ECG Waveform Measurements and Intervals Flashcards

How many small squares represent 0.04 seconds at standard ECG paper speed (25 mm/sec)?

Answer: 1 small square

At 25 mm/sec, each small square is 1 mm wide = 0.04 seconds, so 1 small square = 0.04 sec.

Which measurement in the ECG is most commonly used to detect left ventricular hypertrophy?

Answer: QRS voltage amplitude in precordial leads (Sokolow-Lyon criteria)

The Sokolow-Lyon criteria (S in V1 + R in V5 or V6 ≥35 mm) uses QRS voltage amplitude to suggest left ventricular hypertrophy.

ST elevation ≥1 mm in two contiguous leads is significant because it suggests:

Answer: Acute myocardial infarction (STEMI) until proven otherwise

ST elevation ≥1 mm in two or more contiguous leads is the hallmark ECG finding of STEMI (ST-elevation myocardial infarction), requiring urgent intervention.

The normal axis of the QRS complex in adults falls between:

Answer: -30° to +90°

Normal QRS axis is -30° to +90°, reflecting the predominant left and inferior direction of ventricular depolarization through the His-Purkinje system.

A delta wave on the ECG is associated with:

Answer: Wolff-Parkinson-White (WPW) syndrome pre-excitation

A delta wave is the slurred upstroke at the start of the QRS caused by accessory pathway pre-excitation in WPW syndrome, bypassing the AV node.

T-wave inversion in leads V1–V4 in an adult is most concerning for:

Answer: Anterior ischemia or right heart strain

T-wave inversions in the anterior precordial leads (V1–V4) can indicate anterior wall ischemia, non-STEMI, or right ventricular strain and require clinical correlation.