PATHOLOGY - Small Animal ECGs and Dysrhythmias Flashcards
What is the standard patient positioning for an ECG?
Right lateral recumbency
Which colour of ECG electrode should be placed on the right forelimb?
Red electrode
Which colour of ECG electrode should be placed on the left forelimb?
Yellow electrode
Which colour of ECG electrode should be placed on the left hindlimb?
Green electrode
Which colour of ECG electrode should be placed on the right hindlimb?
Black electrode
What is Einthoven’s triangle?
Einthoven’s triange is a concept used in ECGs to describe the relationship between the three standard limb leads. It forms an equilateral triangle around the heart, with each vertex representing one of the leads
What are the five steps involved in interpreting an ECG?
- Determine the heart rate
- Determine if the rhythm is regular or irregular
- Determine if there are P waves visible, and if the P waves are always preceding a QRS complex, and the QRS complexes are always following a P wave
- Determine what the QRS complex looks like
- Is the P wave positive in lead II
What are the two most common paper speeds used for
ECG?
25 milimeters (mm)/second (s)
50 milimeters (mm)/second (s)
Which two methods can you use to determine the heart rate from an ECG?
Mean heart rate
Instantaneous heart rate
When is it beneficial to calculate the mean heart rate from an ECG?
It is often more useful to calculate the mean heart rate to account for variations in heart rate as the mean heart rate looks at the heart rate over several beats
How do you calculate the mean heart rate from an ECG?
To calculate the mean heart rate, you count the number of beats within 3 seconds and multiply this value by 20 to determine the mean 1 minute heart rate (3s x 20 = 60s). In 25mm/s paper traces, 3 seconds accounts for 75mm of the trace (25mm/s x 3 = 75mm), and for 50mm/a paper traces, 3 seconds accounts for 150mm of the trace (50mm/s x 3 = 150mm)
When is it beneficial to calculate the instantaneous heart rate from an ECG?
The instantaneous heart rate is the heart rate calculated from a single R-R interval, and thus is a good representation of the heart rate if the rhythm is relatively regular
How do you calculate the instantaneous heart rate from an ECG?
To calculate the instantaenous heart rate, count the squares between the R-R peaks. In a 25mm/s trace, each 1mm square will represent 0.04s (1mm ÷ 25mm/s = 0.04s) and for a 50mm/s trace, each 1mm square will represent 0.02s (1mm ÷ 50mm/s = 0.02s). Multiply the number of mm by the appropriate number of seconds and divide 60 (at there are 60 seconds in a minute) by that value
i.e. if there are 12mm between the R-R peaks on a 25mm/s trace:
12mm x 0.04s = 0.48s
60 ÷ 0.48s = 125 bpm
How do you determine if a rhythm is regular or irregular on an ECG?
To determine if a rhythm is regular or irregular, assess if the R-R interval is relatively consistent
What should you be aware of when determining the rhythm based off of an ECG?
In tachycardic patients, smaller changes in R-R interval will be more significant compared to bradycardic patients
Are there P waves visible in the ECG trace?
No, there are no P waves visible in this ECG trace
What is abnormal about this ECG trace?
There are P waves that are not being followed by a QRS complex
What is abnormal about this ECG trace?
There are QRS complexes not being preceded by P waves
What is the normal width of a QRS complex in dogs?
Less than 0.07 seconds (70 milliseconds)
What is the normal width of a QRS complex in cats?
Less than 0.04 seconds (40 milliseconds)
Why is it important to determine if the P wave is upwardly deflecting in lead II of an ECG?
You want to determine if the P wave is upwardly deflecting in lead II on an ECG because an upwardly deflecting P wave is a characteristic finding which suggests the electrical impulse is originating from the sinoatrial (SA) node, which is important to detemine the normal sinus rhythm of the heart
What are the four sinus rhythms?
Sinus rhythm
Sinus arrhythmia
Sinus bradycardia
Sinus tachycardia
What are the characteristic features of a sinus rhythm on ECG?
