Sinus Rhythm With ST Segment Changes Explained

When reviewing an electrocardiogram (ECG), one of the common observations is a shift in the ST segment. While the terminology used in reports may not always be precise, it's more accurate to describe whether the ST segment is depressed or elevated.

Both ST segment elevation and depression are acceptable within defined limits. For instance, ST depression should not exceed 0.05 mV, which is equivalent to half a small square on ECG paper. In chest leads, ST elevation should remain under 3 small squares. These minor variations are considered within normal limits and may not necessarily indicate pathology.

When ST Segment Changes Become Significant

However, when the ST segment deviates beyond these accepted ranges, it is classified as an ST segment change. Significant depression, for example, may suggest underlying cardiac issues. The clinical context is crucial in interpreting these changes accurately.

Common Causes of ST Segment Depression

Several conditions can lead to ST depression. Chronic hypertension often results in cardiac strain, which may manifest as ST depression. Additionally, non-ST elevation myocardial infarction (NSTEMI) can cause similar findings. Other potential causes include drug toxicity, particularly with medications like digoxin, as well as pericarditis, which may also present with ST depression.

Understanding ST Segment Elevation

ST elevation, on the other hand, has multiple possible explanations. It can be a sign of acute myocardial infarction, particularly ST-elevation myocardial infarction (STEMI). However, early repolarization, a benign condition often seen in young, healthy individuals, can also cause ST elevation.

The Importance of Clinical Correlation

It's essential to remember that an ECG reflects the electrical activity of the heart and should not be used in isolation to make a diagnosis. Neither patients nor physicians should interpret ST depression as definitive evidence of ischemia without considering the full clinical picture. A comprehensive evaluation that includes patient history and additional diagnostic tests is necessary to determine the true cause of ST segment changes.