.

There are a number of things that can cause a person to have ST depression in their ECG results.

The conditions that have associations with ST depression include:

  • Myocardial ischemia: This is the term for an imbalance of oxygen supply to the heart. It often occurs when something obstructs blood flow to the heart muscle. This may be due to a partial or complete blockage of a coronary artery and can lead to a heart attack.
  • Hypokalemia: This condition occurs when blood levels of potassium are low. It can cause a number of symptoms, including muscle weakness that can result in paralysis.
  • Left bundle branch block: This condition occurs when the electrical impulses to the heart’s left ventricle become slower. This can make it more difficult for the heart to pump blood efficiently, particularly in people with heart failure.

ST depression also has links to the use of the medication called digitalis. A person may use digitalis to treat certain heart conditions, such as heart failure and arrhythmia.

A person can treat the condition causing their ST depression. Below are some treatment options for some conditions that can cause ST depression.

Treating hypokalemia

Hypokalemia is a symptom of another disorder rather than a disease in itself. To improve a person’s potassium levels, a doctor will treat the underlying condition causing the hypokalemia.

They may also recommend taking potassium supplements.

In severe cases, a doctor may administer potassium chloride orally via the mouth or intravenously through a vein.

Treating myocardial ischemia

Treatment of myocardial ischemia may involve medications or procedures to restore blood flow in the coronary arteries (revascularization).

Beta-blockers can help reduce the number and duration of ischemic episodes in people with myocardial ischemia.

According to the AHA, these medications relieve stress on the heart by slowing down a person’s heartbeat. They do this by blocking the action of certain hormones in the nervous system.

A person may also take:

In some cases, a doctor may recommend revascularization procedures, such as coronary angioplasty with stenting or coronary artery bypass graft surgery.

Treating a left bundle branch block

There is no specific treatment for a left bundle branch block. A doctor may wish to treat any underlying causes that a person may have.

The AHA states that, despite there being no specific treatment, a person with left bundle branch block needs regular checkups with a doctor. This is so they can monitor the person’s condition and ensure that no other changes occur.

In some people with heart failure, a significant bundle branch block may be an indication of cardiac resynchronization therapy (CRT). According to the AHA, CRT involves a surgeon implanting a special pacemaker just below the collarbone to help the heart beat more synchronously and improve symptoms.

If a person has an ST depression, their outlook will depend on what is causing that specific ECG result.

If a person has myocardial ischemia, doctors may treat the condition with medications or procedures to help restore blood flow in the coronary arteries. If they receive an early diagnosis and treat their condition early, they can improve their outlook.

If a person has hypokalemia that is causing their ST depression, it may be the result of one of many conditions. Some conditions that lead to hypokalemia are simple to resolve, though others may be more complex.

A person may also reduce their risk of dangerous complications such as heart disease, stroke, and heart attacks in a number of ways. These include:

An ECG is a test that medical professionals use to analyze the electrical impulses in a person’s heart. An ST depression is a specific finding that may appear in a person’s ECG results. It occurs when the ST segment appears atypically low and sits below the baseline in someone’s results.

An ST depression can occur due to medical conditions, including hypokalemia, myocardial ischemia, and a left bundle branch block. The use of the medication digitalis can also cause this specific ECG result.

A person may treat the underlying condition that is causing their ST depression.

People with an ST depression may also wish to make some lifestyle changes to help improve their heart health. This can include eating a nutritious diet, getting regular physical exercise, avoiding smoking, and maintaining a moderate weight.