Critical Care ECG Interpretation Examination
DEFINED ANSWERS LATEST ALREADY GRADED
A+ (2025/2026
**1.** A patient in the ICU develops a wide-complex tachycardia at 180 bpm. The
patient is awake, hypotensive at 85/50 mmHg, and complaining of chest pain.
What is the priority intervention?
A) Administer adenosine 6 mg IV push
B) Perform immediate synchronized cardioversion
C) Start amiodarone infusion 150 mg over 10 minutes
D) Obtain a 12-lead ECG before any treatment
**Answer:** B
**Rationale:** Unstable wide-complex tachycardia with hypotension, chest pain,
or altered mental status requires immediate synchronized cardioversion. Any
delay to administer medications or perform diagnostics is inappropriate when the
patient is unstable.
---
**2.** The nurse notes ST-segment elevation in leads II, III, and aVF. This
indicates an acute myocardial infarction involving which coronary artery territory?
A) Left anterior descending (LAD)
B) Right coronary artery (RCA) or left circumflex (LCx)
C) Left main
,D) Septal branches
**Answer:** B
**Rationale:** Leads II, III, and aVF represent the inferior wall of the left
ventricle, typically supplied by the RCA (80% of population) or the LCx in a left-
dominant circulation.
---
**3.** A patient’s cardiac monitor shows a rhythm with no discernible P waves,
an irregularly irregular ventricular response, and narrow QRS complexes. This is
most likely:
A) Atrial flutter
B) Atrial fibrillation
C) Multifocal atrial tachycardia
D) Paroxysmal supraventricular tachycardia
**Answer:** B
**Rationale:** Atrial fibrillation is characterized by chaotic atrial activity without
distinct P waves and an irregularly irregular ventricular response. Atrial flutter has
a saw-tooth pattern, MAT has at least 3 distinct P wave morphologies, and PSVT is
regular.
---
**4.** Which ECG finding is characteristic of severe hyperkalemia (K+ >7.0
mEq/L)?
A) Prominent U waves
B) Peaked, tall, tented T waves
,C) Prolonged PR interval and eventual loss of P waves, widened QRS
D) ST-segment depression
**Answer:** C
**Rationale:** While peaked T waves are an early sign of hyperkalemia, as
potassium rises further, P waves flatten and disappear, and the QRS widens,
eventually forming a sine wave pattern that can lead to cardiac arrest.
---
**5.** The nurse observes a rhythm with a heart rate of 40 bpm, a prolonged
constant PR interval, and a dropped QRS complex after every third P wave. This is:
A) First-degree AV block
B) Second-degree AV block, Mobitz type I (Wenckebach)
C) Second-degree AV block, Mobitz type II
D) Third-degree AV block
**Answer:** C
**Rationale:** Mobitz type II is characterized by a constant PR interval with
intermittent non-conducted P waves (dropped QRS) without progressive PR
lengthening. It often progresses to complete heart block and frequently requires
pacing.
---
**6.** A patient on telemetry develops polymorphic ventricular tachycardia. The
QT interval is 580 ms. The patient is bradycardic with frequent PVCs. Which
intervention is the immediate priority after defibrillation if pulseless?
A) Amiodarone 300 mg IV push
, B) Magnesium sulfate 2 g IV over 1-2 minutes
C) Overdrive pacing
D) Isoproterenol infusion
**Answer:** B
**Rationale:** Torsades de pointes associated with prolonged QT requires
magnesium sulfate as the first-line antiarrhythmic, even if the serum magnesium
level is normal. If the patient is unstable and not in cardiac arrest, overdrive
pacing or isoproterenol may be considered, but in cardiac arrest, defibrillation
and magnesium are priorities.
---
**7.** What is the correct duration of the normal PR interval?
A) 0.04–0.10 seconds
B) 0.12–0.20 seconds
C) 0.20–0.28 seconds
D) 0.30–0.40 seconds
**Answer:** B
**Rationale:** The PR interval represents atrial depolarization and conduction
delay through the AV node. Normal is 0.12–0.20 seconds (3–5 small boxes). A
shorter PR indicates pre-excitation; a longer PR indicates first-degree AV block.
