Imaging Flashcards
1
Q
What does an ECG show?
A
The electrical activity of the heart on a graph using electrodes attached to the skin surface. It helps monitor heart rate and rhythm.
2
Q
What causes the electrical activity seen on an ECG?
A
The electrical circuit in the heart made of myocardial cells which contain an abundance of ions allowing them to act as conductors
3
Q
What happens to a cell when it is repolarised?
A
Its interior is negative, and its exterior is positive causing a potential difference across the cell membrane, forcing positive ions to move into the myocardial cells
4
Q
When a cell is repolarised it reaches a threshold, what happens when this is met?
A
The action potential is triggered, and the cell depolarises causing it to contract
5
Q
What is measured on an ECG?
What allows the electrical impulses in the heart to travel?
A
As the cells can switch between positive and negative charge, depolarisation causes a brief change in the voltage across the myocardial membrane the voltage produced by this cardiac action potential is what is measured on the ECG
All the cells are electrically connected through gap junctions which allow the flow of ions allowing electrical impulses to move around the heart
6
Q
What are the 3 ions involved in electrical conduction in the heart by moving into or out of cells?
A
Sodium (Na+), potassium (K+) and Calcium (Ca++)
7
Q
How do most antiarrhythmic drugs treat cardiac arrhythmias?
A
Alter sodium, calcium, and potassium channels – adjusting how excitable a cell is
They can also block any sympathetic activity (example: beta blockers)
8
Q
Where in a normal heart is the first electrical pulse initiated for contraction?
What happens if this doesn’t work?
A
Initiated by an impulse generated by the sinoatrial (SA) node - the hearts pacemaker
If there is a problem in the SA node, the AV node can assume the role of the pacemaker – this is known as an escape rhythm and is slower than if it was generated by the SA
9
Q
Where are pacemaker and non-pacemaker cells located and what is their function?
A
Pacemaker cells:
1. SA node
2. Self generate electricity
Non-pacemaker cells:
1. Atrial and ventricular cardiomyocytes, Purkinje conduction system
2. Conduct the electrical impulses generated by the pacemaker cells
10
Q
What allows pacemaker cells to generate their own electricity?
A
They can spontaneously depolarize, unique ion channels provide this action potential
11
Q
How are non-pacemaker cells protected against random excitement?
A
Have a plateau phase where they cannot be triggered.
12
Q
Do all cells in the heart have the same action potential?
A
No, there are slow and fast response cells which have different action potentials with different responses to electrical activity
13
Q
Label the following points on the ECG and identify which form a complex?
A
QRS complex
14
Q
What is the name given to the baseline of an ECG tracing?
A
The isoelectric line = no voltage change
15
Q
Why would a positive deflection (above line) occur on an ECG?
Why would a negative deflection (below line) occur on an ECG?
A
Occurs when the wave of depolarisation travels towards the lead
Occurs when the wave of depolarisation travels away from the lead
16
Q
What determines the shape of an ECG?
A
The direction of contraction and lead position
17
Q
What does the P wave show on an ECG?
If there is a normal P wave what does this tell us?
A
Electrical impulse generated in the SA node that rapidly spreads across the L+R atrial muscle, causing depolarisation and contraction (atrial systole) until it reaches the AV node
Normal P wave indicates the SA node is working correctly
18
Q
What does the Q wave show on an ECG?
A
An impulse traveling through the AV node into the bundle of His, down the bundle branches into the Purkinje fibres and the interventricular septum depolarising ready to spread the impulse across the ventricles all of this allows the ventricles to fill with blood (diastole).
19
Q
What does the distance between points P and Q indicate on an ECG?
A
Indicates any issues between the AV and SA
20
Q
What does the R wave show on an ECG?
A
The electrical impulses spreading across the ventricular muscle causing the ventricles to depolarise and contract (ventricular systole) ejecting blood.
21
Q
What does the S wave show on an ECG?
What does it indicate?
A
The electrical impulse reaches the last remaining areas of the ventricles (late ventricular depolarisation) and the ventricles then relax (ventricular diastole)
That the impulse has now stead across the whole of the ventricles
22
Q
If the QRS complex is wide on an ECG what does it suggest?
If the QRS complex super narrow (normal described as narrow) on an ECG what does it suggest?
A
Indicates that the ventricles are taking a long time to contract
Indicates blood not moving through the heart properly
23
Q
What does the T wave show on an ECG?
What does a normal T wave indicate?
A
The ventricular muscle repolarising, resetting the electrical charge after contraction, in preparation for the next heartbeat
Everything during that heart beat went well as it is the final part of the complete waveform
24
Q
What is sinus rhythm?
What are the two rules that you must follow to identify that sinus rhythm is occurring?
A
Name given to the normal rhythm of the heart
- ECG shows the SA node is initiating electrical impulses and electrical activity is following the normal path of conduction – this is the rhythm/pattern of the heartbeat
- ECG shows a regular rate
25
What is the RR interval?
If the RR interval is constant...
If the RR interval differs between beats...
The distance between QRS complexes
... the rhythm is regular
... the rhythm is irregular
26
What is sinus arrhythmia?
