Wave: positive or negative deflection from baseline = specific electrical event (eg, P wave = atrial depolarization)

• P wave = 1st defection of complex; atrial depolarization
• Q wave = 1st negative deflection after P wave
• R wave = 1st positive deflection after P wave
• S wave = 1st negative deflection after R wave
• T wave = deflection after QRS; ventricular repolarization
• U wave = deflection after T wave (not often present)

A simple way to determine wave orientation:

• Depolarization = positive
• Repolarization = negative
• Moving TOWARDS electrode = positive
• Moving AWAY from electrode = negative
• Wave orientation = (repolarization/depolarization) x (towards/away from)
• Example: ventricular repolarization (T wave) moving AWAY from electrode => orientation = (-) x (-) = + (upright T wave)

Interval: distance (time) between 2 ECG events (eg, PR interval, QRS, interval, QT interval, RR interval PP interval, etc.)

• Interval = [1 segment] + [1 or more waves]
• PR interval = [P wave] + [PR segment] = from start of atrial depolarization to start of ventricular depolarization
• QT interval = [QRS complex] + [ST segment] + [T wave]

Segment: line (often isoelectric) connecting 2 waves without including them (eg, PR segment)

• Time between 2 specific points on ECG (eg, PR segment, ST segment, TP segment)

QRS complex: [Q wave] + [R wave] + [S wave]

• Represents ventricular depolarization
• Note: does not always include each Q-, R-, & S-waves; may include >1 of same wave (eg, RSR’)

Junction (J) point: where QRS complex ends & ST segment begins

• Used to measure ST-segment deviation in relation to baseline (ie, PR segment & sometimes TP segment