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Chapter 6 Test — The PR Interval: AV Conduction and Its Disorders
27 questions · 27 min · +4 / -1
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Question 1
Question 1
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The figure shows how the PR interval is marked out on the ECG. Between which two points is the PR interval correctly measured?
A.
From the peak of the P wave to the peak of the R wave
B.
From the onset of the P wave to the onset of the QRS complex
C.
From the onset of the P wave to the peak of the R wave
D.
From the end of the P wave to the onset of the QRS complex
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Question 2
Question 2
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Which of the following statements are true about the PR interval?
1. It denotes atrial depolarisation
2. Normal duration is 0.12–0.20 seconds
3. Prolongation denotes impaired AV nodal conduction
4. A short PR interval occurs in WPW syndrome
Select the correct answer using the code given below:
A.
1, 2 and 3
B.
1, 2 and 4
C.
1, 3 and 4
D.
2, 3 and 4
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Question 3
Question 3
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The PR interval on an electrocardiogram principally represents which of the following?
A.
Conduction through the AV node
B.
Ventricular depolarisation
C.
Ventricular repolarisation
D.
Atrial repolarisation
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Question 4
Question 4
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In panel A of the ECG shown, the arrows point to a slurred, slow deflection at the very beginning of each QRS complex, and the PR interval is less than 120 ms with a widened QRS. What do the arrows indicate?
A.
An Osborn (J) wave
B.
A retrograde P wave
C.
A U wave
D.
A delta wave
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Question 5
Question 5
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A 42-year-old man presents with intermittent palpitations and lightheadedness. His ECG shows a pattern consistent with Lown-Ganong-Levine (LGL) syndrome. Which of the following ECG findings is NOT characteristic of this condition?
A.
PR interval is short
B.
QRS is normal
C.
PJ interval is short
D.
PJ interval is long
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Question 6
Question 6
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A 19-year-old man with Wolff-Parkinson-White syndrome has an ECG showing a short PR interval, a delta wave and a widened QRS complex from conduction over an accessory pathway. Which of the following statements about the Bundle of Kent is FALSE?
A.
It conducts faster than the AV nodal pathway
B.
It conducts slower than the AV nodal pathway
C.
It leads to a short PR interval
D.
It leads to a prolonged QRS duration
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Question 7
Question 7
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A 24-year-old woman has a resting ECG showing a PR interval of 100 ms with inverted P waves in leads II, III and aVF and a narrow QRS (85 ms). There is no slurring of the QRS upstroke. Which is the most likely explanation?
A.
Junctional rhythm
B.
Mobitz type II second-degree AV block
C.
Wolff-Parkinson-White syndrome
D.
First-degree AV block
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Question 8
Question 8
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The rhythm strip shown comes from an asymptomatic 30-year-old endurance athlete. Every P wave is followed by a QRS complex, the PR interval is constant at about 280 ms, and the R-R intervals are regular. The most likely diagnosis is:
A.
Third-degree (complete) AV block
B.
First-degree AV block
C.
Mobitz type I (Wenckebach) second-degree AV block
D.
Mobitz type II second-degree AV block
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Question 9
Question 9
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Which is correct about first-degree heart block?
A.
Normal PR and prolonged RR interval
B.
Prolonged PR and normal RR interval
C.
Prolonged PR and prolonged PP interval
D.
Short PR and normal RR interval
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Question 10
Question 10
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A 68-year-old man has a PR interval of 240 ms. Which additional ECG feature would most suggest that the conduction delay lies in the His-Purkinje system rather than in the AV node, and therefore carries a higher risk of progression to complete heart block?
A.
An inverted P wave in lead II
B.
A narrow QRS complex (<120 ms)
C.
Sinus arrhythmia on the rhythm strip
D.
A wide QRS complex with a bundle branch block pattern
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Question 11
Question 11
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A patient with first-degree heart block and a markedly prolonged PR interval complains of recurrent dizziness and exertional breathlessness. Reversible causes have been excluded. The best definitive treatment is:
A.
Atropine
B.
Isoprenaline
C.
Adrenaline
D.
Pacemaker
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Question 12
Question 12
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The Lead II rhythm strip shown demonstrates a PR interval that lengthens with each successive beat until a P wave appears with no QRS after it; the first PR of the next cycle is the shortest. This pattern is:
A.
Mobitz type I (Wenckebach) second-degree AV block
B.
Mobitz type II second-degree AV block
C.
Third-degree (complete) AV block
D.
First-degree AV block
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Question 13
Question 13
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A 60-year-old man presents with occasional dizziness and lightheadedness. His ECG reveals a Mobitz type I (Wenckebach) phenomenon. Which statement best describes this condition?
A.
Accelerated AV nodal conduction
B.
Progressive decrease in the PR interval with each beat and then a missed beat
C.
Progressive increase in the PR interval with each beat and then a missed beat
D.
The PR intervals before and after the missed beat are equal
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Question 14
Question 14
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In a typical Wenckebach (Mobitz I) cycle, which of the following is TRUE?
A.
The PR interval immediately BEFORE the dropped beat is the longest of the cycle
B.
The PR interval immediately AFTER the dropped beat is the longest of the cycle
C.
The P-P interval becomes progressively irregular before the pause
D.
