Electrocardiography

Question 1

What is the purpose of an electrocardiogram?

Answer 1

Recording potential changes of volttage that are generated by the heart during the cardiac cycle and transmitted to the surface of the body

Question 2

Normal waveform in electrocardiogram

Answer 2

Question 3

How many leads are used in recording an ECG?

Answer 3

12

Question 4

What are the ECG leads?

Answer 4

Limb leads:
Bipolar limb leads (use two active electrodes): Lead I, Lead II, Lead III
Unipolar augmented limb leads (Use one electrode): aVR, aVL, aVF

Precordial or Chest Leads:
V1, V2, V3, V4, V5, V6

Question 5

What does each lead measure the potential difference of?

Answer 5

Lead I: Record potential difference between Right arm (Negative) and Left arm (Positive)
Lead II: Record potential difference between Right arm (negative) Left leg (positive)
Lead III: Record potential difference between Left arm (Negative) and Left leg (positive)

Question 6

What does Einthoven’s law state?

Answer 6

Voltage in lead II = Voltage in lead I + Voltage in lead III

Einthoven’s triangle (Two arms and the left leg form apices of a triangle around the heart) leads to the law’s occurence

Question 7

Voltage from each limb lead

Answer 7

Question 8

Location of the first chest lead (V1)

Answer 8

Question 9

Location of the second chest lead (V2)

Answer 9

Question 10

Location of the fourth chest lead (V4)

Answer 10

Question 11

Location of the third chest lead (V3)

Answer 11

Question 12

Location of the fifth chest lead (V5)

Answer 12

Question 13

Location of the sixth chest lead (V6)

Answer 13

Question 14

ECG from each chest lead

Answer 14

Question 15

Which lead is used in analysing ECG results?

Answer 15

Lead II

Produces the ECG waveform in the diagram

Question 16

Significance of the P wave

Answer 16

Caused by Atrial Depolarization

Question 17

Duration and voltage of the P wave

Answer 17

Duration: 0.12 sec
Voltage: 0.1 and 0.3 millivolts

Question 18

Which wave shows atrial repolarization?

Answer 18

Atrial Repolarization is not recorded as it is masked by QRS complex

Question 19

Significance of the QRS complex

Answer 19

Caused by Ventricular Depolarization
Q wave is due to depolarization of interventricular septum
R wave is due to depolarization of the apex and ventricular wall
S wave is due to depolarization of posteriobasal part of the left ventricle and the pulmonary conus

Question 20

Duration and voltage of the QRS complex

Answer 20

Duration: 0.08 – 0.1 sec.
Voltage: 1.0 to 1.5 mv (Lead II)

Question 21

Significance of the T wave

Answer 21

Caused by Ventricular Repolarization

Question 22

Duration and voltage of the T wave

Answer 22

Duration: 0.12 – 0.16 sec
Voltage: 0.2 and 0.3 mv

Question 23

Significance of the U wave

Answer 23

Small +ve wave
Caused by Repolarization of the papillary muscles
Generally is not visible on the ECG

Question 24

Intervals and segments on the ECG

Answer 24

P-R interval
Q-T interval
S-T segment

Question 25

Extent of the P-R interval

Answer 25

Beginning of P wave and beginning of QRS complex

Question 26

Duration of the P-R interval

Answer 26

It is around 0.16 sec (<0.2sec/1 large square)

Question 27

What does the P-R interval represent?

Answer 27

Interval between the beginning of electrical excitation of the atria and the beginning of excitation of the ventricle

Question 28

In what conditions may the P-R interval be prolonged?

Answer 28

1st degree heart block

Question 29

Extent of the Q-T interval

Answer 29

Beginning of Q wave to the end of the T wave

Question 30

Duration of the Q-T interval

Answer 30

0.35-0.4 sec (<2 large squares)

Question 31

What does the Q-T interval represent?

Answer 31

Ventricular depolarization and repolarization

Question 32

In what conditions may the Q-T segment be prolonged?

Answer 32

Increases the incidence of ventricular arrhythmias and sudden death

Question 33

Extent of the S-T segment

Answer 33

End of the S wave and the beginning of T wave

Question 34

Characteristics of the S-T segment

Answer 34

Normally isoelectric

Question 35

In what conditions may the S-T segment deviate above the isoelectric line?

Answer 35

Myocardial ischemia

Question 36

What are the main factors commented on in an ECG?

Answer 36

Rate Rhythm Axis Waves (duration and voltage), segments and intervals

Question 37

Axes of an ECG

Answer 37

Question 38

What does one large square represent?

Answer 38

Question 39

What does one small square represent?

Answer 39

## Footnote One large square contains 25 small squares

Question 40

How many squares in one minute?

Answer 40

300 large squares 1500 small squares

Question 41

Formulae for calculating rate on an ECG

Answer 41

Question 42

ECG for tachycardia

Answer 42

Question 43

ECG for bradycardia

Answer 43

Question 44

How can regular and irregular rhythms be distinguished?

Answer 44

**Regular**: R-R interval is equal **Irregular**: R-R interval is not equal

Question 45

Define the axis of the heart/cardiac axis

Answer 45

Cardiac axis is the general direction in which the heart depolarizes

Question 46

What is the normal axis of the heart?

Answer 46

-30 to +90˚

Question 47

Normal heart axis depolarization

Answer 47

Question 48

Heart axis deviations on ECG

Answer 48

Question 49

Causes of right axis deviation

Answer 49

Right ventricular hypertrophy Right bundle branch block Infant and thin people Right ventricular load (pulmonary embolism/COPD)

Question 50

Causes of left axis deviation

Answer 50

Left ventricular hypertrophy Left bundle branch block Obesity Mechanical shift (ascites, pregnancy and abdominal tumors)

Question 51

What is the clinical significance of an ECG?

Answer 51

Detecting: * Heart rate & rhythm * Axis of the heart * Size of the heart * Abnormal rhythm and conduction * Ischemic damage of the heart