Cardiology: Causes and Treatment of Cardiac Arrhythmias Flashcards
What can cause cardiac arrhythmias?
- Primary heart disease
- Changes in the autonomic nervous system
- Systemic conditions- electrolyte disturbances
What are the 2 types of arrhythmias?
How can one be further seperated
- Tachy- fast
(Supraventricular- AV and above), (ventricular- below AV) - Brady- slow
What does paroxysmal mean?
when an arrhythmia starts and stops abruptly
Why can SVT be paroxysmal or sustained?
Caused by either
An ectopic focus with in the atria- atria tachycardia
Or atrioventricular junction- junctional tachcardia
Or a re-entry circit
What is an accessory pathway?
A piece of myocardium that bypasses the AV node
How can a macro-re-entry circuit develop and what can it conduct?
Can develop using the AV node and accessory pathway
Can donduct either orthogradely (normal direction) or retrogradely (wrong way) through the AVN
How does a ECG appear if the conduction travels down the accessory pathway?
Short P-R interval
QRS may be slightly abnormal (slurred upstroke of the R wave)
What is an example of an SVT associated with accessory pathway?
What breeds are predisposed?
Wolff-Parkinson-White syndrome
Labroadors and Retrivers
What can be a problem with sustained SVT?
How is it treated in an emergency?
Can cause very fast HR (>300bpm) and patients become weak or collapsed
Vagal manoeveres or IV drugs to slow conduction throught the node
Either slow down or stop the SVT- Diltazem
What vagal manoeuvres can be done to help sustained SVT?
- Occular pressure
- Carotid sinus massage
Enhances vagal tone at the AV node - Pre-cordial thump over the apex beat with the dog in lat recum may also break the rhythm
What drugs can be used for emergency treatments of sustained SVT?
- IV esmolol- ultrashort acting beta blockers
- IV verapamil/diltazem
Vagal manoeuvres should be re-attempted after administering the drug
When can beta blockers or calcium channel blockers be given for emergency sustained SVT
May be used orally if successful control is achieved
Oral can be given before in event of no IV
What is radiofrequency ablation: mapping and zapping?
When an accessory pathway is suspected, this can be mapped with cardiac catheterization electrophysiological study; possible to ablate this
What is atrial fibrillation?
AF is a form of SVT which can only occur if there is a critical atrial mass (big hearts). However can occur if threre is marked atrial stretch (DCM)
What is the goal of treatment for atrial fibrillation?
- Control the ventricular response to AF by slowing conduction across the AV node
What are the 5 drugs that may be used to treat atrial fibrillation?
- Digoxin- vagomimetic
- Calcium channel antagonists
- Beta blockers- atenolol
- DC cardioversion
- Amidarone
How does digoxin treat AF?
- Vagomimetic effect
- Slows the number and speed of atrial fibrillation wavelets transmitted to ventricles
- Low, slow oral dosing
- Takes 5-7 days to get to steady-state- check serum
- Not negative inotrope- positive inotrope
What is an example of a calcium channel antagonist?
How does it work to treat AF?
Diltiazem
Slow the ventricular response to AF by its action on the AV node by blocking calcium channels in the nodal tissue
Negative inotrope- doesn’t appear to be problem
How is treatment for AF often started?
Digoxin and Diltiazem as there is better HR control
If there are any contraindications to starting digoxin (anorexia, azotaemia, hypokalaemia) then it will be delayed until the animal shows improvments
When should beta blockers never be used?
With uncontrolled congestive heart failure
How do beta blockers treated atrial fibrillation?
Why do they need to be up-titrated slowly?
Slow conduction across AV node
Negative inotropes and not well tolerated by animals with poor systolic function
What is DC cardioversion?
Electroshock treatment of atrial fibrillation with a defibulator in a patient with minimal structural heart disease and recent AF
What is the function of the drug amiodarone?
Can convert atrial fibrillation back to sinus rythm or make DC cardioversion successful
Significant side affects
What is seen as successful treatment of AF and why?
Aim for a mean HR/24hrs of <125bpm or 140 with poor systolic function
Otherwise myocardial failure can occur as a consequence
How can ventricular tachycardia present?
- Paroxysmal or sustained
- Slow rate or very fast
- If haemodynamically significant (collapsed, pale MMs, weak pulses) treat urgently
What can cause ventricular tachycardia?
Cardiac disease- DCM
Systemic conditions- GDV, splenic masses
When should ventricular tachycardia be treated?
- The arrhythmia is haemodynamically significant
- Very fast >200bpm
- Close coupling with preceding complex (R on T phenomenon
What is the system used for treatment of ventricular arrhythmias?
How does it work?
Vaughan Williams classification system
Class 1-4
Class 1: sodium channel blockers
Class 2: beta blockers
Class 3: block potassium channels
Class 4: calcium channel blockers
- What do K+ channel blockers do?
- Where are calcium channel blockers most important for treating ventricular tachycardia?
- Responsible for reploarisation- lengthen action potential
- Channels important for nodal tissue
What classes of drugs are the following examples?
Lidocaine and mexeletine
Sotalol and Amidarone
Diltazem and Verapamil
Lidocaine and Mexiletine- sodium channel blockers
Solatol and Amidodarone- K+ channel blockers
Diltazem and verapamil- calcium channel blockers
How are ventricular arrhythmias treated in an emergency?
- Usually lidocaine bolus
- If lidocaine not effective, check for hypokalaemia, other electrolyte/acid base disturbances
How are ventricular arrhythmias orally controlled?
- If lidocaine effective- use class 1B- mexiletine (spenny)
- Oral treatment usually continues as class three of SOTALOL
What can amidarone treat?
What needs to be monitored?
May be effective for almost any tachyarrhythmia
Main side effects are hepatotoxicity- liver enzymes and thyroid function
What can cause bradyarrhythmias?
High vagal tone secondary to disease anywhere in the body
- What commonly can cause atrial standstill?
- How is the common presentation treated?
- What else can cause atrial standstill?
- Most commonly associated with hyperkalaemia- addisons etc. SAN still drived rythm but atria does not depolairise
- Treatment is to correct electrolyte balances
- Atrial standstill may also result from atrial cardiomyopathy- replacement of cardiomyocytes with fibrous tissue
What is the most likely cause bradycardia secondary to an AV block?
What should a blood sample be taken for?
Disease of the AV node- fibrosis, myocarditis
Blood taken for troponin I- if high suggests myocarditis
What are the different classes of AV blocks and how do they appear on an ECG
- 1st degree- P-R interval prolonged abore normal P:QRS 1:1
- 2nd degree-
Mobitz type 1- gradual lengthening of PR until non conducted P (high vagal tone)
Mobits type 2- PR interval remains constant until failing to conduct a P, can be consistant (AV node disease) - 3rd degree- no relationship between P and QRS
What is sick sinus syndrome?
What breeds are predisposed?
How is it diagnosed?
Generalised conduction disease- SAN is affected and combinations of bradyarrhythmias are obeserved
Westies, cairns, minature schnauzes
Sometimes failure of any escape complex can lead to 8-10 seconds of sinus arrest or syncope
Atropine response test- exclude vagus and 24hr medical managment
How are bradyarrhythmias treated in an emergency?
- Atropine/glycopyrrolate IV or terbutaline (B2 agonist) IV
