What does a downward arrow in ST segment signify?

A downward arrow in the ST segment indicates acute ST depression. This finding is significant in the context of cardiac health, as ST segment changes on an electrocardiogram (ECG) can provide insight into the presence of ischemia or other cardiac conditions.

Acute ST depression is typically associated with a lack of blood flow to the myocardium, often due to obstructive coronary artery disease or transient ischemic events. It may appear during episodes of angina or other stress tests that put strain on the heart. Recognizing acute ST depression is crucial for timely diagnosis and intervention in cases of myocardial ischemia.

In contrast, the other choices refer to different types of ST segment changes that do not align with the downward arrow's implication. Acute ST elevation often indicates myocardial infarction, while stable ST depression typically suggests a more chronic, consistent pattern due to stable angina. Chronic ST elevation can occur after changes related to previous heart conditions but does not indicate current acute ischemia. Therefore, the presence of a downward arrow in the ST segment is accurately identified as acute ST depression, highlighting its role in the assessment of acute cardiovascular issues.