The electrocardiogram (ECG or EKG) is a non-invasive test that records the heart’s electrical activity, translating its rhythm into a visual tracing. It is a rapid diagnostic tool used to assess cardiac function. Among the many patterns doctors look for, ST elevation immediately signals a potentially life-threatening situation. This abnormality refers to a segment of the tracing that is abnormally high above the baseline, indicating acute injury to the heart muscle.
What the ST Segment Represents on an ECG
The ECG tracing is composed of several waves and segments, each corresponding to a different phase of the heart’s cycle. The ST segment is the flat section connecting the QRS complex (ventricular depolarization) to the T wave (ventricular repolarization). It begins at the J-point, where the QRS complex ends, and extends to the beginning of the T wave.
Normally, the ST segment should be electrically neutral, resting on the isoelectric line, which serves as the baseline. This corresponds to the plateau phase of the heart muscle’s action potential, where there is minimal voltage difference. A flat, level ST segment indicates that ventricular muscle cells are uniformly holding their charge before recovery.
ST Elevation and Acute Heart Attack
ST elevation is the classic sign of a severe, acute heart attack, medically termed an ST-Elevation Myocardial Infarction (STEMI). A STEMI is caused by the complete blockage of a coronary artery, typically by a blood clot forming after a fatty plaque ruptures. This total occlusion prevents blood flow and oxygen from reaching the heart muscle, leading to immediate tissue injury.
The lack of oxygen (ischemia) causes a massive electrical disturbance in the affected cells, creating an “injury current” that shifts the ECG baseline. In a STEMI, the damage extends through the entire thickness of the heart wall (transmural), resulting in the characteristic upward deflection of the ST segment.
The elevated ST segment in specific ECG leads allows professionals to identify the location of the blockage and the injured area. This pattern mandates immediate, time-sensitive interventions to restore blood flow and salvage the heart muscle.
Immediate Medical Intervention
When ST elevation is detected, it triggers an immediate medical response because “time is muscle.” Since heart muscle dies quickly, the primary goal is rapid reperfusion, or restoration of blood flow. Guidelines recommend the ECG be performed and interpreted within 10 minutes of the patient’s arrival to the emergency department.
The gold-standard intervention for a STEMI is primary percutaneous coronary intervention (PCI), also known as coronary angioplasty. This procedure involves inserting a catheter into an artery and guiding it to the blocked coronary artery. A balloon is inflated to compress the clot and plaque, and a stent is usually placed to keep the vessel open.
If PCI is unavailable or delayed, thrombolytic therapy (clot-dissolving medications) is administered intravenously. These drugs dissolve the blood clot causing the blockage, serving as a time-sensitive alternative. The goal is to achieve reperfusion within 90 minutes of first medical contact for PCI, or within 30 minutes for thrombolytic therapy.
Other Conditions That Cause ST Elevation
While an acute heart attack is the most concerning cause, ST elevation can be produced by other non-ischemic conditions that mimic a STEMI, making careful interpretation essential. One common alternative cause is acute pericarditis, which is inflammation of the sac surrounding the heart.
Pericarditis typically causes ST elevation that is widespread (diffuse) across most ECG leads, rather than being confined to a single coronary artery territory. Another common finding is benign early repolarization, a normal electrical variant often seen in young, healthy men. Here, the ST segment often has a concave, upward curve, differentiating it from the convex shape seen in acute heart attacks.
Other conditions, such as left ventricular aneurysm or coronary artery spasm (Prinzmetal’s angina), can also result in ST elevation. These conditions require medical attention but do not carry the same immediate need for emergency reperfusion therapy as a STEMI, emphasizing the need for a comprehensive clinical assessment.