When a dogs heart rate changes with it's breathing (as the dog breathes to its heart rate drops slightly), it can be normal and often doesn't indicate somethings wrong
27
Where is the origin of cause if the QRS complex is super narrow?
Where is the origin of cause if the QRS complex is wide and bizarre?
Supraventricular
Likely to have originated in the ventricles (if electrical activity is initiated within the ventricles and travels by an abnormal path across the ventricular muscle, depolarisation occurs at a slower rate)
28
If there is an issue in the heart and more pace-maker cells are required what can happen?
The non-pacemaker cells can be converted to pace-maker cells.
29
Why is it slow if the ventricles have to produce their own electrical impulse?
They wait for the electrical signal to arrive and when it does not they have to produce their own which is a slower process
30
What are the 8 steps that must be followed when checking an ECG?
What is the additional other 2 checks that can be done?
Additional:
- Measure the amplitude of each wave
- Measure segment interval times
31
How do you measure the amplitude of an egg wave?
Measure its width and height
32
Which lead on an ECG gives you the clearest view?
How many leads are required to give 6 views?
How many leads are required to give 12 views?
Lead 2
4 Leads
10 Leads
33
What are the 3 ways in which you can calculate HR from an ECG?
Regular rhythm = large square method
Fast regular rhythm = small square method
Irregular or slow rhythm = RR interval method
34
When calculating HR what should you always check before you start, especially if you want the calculations to be easier?
That the paper speed is at 25mm/sec
35
If the paper speed is at 35mm/sec what would the following measure as in both seconds and milliseconds:
1 small square
1 large square
5 large squares (just seconds)
1 small square
= 0.04s OR 40ms
1 large square
= 0.20s OR 200ms
5 large squares
= 1 second
36
What is the calculation used for the small square method?
1500 / R-R interval in small squares = ___bpm
37
What is the calculation used for the large square method?
300 / R-R interval in large squares = ___bpm
38
What is the calculation used for the RR method?
no. of boxes X 10 = ___bpm
(6 seconds is 30 large boxes, so count the number of QRS complexes in 30 boxes)
39
Calculate the heart rate:
1500 ÷ 8 = 187bpm
OR
19 x 10 = 190bpm
40
Calculate the heart rate:
27 x 10 = 270bpm
41
Calculate the heart rate:
300 ÷ 3 = 100bpm
1500 ÷ 16 = 93bpm
42
Calculate the heart rate:
5 x 10 = 50bpm
43
What does the RR interval indicate on an ECG?
The distance between two R waves on an ECG.
Represents the interval between heartbeats and regularity of rhythm.
Used to calculate heart rate.
44
What does the PR interval indicate on an ECG?
Measurement from beginning of the P wave to the beginning of the QRS wave.
It reflects conduction through the AV node.
45
What does the ST interval indicate on an ECG?
Measurement between the end of the S wave and the beginning of the T wave.
Represents the interval between ventricular depolarization and repolarization.
46
Assess the following ECG (use the rules):
Does it have sinus rhythm?
HR = 200bpm using RR interval method – tachyarrhythmia
No P waves
QRS complexes narrow and upright
RR interval irregular
Not normal sinus rhythm
47
Assess the following ECG (use the rules):
Does it have sinus rhythm?
HR = 300bpm using RR interval method – tachyarrhythmia
No P waves
QRS complexes wide
RR interval regular
Not normal sinus rhythm
48
Assess the following ECG (use the rules):
Does it have sinus rhythm?
HR = 120bpm using RR interval method – Normal
Several P waves occur without a following QRS complex (after the 2nd, 6th, 9th and 12th QRS complexes)
QRS complexes narrow and upright
RR interval irregular
Not normal sinus rhythm
49
Assess the following ECG (use the rules):
Does it have sinus rhythm?
HR = 30bpm using RR interval method – Bradyarrhythmia
P waves are present, but there is no association with the QRS complexes – no P wave for every QRS and no QRS for every P wave
QRS complexes normal width/height
RR interval regular
Not a normal sinus rhythm
50
What is the difference between bradyarrhythmia or tachyarrhythmia?
What is arrhythmia?
tachyarrhythmia: fast HR
bradyarrhythmia: slow HR
When the heart beats irregularly
51
What are ectopic beats?
Premature or extra beats caused by unusual impulses
52
The following are names of descriptions of where the heart beat originated from, where are the locations?
Sinus
Supraventricular
Ventricular
Sinus - originating from the SA node
Supraventricular – originating or sustained in atrial or atrioventricular node tissue from above the level of bundle of His
Ventricular - from the ventricles
53
What is considered fast and slow HR for cats and dogs?
54
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Sinus Tachycardia
Sinus = normal beat originating from SA node
P wave, QRS complex and T wave present = normal sinus rhythm
Fast but regular rhythm
Causes – increased sympathetic tone, medication, systemic
55
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Sinus Arrhythmia
Normal sinus rhythm
The rate increases on respiration and decreases on expiration
Changes in rate = variation in RR intervals. ‘Regularly irregular’
Common in dogs – high resting vagal tone
56
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Sinus Bradycardia
Sinus = normal beat originating from SA node
P wave, QRS complex and T wave present = normal sinus rhythm
Slow but regular rhythm
Causes – Medications, electrolyte disturbances, vagal stimulation, hypothermia, hypoadrenocorticism, hypothyroidism, raised ICP
57
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Ventricular Fibrillation (VF)
Irregular and deformed wave
No distinct P waves, QRS complexes or T waves
Ventricular myocardium depolarize erratically
Causes = re-entry, triggered activity, automaticity
58
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Ventricular Tachycardia (VT)
Wide and bizarre QRS complexes
No associated P waves
Tachycardia – heart rate > 180bpm
The rapid rate = low cardiac output, reduced preload and stroke volume
Causes = re-entry, triggered activity, automaticity
59
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Atrial Fibrillation (AF)
Narrow, upright QRS complexes
Irregular ventricular rate
Absence of P wave
Irregular RR interval
Undulating baseline
Tachycardiac (abnormally rapid beating), pulse deficits
Cause = re-entry, triggered activity
60
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Hyperkalaemia
Peaked or spiked T waves
Flat, or absent P waves
Prolonged QT interval
Widened QRS complex
Cause – High potassium disrupts electrical signals
61
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Ventricular Premature Contractions (VPCs)
Signal originates in ventricles – no P wave
QRS is ‘wide and bizarre’
Signal interrupts the sinus (normal) rhythm
Premature beat that starts in ventricles
62
What could cause an undulating base line on an ECG that's not because of arrhythmia?
It could be an artefact caused by movement so don't base your diagnosis just off of a wobbly baseline
63
What does this picture show (type of arrhythmia), and what are the key signs that indicate to this and the cause?
Supraventricular Tachycardia
Fast - tachycardia
Can be regular or irregular
P waves absent or hidden in other arts of the wave
P waves can invert below baseline
Narrow QRS complexes, varying heights
T waves follow QRS complexes
Cause = electrical signals re-entring atria
64
Identify HR and rhythm:
200bpm
Supraventricular tachycardia (SVT)
(No obvious P waves/P waves hidden in another part of the wave (P waves can also be inverted below the baseline) narrow QRS complexes (therefore supraventricular in origin), QRS waves have varying heights, T waves follow QRS complexes, RR intervals regular (can be irregular), fast rate)
65
Identify HR and rhythm:
110bpm
Ventricular premature contractions (VPCs)
(No P wave for every QRS, wide and bizarre QRS complexes (therefore ventricular in origin) that interrupt sinus rhythm)
66
Identify HR and rhythm:
190bpm
Ventricular tachycardia (VT)
(Wide and bizarre QRS complexes (therefore ventricular in origin) without associated P waves. Looks like saw teeth. Can be pulsed, or pulseless.)
67
What is the cause of this rhythm and what is the 2nd abnormal rhythm?
Hyperkalaemia
VPC (Black arrow)
(Absent P waves, wide QRS complexes, Peaked T waves (white arrow), prolonged QT interval.)
68
Identify HR and rhythm:
110bpm
Atrial fibrillation (AF)
(Absent P waves, narrow QRS complexes (therefore supraventricular in origin), irregular RR intervals, rippling baseline. RR intervals irregular.)
69
Identify HR and rhythm:
90bpm
Sinus arrhythmia
(Normal sinus rhythm – P wave for every QRS, QRS for every T, QRS shape normal (narrow, therefore supraventricular in origin), T waves present and normal. Variation in RR intervals – if we could see more of the rhythm strip, this pulse would be ‘regularly irregular’ – every time the animal breathes the rate increases (black line), then decreases again between breathes. )
70
Identify HR and both main and second rhythm:
210bpm (s.s.m.)
Main: sinus tachycardia
Second: VPC (black arrow)
(There is a P wave for every QRS complex and a QRS complex for every P wave, except for the wide complex, all other QRS complexes are narrow (therefore supraventricular in origin). RR intervals irregular, rate is fast.)
71
Identify rhythm:
Ventricular Fibrillation
(Chaotic, irregular and deformed waves, no distinct P, QRS or T waves. Can be fine or coarse. Rate fast. Can't identify a base line.)
72
Identify HR and rhythm:
110bpm
Normal sinus rhythm
(P wave for every QRS complex, QRS complex for every P, QRS complexes narrow therefore supraventricular in origin, relationship between P waves and QRS complexes normal, T waves present and normal shape/amplitude, RR interval regular, rate is within normal parameters.)
73
Identify HR and rhythm:
40bpm
Sinus Bradycardia
(Normal sinus rhythm with a P wave for every QRS and a QRS for every P. QRS complexes narrow therefore supraventricular in origin, T waves present. RR interval regular, rate is slow.)
74
What structures can be looked at using an ultrasound in the cardiothoracic region?
Heart
Lung surface
Pleura and pericardium
Lymph nodes, thymus and space occupying lesions
Vascular structures like arteries and veins to check for blockages (not limited to the thorax)
75
What is the named used for an ultrasound of the heart?
What can be seen when you ultrasound the heart?
Echocardiography
Thickness of heart muscles, valves, if the anatomy is normal, assessment of endocardium/myocardium/pericardium, Myocardial function, cardiac size, blood flow (ie. Check if its flowing back), if there’s a hole ie. congenital heart disease
76
When/why would you ultrasound the heart?
Congenital defects – equine
Murmurs – small
Poor Performance – equine
Arrhythmias (disrhythmias) – small
Other indicators based on clinical examination
If patient has collapsed
77
What view of the heart to you get on an ultrasound if you place the probe on vertically/on the transverse plane?
What view of the heart to you get on an ultrasound if you place the probe on horizontally/on the dorsal plane?
View of the hearts median plane/image 1 (like how you would cute a hot dog roll)
View of the hearts transverse plane/mushroom/image 2 (like how you would cute a garlic bread)
78
What can be seen in this ultrasound image?
The heart (probe held transverse, median view)
79
What can be seen in this ultrasound image?
The heart (probe held horizontally, transverse view)
80
What does blue on the doppler mean?
What does red on the doppler mean?
What does the mixing of blue and red on the doppler indicate?
Blue = blood flowing away from transducer
Red = blood flowing towards transducer
If the colours mix it means the blood is mixing directions and it shouldn’t be doing this, it should only move in 1 direction
81
What is wrong with this image?
Hole between aortic wall and left ventricle allowing de-oxygenated blood to travel around the body
82
What are the two issues with this heart?
Pericardial effusion - Pericardium filled with fluid
In left ventricle blood is swirling around heart for some reason, blood gets sticky when mixing and can lead to clotting which can break up and get stuck in the veins, seen by grey flecked bit
83
What's wrong with this image?
Pericardial effusion - fluid in pericardium
84
What can be viewed when ultra-sounding the lungs?
Only the top surface layer, pleura and pleural space (cannot see soft tissue structures)
85
Why would you ultrasound the lungs?
To identify surface pathology (usually just large animals) and in small animals to check for fluid in the lungs
86
What kind of frequency does your ultrasound have to be on to view the lungs?
Ultrasound on high frequency
87
What should be seen on a normal lung ultrasound and why?
What's a good clue that there is an issue with a lung when looking at an ultrasound?
Only visualise smooth, freely gliding surface and minimal fluid in pleural cavity
Sound does not penetrate normal aerated lungs
The pleural line doesn't look normal (disrupted, change in colour or shape)
88
Label the structures on this ultrasound image of a lung:
89
What are the limitations when ultra sounding the cardiothoracic cavity?
Ribs and anatomy (like forelimb for equine) can get in the way of image
Lungs and therefore chest move when breathing, especially if dog is panting
Ultrasound in large animals has to penetrate really far
Patient compliance, small animals may need to be sedated
Ultrasound cannot pass through gas (can only see lung surface)
90
Why does a normal lung not appear black on an x-ray?
Appear grey due to blood vessels
91
What are the 5 opacities?
What can also have an effect on colours?
Superimposition (overlapping structures) will affect the “colour”
92
Identify the following labels:
A = aorta
B = caudal vena cava
C = trachea (bad image of it would be black)
D = diaphragm
E = diaphragm
F = cardiac silhouette/heart
G = cranioventral lung
H = liver
93
Name the lobes on this image:
Right: Cranial, middle, caudal, accessory
Left: Cranial (Cr/Ca) and Caudal
And Accessory(cannot see the borders as they are all gass filled)
94
What is in the lung?
Bronchi, alveoli, interstitial tissue (½ cells thick, help hold everything together) and blood vessels
(remember on radiograph they're all stacked on top of each other)
95
How do bronchi and blood vessels appear on a radiograph?
Bronchi – gas filled tube, soft tissue wall (dark)
Blood vessel – soft tissue wall, fluid filled (SAME OPACITIES!) (greyish white)
96
What are the characteristics of the bronchi on in a normal lung vs. an abnormal lung on a radiograph?
Normal:
Sometimes see walls of larger bronchi near middle
Also exist right to the periphery of the lung lobes but too small to see
Abnormal:
Wall becomes thickened and/or mineralized (opacity is more white) and therefore easier to see
Can see bronchi more clearly in the periphery
Looks like donuts and tramlines
97
Where is interstitial tissue found?
What is the difference between normal and abnormal interstitial tissue on radiographs?
Tissue that surrounds the alveoli and vessels – thin
Normal:
Don’t see it on a radiograph
Abnormal:
It is diffusely thickened (still air in alveoli so can still see borders and soft tissue structures) so we can see it or frank nodules (often tumours - exaggerated in image)
98
What can in the lungs can be mistaken for nodules on a radiograph?
What are other common artefacts in a thoracic radiograph?
Artefacts like nipples
Skin folds
Cartilage mineralisation (common on thorax)
Size and shape of cardiac silhouette (animal dependant)
“Collapse” of dependent lung - do DV first!
99
What is the difference on radiographs between normal and abnormal alveoli?
Normal:
Filled with air (not black due to overlying tissue) and borders
Abnormal:
Filled with fluid (Blood/pus/oedema/other) so no contrast to soft tissue to border obliteration (indicates alveoli and not interstitial tissue) or they could be collapsed
100
Would you take a radiograph to look at blood vessels?
Where are the veins in the lungs?
No but pulmonary vessels can be seen
In the lungs the veins are ventral and central!
101
How could blood vessels look abnormal on radiographs and why would they appear this way?
Smaller: due to blood loss (hypovolemic), dehydration, less blood circulation (image less white more black)
Larger: due to an excess of fluid in the blood and being over perfused
102
What are arteries and veins the same diameter as?
Arteries and veins same diameter as 9th rib
103
What is the plea and how does it appear on a normal radiograph?
Surrounds the lungs but cannot be appreciated on the normal radiograph as it’s a very thin membrane. The lungs occupy the entire space of the pleural membrane
104
What would abnormal pleura look like on a radiograph?
Lungs pulled back from the edge due to contents (air/fluid/mass) in the pleura which squashes the lungs so they can't expand properly (especially with the ribs)
105
What is it called when there is air in the pleural space, and what is the name if it is blood instead?
Air in plural space = pneumothorax
Blood in plural space = Hemothorax
106
Should you be able to see the mediastinum on a radiograph?
No, only visible if there is a growth occurring or something else has gone wrong with it
(grown can sometimes be identified by trachea being pushed upwards)
(sits in middle so covered by heart etc.)
107
What can thoracic radiographs help identify?
What are they not used for?
L heart failure (helps see cardiac enlargement)
Can identify cause of breathlessness/cough
Will not identify CAUSE of heart DISEASE (need to look at a cardiac ultrasound for that)
108
What can make thoracic radiographs difficult to read/interpret?
- movement blur as the heart is always moving
- wide radiographic contrast
- interpretation!
- breed normals/age normals (ie. calcification of the airways in older dogs)
- inspiratory/expiratory - should be taken at point of inspiration as the thorax air provides contrast
109
What positions would you put an animal in for an x-ray of the heart?
What positions would you put an animal in for an x-ray of the lungs?
Lateral - right
Dorsoventral
Ventrodorsal* (do this first to prevent potential lung collapse)
Lateral - right (and left is suspected tumours in lungs)
* NEVER do this if dog in extreme respirtory distress
110
What is this radiograph position. and what must you ensure to achieve the best radiograph?
LATERAL
Sternum needs to be parallel with the spine otherwise trachea can look elevated when its not hence the foam block
Front leg must be pulled out of the way
111
When taking an x-ray of a cat in respiratory distress should you sedate them?
No, it can kill them so if the cat is in shock it will be so focused on breathing you can take a catogram
112
What is this radiograph position?
Dorso-ventral
113
What is this radiograph position?
Ventro-dorsal
114
What does this stand for when assessing the quality of a radiograph:
Pink
Camels
Collect
Extra
Large
Apples
(On Inspiration)
Positioning
Collimation
Centring
Exposure
Labelling/Markers
Processing/Artefacts
(Inspiratory or expiratory?)
115
On a left and right thoracic radiograph what parts of the heart can be seen?
LEFT: The auricular surface (so both left and right ventricles and both atrium)
RIGHT:
116
What is the calculation for VERTEBRAL HEART SCORE (VHS)?
What is the average for dogs and cats?
VERTEBRAL HEART SCORE (VHS) = Length (base to apex) + Width
Average in dogs is 9.7 (range 8.5 - 10.5), 8 in cats
117
What can enlargement of the heart suggest on a radiograph?
1. Generalised enlargement
- Dogs: pericardial effusion or dilated cardiac myopathy (can sometimes just be that the heart is blurry, clue is if there are no clear borders)
- Cat: hypertrophy cardiac myopathy
2. Individual chamber enlargement
- certain valves not working correctly, certain side heart failure, certain chambers and sides enlarged
3. Changes in great vessels
- congenital issues, hypovolemia etc.
118
What on a radiograph can suggest right heart enlargement?
Too much contact with the sternum (sometimes just a trait of the animal and has no adverse effects)
119
What is a valentine heart (dorsal ventral view) in felines?
When both atria are enlarged but ventricles are not - suggests cardiac myopathy
(CM presents as a circle in dogs)
120
What is an angiography?
Are they still used?
When contrast it put into the heart to ensure that the valves are working
No, this can be seen using and echocardiogram
121
What are the two essential questions you must ask yourself when interpreting a radiograph?
IS THE RADIOGRAPHIC
DIAGNOSIS
CONSISTENT WITH THE
CLINICAL FINDINGS?
IS THE QUALITY OF THE
RADIOGRAPH
ADEQUATE TO PERMIT A
CONFIDENT RADIOGRAPHIC
DIAGNOSIS?
122
What is wrong with the radiograph?
its underexposed
123
What is wrong with this radiograph?
its overexposed
(burnt toast analogy)
124
How would you minimise movement blur?
Careful handling
Sedation/GA
(general anaesthetic highly recommended when you think there's a respiratory issue as can control breathing and inflate leg for better imaging)
Reduce exposure time
125
What is the general rule of thumb for the size of the cardiac silhouette in canines when looking at the lateral view and dorsoventral?
Lateral =3.5 rib spaces wide, 2/3rds of thorax in height
DV = 2/3rds width of thorax at rib 6
126
What is the general rule of thumb for the size of the cardiac silhouette in felines when looking at the lateral view and dorsoventral?
