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Clinical Measurements > ECG > Flashcards

ECG Flashcards

1
Q

What does ECG stand for?

A

Electrocardiography

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2
Q

What does an ECG do and how?

A
  • Monitors and records biopotentials produced by the heart during operation
  • A non-invasive externally recorded signal from electrodes placed on the skin
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3
Q

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

A

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

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4
Q

Total Blood Volume

A

4.5-5.5L

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5
Q

What are the 2 circulation types of the circulatory system?

A

Systemic

Pulmonary

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6
Q

How much blood is contained in the veins?

A

80%

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7
Q

What is the CMV?

A

Cardiac minute volume

- 5.6L/min

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8
Q

What is the CMV divided between?

A

Brain and other body organs according to importance and immediate need

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9
Q

What systems are responsible for function of the heart?

A
  • autonomous pulse generator
  • conducting system
  • contractile system
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10
Q

How does the heart conduct?

A
  • 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
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11
Q

Where is the SAN?

A

Top of the right atrium

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12
Q

What are other names for the sinoatrial node?

A

Sinuatrial node
SA node
SAN
Sinus node

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13
Q

What is the role of the SAN?

A
  • 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
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14
Q

“Funny current” If

A
  • 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
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15
Q

Who published the first human electrocardiogram?

A

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

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16
Q

Who invented the first practical electrocardiogram?

A

1903
Willem Einthoven
Dutch physiologist

17
Q

What is the aim of an ECG?

A
  • 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
18
Q

Why may ECG results vary from subject to subject?

A
  • body shape
  • position of heart in chest
  • posture and respiration
19
Q

How can the electrical activity of the heart be examined?

A
  • a projection onto 3 orthogonal planes (sagittal, frontal, transversal)
20
Q

Frontal Plane electrode placement

A

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
21
Q

Transverse Plane electrode placement

A

CHEST LEADS

  • defined locations
  • V1-V6
22
Q

What does Einthoven’s Triangle state?

A

I + (-II) + III = 0

he reversed polarity of lead II in the triangle

23
Q

What does Einthoven’s triangle assume?

A
  • heart is located in an infinite homogeneous volume conductor (or at center of homogenous sphere representing the torso)
24
Q

Define a lead

A

The stretch between 2 limb electrodes

25
Q

What are the limb leads?

A

Standard leads + augmented leads

26
Q

Standard Leads

A
  • 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
27
Q

Augmented Leads

A
  • measure from 1 electrode to central point of other 2 electrodes
  • UNIPOLAR LEADS
28
Q

What do the chest (precordial) leads do?

A
  • UNIPOLAR LEADS
  • each lead records electrical variations that occur almost directly under electrode
  • unipolar leads (measured against reference of Wilson Central Terminal)
29
Q

Wilson’s Central Terminal

A
  • 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
30
Q

Unipolar Leads

A
  • 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
31
Q

Bipolar leads

A
  • three standard

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

32
Q

What are 3 and 5 lead ECGs?

A
  • 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)
33
Q

Recording depolarisation

A
  • 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
34
Q

QRS axis

A
  • 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
35
Q

QRS abnormalities

A
  • ventricular enlargement
  • myocardial damage
  • conduction blocks (hemiblocks)
36
Q

Range of QRS axis

A

-30 to +90

37
Q

LAD

A

-30 to -90

38
Q

RAD

A

+90 to +180

39
Q

How to determine the QRS axis?

A
  • 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

Clinical Measurements (11 decks)

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