An electrocardiogram, commonly known as an ECG or EKG, is a non-invasive diagnostic tool that evaluates heart health. It records the heart’s electrical signals, translating them into a visual tracing. This allows medical professionals to analyze heart rhythm and electrical activity.
Understanding the Electrocardiogram (ECG)
An ECG tracing consists of a series of waves and segments, each representing a specific electrical event within the heart. The P wave reflects the electrical activation of the heart’s upper chambers, the atria. The QRS complex signifies the contraction of the heart’s main pumping chambers, the ventricles. The T wave then indicates the electrical recovery of the ventricles.
Between these waves are segments and intervals. The PR interval measures the time it takes for an electrical impulse to travel from the atria to the ventricles. The ST segment is the flat section between the end of the QRS complex and the beginning of the T wave. In a normally functioning heart, this ST segment is typically an isoelectric (flat) line, indicating no significant electrical voltage difference across the heart muscle.
Defining ST Elevation
ST elevation refers to an abnormal upward shift of the ST segment above the baseline on an ECG tracing. Medical professionals determine ST elevation by comparing the ST segment’s position to a defined baseline, often the PR segment.
The degree of elevation is measured in millimeters, with specific thresholds indicating significance. For example, an elevation of 1 millimeter (0.1 millivolt) or more in limb leads, or 2 millimeters (0.2 millivolts) or more in certain chest leads, when present in two or more adjacent leads, is considered significant.
What ST Elevation Signifies
The presence of ST elevation on an ECG is primarily associated with an acute myocardial infarction, specifically an ST-Elevation Myocardial Infarction (STEMI). A STEMI indicates a complete or near-complete blockage of a coronary artery. This restricts blood flow, leading to a lack of oxygen to a portion of the heart muscle. Prolonged ischemia results in heart tissue damage and death.
The ST segment elevates due to an “injury current.” When heart muscle cells are deprived of oxygen, their electrical properties change, causing a voltage difference between injured and healthy areas of the heart. A STEMI is a medical emergency requiring immediate attention to restore blood flow and minimize heart damage.
Other Causes of ST Elevation
While STEMI is the most concerning cause, ST elevation is not exclusively indicative of a heart attack; various other conditions can also cause this ECG finding. One common non-ischemic cause is benign early repolarization, a normal variant often seen in young, healthy individuals. In this condition, the ST segment typically has a concave, or “saddleback,” shape and may be accompanied by a notch or slur at the J-point.
Pericarditis, an inflammation of the sac surrounding the heart, can also cause widespread ST elevation, often with a concave appearance and PR segment depression. This elevation is diffuse, affecting many ECG leads, and does not correspond to a specific coronary artery territory. Other less common causes include left ventricular aneurysm, a weakened and bulging area of the heart muscle typically resulting from a prior heart attack, which can cause persistent ST elevation. Brugada syndrome, a genetic disorder affecting the heart’s electrical activity, shows ST elevation in specific right precordial leads (V1-V3) often with a “coved” or “saddleback” pattern. Lastly, severe imbalances in electrolytes, such as hyperkalemia (high potassium levels), can also lead to ST elevation. Medical professionals differentiate these conditions by considering the patient’s symptoms, medical history, and other diagnostic tests.
Urgent Medical Action
When ST elevation is detected on an ECG, especially in the context of symptoms suggesting a heart attack, immediate medical action is taken. Emergency medical services (EMS) are activated, and patients are transported rapidly to a hospital equipped for cardiac emergencies. The goal is to restore blood flow to the affected heart muscle as quickly as possible. This process is known as reperfusion therapy.
The most effective reperfusion strategy is typically a percutaneous coronary intervention (PCI), often involving angioplasty and stent placement. During this procedure, a catheter is threaded through a blood vessel to the blocked coronary artery, where a balloon is inflated to open the artery, and a stent is usually placed to keep it open. If PCI is not immediately available, thrombolytic medications, often called “clot-busting drugs,” may be administered to dissolve the blood clot obstructing the artery. Prompt intervention is crucial to minimize the extent of heart muscle damage and improve the patient’s outcome.