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Chapter 9 Test — QT Interval and U Wave: Mastering Duration and Late Repolarization
24 questions · 24 min · +4 / -1
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Question 1
Question 1
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The figure shows the surface ECG aligned with the ventricular action potential. The interval labelled
QT interval
represents which of the following?
A.
Ventricular depolarization only
B.
Ventricular depolarization and ventricular repolarization
C.
Ventricular repolarization only
D.
Septal activation
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Question 2
Question 2
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The ECG shown demonstrates a long, flat ST segment with a normal-looking T wave, producing a prolonged QT interval. Which of the following is the most likely cause?
A.
Hypocalcaemia
B.
Hyperkalaemia
C.
Hypermagnesaemia
D.
Digoxin therapy
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Question 3
Question 3
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Prolonged QT interval is seen in all of the following EXCEPT:
A.
Hypokalemia
B.
Hypocalcemia
C.
Use of macrolide antibiotics
D.
Hypernatremia
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Question 4
Question 4
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Which of the following does NOT cause prolongation of the QT interval?
A.
Hypomagnesaemia
B.
Hyperkalaemia
C.
Erythromycin
D.
Amiodarone
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Question 5
Question 5
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A patient with known squamous cell carcinoma of the lung is brought to the emergency department with vomiting, polyuria, constipation, lethargy and myalgia for 5 days. The ECG obtained is shown. Which change is present?
A.
ST segment depression
B.
Shortened QT interval
C.
Prolonged PR interval
D.
Tall, peaked T waves
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Question 6
Question 6
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Digitalis toxicity produces all of the following ECG changes EXCEPT:
A.
Inverted T wave
B.
Prolonged QT interval
C.
ST depression
D.
Prolonged PR interval
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Question 7
Question 7
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Which electrolyte abnormality classically produces ECG findings of ST-segment depression with prominent U waves?
A.
Hyperkalemia
B.
Hypokalemia
C.
Hypocalcemia
D.
Hypercalcemia
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Question 8
Question 8
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Which of the following is NOT true about torsades de pointes?
A.
It occurs on a background of a prolonged QT interval
B.
The QRS complexes are polymorphic
C.
It is a type of supraventricular tachycardia
D.
The QRS complexes appear to rotate around the isoelectric baseline
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Question 9
Question 9
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A pre-eclamptic woman develops torsades de pointes. She is conscious, with a blood pressure of 118/74 mmHg. The next best step in management is:
A.
Immediate DC shock
B.
IV magnesium sulphate
C.
IV calcium gluconate
D.
IV amiodarone
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Question 10
Question 10
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An investigator is comparing antiarrhythmic drugs. One agent acts primarily by blocking the outward flow of K⁺ during myocyte repolarization, yet is associated with a LOWER rate of ventricular tachycardia, ventricular fibrillation and torsades de pointes than similar drugs. Which drug is being studied?
A.
Sotalol
B.
Procainamide
C.
Verapamil
D.
Amiodarone
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Question 11
Question 11
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All four of the following antiarrhythmic drugs prolong the QT interval. Which one is nevertheless associated with a paradoxically
low
risk of torsades de pointes?
A.
Sotalol
B.
Ibutilide
C.
Amiodarone
D.
Dofetilide
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Question 12
Question 12
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Which of the following fluoroquinolones is most associated with prolongation of the QT interval?
A.
Nalidixic acid
B.
Ofloxacin
C.
Gatifloxacin
D.
Pefloxacin
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Question 13
Question 13
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QT interval prolongation is minimal with which of the following 5-HT3 antagonists?
A.
Ondansetron
B.
Palonosetron
C.
Dolasetron
D.
Granisetron
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Question 14
Question 14
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A 45-year-old woman attending a pre-operative assessment clinic is taking methadone 180 mg/day. The most likely change on her pre-operative ECG is:
A.
Prolonged PR interval
B.
Prolonged QTc
C.
