ECG Rhythm Analysis 2 — Questions and Answers
Question 1: A patient's ECG shows a regular rhythm at 150 bpm with narrow QRS complexes and no visible P waves. What is the most likely rhythm?
- Atrial flutter with 2:1 block (Correct answer)
- Sinus tachycardia
- Ventricular tachycardia
- Accelerated junctional rhythm
Correct answer: Atrial flutter with 2:1 block
Atrial flutter with 2:1 block classically presents at 150 bpm with narrow QRS and flutter waves often hidden in the T wave or QRS complex.
Question 2: Which ECG finding is the hallmark of Wolff-Parkinson-White (WPW) syndrome during sinus rhythm?
- Delta wave with short PR interval (Correct answer)
- Prolonged QT interval
- Wide QRS with LBBB pattern
- Prominent U waves
Correct answer: Delta wave with short PR interval
WPW is characterized by a delta wave (slurred QRS upstroke) and a short PR interval due to ventricular pre-excitation via an accessory pathway.
Question 3: A rhythm strip shows regularly spaced P waves at 75 bpm with QRS complexes at 40 bpm that bear no relationship to P waves. This describes:
- Third-degree (complete) heart block (Correct answer)
- Second-degree Mobitz I block
- Second-degree Mobitz II block
- First-degree heart block
Correct answer: Third-degree (complete) heart block
Complete (third-degree) heart block is defined by complete AV dissociation where P waves and QRS complexes march independently at different rates.
Question 4: On a rhythm strip, the RR interval measures 20 large boxes. What is the heart rate?
- 15 bpm (Correct answer)
- 30 bpm
- 75 bpm
- 100 bpm
Correct answer: 15 bpm
Using the 300 method: 300 ÷ 20 large boxes = 15 bpm.
Question 5: Torsades de pointes is most directly associated with which ECG abnormality?
- Prolonged QTc interval (Correct answer)
- Short PR interval
- ST elevation
- Right bundle branch block
Correct answer: Prolonged QTc interval
Torsades de pointes is a polymorphic ventricular tachycardia that characteristically occurs in the setting of a prolonged QTc interval.
Question 6: Which feature differentiates Mobitz Type I (Wenckebach) from Mobitz Type II second-degree AV block?
- Progressive PR lengthening before the dropped beat in Mobitz I (Correct answer)
- Narrow QRS complexes in Mobitz II
- Irregular P wave rate in Mobitz I
- Shorter PR interval after the dropped beat in Mobitz II
Correct answer: Progressive PR lengthening before the dropped beat in Mobitz I
Mobitz I shows progressive PR prolongation until a P wave fails to conduct, while Mobitz II has constant PR intervals with sudden non-conducted P waves.
Question 7: A patient has an ECG showing P waves that vary in morphology with at least three distinct shapes and an irregular rate. This rhythm is:
- Multifocal atrial tachycardia (MAT) (Correct answer)
- Atrial fibrillation
- Wandering atrial pacemaker
- Sinus arrhythmia
Correct answer: Multifocal atrial tachycardia (MAT)
MAT is defined by three or more distinct P wave morphologies with an irregular rate ≥100 bpm, commonly seen in COPD patients.
ECG Rhythm Analysis 2
A patient's ECG shows a regular rhythm at 150 bpm with narrow QRS complexes and no visible P waves.
What is the most likely rhythm?