ECG ECG Troubleshooting 2 — Questions and Answers
Question 1: A patient's ECG shows a regularly irregular rhythm with a pattern of grouped beating. Which arrhythmia is most likely?
- Second-degree AV block Mobitz I (Wenckebach) (Correct answer)
- Complete heart block
- Atrial flutter with variable block
- Multifocal atrial tachycardia
Correct answer: Second-degree AV block Mobitz I (Wenckebach)
Wenckebach block produces grouped beating due to progressive PR prolongation until a beat is dropped, creating a regularly irregular pattern.
Question 2: When troubleshooting a wandering baseline artifact on a 12-lead ECG, which corrective action is most effective?
- Increase the paper speed to 50 mm/s
- Ask the patient to hold their breath briefly during acquisition (Correct answer)
- Switch to a bipolar limb lead configuration
- Reduce the gain setting on the ECG machine
Correct answer: Ask the patient to hold their breath briefly during acquisition
Respiratory movement is the primary cause of wandering baseline, and having the patient hold their breath during recording eliminates this motion artifact.
Question 3: An ECG shows QRS complexes preceded by P waves in leads I and aVL but inverted P waves before QRS in lead II. What does this indicate?
- Right atrial enlargement
- Ectopic atrial rhythm originating in the low atrium or near the AV node (Correct answer)
- Left bundle branch block
- Dextrocardia
Correct answer: Ectopic atrial rhythm originating in the low atrium or near the AV node
Inverted P waves in the inferior leads (II, III, aVF) with upright P in lateral leads suggest a low atrial or junctional ectopic pacemaker firing retrogradely.
Question 4: A technician records an ECG and notices the QRS in lead I is negative and in aVR is positive. What is the most likely cause?
- Left axis deviation
- Right arm and left arm lead reversal (Correct answer)
- Dextrocardia
- Left bundle branch block
Correct answer: Right arm and left arm lead reversal
Reversal of the right and left arm electrodes produces a negative QRS in lead I and a positive QRS in aVR, the mirror image of normal.
Question 5: What ECG finding is characteristic of hyperkalemia at serum potassium levels above 6.5 mEq/L?
- Prolonged QT interval with U waves
- Peaked, narrow, symmetric T waves (Correct answer)
- Short PR interval with delta waves
- Broad notched P waves
Correct answer: Peaked, narrow, symmetric T waves
Hyperkalemia first manifests as tall, peaked, narrow, symmetric (tent-shaped) T waves due to accelerated ventricular repolarization.
Question 6: A patient with a permanent pacemaker has an ECG showing pacemaker spikes without subsequent QRS complexes. What is the most likely diagnosis?
- Pacemaker oversensing
- Pacemaker failure to capture (Correct answer)
- Pacemaker undersensing
- Normal demand pacing behavior
Correct answer: Pacemaker failure to capture
Failure to capture occurs when the pacemaker spike fires but fails to depolarize the myocardium, producing spikes not followed by QRS complexes.
Question 7: Which ECG change is most consistent with acute pericarditis?
- Diffuse ST elevation with concave morphology in multiple leads (Correct answer)
- ST elevation with convex morphology in a single coronary territory
- New Q waves in leads II, III, and aVF
- ST depression in leads V1-V4
Correct answer: Diffuse ST elevation with concave morphology in multiple leads
Acute pericarditis produces diffuse saddle-shaped (concave) ST elevation in multiple leads without reciprocal changes, distinguishing it from myocardial infarction.
ECG ECG Troubleshooting 2
A patient's ECG shows a regularly irregular rhythm with a pattern of grouped beating.
Which arrhythmia is most likely?