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103: Theme 3 > Introduction to ECG > Flashcards

Introduction to ECG Flashcards

1
Q

Syncytium

A

One large cell having many nuclei that are not separated by cell membrane

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2
Q

Functional syncytium

A

Many cells functioning as one

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3
Q

Pacemaker cells

A

For setting heart’s rhythm

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4
Q

Conducting cells

A

For transmitting rhythm throughout the heart

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5
Q

Contractile cells

A

For contracting to that rhythm (most numerous)

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6
Q

Gap junction

A

Specialised intercellular connection between two cells with adjacent membranes

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7
Q

Intercalated discs

A

Undulating double membrane separating adjacent cells in cardiac muscle fibres

Support synchronised contraction of cardiac tissue

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8
Q

Spread of impulse through the atria

A

Internodal bundles conduct impulse from SA node to AV node

  • bundles ensure synchronous contraction of the atria
  • conducting via atrial muscle would be slow
  • conducting via bundles is much faster
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9
Q

4 internodal bundles

A

Anterior, middle and posterior go to AV nodes

Bachmann’s goes to left atrium

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10
Q

Impulse at AV node

A

Wave of depolarisation passes to AV node

AV node delays wave of excitation to allow atria to contract and empty so ventricles can fill prior to contraction

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11
Q

Delay at AV node

A

Small diameter of AV nodal cells

Reduced number of gap junctions between any two cells

Smaller cells so more gap junctions must be traversed to travel the same distance longitudinally

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12
Q

Ventricular propagation

A

AV node connects to bundle of His followed by purkinje fibre system

Purkinje fibres transmit the impulse rapidly to the main mass of the ventricles

First part of ventricular wall to be depolarised is septum then apex then atrioventricular groove

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13
Q

Purkinje fibres

A

Very large myocytes

Transmit the impulse faster

Up to 5m/s

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14
Q

Bundle of His

A

Transmits impulses from AV node to the ventricles

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15
Q

ECG

A

Gross electrical measurement of the heart

Electrical activity of heart measured on the skin

Individual currents of cardiac myocytes are tiny

Currents detected from wrist and ankle

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16
Q

Lead

A

Configuration of electrodes (usually consisting of a positive electrode, negative electrode and sometimes a ground)

Standard 12 lead ECG looks at heart from 12 different angles

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17
Q

Lead II

A

Positive electrode on left leg

Negative electrode on right arm

Ground electrode on right leg

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18
Q

12 standard leads

A

3 bipolar leads

  • I, II, III
  • frontal plane

3 augmented leads

  • aVR, aVL, aVF
  • frontal plane

6 precordial

  • on the thorax near the heart
  • V1, V2, V3, V4, V5, V6
  • transverse plane (spine to sternum)
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19
Q

Bipolar leads

A

Positive electrode is compared to a negative electrode

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20
Q

Precordial leads

A

Positive electrode is compared to an estimate of what is happening at the centre of the heart

21
Q

Augmented lead

A

Positive electrode is compared to a composite reference electrode made of the two other limb electrodes connected

22
Q

P-wave

A

Depolarisation of atria in response to SA node triggering

23
Q

PR segment

A

Delay of AV node to allow filling of ventricles

24
Q

QRS complex

A

Depolarisation of ventricles, triggers main pumping contractions

If wide or misshapen, ventricular conduction is abnormal

Large Q waves are sign of dead tissue

25
Q

T-wave

A

Ventricular repolarisation

26
Q

ST segment

A

Beginning of ventricle repolarisation, should be flat

27
Q

Ectopic beat

A

Heart contraction that electrically begins somewhere other than the SA node

28
Q

Sinus rhythm

A

Heart rhythm is generated from the SA node

Each P wave is followed by QRS complex

Each QRS complex preceded by P wave

PR interval is always normal (3-5 little boxes)

29
Q

Sinus tachycardia

A

Tachycardia driven by SA node beating too quickly

30
Q

Timing of ECG

A

PR interval- from start of P wave to start of QRS complex

QT interval- from start of QRS complex to end of T wave

ST segment- from end of QRS complex to start of T wave

31
Q

Normal intervals

A

PR interval duration: 3-5 boxes, 120-200ms

QRS complex duration: 2-3 boxes, 80-120ms

QT interval duration: 9-11.5 boxes, 360-460ms

32
Q

Calculating rate

A

1 little box is 40ms
1 big box is 200ms
4 big boxes is 1 second

Rate=300/big boxes

33
Q

The heart: parasympathetic input

A

Vagus nerve

Muscarinic stim ->
Decrease HR, contractility and conduction velocity

Atropine

Vasculature not innervated by parasympathetic system

34
Q

The heart: sympathetic input

A

Sympathetic stimulation ->
Increase HR, contractility, conduction velocity

Stellate nerves
Beta agonists
Beta blockers

35
Q

Beta (1) adrenoreceptors

A

Causes inotrposim and chronotropism

36
Q

Alpha adrenoreceptors

A

Cause vasoconstriction

37
Q

Beta (2) adrenoreceptors

A

Cause vasolidation in skeletal muscle

38
Q

Adrenaline

A

Leads to net decrease in total peripheral resistance via beta (2) receptors that vasodilate vessels of the muscle and liver

39
Q

Noradrenaline

A

Leads to strong increase in total peripheral resistance via alpha (1) receptors that vasoconstrict most vessels of the body

40
Q

Atropine

A

Anticholinergic drug that reduces parasympathetic activity

41
Q

Heart block

A

Type of dysrhythmia

Any kind of impulse conduction block of the heart

Includes AV block, bundle branch block

42
Q

AV heart block

A

A delay or failure of atrial signal stimulating ventricle

Causes:
- ischeamia of AV node/ bundle
- compression of AV bundle by scar or calcified tissue
- inflammation
of the AV node/ bundle
43
Q

Heart block symptoms

A

Can be asymptomatic

Palpitations

Hypotension like: dizziness, malaise, syncope

Risk of sudden death

44
Q

First degree heart block

A

When PR interval > 5 little boxes (200ms)

All P’s followed by QRS

Almost always asymptomatic

Often young people (adolescents)

Delayed AV node transmission

Rarely treated

45
Q

Mobitz type I second degree heart block

A

Second degree- some P waves blocked and are not followed by QRS

Mobitz type I- PR interval gets longer until QRS wave fails to follow P wave

46
Q

Mobitz type II second degree heart block

A

Second degree- some P waves blocked and are not followed QRS

Mobitz type II- PR interval remains the same, likely problem in bundle of his

Can progress to 3rd degree heart block

47
Q

Third degree heart block

A

Atrial signals constantly fail to arrive at ventricles

Ventricular rate is consistent: 30-40bpm

Time between atrial and ventricular beats is variable

PR interval varies radically

Intrinsic ventricular rate is quite slow

Atrial beats are consistent

48
Q

Atrial fibrillation

A

Disorganised electrical activity in atria

  • no P wave
  • flat line or wiggly line instead

Ventricular rate is fast and irregular

Very common in the elderly

Can lead to thrombus formation in the atrium

49
Q

Respiratory sinus arrhythmia

A

Heart beat is slightly faster during inspiration, slightly slower during expiration

Usually only present in children and athletes

Caused by respiratory centres in brain’s medulla

103: Theme 3 (17 decks)

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