General Medical Sciences ECG Rhythm practice questions
Cardiac rhythm interpretation on the ECG requires systematic assessment of rate, regularity, P wave morphology and axis, PR interval, and QRS width to distinguish normal sinus rhythm from atrial, junctional, and ventricular arrhythmias. Recognizing these patterns quickly is essential because rhythm identification directly drives urgent decisions about anticoagulation, pacing, and cardioversion. For General Medical Sciences, the priority is linking each ECG pattern to its underlying electrophysiology and to the correct next clinical step.
A 24-year-old healthy man undergoes a pre-participation sports physical. His ECG shows a heart rate of 72/min, an upright P wave in lead II preceding every QRS complex, and a constant PR interval of 160 ms. Which of the following best describes this rhythm?
A 68-year-old woman presents with palpitations and fatigue for two days. Her pulse is irregularly irregular at 118/min and blood pressure is 128/78 mmHg. ECG shows no discrete P waves, a fibrillatory baseline, and an irregularly irregular ventricular response consistent with atrial fibrillation. Which of the following is the most appropriate next step in reducing her long-term risk of stroke?
A 70-year-old man has a routine ECG showing progressive lengthening of the PR interval over three consecutive beats, followed by a P wave that is not conducted to a QRS complex. The pattern then repeats, and he has no symptoms. Which of the following best describes this rhythm?
A 19-year-old woman has intermittent episodes of palpitations and lightheadedness. Between episodes, her ECG shows a PR interval of 100 ms, a slurred upstroke at the onset of the QRS complex, and a QRS duration of 130 ms. Which of the following is the most likely diagnosis?
A 58-year-old man with a history of myocardial infarction develops palpitations and lightheadedness. He is diaphoretic, his blood pressure is 78/50 mmHg, and he has a palpable pulse. ECG shows a regular wide-complex tachycardia at 190/min with no discernible P waves. Which of the following is the most appropriate immediate management?
ECG Rhythm, answered
What is the fastest way to confirm a rhythm is sinus in origin?
Check for an upright P wave in lead II that precedes every QRS complex with a constant PR interval between 120 and 200 ms; if any of these features are missing, the rhythm is not sinus.
How do I tell Mobitz type I apart from Mobitz type II on an ECG?
Track the PR interval across several beats: progressive lengthening before a dropped QRS points to Mobitz type I, while a fixed PR interval with a sudden, unpredictable dropped beat points to Mobitz type II.
Why does atrial fibrillation raise the risk of stroke?
Loss of coordinated atrial contraction allows blood to stagnate in the left atrial appendage, promoting thrombus formation that can embolize systemically, most often to the brain.
Why is adenosine avoided in an unstable wide-complex tachycardia?
Adenosine is intended to help manage a stable, likely supraventricular rhythm; in an unstable patient, the priority is immediate synchronized cardioversion rather than a trial of a short-acting AV nodal agent that could delay stabilization.
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