Prominent U wave
D.
Tented T waves
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Question 15
Question 15
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What is the ECG change associated with the use of the anti-tubercular drug bedaquiline?
A.
QT interval prolongation
B.
PR interval prolongation
C.
QRS widening
D.
ST-segment elevation
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Question 16
Question 16
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A man with a psychotic disorder is on an antipsychotic, an antidepressant and an antihypertensive. He suddenly develops tachycardia and chest tightness, and is found to have metabolic acidosis. His ECG shows a widened QRS complex and a prolonged QT interval. Which drug is responsible?
A.
Amitriptyline
B.
Amlodipine
C.
Chlorthalidone
D.
Enalapril
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Question 17
Question 17
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A 58-year-old woman on sotalol has an ECG showing a measured QT interval of 480 ms with an RR interval of 800 ms. Using Bazett's formula, what is her corrected QT (QTc)?
A.
537 ms
B.
429 ms
C.
600 ms
D.
480 ms
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Question 18
Question 18
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A 34-year-old woman on citalopram has a QTc of 505 ms on a routine ECG. Which statement best describes this finding?
A.
It is normal for a woman, as the female threshold is 500 ms
B.
It is borderline; repeat the ECG in six months
C.
A QTc above 500 ms in either sex carries a high risk of torsades
D.
It is diagnostic of congenital long QT syndrome
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Question 19
Question 19
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An ECG machine reports a QTc of 470 ms in a patient whose heart rate is 120 bpm. Which of the following is the most appropriate interpretation?
A.
ECG machines use Fridericia's formula by default, so no further correction is needed
B.
Bazett's formula underestimates QTc at fast heart rates, so the true value is probably higher
C.
The QT interval does not vary with heart rate, so no correction is required at all
D.
Bazett's formula overestimates QTc at fast heart rates, so the true value is probably lower
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Question 20
Question 20
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At a heart rate of 75 bpm, which bedside observation on the rhythm strip suggests that the QT interval is likely to be prolonged and should be formally calculated?
A.
The QT occupies more than half of the RR interval
B.
The QT occupies more than one-third of the RR interval
C.
The QT spans more than two large squares
D.
The QT is longer than the PR interval
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Question 21
Question 21
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A 62-year-old woman on furosemide has a serum potassium of 2.6 mEq/L. The ECG machine reports a QTc of 520 ms. On manual review of the single complex shown, the T wave clearly ends and is followed by a separate rounded deflection; measuring with the tangent method to the true T-wave end gives a QTc of 440 ms. What is the best explanation?
A.
T-wave alternans has confused the algorithm
B.
True QT prolongation from hypokalemia — the manual measurement is unreliable
C.
Bazett's formula was applied to values in milliseconds instead of seconds
D.
The machine has included the U wave in the measurement, producing a pseudo-prolonged QT
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Question 22
Question 22
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A 70-year-old woman develops recurrent torsades de pointes 6 hours after receiving IV haloperidol. Which of the following is CONTRAINDICATED in her management?
A.
Overdrive pacing at 90–110 bpm
B.
IV magnesium sulphate 2 g over 1–2 minutes
C.
IV amiodarone
D.
IV potassium replacement to a target of >4.0 mEq/L
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Question 23
Question 23
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A patient has recurrent, self-terminating runs of torsades de pointes despite IV magnesium and correction of potassium and magnesium. The underlying heart rate is 46 bpm and each run follows a pause. Which of the following is the definitive next step?
A.
IV lignocaine bolus
B.
IV amiodarone infusion
C.
Overdrive pacing at 90–110 bpm
D.
Oral beta-blocker
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Question 24
Question 24
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An
inverted
U wave is noted in the precordial leads of a 58-year-old hypertensive man with exertional chest pain. This finding is most suggestive of:
A.
Myocardial ischaemia
B.
Therapeutic digoxin effect
C.
Hypokalemia
D.
Hypercalcaemia
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