EKG certification Certification EKG Interpretation & Waveforms 1 — Questions and Answers
Question 1: A rhythm strip shows a regular rhythm at 75 bpm with narrow QRS complexes. Each QRS is preceded by a P wave, but the PR interval measures 0.26 seconds. What is the MOST accurate interpretation?
- Normal sinus rhythm
- First-degree AV block (Correct answer)
- Second-degree AV block, Mobitz Type I
- Junctional rhythm
Correct answer: First-degree AV block
A PR interval greater than 0.20 seconds (one large box on standard EKG paper) indicates first-degree AV block. The rhythm is otherwise regular with a consistent 1:1 P-to-QRS relationship and narrow complexes, ruling out more advanced blocks or junctional rhythm.
Question 2: On a standard EKG, the QRS complex represents which electrical event in the heart?
- Atrial depolarization
- Ventricular repolarization
- Ventricular depolarization (Correct answer)
- Atrial repolarization
Correct answer: Ventricular depolarization
The QRS complex reflects the rapid depolarization (electrical activation) of the ventricular myocardium. Atrial depolarization produces the P wave, ventricular repolarization produces the T wave, and atrial repolarization is hidden within the QRS complex.
Question 3: A patient's EKG shows ST-segment elevation in leads V1–V4 with reciprocal ST depression in leads II, III, and aVF. Which area of the myocardium is MOST likely affected?
- Inferior wall
- Lateral wall
- Anterior wall (Correct answer)
- Posterior wall
Correct answer: Anterior wall
Leads V1–V4 are the precordial leads that directly overlie the anterior wall of the left ventricle. ST elevation in these leads with reciprocal changes inferiorly is the classic pattern of an anterior STEMI, typically from LAD occlusion.
Question 4: Which of the following BEST describes a left bundle branch block (LBBB) on a 12-lead EKG?
- Narrow QRS with a tall R wave in V1
- Wide QRS (≥0.12 s) with a broad, notched R wave in lateral leads (I, aVL, V5–V6) (Correct answer)
- Wide QRS with an RSR' ('rabbit ear') pattern in V1 and a deep S wave in V6
- Prolonged PR interval with normal QRS morphology
Correct answer: Wide QRS (≥0.12 s) with a broad, notched R wave in lateral leads (I, aVL, V5–V6)
LBBB produces a wide QRS (≥120 ms) because ventricular depolarization must travel through non-specialized myocardium. The broad, notched (M-shaped) R wave in lateral leads I, aVL, V5, and V6 is the hallmark. The RSR' pattern in V1 describes RBBB, not LBBB.
Question 5: A rhythm strip reveals a regular ventricular rate of 150 bpm with narrow QRS complexes. P waves are present but are inverted in leads II, III, and aVF and immediately precede each QRS. What is the MOST likely rhythm?
- Sinus tachycardia
- Atrial flutter with 2:1 block
- Junctional tachycardia (Correct answer)
- Ventricular tachycardia
Correct answer: Junctional tachycardia
Inverted P waves in the inferior leads (II, III, aVF) immediately before narrow QRS complexes indicate retrograde atrial activation originating near or at the AV node — the hallmark of junctional tachycardia. Sinus tachycardia produces upright P waves in lead II; atrial flutter shows sawtooth flutter waves; ventricular tachycardia produces wide QRS complexes.
Question 6: On a standard EKG running at 25 mm/s, one large box on the horizontal axis represents how much time?
- 0.04 seconds
- 0.10 seconds
- 0.20 seconds (Correct answer)
- 0.40 seconds
Correct answer: 0.20 seconds
At the standard paper speed of 25 mm/s, each large box (5 mm wide) equals 0.20 seconds. Each small box (1 mm wide) equals 0.04 seconds. This calibration is fundamental for measuring intervals such as PR, QRS, and QT correctly.
EKG certification Certification EKG Interpretation & Waveforms 1
A rhythm strip shows a regular rhythm at 75 bpm with narrow QRS complexes.
Each QRS is preceded by a P wave, but the PR interval measures 0.26 seconds.
What is the MOST accurate interpretation?