Chapter 11: Fundamentals Of Electrocardiography

Question 1

When does the repolarization begins in ventricular muscles?

Answer 1

0.25 to 0.35 seconds after the depolarization

Question 2

When does the atrial repolarization?

Answer 2

0.15 to 0.20 seconds after the termination of P wave, which is the beginning of the QRS Complex

Question 3

In ECG how many large or small boxes vertically represent 1 mV ?

Answer 3

10 small boxes or 2 large boxes?

Question 4

What is the standard speed of ECG ?

Answer 4

25 Mm / second

Question 5

Each small boxes of ECG = ?

Answer 5

0.04 seconds or 40 Ms.

Question 6

Each large box in horizontal direction is equal to?

Answer 6

0.20 seconds or 200 Ms.

Question 7

Normal duration of the PR interval?

Answer 7

0.16 seconds or 160 Ms or 4 small boxes.

Question 8

QT interval duration?

Answer 8

QT interval represents the contraction of ventricles. It starts from the beginning of Q wave to the end of T wave.
It is 0.35 seconds long or 8.75 small boxes.

Question 9

What is the normal RR interval?

Answer 9

0.83 seconds or 60/0.83

Question 10

What is the polarity and trajectory of the current flow in the heart?

Answer 10

The current flow has an elliptical trajectory with the positive pole of the vector directed towards the apex of the heart and negative towards the base.

Question 11

Einthoven’s Law?

Answer 11

Potential of lead 1+ potential of lead 3= potential of the lead 2

Question 12

What is the voltage of the QRS Complex and P wave in limb leads ?

Answer 12

1.0 to 1.5 mV from top of the R wave to the bottom of the S wave.
P wave= 0.1 to 0.3 mV
T wave= 0.2 and 0.3 mV

Question 13

What is the normal duration of the PR interval?

Answer 13

0.16 seconds

Question 14

Lead 1 perspective?

Answer 14

The negative electrode is on the right arm and positive electrode on the left arm. Therefore, the lead 1 perspective of the heart from the right will be negative and the left will be positive.

Question 15

Lead perspective of lead 2

Answer 15

The negative terminal is connected to the right arm and positive terminal to the left leg. Therefore the right arm is negative with respect to the left leg.

Question 16

Lead perspective of the lead 3

Answer 16

Negative left arm and positive left leg. The ECG is positive when the vector axis is normal.

Question 17

Why doesn’t it matter which bipolar limb lead recording is available when diagnosing cardiac arrhythmias ?

Answer 17

The recordings from the bipolar limb leads are all similar to one another and the diagnosis of cardiac arrhythmias depends on the time relationship between the different waves of the cardiac cycle.

Question 18

Why does it matter to record all standard limb, augmented and precordial leads when diagnosing structural damage or contraction abnormalities of the heart ?

Answer 18

Because the changes in ECG vary based on the lead perspective. Some leads can be abnormal while others may show reciprocal changes or can be completely normal.

Question 19

Why are the QRS in lead V1 and V2 predominantly negative?

Answer 19

The lead V1 and V2 are located at the level of the base of the heart. Which is the negative polarity direction of the cardiac depolarization vector.

Question 20

Lead V4 to V6 are predominantly positive. Why ?

Answer 20

These leads are placed at the level of the apex of the heart which is the net electropositivity direction of the cardiac depolarization vector.

Question 21

Physics of augmented limb leads?

Answer 21

In this type of ECG recording. Two limbs are connected to the Wilson’s central terminal through electrical resistance and the third limb is connected to the positive terminal.

Question 22

For every 1 mmHg imbalance of starling equilibrium how much will the Net filtration rate increase for the entire body?

Answer 22

6.67 ML/min

Question 23

What is the significance of Lymphatic system?

Answer 23

The main function of the lymphatic system is to return fluid and proteins in the interstitial space to the blood circulation. Without the returning of interstitial proteins to blood through the lymphatic system a human will die in 24 hrs.

Question 24

What is the average total amount of fluid that returns to circulation/ day ?

Answer 24

2 to 3 litters

Question 25

All fats in food are transported from the GI tract through which organ?

Answer 25

The lymphatic vessels

Question 26

What is the quantity of Lymph flowing through the thoracic duct of a resting human?

Answer 26

100 mL/ hour

Question 27

Why there is sealing of the lymphatic flow rate?

Answer 27

The lymphatic flow rate can only increase until the interstitial hydrostatic pressure reaches 1 to 2 mm Hg greater than the atmospheric pressure. Beyond that the lymphatic flow rate does not increase due to the fact that a further increase in intestinal hydrostatic pressure will compress and collapse the large lymphatic vessels entry portals.

Answer 28

a