Intro to ECG

Question 1

what is the electrocardiogram?

Answer 1

The electro/chemical changes that cause myocardial contraction that are shown by the
cardiac action potential.

Question 2

What must happen in order for the myocyte to contract?

Answer 2

For the myocyte (cardiac cell) to contract, the potential difference across the cellular
(semi-permeable) membrane and must change from negative to positive in relation to
the inside of the cell.

Question 3

What do changes in potential difference occur through?

Answer 3

Changes in potential difference occur through the flow of ions through specialised ion
channels in the cellular membrane and also relatively freely through gap junctions.

Question 4

What does the electric dipole, in the cariac electrical field, consist if?

Answer 4

The electric dipole (lead)
consists of two equal and opposite
charges,
+q and –q, separated by a distance d.

Question 5

Why is the electric dipole a vector?

Answer 5

It has direction as well as magnitude .

Question 6

What do the 6 frontal plane leads consist of and what are the first 3 derived from?

Answer 6

The six frontal plane leads or limb leads
consist of three bipolar leads (I, II and III) First
3 Derived from Einthoven bipolar lead.

Question 7

What are the 3 unipolar leads?

Answer 7

Three unipolar leads (derived leads: I, II, III, to
form aVR, aVL, aVF)

Question 8

Where does the V1 lead go?

Answer 8

4th IC, right sternal edge

Question 9

Where does the V2 lead go?

Answer 9

4th IC, left sternal edge

Question 10

Where does the V3 lead go?

Answer 10

equidistant V2-V4

Question 11

Where does the V4 lead go?

Answer 11

5th IC, midclavicular line

Question 12

Where does the V5 lead go?

Answer 12

left anterior axillary line In horizontal
line with V4,

Question 13

Where does the V6 lead go?

Answer 13

mid axillary line, horizontal with V4
and V5,

Question 14

What is the pathway for sinus rhythm?

Answer 14

• Initiated by sino-atrial node (SA node)
• Traverses atria
• Through atrio-ventricular node
  (AV node)
• His/Purkinje rapid conduction
• Ventricular myocardium

Question 15

What does the P wave represent?

Answer 15

Depolarisation of both atria

Question 16

What is the PR interval and what is it a measurement of?

Answer 16

-Onset of P wave to onset of QRS complex
-Measurement of AV node conduction time

Question 17

What is the typical value of PR interval?

Answer 17

Typically, 120 – 200ms (3 – 5 small
squares)

Question 18

What does the QRS complex represent?

Answer 18

Depolarisation of ventricles

Question 19

Where is the electrical current flowing through in the QRS complex?

Answer 19

Following traversing AV
node/His/Purkinje system

Question 20

What is the typical range of the QRS complex?

Answer 20

Typical range : 80 – 110ms

Question 21

What is the first negative deflection in the QRS complex?

Answer 21

The 1st negative deflection - Q

Question 22

What is the first positive deflection in the QRS complex?

Answer 22

The 1st positive deflection - R

Question 23

What is the 2nd negative deflection or if a negative follows a positive?

Answer 23

The 2nd negative deflection or if a negative follows a
positive - S

Question 24

What is the QT interval?

Answer 24

Onset of QRS to end of T
wave

Question 25

What does the QT interval represent?

Answer 25

Ventricular depolarisation
and repolarisation

Question 26

What can long QT syndrome cause?

Answer 26

Long QT syndrome – sudden
death

Question 27

What is the typical range of the QT interval?

Answer 27

Typically, 350 – 420 msecs

Question 28

What is the ST segment?

Answer 28

Isoelectric (flat) segment
between the end of QRS and
start of T wave

Question 29

Where does ischaemia manifest on an ECG?

Answer 29

ST segment

Question 30

What does ST depression indicate?

Answer 30

Ischaemia

Question 31

What does ST elevation indicate?

Answer 31

Myocardial infarct