Electrocardiography

Question 1

Explain cardiac conduction system?

Answer 1

1-SA node creates excitaition signal
2-signal travels in atria to AV node to delay the signal until your atria are empty of blood
3-bundle of His carries the signal to the purkinje fibers
4-purkinje fibers carries signal to ventricles to contracts

Question 2

Which is the primary pace maker of the heart?and how many electrical cells does it have?

Answer 2

Sinoatrial node SA; 2-4million cells (less than that means brady and more means tachy)

Question 3

Where does the fibrous skeleton of the heart lies?

Answer 3

Between the atria and ventricles

Question 4

Explain each wave of EKG?

Answer 4

P wave—>atrial depolarization (SA node)
PQ—>isoelectric AV delay
QRS—>ventricle depolarization
ST—>isoelectric, plateau of action potential of vent myocyte
T—>ventricular repolarization
After T wave is ventricular relaxation

Question 5

*main conductive node?

Answer 5

SA node cells: 60-100 beats per min

Question 6

How much is the conduction rate of each of the heart electrical cells?

Answer 6

SA: 60-100BMP
Atrial cells: 55-60BPM
AV:40-60BPM
Bundle of His: 40-45BPM
Purkinje fibers:20-40BPM

Question 7

Explain the 5 phases of muscle cell action potential?

Answer 7

Phase 4: resting potential -90
Phase 0: rapid depolarization (f-Na+)
Phase 1: rapid early repolarization (K+)
Phase 2: plateau phase and is the longest (Ca2+)
Phase 3:rapid repolarization (K+)

Question 8

Which one is more negative , muscle cell action potential or pacemaker action potential ?

Answer 8

Muscle cell action potential is more negative

Question 9

What is the speed and voltage at which each EKG is set?

Answer 9

25mm/sec and 10mm/mV

Question 10

Why is atrial repolarization not shown on EKG?

Answer 10

Bcz it occurs at the same time as ventricular depolarization

Question 11

What are the events that occur during cardiac cycle in order?

Answer 11

1-electrical event
2-mechanical event
3-pressure changes
4-volume changes
5-heart sounds

Question 12

In which leads is P wave is positive and upright? and inverted in which

Answer 12

Upright in Leads 1 and 2
And inverted in aVR

Question 13

Which term is used to refer to when the rhythm originates in sinus node and conducts to ventricles?

Answer 13

Sinus rhythm

Question 14

……….is the variation of the heart rate that occurs during respiration and inspiration. The beat to beat variation in R-R interval in which rate increases in inspiration

Answer 14

Sinus arrythmias

Question 15

**normal P amplitude and duration?

Answer 15

P amplitude: 0.25mV (<2.5 small squares)
P duration: 0.12 sec (<3 small squares)

Question 16

Where is P wave best seen?

Answer 16

Lead 2 and V1(biphasic in V1)

Question 17

What does it mean if PR is short?

Answer 17

Arrythmia

Question 18

PR duration?

Answer 18

0.12-0.20 sec

Question 19

Normal QRS duration?

Answer 19

0.08-0.1 sec (2.5 small squares)
>0.1=bundle branch block

Question 20

At which point does QRS terminate?

Answer 20

J point

Question 21

What does a tall T wave(>10mm amplitude) indicate?

Answer 21

MI and Hyperkalemia

Question 22

What does long QT interval indicate?

Answer 22

QTc>480ms in females and QTc>470ms in males = sudden death risk

Question 23

What does the presence of U wave indicate?

Answer 23

Found in athletes and is ass with hypokalemia and hypercalcemia. Can be normal

Question 24

Which leads are in horizontal position

Answer 24

Pericordial leads(V1-V6)

Question 25

**Which cords show inferior of heart?

Answer 25

2,3 , aVF

Question 26

Which cords show anterior surface?

Answer 26

V1-V4

Question 27

**Which cords show lateral surface?

Answer 27

1, aVL, V5 and V6

Question 28

Which cords show right atrium and cavity of left ventricle?

Answer 28

V1 and aVR

Question 29

Describe the ECG electrode placement:

Answer 29

V1:right 4th intercostal space
V2:left 4th ICS
V3:left 4th ICS b/w V2and V4
V4:left 5th ICS on midclavicular line
V5: left horizontal with V4 on anterior axillary line
V6: left horizontal with V4 on mid axillary line

Question 30

What do you do before interpreting ECG?

Answer 30

Patient name
Date
Calibration check

Question 31

How many big squares b/w R-R is equivalent to heart rate 60bmp, and how many is equivalent to 100bpm?

Answer 31

5 big squares=60bpm
3big squares=100bpm

Question 32

What is the normal range for cardiac axis?

Answer 32

Between -30 and 90 degrees