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Chapter 2 Test — Lead System and Perspectives
18 questions · 18 min · +4 / -1
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Question 1
Question 1
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The rhythm strip shown was recorded at standard settings, with the calibration pulse visible at the left margin. On such a tracing, one small square (1 mm x 1 mm) represents:
A.
0.20 s horizontally and 0.5 mV vertically
B.
0.20 s horizontally and 0.1 mV vertically
C.
0.04 s horizontally and 0.1 mV vertically
D.
0.04 s horizontally and 0.5 mV vertically
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Question 2
Question 2
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A 62-year-old hypertensive man has an ECG reported as showing normal QRS voltages. On reviewing the tracing you notice that the calibration pulse is only 5 mm tall (half standard). What is the most important consequence of this?
A.
All recorded amplitudes are halved, so left ventricular hypertrophy may be missed
B.
All recorded amplitudes are doubled, so left ventricular hypertrophy may be over-diagnosed
C.
The heart rate calculated from the strip will be twice the true rate
D.
All intervals are halved, so a prolonged QT interval may be missed
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Question 3
Question 3
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A standard 12-lead ECG is being recorded. How many electrodes are applied to the patient, and in which plane do the precordial leads view the heart?
A.
10 electrodes; frontal (coronal) plane
B.
12 electrodes; horizontal (transverse) plane
C.
12 electrodes; frontal (coronal) plane
D.
10 electrodes; horizontal (transverse) plane
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Question 4
Question 4
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While teaching students the setup of lead I on a standard ECG, you explain that the right arm electrode serves as the negative pole. Which electrode is the positive pole for lead I?
A.
Left arm
B.
Left leg
C.
Right leg
D.
Left arm and left leg together
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Question 5
Question 5
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In a physiology tutorial you are told that on a given ECG lead I measures 1 mV and lead II measures 2 mV. Applying Einthoven's law, what is the value of lead III?
A.
1 mV
B.
2 mV
C.
3 mV
D.
4 mV
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Question 6
Question 6
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In a standard ECG, an augmented limb lead measures the electrical potential difference between:
A.
Two limbs
B.
One limb and the other two limbs combined
C.
One limb and a neutral (ground) electrode
D.
Two limbs and two other limbs
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Question 7
Question 7
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Lead II is recommended as the default lead for P-wave analysis, PR interval measurement and rhythm identification. The main reason is that:
A.
It is the only limb lead that uses Wilson's central terminal as its reference
B.
It lies at +90 degrees, directly over the AV node
C.
It lies at +60 degrees, almost parallel to the normal direction of atrial depolarization
D.
Its signal is electronically amplified 1.5 times, making P waves larger
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Question 8
Question 8
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An ECG shows a mean frontal QRS axis of +90 degrees. In which lead would the R wave have the maximum voltage?
A.
Lead III
B.
Lead I
C.
aVF
D.
aVL
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Question 9
Question 9
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The hexaxial reference diagram shown divides the frontal plane into four quadrants. If a patient's mean QRS axis falls in the sector marked with the question mark, the correct interpretation is:
A.
Right axis deviation
B.
Normal axis
C.
Left axis deviation
D.
Extreme (northwest) axis deviation
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Question 10
Question 10
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According to the hexaxial reference system as described in this chapter, the normal mean frontal-plane QRS axis lies between:
A.
-30 degrees and +120 degrees
B.
0 degrees and +90 degrees
C.
-90 degrees and +90 degrees
D.
-30 degrees and +90 degrees
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Question 11
Question 11
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Left axis deviation is recognised on the ECG as:
A.
Positive QRS in lead I and positive QRS in lead II
B.
Positive QRS in lead I and negative QRS in lead II
C.
Negative QRS in lead I and negative QRS in lead II
D.
Negative QRS in lead I and positive QRS in lead II
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Question 12
Question 12
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Which of the following statements about the six precordial (chest) leads is correct?
A.
They are bipolar, each measuring the difference between two adjacent chest electrodes
B.
They are unipolar and measure voltage relative to Wilson's central terminal, which is approximately 0 mV
C.
They view the heart in the frontal plane and are used for axis determination
D.
Their signals are amplified 1.5 times so that they become readable
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Question 13
Question 13
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The diagram shows the standard positions of the six precordial electrodes. Which of the following is the correct position for V4?
A.
4th intercostal space at the right sternal border
B.
5th intercostal space at the midclavicular line
C.
5th intercostal space at the midaxillary line
D.
4th intercostal space at the left sternal border
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Question 14
Question 14
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A technician records an ECG with the V1 and V2 electrodes placed in the 3rd intercostal space instead of the 4th. Which pattern is this error most likely to produce?
A.
Tall R waves in V1-V2 with an early transition, mimicking posterior MI
B.
Reversed R-wave progression, mimicking dextrocardia
C.
False ST elevation with an rSr' pattern, mimicking STEMI or Brugada syndrome
D.
Complete inversion of lead I with an upright aVR
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Question 15
Question 15
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The precordial complexes shown demonstrate normal R-wave progression. In a normal ECG, the transition zone - where R wave height approximately equals S wave depth - is expected in:
A.
V5-V6
B.
V1-V2
C.
V3-V4
D.
V2-V3
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Question 16
Question 16
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The 12-lead ECG shown is from a patient in sinus rhythm. Lead I is completely inverted and aVR is upright, yet R-wave progression across V1-V6 is entirely normal. The most likely explanation is:
A.
Left posterior fascicular block
B.
Dextrocardia
C.
Acute inferior wall myocardial infarction
D.
Right arm - left arm electrode reversal
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Question 17
Question 17
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RA-LA lead reversal and dextrocardia both produce a negative lead I, a positive aVR and swapped leads II and III. Which single finding best distinguishes between them?
A.
The mean frontal-plane QRS axis
B.
The polarity of the P wave in aVR
C.
The PR interval measured in lead II
D.
R-wave progression across the precordial leads
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Question 18
Question 18
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A resident diagnoses an inferior wall myocardial infarction on the basis of ST elevation and a Q wave seen only in lead III. What is the most appropriate response?
A.
Record posterior leads V7-V9, as lead III changes reflect the posterior wall
B.
Lead III is the most variable lead; require concordant changes in lead II and aVF before diagnosing inferior MI
C.
Lead III changes indicate a high lateral rather than an inferior infarction
D.
Lead III alone is sufficient, because it is an inferior lead
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