Lateral: Width of heart is two rib spaces (intercostal spaces) (2/3rds roughly in height)
DV: Width is 2/3rds width of thorax at 5th rib
127
What view are needed for the following radiographs (small animals):
Thorax
Abdomen
Pelvis + Spine
Limbs
Skull
What is the requirement for two radiographs of separate views?
Thorax
- RLR + DV (LLR + VD)
Abdomen
- RLR/LLR + VD
Pelvis + Spine
- RLR/LLR + VD
Limbs
- Mediolateral + CrCd/CdCr/DP/PD
Skull
- RLR/LLR + DV
The views need to be 90º form each other
128
What radiographic views do the large animal distal limb require?
4 views
- lateromedial
- dorsalpalmar/dorsal planter
- 2x45º angles from these views
129
What patient prep is involved in small animal radiographs?
Animal must be starved preferably for 24hrs especially is sedition is required
Animal needs to urinate and dedicate before images are taken
130
What are radiographic grids?
What is the purpose of radiographic grids?
When are radiographic grids used?
Thin sheets of alternating lead and plastic, the lead absorbs radiation
Some x-rays scatter (travel in random directions) when passing through the animal/tissue which is a safety issue and leads to poor quality images, radiographic grids reduce these effects.
Only when the tissue is over 10cm thick due to extra exposure required when using them
131
How are lead strips orientated in radiographic grids?
What are the 3 subgroups of grids?
Orientated to the primary beam so that they can pass through to the receptor but the majority of the scatter cannot = selective filtering
1. Parallel = l l l l l l l l l l
2. Focused = / / / / l l l l l \ \ \ \ (orientated in direction of primary beam)
3. Pseudo-focused = l l l l |||| l l l l (shorter at edges allowing more primary beam through)
132
What determines how much radiation is received by the receptor?
What is 'Grid Factor'?
The width and height of the bars on the grids strips
Not all of the primary beam gets through the slats, to combat this the exposure must be increased 2-3 times - this increase is the 'Grid Factor'
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When setting up a grid (especially focused) what must you ensure?
Give an example of when using a grid, even in tissue over 10cm thick, wouldn't be appropriate?
That the primary beam is centred, the tube head is at the correct height, good source to image receptor distance and that the grid is the correct way up so that the x-rays correspond with the slats
If the x-ray machine is low powered as longer exposure would be required which would increase the risk of movement significantly
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What are the two main types of grids?
Stationary = over cassette on table, have a protective covering eg. plastic
Moving = installed in the table, cassette placed in 'Bucky tray' its long axis in line with images long axis
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What are radiographs processed once taken?
Processed by different computer softwares depending on tissue type/area of body
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What are the benefits of using computer software to process radiographs?
- many structures can be visualised due to wide latitude
- compensates for under/over exposure
- fast
- allows pot-processing manipulation
- easy storage and distribution
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What is post-processing manipulation?
What is the downside to this?
What can it not do?
When the image is edited to change the contrast, brightness and magnification.
Over manipulation can obscure any issues that could be presenting with the animal or create artefacts.
it cannot retrieve structures that weren't picked up on when the image was taken due to over or under exposure
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What file types are used for radiographic images?
- DICOM = large files (30MB), used for diagnosis, have lots of details like patient info.
- Pictures (jpeg etc.) = compressed image of what was on the screen, has no extra details, should never be used for diagnosing, apart from brightness cannot be manipulated
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How should radiography files be kept and stored?
- need to be backed up
- PACS server used by practices for easy access and sharing of images
- can have physical copy back ups
- must be protected
- must be tranferrable
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What is a contrast media/agent?
Substance injected into body with a different radiopacity to tissues. It provides information on organs (especially hollow organs)
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What are the two main groups of contrast media?
1. Negative - gasses, radiolucent properties, low density
2. Positive - high atomic numbers, radiopaque properties
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What are the ideal properties of contrast media?
- diff. radio opacity with desired contrast
- not toxic nor an irritant
- persist study duration
- totally eliminates post study
- easily administered
- cost effective
- indicates clear borders
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What must always be done before using a contrast?
What must also be done before using Water Soluble Iodine as a contrast?
Must take a plain radiograph to...
- assess technique
- potential diagnosis
- assess patient prep.
- decide technique
- for comparison
- to check you're using right contrast
Patient sedated and hydrated with non-ionic prep.
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What are some of the advantages and disadvantages of using a negative contrast?
Advantages:
- used in bladder + GI tract
- can use with positive for double contrast
- mostly safe
- cheap, quick, convenient
Disadvantages:
- doesn't prove much mucosal detail alone
- slow to leave body
- some use CO2 due to potential risk of embolisms
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What are 2 types of positive contrasts?
1. Barium Sulphate = GI tract
2. Water soluble iodine
- ionic = IV injections, urinary tract, cavities
- non-ionic = subarachnoid space
- GI preparations = GI studies
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What are some of the advantages and disadvantages of using Barium Sulphate as a positive contrast?
Advantages
- inert
- low toxicity
- great mucosal detail
- if in mineral suspension helps with GI upset
- cheap
Disadvantages
- inhalation causes severe tissues reaction in alveoli (don't use under GA)
- cation must betake if given orally
- irritant to body cavities
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What are some of the advantages and disadvantages of using Water Soluble Iodine as a positive contrast?
