Arrhythmias 1 Flashcards
What are the 2 main indications for doing an ECG?
- Arrhythmias, tachy or bradycardia i.e HB too fast, slow or eratic
- For monitoring anaesthesia
Other indications for ECG
Cardiac/ cardiotoxic drugs
Electolyte disturbances or after IV electrolytes
Reperfusion
Enlarged cardiac chambers
Pericardiocentesis
What is the physio rhythm?
Originates in SA node (nomotop)
Resp rhythm is physio in dogs because have higher vagal tone, sinus rhythm is physio in cats
Escape beats- from outside sinus, lower pacemakers at lower frequencies
Sometimes AV blocks can be physio in dogs
Normal sinus= sinus arrhythmia
Is this the normal PQRS complex?
P wave: atrial depol- followed by a small break of the AV node where NO wave form is visible
QRS complex- the impulse travelsv quiclkly to the ventric fibres
ALL depol is followed by repol (T-wave) but T-wave of atrial repol is. not seen on ecg
Physio sinus arr and wandering pacemaker
This is resp arr!! insp shorter distances that exp
Atria can be activated from different points hence the variation
heart beats are at the end and beginning of systole
Classification of arr
1.Impulse form:
- normal or incr HR
- abnormal automaticity
- Triggered activity
- Reentry or block
Conduction
- slow, block can be uni or bidirectional
- Normal or decr HR
Arr- dysrhythmias
- tachy, brady, arr
- Ectopic beats (except physio escape beats)
Impulse formative disorders, what are the 2 origins?
Nomtop- when from the sinus node
Heterotop/ectopic- from outsude the node!
Nomtop
Sinus tachycard
Sinus bradycard
Arrest
Hterotop/ectopic
Supra vetric:
- Atrial extrasystolde (outside atria)
- Foacal atrial tachycard
- Atrial fibrillation= disorganised
- atrial flutter= large reentry
- junctional tachycard
- junctional extrasystole
Ventricular:
- extrasystole
- Tachycard
- Fibrillation, flutter
When is both supraventric and ventric : uses bypass tracts or bypass tachycard: atrioventric reciprocating tachycard
Ectopic/ extrasystole/ premature contractions
From anywhere outside the primary!!
Cannot distinguish whether it is coming from atria or ventricles via ausc
Ectopic escape beats
From outside the sinus node
- big pause when there is no sinus node activity
- in one example- there are no P-waves just QRS complexes, the HR is slow
Premtaure supraventric extrasystole
The extra beat is very similar to the sinus beat. there appears to be a very small distance btw the QRS complexes
The QRS complex is NARROW!!
Premature ventric contraction, ventricular extrasystole
Early beat is visible
The QRS complex is WIDE!! (how to distinguish from supraventric extrasystole)
Supraventricular premature beat, Non-compensated pause, resetting
If supraventric comes too early- there may be a conduction block!
Measure the distances btw the abnormal beats
Supra (originates in sinus) also depolarizes the atria. Sinus beat will come normally
Ventricular premature contraction, fully compensated pause, no resetting
It is exactly 2 QRS complexes i.e 2 cardiac cycles
Does not depol the atria therefore the next sinus beat will be a bit abnormal
IImpulse formative disorders- how to distinguish btw supraventric and ventric tachycardia
Supraventric will have positive deflections
Ventric tachycard will have negative deflections
Points to look out for if diagnosing ventricular extrasystole (VPC)
- wide QRS
- No P-wave
- Abnormal T-wave
Diagnosing Supraventricular extrasystole?
Appearance of typical sinus beat
Supraventricular escape beat diagnosis
In this case it was originating from the AV node so there was no P-wave!
Diagnosing ventricular escape beats
V. slow rhythm
All beats are abnormal
If sinus in origin then no P-wave (can you conclude that if the origin is SA or AV node that there will be no P-wave?)
LArge, wide, negative QRS complexes
Impulse conductive disorders: SA blocks
1st degree: slow conduction
2nd degree: maybe conduction
3rd degree: no conduction
Bundle branch block (BBB) can be left or right
Intraventricular conduction blocks!
Blocks can be…
Functional: R bundle branch block is frequent! or when the beat comes too early, before the tissues have regained conductivity
Physio: premature ventric beat with aberrant conduction
Blocked premature supraventricular beat-completely blocked T-wave! In these cases the block is physio but the premature stimulus of the atria is patho!
3 main Causes of arr
- Structural HD/HF
- Systemic illness
- Primary: congenital or acquired
Structural HD/HF causing arr
Remodelling of heart
Neurohormonal: symp/parasymp, RAAS, Endothelin
Inflamm mediators and FR’s
Hypoxia: atrial fibrillation, in CHF ventric arr are seen
Systemic illnesses as cause of arr
Hypoxia, veg tone, temp, electrolytes (Na and K), drugs and toxins
- Kidney failure, obstruction of urethra (electrolyte disturbances?)
- Addisons
- Digoxin OD
- Anaesth!!!!
- Sepsis, trauma, hypovolaemic shock
- Splenic tumour/torsion
- Gastric torsion
- Brain/SC injury
- Pancreatitis
- Ileus
Congenital/ acquired i.e primary causes of arr
Channelopathies
Fibrosis, infarcts, amyloidosis
Boxer/bulldog/cat: arrhythmogenic cardiomyopathy- hyper or hypothyreoisis
Mini shnauzer and westie: SSS
Cocker spaniel: AV block
Lab, Boxer: Wolf Parkinson White syndrome- AV acc pathways
Consequences of arr
Mostly none!
