CCI - Cardiovascular Credentialing International ECG Rhythm Interpretation Questions and Answers — Questions and Answers
Question 1: A patient's cardiac monitor displays a rhythm with a ventricular rate varying between 110 and 150 bpm. The R-R intervals are irregularly irregular, and no discernible P waves can be identified. Which of the following is the most likely interpretation?
- Sinus Tachycardia
- Atrial Flutter with variable block
- Atrial Fibrillation (Correct answer)
- Multifocal Atrial Tachycardia
Correct answer: Atrial Fibrillation
The hallmark ECG characteristics of Atrial Fibrillation are an "irregularly irregular" rhythm, which accounts for the variable R-R intervals, and the absence of clear, identifiable P waves, which are replaced by chaotic fibrillatory waves. [12, 13, 18, 23, 28]
Question 2: Which of the following ECG findings is the defining characteristic of a third-degree atrioventricular (AV) block?
- A progressively lengthening PR interval followed by a dropped QRS complex.
- A constant and prolonged PR interval (>0.20 seconds) for every QRS.
- A regular rhythm with a rate of 40-60 bpm and inverted P waves.
- Complete dissociation of P waves and QRS complexes, with atria and ventricles beating independently. (Correct answer)
Correct answer: Complete dissociation of P waves and QRS complexes, with atria and ventricles beating independently.
In third-degree (complete) AV block, no atrial impulses are conducted to the ventricles. This results in the atria (P waves) and ventricles (QRS complexes) being controlled by separate pacemakers, leading to a complete dissociation between the two on the ECG. [2, 11, 19, 21, 27]
Question 3: A monitor alarm sounds, revealing a regular, wide-complex rhythm at a rate of 170 bpm. The patient becomes dizzy and hypotensive. This presentation is most consistent with which life-threatening arrhythmia?
- Ventricular Tachycardia (Correct answer)
- Supraventricular Tachycardia with aberrancy
- Atrial Fibrillation with a rapid ventricular response
- Sinus Tachycardia
Correct answer: Ventricular Tachycardia
Ventricular Tachycardia is defined as a rhythm originating in the ventricles with a rate over 100 bpm and a QRS duration of >0.12 seconds (wide complex). [6, 10, 25, 26] It is a life-threatening arrhythmia because the rapid rate and poor coordination of contraction can lead to severe hemodynamic compromise, as evidenced by the patient's dizziness and hypotension.
Question 4: An ECG rhythm strip shows a ventricular rate of approximately 75 bpm. The baseline has a distinctive, repetitive "sawtooth" appearance, with four atrial waves for every one QRS complex. What is the most likely rhythm?
- Atrial Fibrillation
- Atrial Flutter (Correct answer)
- Sinus Bradycardia with U waves
- Junctional Rhythm
Correct answer: Atrial Flutter
The classic "sawtooth" pattern of the baseline is the hallmark of Atrial Flutter, which is caused by rapid, regular atrial depolarizations (flutter waves). [1, 4, 15, 16, 20] An atrial rate of ~300 bpm with a ventricular rate of 75 bpm indicates a 4:1 AV conduction block.
Question 5: When analyzing an ECG, the PR interval reflects the time for the electrical impulse to travel from the SA node through the AV node. What is the normal duration for this interval?
- 0.06 - 0.11 seconds
- > 0.20 seconds
- < 0.12 seconds
- 0.12 - 0.20 seconds (Correct answer)
Correct answer: 0.12 - 0.20 seconds
A normal PR interval is between 0.12 and 0.20 seconds (120-200 milliseconds). An interval longer than 0.20 seconds indicates a first-degree AV block, while an interval shorter than 0.12 seconds may suggest a pre-excitation syndrome. [3, 7, 9, 14, 17]
Question 6: While observing a cardiac monitor, you note an occasional complex that occurs earlier than expected, is wide and bizarre in shape, and is not preceded by a P wave. This ectopic beat is followed by a full compensatory pause. What is this beat called?
- Premature Atrial Contraction (PAC)
- Premature Junctional Contraction (PJC)
- Premature Ventricular Contraction (PVC) (Correct answer)
- Aberrantly Conducted PAC
Correct answer: Premature Ventricular Contraction (PVC)
The key features described—a premature beat, a wide and abnormal QRS complex (≥0.12s), the absence of a preceding P wave, and a subsequent compensatory pause—are the classic ECG characteristics of a Premature Ventricular Contraction (PVC). [5, 8, 22, 29]
CCI - Cardiovascular Credentialing International ECG Rhythm Interpretation Questions and Answers
A patient's cardiac monitor displays a rhythm with a ventricular rate varying between 110 and 150 bpm.
The R-R intervals are irregularly irregular, and no discernible P waves can be identified.
Which of the following is the most likely interpretation?