The R-R intervals progressively lengthen before the pause
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Question 15
Question 15
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A 28-year-old healthy man undergoes a routine ECG at a pre-employment check-up. The ECG shows progressively increasing PR intervals followed by a non-conducted P wave. The QRS is narrow. He denies chest pain, syncope or dyspnoea. What is the most appropriate next step?
A.
Start atropine and prepare for pacemaker insertion
B.
Reassure; no specific treatment needed
C.
Admit for telemetry and cardiac enzyme monitoring
D.
Begin beta-blocker therapy
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Question 16
Question 16
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The rhythm strip shown demonstrates regular P waves with a constant PR interval in the conducted beats, and an abrupt non-conducted P wave without any preceding PR lengthening. The most likely diagnosis is:
A.
First-degree heart block
B.
Second-degree infranodal (Mobitz II) heart block
C.
Complete heart block
D.
AV dissociation from an accelerated junctional rhythm
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Question 17
Question 17
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A 65-year-old hypertensive man with a previous myocardial infarction presents with dizziness and near-fainting. His ECG shows a Mobitz type II pattern. Which of the following is NOT seen in this pattern?
A.
Infranodal site of block
B.
PR interval is normal before a missed beat
C.
PR interval progressively increases before a missed beat
D.
PR intervals before and after the missed beat are equal
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Question 18
Question 18
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All of the following may be seen in Mobitz type II heart block EXCEPT:
A.
Block in the bundle of His
B.
Atrial rate greater than the ventricular rate
C.
Constant PR interval in the conducted beats
D.
Complete P-QRS dissociation
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Question 19
Question 19
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A 72-year-old man has second-degree AV block with a constant PR interval, sudden non-conducted P waves and a QRS duration of 140 ms. Which statement about this rhythm is correct?
A.
The block is infranodal and pacing is required in virtually all cases
B.
The block is in the AV node and will improve with atropine
C.
It reliably converts to sinus rhythm with a beta-blocker
D.
It is benign and needs only observation
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Question 20
Question 20
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A rhythm strip shows sinus beats with a constant PR interval, and then a P wave with no QRS after it. On close inspection the T wave immediately before that P wave is peaked and deformed compared with all the other T waves. The most likely explanation is:
A.
A non-conducted premature atrial contraction
B.
Sinoatrial exit block
C.
Third-degree (complete) AV block
D.
Mobitz type II second-degree AV block
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Question 21
Question 21
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The rhythm strip shown demonstrates regular P waves at a constant rate, with only every alternate P wave followed by a QRS complex; the conducted PR intervals are constant. Which of the following is the correct statement about this rhythm?
A.
It is definitely Mobitz type I, because the PR of the conducted beats is constant
B.
It is definitely Mobitz type II, because exactly half the P waves are blocked
C.
It cannot be typed as Mobitz I or II from this strip; QRS width and a longer recording help decide
D.
It is third-degree AV block, because half the P waves fail to conduct
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Question 22
Question 22
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In the rhythm strip shown, the upward arrows mark P waves and the downward arrows mark QRS complexes. The P-P interval is regular, the R-R interval is regular, the P rate is clearly faster than the QRS rate, and the PR interval is different for every beat. The diagnosis is:
A.
2:1 second-degree AV block
B.
Mobitz type I (Wenckebach) block
C.
Third-degree (complete) AV block
D.
First-degree AV block
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Question 23
Question 23
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A 70-year-old man presents with multiple recurrent fainting episodes. His ECG shows P waves at 75/min and QRS complexes at 35/min, with no relationship between the two. What is the diagnosis?
A.
Mobitz type II heart block
B.
Stokes-Adams syndrome
C.
First-degree heart block
D.
Wolff-Parkinson-White syndrome
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Question 24
Question 24
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Two patients both have third-degree AV block. Patient X has a regular QRS at 50/min with a QRS duration of 90 ms. Patient Y has a regular QRS at 28/min with a QRS duration of 150 ms. Which statement is correct?
A.
Patient X has a junctional escape and Patient Y a ventricular escape; Y's rhythm is the less reliable
B.
Patient X has a ventricular escape and Patient Y a junctional escape; X's rhythm is the less reliable
C.
Both have junctional escape rhythms; the difference is only in vagal tone
D.
Patient X's block must be infranodal and Patient Y's must be AV nodal
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Question 25
Question 25
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Complete heart block complicating an acute
anterior
myocardial infarction differs from that complicating an
inferior
MI in which of the following ways?
A.
It typically presents as first-degree block that never progresses
B.
It is AV nodal, gives a narrow-complex escape at 40-60/min and is usually transient
C.
It is infranodal, gives a wide-complex escape below 40/min and needs emergency pacing
D.
It is always reversible with atropine alone, without pacing
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Question 26
Question 26
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A monitor strip shows P waves and QRS complexes that are largely independent of each other. Which single finding best proves that this is AV dissociation WITHOUT complete heart block?
A.
A narrow QRS complex
B.
A regular R-R interval
C.
An atrial rate of 70/min
D.
The presence of capture beats
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Question 27
Question 27
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On a rhythm strip the ventricular (QRS) rate is 68/min and the sinus P rate is 62/min, with no fixed PR relationship and a narrow QRS. Which is the most likely mechanism?
A.
Wenckebach block with 3:2 conduction
B.
Third-degree AV block with a slow junctional escape
C.
AV dissociation due to an accelerated junctional rhythm
D.
Mobitz type II second-degree AV block
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