Small Animal Cardiology and Respiratory Medicine: ECG/Interactive Flashcards
What is the definition of an ECG?
A recording of the changed in electrical potential difference (voltage) in the heart occuring during depolarisation and repolarisation of the myocardium plotted against time
What part of the heart is the pacemaker?
Sinoatrial node
Describe how the PQSRT complex is formed?
- SAN spontaneously depolarises and spreads across right and left atrium forming the P wave
- As this reaches the AVN conduction is slowed giving the P-R interval
- The wave reaches the bundle of His which branches to purkinje fibres and the ventricle depolarises forming the QRS complex
- The ventricle then repolarises slowly giving the T wave
How should the patient be connected to the ECG machine?
Gently restrained in right lateral recumbancy
Crocodile clip electrodes attached to loose skin just above elbows and stifles
Red- right fore
Yellow- Left fore
Green- Left hind
Black- right hind- earth lead
Which ECG lead is themost important lead to examine and why?
Lead II
This shows the largest complexes in dogs and cats
Where do each of the leads record changes in electrical potential difference between?
Lead I- right fore and left fore
Lead II- right fore and left hind- parrallels the position of the heart
Lead III- the left fore and left hind
How can HR be worked out on an ECG?
Obtained over a 6 second strip- no of QRS complexes x 10
For dysrythmias it is better to determine mean HR over longer period of time
After HR is worked out what should be checked?
P: QRS ratio should be 1:1
When first looking at an ECG checking the predominant rhythm what should be checked?
Inspect regularity and morphology for any dysrythmia
P waves should be identified if possible- regularity and uniformity
QRS- normal and narrow
QRS always followed by T waves- can be negatie, positive or biphasic in dogs, cats usually positive
How do you measure and multiply an ECG?
Standard lead II measurments are taken at 50mm/s and a sensitivity of 1mv=1cm
1mm box is 0.1mV x 0.02s
Measure P wave amplitude (height) (mV)
Measure P wave duration (length)(seconds)
Measure P-R interval
Measure height of R wave
Measure duration of QRS complex
Measure QT interval
T wave is noted to be positive, negative or biphasic
ST segment should be at a similar level of the baseline P-QRS
What are some common ECG abnormalities from measurment?
Prolonged P wave- left atrial enlargment
Tall P wave- right atrial enlargment
Tall R wave- left ventricular enlargment
Prolonged QRS complex- ventricular enlargment
What is the name for normal heart rythm?
Sinus rhythm
P wave preceding every QRS complex and a QRS following a P wave
It can vary with respiration- sinus arrythmia- normal in dogs indicating normal, high resting vagal tone
How is a sinus arrest presented on an ECG?
What casues it?
The ECG shows a gap with no electrical activity for a period exceeding normal R intervals
Often a manifestation of high vagal tone- may be normal in brachiocephalics
What is an AV block and how many different types are there?
When the AV node either slows or blocks conduction of the atrial depolarisation into the ventricles
3 types- first degree, second degree, third degree
How is a first degree AV block presented on an ECG?
P:QRS ratio remains 1:1 but the P-R interval is longer than normal.
May be due to high vagal tone or effect of certain drugs/disease
How is a second degree AV shosn on an ECG?
Some P waves not followed by a QRS complexes
May be normal and physiological (horses) but may reflect disease of the AVN
QRS should look normal
What are the two types of second degree AV block and how are they different?
Wenckeback phenomenon- Mobitz type 1 AV block
Single non-conducted P wave- every now and then
Mobitz type 2 AV block
Every other P wave is non conducted or higher every 2/3
What is a 3rd degree AV block on an ECG?
P waves bear no relationship with the QRS complex
P waves occur at their own normal rate and QRS cmoplexes arise due to much slower automaticity of the purkinje system
What is atrial fibrillation?