Regular rhythm
P waves preceding the QRS complexes
QRS complexes following the P waves
Narrow QRS complexes
P wave is positive on lead II
What are the characteristic features of a sinus arrhythmia on ECG?
The same features as a sinus rhythm but with a regulalrly irregular rhythm
What are the characteristic features of a sinus bradycardia on ECG?
The same features as a sinus rhythm but with a lower heart rate
What are the characteristic features of a sinus tachycardia on ECG?
The same features as a sinus rhythm but with a higher heart rate
What is a wandering pacemaker?
A wandering pacemaker is an atrial rhythm resulting in varying P wave morphologies on an ECG due to the pacemaking activity of the heart originating from different locations within the atria. This is different from sinus rhythm pacemaking activity, where the sinoatrial node is responsible for each heartbeat
(T/F) A wandering pacemaker is an abnormal finding in small animals
FALSE. A wandering pacemaker is a normal finding in small animals
What is the difference between supraventricular and ventricular premature contractions?
Premature contractions are characterised on the basis of where they originate. Supraventricular premature contractions originate from ectopic sites above the ventricles - i.e. the atrial myocardium, atrioventricular junction or atrioventricular node - whereas ventricular premature contractions originate in the ventricles
What are atrial premature contractions?
Atrial premature contractions are where the electrical impulse that triggers the atrial contraction originates in the atrial myocardium rather than the usual sinoatrial node
What are the characteristic features of an atrial premature contraction on an ECG trace?
- Normal QRS complex that occurs earlier than the next expected QRS complex
- Variable P wave morphologies may be noted before or after the premature complex or may be hidden in the preceding sinus complex or within the premature complex
List three examples of supraventricular tachyarrhythmias (SVT)
Sinus tachycardia
Atrial flutter
Atrial fibrillation
What is atrial flutter?
Atrial flutter is an arrhythmia where there is an electrical impuse from the sinoatrial (SA) node followed by a short circuit allowing this electrical impulse to quicky move around the right atrium causing rapid atrial contractions. These electrical impulses bombarde the atrioventricular (AV) node, and since the AV node acts as a filter, only intermittent atrial electrical impulses will be conducted through the atrioventricular (AV) node
What is the characteristic feature of atrial flutter on an ECG?
‘Saw tooth’ baseline
Narrow, normal QRS complexes that can have a regular or irregular rhythm
What does atrial flutter often progress to?
Atrial fibrillation
Which dog breed is prone to atrial fibrillation?
Bernese Mountain dogs
What is atrial fibrillation?
Atrial fibrillation is where there are uncoordinated supraventricular ectopic electrical impulses. These electrical impulses bombarde the atrioventricular (AV) node, and since the AV node acts as a filter, only intermittent atrial electrical impulses will be conducted through the atrioventricular (AV) node, causing an irregular rhythm
What are the characteristic features of atrial fibrillation on an ECG?
No P waves
Fibillatory (F) waves
Narrow, normal QRS complexes with an irregular rhythm
What are fibillatory (F) waves?
Fibillatory (F) waves is where there is an irregular baseline on an ECG
What are conduction abnormalities?
Conduction abnormalities are when there is an issue in generating an electrical impulse or an issue conducting an electrical impulse, resulting in bradycardia
List four examples of conduction abnormalities
Sinus pause
Sinus arrest
Sick sinus syndrome
Atrioventricular (AV) heart blocks
What is a sinus pause?
A sinus pause is a brief cessation of electrical impulse formation by the sinoatrial node
A sinus pause can be completely normal
What is a sinus arrest?
A sinus arrest is a prolonged cessation of electrical impulse formation by the sinoatrial node, often followed by a ventricular escape beat
What is a ventricular escape beat?
A ventricular escape beat is a self-generated electrical impulse intiated by and causing contraction of the ventricles which appears as a wide, abnormal QRS complex on an ECG
What is sick sinus syndrome?