---
**8.** A 12-lead ECG reveals ST-segment depression in leads V1–V3 and tall R
waves in those leads. The nurse suspects:
DEFINED ANSWERS LATEST ALREADY GRADED
A+ (2025/2026
**1.** A patient in the ICU develops a wide-complex tachycardia at 180 bpm. The
patient is awake, hypotensive at 85/50 mmHg, and complaining of chest pain.
What is the priority intervention?
A) Administer adenosine 6 mg IV push
B) Perform immediate synchronized cardioversion
C) Start amiodarone infusion 150 mg over 10 minutes
D) Obtain a 12-lead ECG before any treatment
**Answer:** B
**Rationale:** Unstable wide-complex tachycardia with hypotension, chest pain,
or altered mental status requires immediate synchronized cardioversion. Any
delay to administer medications or perform diagnostics is inappropriate when the
patient is unstable.
---
**2.** The nurse notes ST-segment elevation in leads II, III, and aVF. This
indicates an acute myocardial infarction involving which coronary artery territory?
A) Left anterior descending (LAD)
B) Right coronary artery (RCA) or left circumflex (LCx)
C) Left main
,D) Septal branches
**Answer:** B
**Rationale:** Leads II, III, and aVF represent the inferior wall of the left
ventricle, typically supplied by the RCA (80% of population) or the LCx in a left-
dominant circulation.
---
**3.** A patient’s cardiac monitor shows a rhythm with no discernible P waves,
an irregularly irregular ventricular response, and narrow QRS complexes. This is
most likely:
A) Atrial flutter
B) Atrial fibrillation
C) Multifocal atrial tachycardia
D) Paroxysmal supraventricular tachycardia
**Answer:** B
**Rationale:** Atrial fibrillation is characterized by chaotic atrial activity without
distinct P waves and an irregularly irregular ventricular response. Atrial flutter has
a saw-tooth pattern, MAT has at least 3 distinct P wave morphologies, and PSVT is
regular.
---
**4.** Which ECG finding is characteristic of severe hyperkalemia (K+ >7.0
mEq/L)?
A) Prominent U waves
B) Peaked, tall, tented T waves
,C) Prolonged PR interval and eventual loss of P waves, widened QRS
D) ST-segment depression
**Answer:** C
**Rationale:** While peaked T waves are an early sign of hyperkalemia, as
potassium rises further, P waves flatten and disappear, and the QRS widens,
eventually forming a sine wave pattern that can lead to cardiac arrest.
---
**5.** The nurse observes a rhythm with a heart rate of 40 bpm, a prolonged
constant PR interval, and a dropped QRS complex after every third P wave. This is:
A) First-degree AV block
B) Second-degree AV block, Mobitz type I (Wenckebach)
C) Second-degree AV block, Mobitz type II
D) Third-degree AV block
**Answer:** C
**Rationale:** Mobitz type II is characterized by a constant PR interval with
intermittent non-conducted P waves (dropped QRS) without progressive PR
lengthening. It often progresses to complete heart block and frequently requires
pacing.
---
**6.** A patient on telemetry develops polymorphic ventricular tachycardia. The
QT interval is 580 ms. The patient is bradycardic with frequent PVCs. Which
intervention is the immediate priority after defibrillation if pulseless?
A) Amiodarone 300 mg IV push
, B) Magnesium sulfate 2 g IV over 1-2 minutes
C) Overdrive pacing
D) Isoproterenol infusion
**Answer:** B
**Rationale:** Torsades de pointes associated with prolonged QT requires
magnesium sulfate as the first-line antiarrhythmic, even if the serum magnesium
level is normal. If the patient is unstable and not in cardiac arrest, overdrive
pacing or isoproterenol may be considered, but in cardiac arrest, defibrillation
and magnesium are priorities.
---
**7.** What is the correct duration of the normal PR interval?
A) 0.04–0.10 seconds
B) 0.12–0.20 seconds
C) 0.20–0.28 seconds
D) 0.30–0.40 seconds
**Answer:** B
**Rationale:** The PR interval represents atrial depolarization and conduction
delay through the AV node. Normal is 0.12–0.20 seconds (3–5 small boxes). A
shorter PR indicates pre-excitation; a longer PR indicates first-degree AV block.
---
**8.** A 12-lead ECG reveals ST-segment depression in leads V1–V3 and tall R
waves in those leads. The nurse suspects:
