Small animal cardiology arrhythmias Flashcards
How does the cardiac conduction system work
SAN is primary pacemaker, get impulse spreading via atrial myocardial cells to the AV node
AV slows down conduction, allowing atria time to contract fully, then get conduction down bundle of His to purkinje fibres
Purkinje fibres send impulses to large areas of ventircular myocardium at same time to get coordinated ventricular contraction
What do the parts of the ECG trace represent
P wave = atrial depolarisation
P-R interval = delay as impulse is at AV node
QRS complex = depolarisation of ventricles
T wave = ventricular repolarisation
What can T wave look like
positive, negative or biphasic
Which lead gives the biggest complexes and best mimics electrical activity
Lead 2 since most parallel to heart
What does it mean if there is no QRS for a P
Conduction pathway is being blocked
What does it mean if there is no P for a QRS
Either the P wave is hidden within the QRS
Or the stimulation for the ventricular activation is coming from below the atrium
What does a tall and narrow vs wide and bizzare QRS complex mean
Tall and narrow = normal as has used his-purkinje system to get rapid ventricular depolarisation; supraventricular rhythm
If it is wide and bizarre means didn’t use his-purkinje i.e impulse being generated from ventricle
What is sinus arrhythmia
Related to vagal tone
Cyclic variation in heart rate associated with respiration; so increased HR on inspiration
Rhythmic irregularity
Is sinus arrhythmia more common in dogs or cats and why
Dogs because it is due to vagal tone and cats are usually more stressed
What does wandering pacemaker mean
Where P wave morphology varies
Related to which part of the SAN the impulse came from
Also related to vagal tone and is normal in dogs
What are supraventricular premature complexes
P waves come in early i.e somewhere within atria is generating an impulse where it shouldn;t be i.e NOT SAN
What are supraventricular tachycardia and what is the main question to ask
Narrow QRS complex tachycardia
Ask whether irregular or not
If supraventricular tachycardia is irregular what is it
Atrial fbrillation
If supraventricular tachycardia is regular what is it most likely to be
Most likely focal atrial tachycardia
(but there are some other options)
What is focal atrial tachycardia
A fast regular rhythm with narrow QRS complexes but P wave morphology is different from normal sinus P wave due to ectopic focus in atria generating it
P wave may be before, within or after QRS
What is the main differential for focal atrial tachycardia and how can we tell them apart
Sinus tachycardia
If very fast i.e >300 must be FAT since SAN cannot go that fast
Ocular pressure or gag reflex to stimulate vagus will slow rate which can allow you to see P waves and work out whether sinus tachycardia or FAT
What is atrial fibrillation
Fast irregular rhythm where there is no organised activity in the atria just some small circuits
Some of these reach the AVN and cause depolrasiation
Associated with severe structural heart disease where atrial size reaches a large enough size to develop these wavelets of activity
What does a atrial fibrillation ECG look like
No P waves
Narrow QRS (since coming down his-purkinje)
Which breeds can get lone AF i.e atrial fibrillation without structural heart disease and what is it a risk for
Giant breeds
= risk for DCM
What are the 4 types of ventricular tachycardias
ventricular premature complexes
Ventricular tachycardia
Ventricular fibrillation
Accelerated idioventricular rhythm (slow vtac)
What are ventricular premature complexes assocaited with and what does the ECG look like
Associated with structural heart disease or systemic disease
See wide and bizarre QRS
T wave amplitude large and opposite direction to QRS
May or may not see P waves; but won’t be associated with the ectopic QRS beats
What is bigemini VPC
Alternating pattern of sinus and ventricular beats
What is trigemini VPC pattern
Sinus beat, sinus beat, venitrcular beat
Pattern
What is monomorphic vs polymorphic VPCs
Monomorphic = ventricular beats always look similar i.e in same direction
Polymorphic = ventricular beats look different i.e some +ve some -ve
What do polymorphic ventricular beats mean
There is more than one area of damaged ventricle generating a beat; this is dangerous
What is ventricular tachycardia associated with and what does it look like
Wide QRS complexes, fast regular rhythm
Associated with structural heart disease or systemic disease
- dangerous
What is ventricular fibrillation and what does it look like
Terminal irregular rhythm with undulations of different shapes and sizes and no discernable P / QRS / T
Needs CPR and defibrillatino
What are the criteria of malignancy with ventricular arrhythmias
Complexity: bigemini > couplets> triplets> vtac
Burden i.e no. abnormal beats
R on T phenomenon
Rate (R-R interval)
What criteria of malignancy are associated with risk of sudden cardiac death
Frequent couplets/triplets
Coupling interval >260 beats/min
What is R on T phenomenon and what is it a risk for
Where there are two ventricular beats so close together that it is hard to tell where one ends and other starts
= dangerous due to risk of entering ventricular fibrillation
What is accelerated idioventricular rhythm and what is it associated with
= ventricular rhythm at a slower rate than vtac ~150-180bpm
Nor haemodynamically significant and often benign and self limiting
= Assocaited with extra-cardiac disease; treat THIS not the rhythm
Some key differences between pacemaker action potential and ventricular myocyte action potential
Ventricular myocte; depolarised by Na+ entry; then has plateau phase where calcium comes in and K+ leaves; then repolarisation down to rest by K+ exit
In pacemaker: there is spontaneous depolarisation to threshold, then depolarisation by calcium entry, repolarisation by K+ exit with NO plateau phase; hyperpolarisation which is corrected by sodium and calcium entry
What can we do to treat focal atrial tachycardia and what route can we give drugs
Can give drugs oral since they are stable
Acute management:
- Calcium channel blockers: diltiazem
- K+ channel blockers: sotalol, amiodarone
Vagal maneouvres
- Beta blockers; esmolol
Chronic = similar, can do radiofreq ablation of accessory pathway?