Sick sinus syndrome is a general term for dysfunction of the sinoartial (SA) node and electrical impulse conduction
What are the characteristic features of sick sinus syndrome on an ECG?
Phases of sinus bradycardia, sinus arrest and sinus tachycardia
What is used to treat sick sinus syndrome?
Pacemaker implantation
Which dog breeds are predisposed to sick sinus syndrome?
West Highland Terriers
Minature Schnauzers
What can be used to treat bradyarrhythmias?
Pacemaker implantation
What are atrioventricular (AV) heart blocks?
Atrioventricular (AV) heart blocks is a term used to describe dysfunctional conduction of electrical impulses through the atrioventricular (AV) node
What is a first degree atrioventricular (AV) heart block?
A first degree heart block is a delay in the electrical impulse as it travels through the atrioventricular (AV) node
What is the characteristic feature of a first degree atrioventricular (AV) heart block on an ECG?
Consistent lengthening of the P-R intervals
Remember the P-R interval represents the time between the beginning of atrial depolarisation and ventricular depolarisation. If there is a delay in conduction through the atrioventricular (AV) node, this would prolong the time between these factors
What is a second degree atrioventricular (AV) heart block?
A second degree heart block is an intermittent blockage in the electrical impulse as it travels through the atrioventricular (AV) node
What is the characteristic feature of a second degree atrioventricular (AV) heart block on an ECG?
Intermittent P waves that are not followed by a QRS complex
What is the characteristic feature of a Mobitz type I second degree atrioventricular (AV) heart block?
There will be a progressive prelongation of the P-R interval prior to the atrioventricular (AV) block
What is the characteristic feature of a Mobitz type II second degree atrioventricular (AV) heart block?
There will be no prelongation of the P-R interval prior to the atrioventricular (AV) block
What is a third degree atrioventricular (AV) heart block?
A third degree heart block is a complete blockage of the electrical impulse as it travels through the atrioventricular (AV) node
What are the characteristic features of a third degree atrioventricular (AV) heart block on an ECG?
P waves that are unrelated to the junctional and ventricular escape beats
What is a junctional escape beat?
A junctional escape beat is a self-generated electrical impulse intiated by the atrioventricular junction, causing contraction of the ventricles which appears as a normal, narrow QRS complex on an ECG
What is a ventricular escape beat?
A ventricular escape beat is a self-generated electrical impulse intiated by and causing contraction of the ventricles which appears as a wide, abnormal QRS complex on an ECG
What is an atropine response test?
An atropine response test is the adminstration of atropine to determine if an atrioventricular (AV) heart block is caused by a cardiac aetiology or because of increased vagal tone. If the AV block improves during the atropine response test, this suggests the block was caused by increased vagal tone
What are intraventricular conduction disturbances?
Intraventricular conduction disorders are a group of conduction disturbances where there has been damage to the ventricular conduction system, and ventricular conduction of that area will require cell-to-cell conduction, rather than specialised fast conduction
What is the characteristic feature of a intraventricular conduction disturbance on an ECG?
Wide QRS complexes
List two examples of intraventricular conduction disturbances
Right bundle branch block (RBBB)
Left bundle branch block (LBBB)
What is a right bundle branch block (RBBB)?
A right bundle branch block (RBBB) is where there is damage to the right bundle branch and therefore the right ventricle will depolarise after the left ventricle
What are the characteristic signs of a right bundle branch block (RBBB) on an ECG?
Normal sinus rhythm
Wide QRS complexes
Deep S waves on lead II
What can cause a right bundle branch block (RBBB)?
Right ventricular enlargement
What is a left bundle branch block (LBBB)?
A left bundle branch block (LBBB) is where there is damage to the left bundle branch and therefore the right ventricle will depolarise before the left ventricle
What are the characteristic signs of a left bundle branch block (LBBB) on an ECG?
Normal sinus rhythm
Wide QRS complexes
Tall R waves on lead II
What can cause a left bundle branch block (LBBB)?
