# Clinical Science Questions and Answers – Electrocardiography

This set of Clinical Science Questions and Answers for Entrance exams focuses on “Electrocardiography”.

1. The number of leads necessary for an ECG is _________
a) 3
b) 6
c) 12
d) 24

Explanation: To have an ECG, the number of leads necessarily needed is 3. These three leads are placed on the four limbs in various combinations to derive the ECG. A 12 lead ECG is used for a greater in-depth analysis. It is used while taking a treadmill test.

2. Which of the four limbs acts like a ground and thus is not a part of the ECG test?
a) Right Arm
b) Left Arm
c) Right Leg
d) Left Leg

Explanation: In the various combinations to take ECG, the right leg is considered to be grounded and so no leads are placed on it to take an ECG. It may sometimes have a lead line for grounding but otherwise, that leg does not take part in ECG testing.

3. What result do the various combinations of limb leads give?
a) Einthoven’s Triangle
b) Beethoven’s Triangle
c) Bermuda’s Triangle
d) Electrical Triangle

Explanation: The leads are arranged in 3 combinations making one limb positive, one negative and the third as a neutral. There is a vector arrow drawn from the negative side to the positive side. The three arrangements thus result in a triangle which is called the Einthoven’s triangle.

4. The most common placement of the leads from the Einthoven’s triangle is __________
a) Positive Left Arm and Negative Right Arm
b) Positive Left Leg and Negative Right Arm
c) Positive Left Leg and Negative Left Arm
d) Positive Right Arm and Negative Left Leg

Explanation: The Einthoven’s triangle forms a cyclic vector in form of direction. The most important readings are from the 2nd placement of leads in which the Left Leg is positive, the Right Arm is Negative and the Left Arm is neutral. The vector direction is from the right arm to the left leg.

5. A typical ECG wave is _______
a) Periodic
b) A-periodic
c) Quasi – Periodic
d) Non – Periodic

Explanation: ECG wave comprises PQRSTU segments. In this, P, R, T, U are all waves that go above the baseline and Q, S are waves that go below. However, P wave and R wave are not periodic. Periodicity is checked between the successive R waves. Quasi periodic waves are those which are periodic in a certain interval. Since the ECG signal is periodic in R to R interval or P to P interval, its a Quasi periodic wave.
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6. The amplitudes of the segments of the wave are ____________

a) P = 0.25 mV, Q = 0.4mV, R = 1.60mV, T = 0.1 – 0.5 mV
b) P = 2.0 mV, Q = 0.1mV, R = 1.60mV, T = 0.1 – 0.5 mV
c) P = 25.0mV, Q = 4.0mV, R = 16.0 mV, T = 10 – 50 mV
d) P = 0.25 mV, Q = 0.60mV, R = 1.60mV, T = 0.1 – 1.0 mV

Explanation: The waves of ECG are a result of electrical impulses and so they have an amplitude. The various waves are a result of the stepwise contractions of the heart. P wave is the depolarization of the atria, QRS complex is formed due to depolarization of the ventricles and then T wave represents the re-polarization of the ventricles.

7. Bradycardia ECG will show what kind of wave?
a) The impulses have increased
b) The impulses have decreased
c) Pronounced P waves
d) Pronounced T waves

Explanation: Bradycardia is a symptom where the heartbeat is below the normal range. The heart pumps blood slowly so the impulses are not so pronounced. In tachycardia, the impulses increase. The waves are shorter and sharper.

8. Which of these conditions are natural conditions for tachycardia?
a) Running
b) Grief
c) Shock
d) Sleep

Explanation: When a person has run for a stretch, their heart rate goes up. This is a normal tachycardia condition and eventually, the heart rate will go back to normal. When the body gets used to running due to training, the heart also adjusts and is able to pump blood better without raising the heart rate by much.

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