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2A CARDIOVASCULAR > ECGs > Flashcards

ECGs Flashcards

1
Q

What does an ECG represent?

A

-the electrical events of the cardiac cycle
-each event has a distinct waveform
-used to evaluate cardiac pathophysiology

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2
Q

Cardiac cycle review

A

1) atrial contraction - D
2) isovolumetric contraction - S
3) rapid ejection - S
4) reduced ejection - S
5) isovolumetric relaxation - D
6) rapid filling - diastole - D
7) reduced filling - D

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3
Q

CC - atrial contraction

A

AV open, SV closed

-P wave
-SAN impulse
-electrical depolarisation of atria
-atrial contraction
-atrial pressure increase
-atrial pressure > ventricular pressure
-blood flows -> ventricles
-atrial booster
-atrial contraction complete
-maximal ventricular volume - EDV
-LAP - a-wave - atrial contraction causes small increase in venous pressure

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4
Q

CC - isovolumetric contraction

A

All valves closed

-QRS complex
-SAN impulse
-ventricular depolarisation - excitation-contraction coupling, myocyte contraction
-ventricular contraction
-ventricular pressure increase, ventricular blood volume constant = ISOVOLUMETRIC CONTRACTION
-LAP - c-wave - bulging of mitral valve leaflets back into atrium (x-descent follows peak of c-wave)

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5
Q

CC - rapid ejection

A

AV closed, SV open

-intraventricular pressure > aortic/pulmonary artery pressure -> SV open
-rapid ejection of blood from ventricles -> aorta/pulmonary artery
-low pressure gradient across valve (due to large opening) -> low resistance
-maximal outflow velocity (early in ejection phase), maximal systolic aortic/pulmonary artery pressures
-LAP - initial decrease as atrial base is pulled down so chamber expands -> BF -> atria continued -> atrial pressure increases (increasing pressure is maintained until AV valves open at end of isovolumetric relaxation)

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6
Q

CC - reduced ejection

A

AV closed, AV open

-T wave
-beginning of ventricular repolarisation
-decline in ventricular active tension & pressure generation
-rate of ejection falls
-Vp < outflow tract pressure - however outward flow still occurs due to kinetic/inertial energy of blood
-LAP/RAP - gradual pressure increase due to continued venous return from the lungs/systemic circulation

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7
Q

CC - isovolumetric relaxation

A

All valves closed

-intraventricular pressures fall
-aortic/pulmonary valves close (aortic valve closure precedes pulmonary - 2nd heart sound - beginning of isovolumetric relaxation) - (small backflow of blood into ventricles - dicrotic notch in aortic/pulmonary pressure tracings)
-aortic & pulmonary pressures rise slightly - dicrotic wave
-slow aortic/pulmonary pressure decline
-ventricular pressures decrease however volume is constant = ISOVOLUMETRIC RELAXATION
-volume of blood remaining in ventricle is ESV

(SV = EDV - ESV)

-LAP - continues to rise due to venous return - peak LAP at end of isovolumetric relaxation - v-wave

Ap > Vp -> AV open

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8
Q

CC - rapid filling

A

AV open, SV closed

-end of phase 5 - ventricles continue to relex
-Vp < Ap -> AV valves open
-passive ventricular filling begins
-brief decline in ventricular pressure due to continued ventricular relaxation
-ventricles completely relaxed
-pressure rises as ventricles are filled with blood from atria (blood moves down pressure gradient)
-LAP - opening of mitral valve causes rapid fall in LAP - before mitral valve opens - peak of LAP = v-wave - mitral valve opens, atrial pressure decreases = y-descent

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9
Q

CC - reduced filling

A

AV open, SV closed

-ventricles continue to fill with blood & expand
-ventricles become less compliant & intraventricular pressure rises
-increase in intraventricular pressure
-pressure gradient across AV valves reduces
-rate of ventricular filling falls = REDUCED FILLING
-90% of ventricular filling is complete by end of this phase
-aortic/pulmonary pressures continue to fall during this phase

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10
Q

Co-ordination of the heart review

A

-SAN pacemaker cells depolarise
-electrical impulse generated
-impulse spreads across atria
-atria contract

-annulus fibrosus (cardiac skeleton, fibrous tissue band) separates atria from ventricles -> prevents impulse travelling directly from atria -> ventricles

-impulse spreads through atria -> AVN

-AVN delays impulse
-AVN transmits impulse down bundle of His

-impulse reaches end of bundle of His
-impulse spreads through ventricle walls via Purkinje fibres

-impulse spreads up ventricle walls
-ventricles contract

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11
Q

Diastole

A

0.3s

When the ventricles relax & fill with blood

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12
Q

Systole

A

0.5s

When the ventricles contract to pump blood into pulmonary/systemic circulations

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13
Q

What type of wave is produced by an electrical impulse that travels towards the electrode?