Advantages
- versatile so can go to lots of bodily regions
- absorbs rapidly in body cavities
Disadvantages
- ionic compounds have side effects
- ionic compounds are toxic
- injections given and this as an IV may not mix
- risk of iodine acute kidney injury
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When using contrast the structures examined are given certain names, what names are given to these structures:
1. Spine + Subarachnoid space
2. Bladder
3. Urethra
4. Heart + blood vessels
5. Joints
6. Lacrimal sytem
1. myelography
2. cystography
3. urethrography
4. angiography
5. arthrography
6. darcyocystography
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What names are given to the following descriptions:
1. infusion of positive contrast
2. infusion of air
3. infusion of positive contrast followed by air
1. positive contrast __(name of structure)__
2. pneumo-__(name of structure)__
3. double contrast __(name of structure)__
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What is an ultrasound?
What is the most commonly used ultrasound?
What are two different types of ultrasound?
Reflection of sound at boundaries in the body
2D B-mode
M/Motion mode
Doppler mode
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What is M mode on an ultrasound?
Single beam of sound that does not move. Echoes received are viewed along timeline.
(example is looking at how the hearts valves and walls move over time)
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What is doppler mode o an ultrasound?
When the frequency of sound is reflected by moving objects
(example is blood cells which act as lots of reflectors)
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On a doppler ultrasound what happens blood flows towards the probe and what happens when it flows away?
What is the difference between the two called?
Towards = sound reflects at high frequency than original
Away = sound reflects at lower frequency than the original
Doppler shift (its magnitude related to the velocity of the blood cells)
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What does the mnemonic BART stand for?
Blue
Away
Red
Towards
(doppler ultrasound colours that show velocity and direction)
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When taking a Doppler there is also a graph what do the y and x axis stand for and what does it mean if the line is above or below the baseline?
Y axis = velocity
X axis = time
Above baseline = flow towards probe
Below baseline = flow away from baseline
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There are two types of doppler than can be used, what are these?
1. Continuous wave
- all velocities in beam path measured
- cannot discriminate depth
- can measure high velocity
2. Pulse-wave
- Evaluates velocity in specific area
- determines depth from original signal
- limit to velocity is can measure (too high = artefact)
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What are the clinical uses for doppler?
Measures abnormal flow.
Velocity related to pressure so can look at pressure gradients over valves
Volume of flow
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Why are artefacts sometimes considered useful when taking an ultrasound?
They can indicate the nature of a structure
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The following are artefact examples, describe what each of them are:
Electrical noise
Acoustic (Clean) shadowing
Acoustic enhancement
Reverberations
Mirror
Electrical noise
- non-uniform echoes with varying sizes seen in dark areas. Caused by surrounding electrical equipment or turning the gain too high
Acoustic (Clean) shadowing
- anechoic shadowing of deep structures due to Toal reflection. Occurs deep to tissues interfaces with marked impedance differences (different levels of resistance)
Acoustic enhancement
- fluid causes sound not to reflect so it reaches bottom of structure, opposite effect of acoustic shadowing
Reverberations
- occurs due to a mix of fluid and gas or poor contact between skin and probe. Causes parallel lines that get faster deeper. No anatomical view if first cause as all reflected back at the boundary.
Mirror
- reversed image of structure seen due to curved surface (common with diaphragm) that effects time taken for sound to travel back. Adjusting transducer angle, gain and TBC setting may help.
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In ultrasound reverberations are a type of artefact, 'dirt shadowing' is a category of this type of artefact. What is it?
It's when sound gets stuck in an air bubble and therefore takes ages to return. Ultrasound assumes this long time means it's a very far away, deep structure.
161
Why does dysrhythmia need treated?
Degeneration can lead to a fatal rhythm and have impacts on the cardiac output especially if long term
162
The cardiac muscle has a stable resting potential, what is this determined by?
Determined by potassium concentrations
163
Explain how the cardiac muscle is depolarised and then repolarised:
4 stages
1 = Depolarising - sodium permeability increases allowing an influx in sodium ions depolarising the cell and reaching actin potential
2 = Maintaining - voltage gated calcium ion channels switch between open and closed allowing a slow influx maintaining depolarisation
3 = Repolarising - calcium and sodium channels close on potassium channels open
4 = cell reset and waiting for next impulse
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Why is cardiac muscle action potential much longer than other neurones?
Cardiac action potential is mainly mediated by voltage gated calcium channels instead of sodium like the others.
The calcium channels open and close gradually and so the action potential builds up over a long period of time instead of rapid fire.
165
Action potential plus pacemaker potential is the .....
Absolute refractory period
166
Describe what goes on in a pacemaker cell for it to randomly depolarise?
3 stages (0, 3, 4)
0 = Depolarisation - voltage gated calcium channels open allowing an influx and reaching action potential
3 = Repolarisation - calcium channels close and voltage gated potassium channels open
4 = Slow depolarisation - potassium channels close and sodium and calcium channels spontaneously open allowing a slow influx until -40 (this is unique to pacemaker cells)
cycle begins again!
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What determines HR in the pacemaker cell?
How long the stage of slow depolarisation is
168
What increases calcium movement in cells?
