Month: February 2026

The QT Interval is an electrocardiogram (ECG) measurement that represents the time from the start of ventricular activation to the end of ventricular recovery. It is a **test-derived interval**, not a symptom or a diagnosis by itself. It is commonly encountered in cardiology when assessing arrhythmia risk, medication safety, and electrolyte or metabolic disturbances. It is also a key concept in inherited and acquired disorders of cardiac repolarization.

The ST Segment is a specific portion of the electrocardiogram (ECG) tracing. It represents the interval between ventricular depolarization and ventricular repolarization. It is an ECG measurement (a test finding), not a symptom or a disease by itself. It is commonly encountered when interpreting ECGs for ischemia, infarction, pericarditis, and conduction abnormalities.

The QRS Complex is the ECG (electrocardiogram) waveform that represents ventricular depolarization. It is a component of a diagnostic test (the surface ECG), not a symptom or a disease by itself. It is commonly encountered in cardiology when interpreting rhythm, conduction, ischemia, and structural heart patterns. Its shape, width, and direction can offer clues about how electrical impulses travel through the ventricles.

PR Interval is an electrocardiogram (ECG) measurement that represents the time from atrial activation to the start of ventricular activation. It is an ECG parameter, not a symptom or a diagnosis by itself. It is commonly encountered on routine 12-lead ECGs and rhythm strips in cardiology, emergency care, and inpatient telemetry. It is used to assess atrioventricular (AV) conduction and to support rhythm interpretation.

Repolarization is the phase when heart muscle cells reset their electrical charge after activation. Repolarization is a normal physiology concept, not a single disease, but it is often discussed as an electrocardiogram (ECG) finding. Repolarization is commonly encountered when interpreting the ST segment, T wave, and QT interval on a 12-lead ECG. Repolarization becomes clinically important when it appears abnormal or when it relates to arrhythmia risk or ischemia evaluation.

Depolarization is the electrical activation of a cell, when its membrane voltage becomes less negative. It is a normal physiology concept rather than a disease, symptom, or treatment. In cardiology, Depolarization describes how heart muscle and conduction cells generate and propagate electrical signals. It is most commonly encountered when interpreting the electrocardiogram (ECG) and evaluating arrhythmias and conduction disorders.

Purkinje Fibers are specialized heart muscle cells that rapidly conduct electrical impulses. They are part of the cardiac conduction system (anatomy/physiology). They are commonly discussed when learning how the electrocardiogram (ECG) reflects ventricular activation. They also matter clinically in bundle branch blocks, ventricular arrhythmias, pacing, and electrophysiology procedures.

The Bundle of His is a normal structure in the heart’s electrical conduction system. It is an anatomic pathway that carries impulses from the atrioventricular (AV) node into the ventricles. It is commonly discussed when learning electrocardiography (ECG), heart block, and bundle branch block. It is also encountered in electrophysiology (EP) procedures and modern pacing strategies.

The AV Node is a small structure in the heart’s electrical conduction system. It is an anatomy and physiology topic rather than a disease or test. It helps coordinate how electrical signals travel from atria to ventricles. It is commonly encountered when interpreting electrocardiograms (ECGs) and evaluating arrhythmias or atrioventricular (AV) block.

The SA Node is the heart’s natural pacemaker. It is an anatomy structure made of specialized electrical cells in the right atrium. It initiates most normal heartbeats and helps set resting and exercise heart rate. It is commonly discussed in electrocardiogram (ECG) interpretation, arrhythmias, and pacemaker decisions.