Common Lead Systems in Electrocardiography

Multiple Choice Questions (MCQs)

1. What does Lead I measure in bipolar limb leads?
   a) Electrical activity between the right arm and left leg
   b) Electrical activity between the right arm and left arm
   c) Electrical activity between the left arm and left leg
   d) Electrical activity from the heart’s anterior surface
   Answer: b) Electrical activity between the right arm and left arm
2. Which lead in augmented unipolar limb leads shows inverted deflections compared to others?
   a) aVR
   b) aVL
   c) aVF
   d) Lead II
   Answer: a) aVR
3. Which of the following is true about Einthoven’s Law?
   a) Lead I + Lead II = Lead III
   b) Lead II = Lead I + Lead III
   c) Lead III = Lead I – Lead II
   d) Lead I = Lead III – Lead II
   Answer: b) Lead II = Lead I + Lead III
4. Where is the V4 electrode placed in precordial leads?
   a) 4th intercostal space at the right sternal border
   b) 4th intercostal space at the left sternal border
   c) 5th intercostal space at the midclavicular line
   d) Midaxillary line at the same level as V4
   Answer: c) 5th intercostal space at the midclavicular line
5. What is the primary purpose of augmented unipolar limb leads?
   a) Record anterior surface electrical activity
   b) Measure electrical activity between two points
   c) Provide precise localization of electrical potential direction
   d) Record lateral wall activity
   Answer: c) Provide precise localization of electrical potential direction
6. Which precordial lead provides information about the right side of the heart?
   a) V1
   b) V4
   c) V6
   d) V8
   Answer: a) V1
7. What does the Einthoven’s triangle represent?
   a) The spatial relationship of the heart’s posterior leads
   b) The spatial relationship of bipolar limb leads with the heart at the center
   c) The electrical axis of the precordial leads
   d) The voltage distribution of augmented leads
   Answer: b) The spatial relationship of bipolar limb leads with the heart at the center
8. Which lead measures electrical activity between the left arm (-ve) and left leg (+ve)?
   a) Lead I
   b) Lead II
   c) Lead III
   d) aVR
   Answer: c) Lead III
9. Where is the V2 electrode placed in precordial leads?
   a) 5th intercostal space at the midclavicular line
   b) 4th intercostal space at the left sternal border
   c) Midway between V2 and V4
   d) 4th intercostal space at the right sternal border
   Answer: b) 4th intercostal space at the left sternal border
10. Which augmented unipolar limb lead has the left leg as the positive electrode?
    a) aVR
    b) aVL
    c) aVF
    d) Lead III
    Answer: c) aVF

Fill in the Blanks

1. Lead II measures electrical activity between the right arm and ________.
   Answer: left leg
2. The triangle formed by the three bipolar limb leads is known as ________.
   Answer: Einthoven’s Triangle
3. The electrode in lead V1 is placed at the ________ intercostal space at the right sternal border.
   Answer: 4th
4. ________ is the augmented unipolar limb lead with the right arm as the positive electrode.
   Answer: aVR
5. Precordial leads are also known as ________ leads.
   Answer: unipolar chest

True or False

1. Einthoven’s law states that Lead II = Lead I + Lead III.
   Answer: True
2. The V6 electrode is placed at the 4th intercostal space on the left sternal border.
   Answer: False
3. Augmented unipolar limb leads provide information about the electrical activity of the anterior surface of the heart.
   Answer: False
4. The aVL lead has the left arm as the positive electrode.
   Answer: True
5. Bipolar limb leads measure electrical potential between two points on the body.
   Answer: True

Subjective Questions

1. Explain the purpose and placement of precordial leads (V leads).
   Answer:
   Precordial leads, also known as chest leads, record electrical potentials from the anterior surface of the heart, providing detailed information about right and left heart enlargement and electrical activity across the heart. Placement:
   • V1: 4th intercostal space, right sternal border
   • V2: 4th intercostal space, left sternal border
   • V3: Midway between V2 and V4
   • V4: 5th intercostal space, midclavicular line
   • V5: Anterior axillary line at the same level as V4
   • V6: Midaxillary line at the same level as V4
2. Describe the differences between bipolar limb leads and augmented unipolar limb leads.
   Answer:
   • Bipolar Limb Leads: Measure electrical potential between two points on the body (e.g., Lead I: Right arm to Left arm). They form Einthoven’s Triangle and represent spatial relationships.

Augmented Unipolar Limb Leads: Compare the electrical activity at one limb (positive pole) to the combined activity at the other two limbs (negative pole). These leads (aVR, aVL, aVF) provide precise localization of electrical potential direction in the myocardium