Weakness and syncope if there is interference with the HR
Ventric or brady may result in sudden death
Worsening of already exisitng HF
Bradyarr can cause HF or tachiocariomyopathy (dont know how it would tho?)
May damage the myocard– dilated cardiomyopathy
Treatment of arr
first must DIAGNOSE!!! via eCG
Cardiac vs extracradiac
No treatment if no signs or haemodynamic changes
Remember that most antiarr are proarr
treatable vs non treatable
Treatable: tachy/brady, supraventric and ventric
Usually we don’t treat:
- atrial or ventric infrequent extrasystoles
- Slow idioventricular or junctionsl rhythms
- Lone atrial fibrillation
- 1st/2nd degree AV blocks
- BBB’s
- Intraventricular blocks
- Ventric arr caused by extracardiac cause
How to treat the arr
- Treat the cause! e.g if CHF give diuretics, O2, Pimobendan
- By Phys methods! Ocular pressire/vagal maneuver- to induce a high vagal tone to overcome the symp tone. Usually in combo with drugs
Carotis massage, chest thump
- Drugs
- Artificial pacemaker
- Electric cardioversion
- Radiofrequency catheter ablation
- External defibrillators
Using catheter mapping and ablation to treat atrial flutter
Occurs when there is re-entry into either the R or L atrium, the AV node tries to filter it out!!
Catheter places in the isthmus btw the tricuspid valve and the eustacian valve of the IVC
There are multiple pairs of electrodes on the catheter - can locate the circuit when the position correlates with conduction!
Heat and E is used to destroy the piece of muscle- no conducting ability anymore!
Classes of anti-arr drugs according to the Vaughan-Williams classification
- Na channel blockers (membrane stabilizers)
- Beta blockers
- K channels blockers- delay repol
- Ca channel blockers
- Digoxin
- Atropine
Na channel blockers
Reduce slope of phase O and reduce peak of AP
Works on cells that use Na for depol ie the atrial and ventric working and purkinje but not on SA or AV nodes
treat VENTRIC ARR!!
They delay depol and shorten repol
SE’s: hypoT, convulsions, decr liver metab
Will not work if there is hypokalaemia
Na channel blockers: 1a
Procainamide
- SVT (bypass tract)
- Ventric arr
Na channel blockers: 1b
Lidocaine and mexiletin
- Ventric arr
- (some SVT)
Rapid binding and dissociation
Refractory channels
Ischaemic areas
Usually dilate vessels therefore would decr BP
SE: convulsions
Na channel blockers
Flecainide and Propafenon
-SVT- bypass tract, atrial flutter!
Slow binding and dissociation
Beta blockers
Used to treat supraventric arr (they slow the HR0 and ventric arr (in combo)
Block the symp discharge to the heart and therefore slow impulse conduction in the AV node
(-) ino, chrono, bathmo, dromo
Beta blockers: 1st gen
Non-selective
Propranolol
Beta blockers: 2nd gen
Selective beta 1: Atenolol and Metoprolol
3rd gen beta blockers
Carvedilol and bucindolol
Non-selective
aplha blockade
Antiox
Repolarization delaying drugs- K channel blockers
Amiodarone and Sotalol
Have multiple class effect (I, II, III and IV for amiodarone)
Prolong AP and therefore refractory state (are good for reentry?)
Treat both atrial and ventric arr
Calcium channel blockers
Dihydropyrimidines: Amlopdipine
Used to treat hyperT as it dilates the vessles. Used at the end of HF
Non-dihydropyrimidines: Verapamil and Diltiazem
Slow AV conduction
Heart>vessels
Cardiac specific: verapamil>diltiazem>amlodipine
Treat: SVT arr! they decr the ventric rate in atrial fibrill
(-) ino: verapamil>diltiazem
If OD: give IV calcium
Digoxin
decr symp and incr parasymp tone
Restore baroreceptor function
(+) ino- mild
Not IV- sympathomimetic effect! maybe proarr
Treats: SVT by decr the speed of AV conduction
Atropine response test
Record baseline eCG
Admin 0.04mg/kgbw of atropine SC
Wait for 30 mins
Record eCG for min of 2 mins
Result: dogs with vagally mediated bradycard will have sinus tachycard>140 bpm (i.e parasymp induced brady)
Some dogs with sinus node disease or patho AV blocks will aslo respond to this test
Protocol for a new arr case
Diagnose with eCG
Exclude HD
Full work up- include electrolytes
Atropine responce test
- O2
- Sympto: fluids and diuretics
- treat the arr
- treat the cause if you know it??
- find out if its cardiac (phys, echo, BP) or extracardiac (general parameters, electrolytes, Lyme?)
- Imaging of abd and thorax
Case study of 10yr old male boxer
Syncope
Detected arr during phys
Echo was normal
Labs: LOW BG
Abd US: focal lesion in the pancreas
Diagnosis: INSULINOMA! i.e a severe systemic disease- mind immediately jumps to the fact that boxers are predisposed to R ventric exntrasystole