When the atria are sufficiently large or stretched normal cell conduction representing P wave lost
Leads to many irregular depolarisations in the atria which randomly hit the AV node
QRS complexes and T waves look normal but rate is fast and the interval between them is highly variable- no P waves
What causes a supraventricular premature complex/supraventricular tachycardia?
If an ectopic focus in the atria or at the atrioventricular junction depolarises the atria prematurely a premature complex with the appearance of a normal QRS complex is produced
What is the name for a run of supraventricular premature complexes?
Paroxysmal supraventricular tachycardia
What causes a ventricular premature complex/ventricular tachycardia and how does this affect the complex?
An ectopic focus may also arise in the ventricular myocardium- it doesn’t follow the normal His-purkinje so is spread cell to cell- slow process so the complex is wide and bizarre
The T wave is in the opposite direction of the QRS complex
What causes paroxysmal ventricular tachycardia and sustained ventricular tachycardia?
A run or ventricular premautre complexes
If sustained it causes sustained ventricular tachycardia
What are the hallmarks of ventricular premature complexes?
Ventricular ectopic complexes- Wide and bizzare
And slur into oppositely directed T waves
How would you know a ventricular ectopic origniated in the right/left ventricle?
Ventricular ectopics which are positive in leads I and II with negative T waves are probably originating in the right ventricle
Negatvie leads in I and II with positive T waves probably originate in the left ventricle
Describe a ventricular fibrillation ECG
Complete loss of coordinates ventricular depolarisation/repolarisation- chaotic
What ‘other’ factors influence the ECG?
Autonomic nervous system- vagal tone, sympathetic drive
Electrolyte distrubances- electrical activity depends on conc of electrolyes
Cardiac disease- chamber enlargment
Other diseases- gastric stetch, spleen tumours
What may hyperkalaemia show on an ECG?
Sinoventricular rythm but no discernable P waves
Normal QRS- tall spikey T waves
What type of ultrasound transducers are required to get between ribs and lung lobes?
Sector transducers- inverted fan shaped image
What is the difference between long axis and short axis views in echocardiography?
Long axis- base to apex
Short axis- cross sectional views
What does the right pasternal long axis view show?
What is the right pasternal long axis view used for?
Shows all 4 chambers of the heart and thickness of the walls
Used for:
- Assess LV shape- normal, elliptical, rounded
- Subjectively assess contractility
- Right should be no more then one third of left heart dimensions
- LV walls should be one-quarter to one-thirds chamber diameter
- Mitral valve assessed- regurgitation?
- Can calculate EDV (start of QRS) and ESV (end of T wave/ smallest LV dimension)
- Atrial septum is assessed
What is seen with the RPS long axis 5 chamber view?
What can be assessed with this view?
All chambers and the aorta viewed
Used to assess abnormalities of the aortic valves
Colour flow can be used to look for turbulence in this region- stenosis
Colour flow can also be used to check septum for a ventricular septal defect
What is seen with the right parasternal short axis view- papillary muscle level?
What is this view used for?
The RV and LV
Used to position the M-mode cursor- at chordae tendinae
What is the M-mode cursor?
The M-mode cursor plots one dimension and is therefore a motion-time graph
Movement of the structures is displayed relative to the ECG
That wavy shit
Name each of the views A-E
A- RPS short axis below papillary muscle
B- Between pappillary muscle level- mushroom view
C- Left ventricular M-mode- chordae tendinae level
D- RPS short axis- mitral valve level (fishmouth view of mitral valve)
E- RPS short axis view at level of aortic valves
What is seen with M-mode cardiography?
Body wall
Right ventricle- only a bit
Intraventricular septum- IVS
Left ventricular lumen- LV
Left ventricular wall- LVpw
What is measured with M-mode echocardiography?
End diastolic measurements- start of QRS- broadest levt ventricular lumen
Systolic measurments- smallest left ventricle lumen
Can also measure:
Intraventricular septum diastole/systole
LV posterior wall diastole/systole
Measurements compared to breed specific reference values
How is fractional shortening calculated and what is normal?
When is fractional shortening not reliable?