A

Upright positive deflection

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14
Q

What conditions can ECGs identify?

A

Arrhythmias
Myocardial ischaemia/infarction
Pericarditis
Chamber hypertrophy
Electrolyte disturbances (hyper/hypokalaemia)
Drug toxicity

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15
Q

Name the 3 pacemakers of the heart

A

Sinoatrial node
Atrioventricular node
Ventricular cells

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16
Q

What is the dominant pacemaker?

A

SAN

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17
Q

SAN intrinsic rate

A

60-100bpm

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18
Q

What are the back up pacemakers?

A

AVN
Ventricular cells

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19
Q

AVN intrinsic rate

A

40-60bpm

20
Q

Standard calibration of ECG machine

A

25mm/s
0.1mV/mm

21
Q

What does an ECG look like?

A
22
Q

Heart order of impulse conduction

A

SAN -> AVN -> Bundle of His -> Bundle branches -> Purkinje fibres

23
Q

What does the P wave represent

A

Atrial depolarisation

24
Q

What does QRS represent?

A

Ventricular depolarisation

25
Q

What does T wave represent?

A

Ventricular repolarisation

26
Q

What does the PR interval represent?

A

Atrial depolarisation, delay in AV junction (delay allows time for atria to contract before the ventricles contract)

27
Q

What do ECG leads measure?

A

Difference in electrical potential between 2 points

28
Q

Bipolar leads

A

-2 points on body
-positive & negative

29
Q

Unipolar leads

A

-1 point on body, 1 virtual reference point with zero electrical potential
-centre of heart

(only require positive electrode for monitoring)

30
Q

How many leads are calculated using the 10 electrodes?

A

12 leads using 10 electrodes

(6 precordial, 4 limbs (1 neutral))

31
Q

How many chest electrodes and chest leads are there?

A

6 electrodes
6 leads

32
Q

What information do chest electrodes give?

A

Info. about heart’s horizontal plane

33
Q

How many limb electrodes & limb leads are there?

A

4 electrodes
6 frontal leads

34
Q

What information do limb electrodes give?

A

Info. about heart’s vertical plane

35
Q

Einthoven’s triangle

A

Placement of limb electrodes & frontal leads

  1. Lead I
  2. Lead II
  3. Lead III
  4. Augmented vector right (aVR)
  5. Augmented vector left (aVL)
  6. Augmented vector foot (aVF)

Leads 1-3 - bipolar
Augmented leads - unipolar

36
Q

Common abnormalities of the P wave

A

P wave = atrial depolarisation

Right atrial enlargement - tall > 2.5mm - P pulmonale

Left atrial enlargement - notched (M-shaped) - P mitrale

Long PR interval - first degree heart block

37
Q

First degree heart block

A

-split-second delay in the time that it takes electrical impulses to move through the AVN

38
Q

Common abnormalities of the QRS complex

A

Depth of the S wave should not excess 30mm

Pathological Q wave
- >2mm deep, >1mm wide
- >25% amplitude of the subsequent R wave

39
Q

What does the QRS axis represent?

A

Overall direction of the heart’s electrical activity

40
Q

What do abnormalities of the QRS axis suggest?

A

Ventricular enlargement or conduction blocks

41
Q

Common abnormalities of the ST segment

A

-usually flat (isoelectric)
-elevation/depression of ST segment by 1mm or more can be pathological

42
Q

Common abnormalities of the T wave

A

-should be at least 1/8 but less than 2/3 the amplitude of R
-T wave amplitude rarely exceeds 10mm
-abnormal T waves - symmetrical, tall, peaked, biphasic or inverted

43
Q

How does the QT interval change when heart rate increases?

A

Decreases

44
Q

Common abnormalities of the QT interval

A

-QT interval decreases when heart rate increases
-regular interval = 0.35s-0.45s
-should not be more than half of the interval between adjacent R waves

45
Q

U waves

A

-small, round, symmetrical and positive in lead II
-amplitude <2mm (regular)
-U wave should be same direction as T wave

46
Q

How do you determine heart rate from an ECG?

A

For regular rhythms - rule of 300/1500

-count number of big/small boxes between two QRS complexes
-divide this into 300/1500 for regular rhythms

For irregular rhythms - 10 second rule

-count number of beats present on the ECG
-multiply by 6

47
Q

Explain the quadrant approach for the QRS axis

A

-QRS complex in leads I & aVF
-determine if they are positive/negative
-the combination should place the axis into 1/4 of the quadrants

LAD = left axis deviation
RAD = right axis deviation

2A CARDIOVASCULAR (3 decks)

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