CMC CMC Cardiac Diagnostics & Imaging 1 — Questions and Answers
Question 1: What does the PR interval on an ECG represent?
- Ventricular depolarization duration
- Conduction time from atrial depolarization through the AV node to ventricular activation (Correct answer)
- Ventricular repolarization
- Atrial repolarization only
Correct answer: Conduction time from atrial depolarization through the AV node to ventricular activation
The PR interval reflects total conduction time from SA node firing through the AV node and His-Purkinje system to ventricular activation.
Question 2: ST elevation in ECG leads II, III, and aVF is most consistent with infarction of which cardiac territory?
- Anterior wall (LAD territory)
- Lateral wall (circumflex territory)
- Inferior wall (RCA territory) (Correct answer)
- Posterior wall
Correct answer: Inferior wall (RCA territory)
Leads II, III, and aVF are inferior leads; ST elevation in these leads indicates inferior STEMI, usually from RCA occlusion.
Question 3: A corrected QT interval (QTc) greater than 500ms on ECG significantly increases the risk of which arrhythmia?
- Complete heart block
- Torsades de Pointes (Correct answer)
- Wolff-Parkinson-White pre-excitation
- Atrial flutter
Correct answer: Torsades de Pointes
QTc >500ms indicates severe repolarization prolongation, greatly increasing the risk of Torsades de Pointes and sudden cardiac death.
Question 4: Which ECG change is one of the earliest and most characteristic findings in hyperkalemia?
- Prominent U waves
- Short QT interval
- Peaked, tall, narrow T waves (Correct answer)
- Delta waves
Correct answer: Peaked, tall, narrow T waves
Peaked T waves are the earliest ECG sign of hyperkalemia and result from accelerated ventricular repolarization.
Question 5: Why is new left bundle branch block (LBBB) in a patient with chest pain clinically significant?
- It is always a normal variant in adults
- New LBBB may be a STEMI equivalent requiring emergent catheterization (Correct answer)
- It indicates only benign vagal tone
- It confirms pulmonary embolism
Correct answer: New LBBB may be a STEMI equivalent requiring emergent catheterization
New LBBB with ischemic symptoms meets Sgarbossa criteria and should be treated with the same urgency as ST-elevation MI.
Question 6: Which arrhythmia produces characteristic 'sawtooth' flutter waves at approximately 300 beats per minute on ECG?
- Atrial fibrillation
- Atrial flutter (Correct answer)
- Ventricular tachycardia
- Junctional tachycardia
Correct answer: Atrial flutter
Atrial flutter produces regular sawtooth-pattern flutter waves at ~300 bpm due to a macro-reentrant circuit in the right atrium.
CMC CMC Cardiac Diagnostics & Imaging 1
What does the PR interval on an ECG represent?