ECG Waveform Measurements and Intervals Flashcards

The ST segment on the ECG represents:

Answer: The period between ventricular depolarization and repolarization

The ST segment represents the early phase of ventricular repolarization and is evaluated for elevation or depression suggesting ischemia or injury.

Which calculation method uses the number of large squares between two R waves to estimate heart rate?

Answer: 300 divided by number of large squares

The '300 rule' divides 300 by the number of large squares between two consecutive R waves to estimate heart rate quickly.

What does a delta wave at the onset of the QRS complex suggest?

Answer: Pre-excitation syndrome (e.g., WPW)

A delta wave — a slurred upstroke at the start of the QRS — indicates pre-excitation of the ventricles via an accessory pathway, as seen in Wolff-Parkinson-White syndrome.

An isoelectric baseline on the ECG refers to:

Answer: The normal baseline between waveforms with no electrical activity

The isoelectric line is the flat baseline between ECG waveforms, representing zero electrical potential and used as the reference point for ST segment analysis.

The normal amplitude (height) of the R wave in lead II is typically:

Answer: 5–25 mm

In most leads, a normal R wave measures 5–25 mm; excessively tall R waves may indicate ventricular hypertrophy.

Which interval is most commonly used to assess AV conduction time?

Answer: PR interval

The PR interval reflects the time for impulse conduction from the SA node through the atria and AV node to the ventricles.