What impact does more calcium have on contraction force of the heart?
What impact does and increase in calcium have on HR?
The sympathetic nervous system, more nor-epinephrine means more calcium movement
Increases in calcium is important as plays a large role with actin and myosin cross bridges and therefore muscle contraction force
Increase in calcium increases heart rate as calcium plays a role in muscle and pace maker cells and the calcium in now moving faster
Muscle cells - decreased plateau phase
Pacemaker - calcium channels open quicker so action potential reached faster and reset quicker
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What causes dysrhythmia?
- congenital, developmental or trauma structural cardiac disease (changes shape, size of muscle changing movement of electrical system)
- drugs and toxins (can change sympathetic system etc.)
- metabolic diseases/electrolyte imbalance (such as potassium or calcium e.g. renal disease)
- systemic disease (sepsis, neoplasia)
- sympathetic tone (increased epinephrine release e.g. pain, fear)
170
How can you treat dysrhythmias?
- treat underlying problem
- agonist/antagonist on receptors
- drugs affecting ion channels (not via receptor)
171
What drug can be used to block the sympathetic nervous system if it's gone a bit too far and heart rate is too high and the heart can no longer fill properly? (supraventricular tachycardia)
What are 2 examples of these types of drugs?
Beta blockers, agonists that block the beta 1 and 2 receptors
Propranolol
Atenolol
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How do drugs that slow down heart rate by acting like the parasympathetic system work?
ACh binds to muscarinic receptors which blocks adenylyl cyclase, reduces cyclic amp and reduces calcium uptake (which then impacts calcium release). It also opens the potassium channels on the other side allowing potassium to leave the cell, taking the baseline of -65 even lower as it removes the + ions without replacing hyperpolarising the membrane making it harder to reach depolarisation threshold slowing down heart rate and reducing contraction.
173
How do muscarinic antagonists work?
What is an example?
They block the muscarinic receptors preventing hyperolarisation and down regulation of cyclic AMP reversing effects of muscarinic receptors and the parasympathetic NS, HR and contraction force should increase. (an example would be used for patients with severe brachycardia)
Atropine
174
What is parasympathetic/vagal tone?
Being chronically unwell
Can also be caused by severe abdominal pain
It causes your HR and contraction force decrease
175
What do muscarinic agonists do?
What is an example of a drug that does this?
They bind to the muscarinic receptors and mimic acetyl choline by blocking adenylyl cyclase and reducing cAMP and calcium effects whilst hyper polarising the cell slowing the heart rate and contraction force.
Muscarine found in mushrooms
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Muscarinic agonists ..1... the parasympathetic nervous system
Muscarinic antagonists ..2... the PSNS
In using these what are you trying to achieve?
1. activates/mimics
2. blocks/suppresses
Trying to get the heart rate back to the normal baseline
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What is adenosine?
When would you use adenosine?
Drug that acts on a specific receptor (like an agonist) in the heart that acts like a muscarinic receptor: blocking cyclic amp, increasing potassium reflux, slowing down calcium manipulation
Resulting in a fast drop in heart rate and contraction force.
In emergencies on severe tachycardia patients as short acting and very fast, not pleasant for patient
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What do sodium channel blockers do?
Which is most commonly used in practice?
Why are they often used as local anaesthetics?
Slows down action potential as impacts the depolarisation phase, also slows the heart as it also has an effect on those sodium channels
Lidocaine
Reduces action potential movement as these cause the feeling of pain as they pass the signal from the pain stimulus to the brain
179
What type of drugs are needed when dealing with ventricular tachycardia?
Must be drugs acting on the ion receptors. Drugs that act on the PSNS and the SNS won't work as it has nothing to do with the sinoatrial node. It is the ventricular muscle not working on its own accord.
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How do potassium channel blockers work?
When would you use potassium channel blockers?
Give two examples of potassium channel blocker:
Block the potassium channels slowing down depolarisation which means it takes longer for the cells to reset themsevm for the next wave of depolarisation. So they slow down heart rate and contraction force.
If the sodium channels blockers, like lidocaine weren't working or in an emergency or for longer term treatments.
- Amiodarone (short acting, emergency use like CPR)
- Sotalol (longer acting, if you had a damaged myocardium that was causing ventricular tachycardia while it healed something like this can be a longer acting treatment for a few weeks until it sorts itself)
181
What are the 3 types of ion channel blockers?
Calcium
Sodium
Potassium
182
When would calcium channel blockers be used and why?
Are they really used for the heart?
To slow conduction, reduce contraction force and cause coronary vasodilation as calcium influx will slow prolonging the plateau [hase and less calcium will be released from the sarcoplasmic reticulum as calcium induces calcium release.
No, more preferred for reducing blood pressure
183
What is the name of the drug that inhibits the potassium sodium pump and what effect does this have on the heart?
Why is it so dangerous?
Digoxin - increases the atrioventricular refractory period slowing down the heart and improves filling. It also causes the cell to maintain calcium as it changes its movement across the membrane which increases contraction force.
Very fine line when working with, can easily kill the patient and can have an effect on any pump in any part of the body so any there drugs that have side effects that could react with the pump will then react badly with the digoxin
