What Is Significant ST Depression?

Written by jacquelyn jeanty
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What Is Significant ST Depression?
A significant ST depression reading indicates poor blood circulation in the heart. (Which way to the heart? Labyrinth, a silhouette and a heart image by Stasys Eidiejus from Fotolia.com)

According to the American Heart Association, every year over 5.3 million Americans experience symptoms of chest discomfort severe enough to warrant emergency room care. In order to identify the source of chest pain, doctors take an EKG, or electrocardiogram, reading to determine what's taking place. A significant ST depression can appear as one of the many indicators of heart disease and impending cardiac arrest.


According to the American Heart Association, a significant ST depression--also known as a Non ST Segment Elevation, or NSTEMI--appears as an irregular pattern on an EKG. Individuals suffering from acute coronary syndrome, or more specifically, unstable angina, can exhibit this type of pattern on an EKG. An EKG shows a graphic representation of the electrical activity taking place in the heart. A significant ST depression appears as a dip in the line that traces a heart's electrical signalling as blood is pumped through its chambers.


Acute coronary syndrome develops as the arteries leading to the heart begin to accumulate plaque deposits. When this happens, areas of the heart fail to receive the amounts of oxygen needed for normal function. According to the American Heart Association, unstable angina appears in cases where a plaque deposit has ruptured, causing platelets to accumulate where the rupture has taken place. These processes result in a condition called ischemia, which impedes normal blood flow throughout the heart's chambers. The appearance of a significant ST depression on an EKG indicates the areas of the heart affected by these processes.

EKG Readings

An electrocardiogram graph contains the letters P, Q, R, S and T, according to Angina.com, a medical reference site. When hooked up to a patient, an EKG records how electrical impulses move through the heart's atria and ventricles by drawing a continuous line through these points. A significant ST depression appears as a dip between points S and T on the graph. A lack of blood flow to the heart can also appear as an ST elevation or crest between points S and T. In many cases, individuals who show an ST elevation have experienced a heart attack. The appearance of a significant ST depression indicates ischemia in a portion of the heart, which can potentially trigger an attack.


According to the Merck Manual, when areas of the heart fail to receive adequate oxygen supplies, they fail to conduct the electrical signals necessary for normal blood flow. As a result, these areas develop damage that can cause individual cells to die off. Damaged or dead muscle tissue can generate a significant ST depression on an EKG reading. Abnormal electrical activity can cause the heart to beat abnormally, leaving blood to pool in areas rather than flow through normally. When this happens, the damaged areas secrete troponin and creatine-kinase-MB (CK-MB) into the bloodstream, which are the chemicals that regulate muscular contractions. According to the American Heart Association, abnormal levels of troponin and CK-MB in the blood are key indicators of heart disease and tissue damage.


According to the American Heart Association, acute coronary syndrome can cause symptoms of acute pain or pressure in the chest, shoulders or back, shortness of breath and fatigue, all of which warrant prompt medical attention. A person's overall medical history will determine the basis for a significant ST depression, which may or may not require invasive surgery. In some cases, a person may have experienced a heart attack, in which case steps must be taken to reopen the artery to allow normal blood flow. Individuals who've not experienced a heart attack may be prescribed aspirin or blood thinners with follow-up blood testing to determine whether troponin or CK-MB is present in the blood.

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