ECG Waveform Measurements and Intervals Flashcards

What is the significance of a pathological Q wave on an ECG?

Answer: It may represent transmural myocardial infarction (scar tissue)

Pathological Q waves (≥40 ms wide or ≥25% of the QRS height) represent areas of electrically silent myocardium, typically indicating old transmural infarction.

The U wave on an ECG is best seen in which leads?

Answer: V2 and V3

The U wave is most prominent in the mid-precordial leads V2 and V3, where it appears as a small positive deflection following the T-wave.

Peaked, narrow, symmetrical T-waves in multiple leads are a classic ECG sign of:

Answer: Hyperkalemia (early sign)

Tall, peaked, narrow, symmetrical T-waves are an early ECG manifestation of hyperkalemia, reflecting altered ventricular repolarization from elevated extracellular potassium.

Which interval is measured from the beginning of the Q wave to the end of the S wave?

Answer: QRS duration

The QRS duration is measured from the first deflection of the QRS complex (onset of Q or R) to the end of the S wave (J point), representing total ventricular depolarization time.

Osborn waves (J waves) on an ECG are associated with which condition?

Answer: Hypothermia

Osborn (J) waves are positive deflections at the J-point, most prominent in lateral leads, and are a characteristic ECG finding in hypothermia.

A PR interval greater than 0.20 seconds with all P waves conducting to QRS indicates:

Answer: First-degree AV block

First-degree AV block is defined as a PR interval >0.20 sec where every P wave is followed by a QRS, indicating delayed but intact AV nodal conduction.