LV internal diameter diastole - systole / diastole x100%
Normal is above 25%
Not reliable if- significanct mitral regurgitation, wall motion abnormalities, right sided heart disease with pressure overload
What is fishmouth view/mitral valve used to measure?
AMV- anterior mitral valve leaflet and PMV- posterior mitral valve leaflet
Irregular thickening of leaflets with DVD
Can occasionally see mitral stenosis
Mitral E point to septal seperation (top of E to septum distance)- increases with LV dilations, rounding of LV or poor stoke volume
What is the M-shape created from fishmouth M-mode?
The AMV inscribes the M-shape with two peaks
The E peak- Early passive diastolic filling- after T wave
The A Peak- Atrial contraction- after P wave
Posterior leaflet should do opposite- W shape
How is the LV volumes and ejection fractions calculated?
In RPS long axis view
Work out EDV and ESV and %
Use simpsons method of discs
Normal is >50%
What is the index of sphericity of the LV?
Attempting to quantify subjective assessment of rounding of LV
LV length- diastole / LV ‘width’ (M-mode)
anything above 1:7 normal
What is the difference between concentric and eccentric hypertyrophy?
Concentric- thickening and reduced lumen
Eccentric- over all enlargment
Eccentric- big ego
What disease is seen in cats and causes them to have thickened walls of the heart?
What needs to be ruled out?
Hypertrophic cardiomyopathy in cats
Things that cause pressure overload- Aortic stenosis and systemic hypertension
What does the short axis view at the level of aortic valves show?
What can be measures and compared at this view?
Short axis of the left atrium and aortic leaflets seen (mercedes)
Measure aortic root and LA in diastole for 2D measurment
Normal LA:Ao is <1.5
What is doppler echocardiography?
What are the three different types?
Doppler effect is noted when sound waves are transmitted and reflected off a moving target- RBCs
The difference between ultrasound frequencies transmitted and received is related to the velocity of the moving RBCs
Spectral
Colour flow
Tissue- myocardial motion
What is required to make spectral doppler echocardiography accurate?
Must be parrallel to flow of blood
Otherwise velocities significantly underestimated
How does blood moving towards the transducer and away show differently?
Blood moving towards the transducer is displayed above the baseline
Blood moving away from the transducer is displayed below the baseline
How is laminar/turbulent flow indicated on pulsed wave doppler?
A clean envelope as blood accelerates and decellerates
Turbulent flow is indicated by spectral dispersion and loss of clean envelopes
What is the difference between Continuous wave doppler and Pulse wave doppler?
PW- spatially specific, just sample RBC velocity within the sample volume.
But limit to depth you can sample and peak velocity you can record
CW- samples all along the cursor line- peak velocities displayed but not spatially specific
Can record depth and high peak velocities
What is colour flow doppler?
Colour applied to how above or below baseline the velocity is
BART map- blue away, red towards transducer
What is the Nyquist limit?
There is only a certain red level and velocity than can be reached which is the nyquist limit
It is a circle so becomes blue again and shows aliasing
How does turbulence show in colour flow doppler?
Colour variance- green/yellow
What view is used for aortic stenosis?
Sub-costal view
Optimal alignment with aortic outflow
What is the modified bernouilli equation used for?
Calculates the pressure gradient difference- beterrn LV and Aorta
PG = 4V^2
0-40 mmHg- mild
40-80 mmHg- moderate
>80mmHg- severe
Normal aortic velocity -1.7m/s
What are the normal cardiac pressures in aorta, LA, pulmonary artery, LV, RV, RA?
Aorta- 120/80 normal sytemic pressure
Left atrium- 6mmHg
LV- 120/0 mmHg
RV- 25/0 mmHg
RA- 4 mmHg
What causes caval syndrome and does it cause and how is it treated?
Dirofilariasis worms in the RA
Causes pulmonary hypotension and thromboembolism and pressure overload on RV- right sided CHF
Need to extract worms via jugular vein