Left ventricular enlargment
List four examples of ventricular arrhythmias
Ventricular ectopic beats
Ventricular escape rhythm
Accelerated idioventricular rhythm
Ventricular tachycardia
What are ventricular arrhythmias?
Ventricular arrythmias are when the electrical impulses originate within the ventricle rather than the sinoatrial node resulting in an abnormal contraction
What are the characteristic features of ventricular arrythmias?
No P waves
Wide QRS complexes with abnormal morphology
What is another term used to describe ventricular ectopic beats originating from the left ventricle?
Right bundle branch block (RBBB) morphology
However remember that true RBBBs have abnormal QRS complexes preceded by P waves, however ventricular ectopic beats do not have a P wave
What is another term used to describe ventricular ectopic beats originating from the right ventricle?
Left bundle branch block (LBBB) morphology
However remember that true LBBBs have abnormal QRS complexes preceded by P waves, however ventricular ectopic beats do not have a P wave
How do you differentiate between premature ventricular ectopic beats and ventricular escape beats?
Premature ventricular ectopic beats occur early, i.e. will be seen straight after a normal QRS complex, however ventricular escape beats follow a sinus arrest rhythm
What is ventricular bigeminy?
Ventricular bigeminy is where there is arrhythmia in which there is a single irregular heartbeat, following each regular heartbeat
What is ventricular trigemini?
Ventricular trigeminy is where there is a single irregular heartbeat originating from the ventricle, following two regular heartbeats
What are ventricular couplets?
Ventricular triplets is where there are two consecutive irregular heartbeats originating from the ventricle
What are ventricular triplets?
Ventricular triplets is where there are three consecutive irregular heartbeats originating from the ventricle
What is a ventricular escape rhythm?
A ventricular escape rhythm is a self-generated electrical discharge initiated by, and causing contraction of the ventricles of the heart and tends to have a low heart rate
What is a accelerated idioventricular rhythm (AIVR)?
An accelerated idioventricular rhythm is a ventricular rhythm with a rate of between 40 and 120 beats per minute, approximately (i.e. it is more of a physiological rate)
What is ventricular tachycardia?
A ventricular tachycardia is a series of ventricular arrhythmias with a heart rate of over 180bpm
What can ventricular tachycardia progress to?
Ventricular tachycardia can progress to ventricular fibrillation which can be fatal
List four examples of indicators for pacemaker implantation
High-grade second degree atrioventicular (AV) block
Third degree atrioventricular (AV) block
Sick sinus syndrome
Atrial standstill
What are the two main components of a pacemaker?
Generator
Lead
What are the two main kinds of pacemaker?
Transvenous pacemaker
Epicardial pacemaker
What is the difference between a transvenous and epicardial pacemaker?
The lead of a transvenous pacemaker is inserted into the jugular vein and guided into the right ventricle, whereas the lead of the epicardial pacemaker is placed onto the epicardium itself and thus requires the thoracic cavity to be surgically opened
When is it appropriate to use epicardial pacemakers?
Epicardial pacemakers are used in cats and small animals
Why can pacemaker implantation be such a risky procedure?
Pacemaker implantation is done to treat bradyarrhythmias and this can be such a risky procedure as this needs to be done under general anaesthesia which causes bradycardia and thus will exacerbate the already low heart rate
What can be done to reduce the risk of pacemaker implantation?
An external pacer can be used which will deliver electrical impulses to the heart externally through electrodes placed on the patient’s chest to help to maintain to stable heart rate
Why is it crucial when inserting a pacemaker to make sure the pacemaker is adequately detecting cardiac electrical activity?
The lead delivers electrical impulses to the heart but also senses the heart’s electrical activity and relays this information back to the pulse generator to allow for the pacemaker to deliver appropriate electrical impulses. If the pacemaker is not adequately detecting cardiac electrical activity, this can lead to ventricular fibrillation which can progress to death
