Certified Cardiographic Technician (CCT) Practice Exam 2026 – Your All-in-One Guide to Exam Success!

The baseline used for evaluating ST segments for elevation is the PR segment. This segment is considered the isoelectric line during the assessment of ST segment deviations because it represents the electrical activity of the heart during the early phases of ventricular depolarization and repolarization, prior to the QRS complex.

In clinical practice, the PR segment helps in determining the starting point for measuring ST segment elevation or depression. A deviation from the baseline that indicates a potential ischemic event occurs when the ST segment is elevated or depressed in relation to this PR segment baseline. This foundational understanding is crucial for the identification of conditions such as ST elevation myocardial infarction (STEMI).

In this context, evaluating ST segment changes against the PR segment ensures an accurate clinical interpretation of the ECG. The other options, such as the QRS interval or T wave, do not serve as appropriate baselines for assessing ST segment changes due to the different phases of myocardial activity they represent.