ECG

Question 1

What does ECG stand for?

Answer 1

Electrocardiography

Question 2

What does an ECG do and how?

Answer 2

• Monitors and records biopotentials produced by the heart during operation
• A non-invasive externally recorded signal from electrodes placed on the skin

Question 3

What are the 2 biggest causes of death in men aged 25-64?

Answer 3

Malignant neoplasms (cancers) - 34%
and
Heart and other circulatory diseases - 28%

Question 4

Total Blood Volume

Answer 4

4.5-5.5L

Question 5

What are the 2 circulation types of the circulatory system?

Answer 5

Systemic

Pulmonary

Question 6

How much blood is contained in the veins?

Answer 6

80%

Question 7

What is the CMV?

Answer 7

Cardiac minute volume

- 5.6L/min

Question 8

What is the CMV divided between?

Answer 8

Brain and other body organs according to importance and immediate need

Question 9

What systems are responsible for function of the heart?

Answer 9

• autonomous pulse generator
• conducting system
• contractile system

Question 10

How does the heart conduct?

Answer 10

• electrical impulse originates in the SAN (sino-atrial node)
• signal passed onto the AVN (atrioventricular node)
• propagation delayed so that blood flows into ventricles first
• pulse spreads quickly via Bundle of His (A-V bundles) and Purkinje fibres through ventricles

Question 11

Where is the SAN?

Answer 11

Top of the right atrium

Question 12

What are other names for the sinoatrial node?

Answer 12

Sinuatrial node
SA node
SAN
Sinus node

Question 13

What is the role of the SAN?

Answer 13

• generates sinus rhythm
• group of cells
• wall of right atrium
• near SVC entrance
• modified cardiac myocytes
• have some contractile filaments but do not contract
• lack fast sodium current component
• this means slower calcium currents are responsible for sino-atrial upstroke

Question 14

“Funny current” If

Answer 14

• means the membrane potential of the SAN never reaches a resting potential
• responsible for the pacing activity of the SAN
• called funny because it has opposite effects to those of most other heart currents

Question 15

Who published the first human electrocardiogram?

Answer 15

1887
Augustus D. Waller
British physiologist
St Maru’s Medical School

Question 16

Who invented the first practical electrocardiogram?

Answer 16

1903
Willem Einthoven
Dutch physiologist

Question 17

What is the aim of an ECG?

Answer 17

• record electrical signals from the heart at body surface
• describe a unique voltage generator in the chest
• look at heart activity from different view points by placing electrodes in different places

Question 18

Why may ECG results vary from subject to subject?

Answer 18

• body shape
• position of heart in chest
• posture and respiration

Question 19

How can the electrical activity of the heart be examined?

Answer 19

• a projection onto 3 orthogonal planes (sagittal, frontal, transversal)

Question 20

Frontal Plane electrode placement

Answer 20

LIMB LEADS

• attached to ends of limbs (wrists and ankles) OR origins of limbs (upper thigh and shoulders)
• makes no difference as limb viewed as a long wire conductor originating from a point on the trunk of the body

Question 21

Transverse Plane electrode placement

Answer 21

CHEST LEADS

• defined locations
• V1-V6

Question 22

What does Einthoven’s Triangle state?

Answer 22

I + (-II) + III = 0

he reversed polarity of lead II in the triangle

Question 23

What does Einthoven’s triangle assume?

Answer 23

• heart is located in an infinite homogeneous volume conductor (or at center of homogenous sphere representing the torso)

Question 24

Define a lead

Answer 24

The stretch between 2 limb electrodes

Question 25

What are the limb leads?

Answer 25

Standard leads + augmented leads

Question 26

Standard Leads

Answer 26

- 3 standard (I, II, III) - BIPOLAR LEADS - form a triangle - heart electrically constitutes the null point - reference electrode on the right foot - utilise a single positive and single negative electrode between electrical points are measured

Question 27

Augmented Leads

Answer 27

- measure from 1 electrode to central point of other 2 electrodes - UNIPOLAR LEADS

Question 28

What do the chest (precordial) leads do?

Answer 28

- UNIPOLAR LEADS - each lead records electrical variations that occur almost directly under electrode - unipolar leads (measured against reference of Wilson Central Terminal)

Question 29

Wilson's Central Terminal

Answer 29

- central terminal gives reference for precordial unipolar - formed by connecting a 5Kohm resistor from each terminal of he limb leads to a common point called the central terminal - = (I + II + III)/3

Question 30

Unipolar Leads

Answer 30

- augmented and precordial - have a single positive recording electrode - augmented leads utilise central point of other 2 electrodes as a composite negative electrode - precordial leads utilise combination of 3 bipolar leads points to give a virtual zero potential as a composite negative electrode - Wilson's central terminal

Question 31

Bipolar leads

Answer 31

- three standard | - utilise single positive and single negative electrode between which electrical potentials are measured

Question 32

What are 3 and 5 lead ECGs?

Answer 32

- for continuous monitoring and viewed only on the screen of an appropriate monitoring device (e.g. during an operation or whilst being transported in an ambulance)

Question 33

Recording depolarisation

Answer 33

- Position deflection = a wave of depolarisation heading toward towards the positive electrode - Maximal deflection = if wave of depol travels parallel to lead axis - EG = wave of depol travels towards the left leg produces a positive deflection in both leads II and III because positive electrode for both leads is on left leg

Question 34

QRS axis

Answer 34

- represents net overall direction of heart's electrical activity - average all electrical signals from heart - direction of activity based on axial reference system - can inform reader of changes in sequence of ventricular activation

Question 35

QRS abnormalities

Answer 35

- ventricular enlargement - myocardial damage - conduction blocks (hemiblocks)

Question 36

Range of QRS axis

Answer 36

-30 to +90

Question 37

LAD

Answer 37

-30 to -90

Question 38

RAD

Answer 38

+90 to +180

Question 39

How to determine the QRS axis?

Answer 39

- in the lab use leads I and III - measure height of R wave and QRS complex and plot of grid paper - use intersect to determine heart axis