STsegmentet

STsegmentet refers to the portion of the electrocardiogram (ECG) that lies between the end of the S wave (the J point) and the beginning of the T wave. It corresponds to the early phase of ventricular repolarization and is normally isoelectric, closely aligned with the baseline. In a healthy heart the ST segment is considered to be on the baseline, though small deviations can occur depending on lead, body habitus, and individual variation.

Clinical significance arises when the ST segment deviates from baseline. ST-segment elevation, seen as an upward displacement of the segment, can indicate acute transmural myocardial injury such as a myocardial infarction, especially when it appears in contiguous leads and evolves over time. ST-segment depression, a downward displacement, is commonly associated with myocardial ischemia or subendocardial infarction. Diffuse ST elevation with concurrent PR-segment depression is classically associated with pericarditis. Other conditions that can alter the ST segment include early repolarization patterns, left or right bundle branch block, ventricular hypertrophy, electrolyte disturbances, and the effects of certain drugs.

Interpretation requires attention to the patient’s presentation and serial ECGs. The J point serves as the reference from which ST-segment deviation is measured, and many clinicians compare current findings with prior tracings to identify dynamic changes. Because ST changes can be transient or lead-specific, they are interpreted in the context of symptoms (such as chest pain), risk factors, and ancillary tests.