What are the two broad ways to treat atrial fibrillation and which is more usually done
Rate control or rhythm control
- Generally no point doing rhythm control because where there is severe structural heart disease, would just go striaght back
How to do rate control for atrial fibrillation
Calcium channel blockers to slow conduction through AV node; diltiazem (+/- digoxin)
What is the only time we might use digoxin and why don’t we use it more often
Has a narrow therapeutic window so not commonly used
Can be used in atrial fibrillation to control the rate
What is the aim for atrial fibrillation control with medication
Bring heart rate down to <125bpm on home holter ECG
Or <160bpm in the clinic
Emergency mangement of sustained Vtac
IV lidocaine (sodium channel blocker to stop venitrcular arrhythmia)
Then if not responding add amiodarone
+ can add in sotalol (K+ blocker)
Chronic oral management of ventricular arrhtyhmias once converted to sinus rhythm
Sotalol; K+ channel blocker
Amiodarone;k+ blocker
Mexiletine (Na+ channel blocker)
What is AV block
Abnormal atrioventricular conduction with delay/failure of conduction of a sinus impulse through AV node
What are some possible causes of bradyarrhythmias
Increased vagal tone
Intrinsic AV node disease e.g degenerative fibrosis
Drugs e.g beta-blockers, digoxin, Ca2+ channel blocker
What is 1st degree AV block and what is it associated with
Delayed conduction through AV node assocaited with high vagal tone
So see prolonged PR interval with normal QRS
What is type 1 second degree AV block
Where there are intermittent single non-conducted P waves (PR interval lengthens prior to the block)
= assocaited with high vagal tone
What is type 2 second degree AV block
Where there are single or multiple non-conducted P waves but with constant PR itnerval
= assocaited with pathology
How can we subdivide two 2 second degree AV block
Into high or low grade depending on how many P waves in a row have not been conducted
higher grade means that ventricles have longer period without contracting so more likely to see syncope etc
What is third degree AV block
Persistent failure of AV conduction
There is no relationship between P waves and QRS complexes
What may ventricles be depolarised by in third degree AV block
BY junctional beats from the AV node/his bundle –> generates narrow QRS complex
Or ventricular escape rhythm from ventricle which generates wide and bizarre complex at slower rate than sinus rhythmW
What is the cause of third degree AV block
Myocardial damage/AV node degeneration
typically irreversible
What is the difference betwen premature and escape beats and how would we treat them differently
Premature means come early from ventricle so wide and bizarre
Escape beats = coming from ventricle but after long pause in ventricular rhtyhm; also wide and bizarre
Would treat premature beats with lidocaine but NOT escape beats because these are what is keeping the animal alive
What rate is ventricular escape rhythm in dogs/cats
Dogs <60bpm
Cats 80-140bpm
What is atrial standstill
Where impulses not conducted through the atrial myocardium so there are no P waves
INstead have a slow ventricular rhythm
QRS complexes may be normal or wide/bizarre
What are two possible causes of atrial standstill
Secondary to hyperkalaemia
Due to primary atrial myocardial disease = persistent i.e not reversible
What would we classify as sinus arrest and what are some possible causes
Pause of >3 times normal R-R interval
e.g as part of SSS, due to drugs like amiodarone/digoxin, electrolyte imbalances, myocarditis, idiopathic
What is sick sinus syndrome and what are the clincial signs and signalment
Abnormal sinus node function
Signs = weakness, lethargy, ataxia, collapse
Commonly seen in small breed dogs e.g terries, westies
ECG findings with sick sinus syndrome and treatment
Sinus bradycardia
Low mean HR
Intermittent sinus arrest
Intermitten 1st/2nd degree AV block
May see supraventricular tachycardia
Need a pacemaker to fix
What is the atropine response test for bradyarrhytmias
Used to assess the degree to which AV block or SSS is vagally mediated
Give IM or SC atropine and repeat ECG at 20, 30 and 40 mins
A positive response will be increase in HR >150bpm, abolition of sinus arrest, significant improvement in AV vlock
Treatment of bradyarrhythmias
Treat underlying disease e.g hyperkalaemia if present
Use pacemaker if indicated
Chronitropic drugs e.g terbutaline, theophylline
WHen is a pacemaker indicated
Unstable high grade 2nd/3rd grade AV block
Sick sinus syndrome
