Cardiovascular Module 2

Question 1

Explain what PQRST denotes

Answer 1

P: Atrial depolarisation
QRS: Ventricular depolarisation
T: Repolarisation

Question 2

What are the 4 mechanisms of arrhythmias?

Answer 2

1. Enhance normal Automacity
   - Normal pacemaker becomes more rapid and
   overtakes SA node
   - DDx: drugs, toxins, acquired heart disease
2. Abnormal Automacity
   - Normal pacemaker cell is suppressed (drugs,
   toxins, vagal tone) and non-pacemaker cells gains
   ability to depolarise (acquired heart disease)
3. Re-entrant Currents
   - Short circuit forms between atrial and ventricles -
   congenital arrhythmia
   - Short circuit forms between ischaemic or fibrous
   tissue (acquired heart disease)
4. Blocks
   - AV nodes or other sites - congenital, acquired,
   drugs, toxins

Question 3

What are the causes of arrhythmias?

Answer 3

1. Congenital
   - AV conduction pathways
   - GSD - congenital tachycardia (either die in their
   sleep of grow out of it)
   - Alternative pathways bypassing AV node:
   labradors (supreven. tachy)
2. Acquired Primary Cardiac Disease
   - Ischaemia, fibrosis and other damage from DCM,
   HCM, MVD
3. Secondary to Non-cardiac disease
   - Sepsis
   - T4
   - Splenic mass
   - Anaesthesia
   - Abnormal autonomic tone

Question 4

How to read an ECG?

Answer 4

1. What is the heart rate?
   - 50mm/s page speed
   
   • Number of complexes in 3 secs x20
   • 15cm = 3secs
     - 25mm/s page speed
   • number of complexes in 6secs x10
   • 15cm = 6 secs
2. Regular rhythm or irregular
3. P-QRS relationship
4. Rhythm diagnosis - does this need tx? clinical
   signs? If incidental is it primary heart? or
   secondary?

Question 5

What is a normal heart rate? Brady v. Tachy?

Answer 5

70-140BPM
<55 BPM - bradyarrhythmia
>180 - tachyarrhythmia

Question 6

Types of tachyarrhythmias?

Answer 6

1. Supraventricular origin
   A. regular v. irregular
   a. Regular - SVT atrial flutter
   b. Irregular - sinus + APCs - A-fib
2. Ventricular origin
   A. Regular v. Irregular
   a. Regular - VT
   b. Irregular - Sinus + VPCs

Question 7

What are VPCs?

Answer 7

Ventricular premature complexes
- May have pulse deficits
- Originates from ventricles

Question 8

What are APCs?

Answer 8

Atrial premature complexes
- Looks like a p-wave
- May be deficits but doesn’t always need tx

Question 9

What is caused by Atrial Fibrillation?

Answer 9

Most common tachyarrhythmia in dogs - structural and chemical remodelling of the atrium
- Loss of atrial kick leading to decrease of 20% output
- Loss of exercise capacity and dependance on HR increase to generate a cardiac rhythm
- Tachycardia lasting over 24 hours can result in heart remodelling, ischaemic changes and fibrosis - reversible if rhythm controlled

Caused by lots of random circuits bombarding the AV node and AV node trying to make sense of it

Question 10

What does A-fib look like on ECG?

Answer 10

• No discernable P-waves
• Irregular R-R intervals
• Supraventricular complexes
• Undulating baseline

Question 11

A-fib treatment options?

Answer 11

Digoxine +/- diltiazem
Amiodorone protocol
Sotalol
Cardioconversion - need to make sure patients are carefully selected

Question 12

What causes atrial flutter?

Answer 12

Area in the right atrium where re-entry circuits occur
- Big dogs
- Can burn the tissue in RA to stop in the circuit

Question 13

What does R on T phenomenon mean?

Answer 13

Very unstable rhythm
Means repolarisation and depolarisation are happening at the same time

Question 14

What are non-pharmocological treatment options for tachyarrhythmias?

Answer 14

• Vagal manoeuvre
• Shock - shock on the r-wave, needs to be
  anaesthetised to get at the right time
• Pre-cordial thump - cause a VPC to break rhythm

Question 15

What are the pharmacological treatments for tachyarrhythmias?

Answer 15

No Body Kills Cats

Class 1 = Na channel blockers (important for
depol/repol of ventricles)
- Lidocaine/quinodine

Class 2 = Beta-blockers (heart bathed in SNS with
beta receptors)
- Atenolol/Esmolol

Class 3 = Potassium channel blockers (important for
generating action potential within atria)
- Sotalol (class 2 as well)
- Amiodarone (1+2+3)

Class 4= Calcium channel blockers (important for
generating action potential within atria)
- Diltiazem

Digoxin: Cardiac glycoside
- Affected by hypo/hyperkalaemia
- Inhibits Na/K ATPase and competes with K+ at
binding sites
- Dirty drug

Question 16

When to treat tachyarrhythmias

Answer 16

HR >180bpm
R on T
Clinical signs
Hypotensive - systolic less than 100mmHg
Pulse deficits

Question 17

When to use what classes of drugs for tachyarrhythmias?

Answer 17

1&3 - ventricular arrhythmias

3&4 - atrial arrhythmias

Beta-blockers work everywhere

Question 18

How to treat V-tach

Answer 18

Lidocaine - 2mg/kg
- Repeat 3x
- Follow with CRI 50-100mcg/kg/min

Non-lidocaine option
- Amiodarone - takes time to be effective (2 days)
- Quinidine - lots of CS
- Mexiletine (CLASS1) - similar to lidocaine,
sourcing problem
- Flecainide - difficult to source
- Procainamide - IV expensive
- Sotalol

Non-pharmacological
- Pre-cordial thump
- Electrical cardioconversion

Question 19

What are vagal manoeuvre options?

Answer 19

1. Angle of jaw - push quite hard on carotid artery
   (thoracic inlet)
2. Push on eyes
3. Make gag
4. Cover nasal planum and breathe against it

Question 20

What is a bradyarrhythmia caused by?

Answer 20

A slow dominant pacemaker

Failure of the SA node - can be intermittent or permanent

80bpm and metronomic = pathoneumonic

Question 21

What is the atropine test used for?

Answer 21

Withdraws vagal tone and should increase heart rate
Give IM (otherwise IV could cause bradycardia initially - takes half an hour to work)

Question 22

When is surgical intervention necessary for bradyarrhythmias?

Answer 22

1. 3rd degree av block
2. Persistent atrial standstill
3. Intermittent sinus arrest
4. High grade 2 block with CS
5. SSS if causing CS

Question 23

What are causes of bradyarrhythmias?

Answer 23

1. Primary heart disease - AV node (pacemaker), neoplasia, cardiac remodelling
2. Endocrine Disease - Hypot4 (levo), addisons, urinary block
3. High vagal tone - masses, GI disease (vagolytic drugs:atropine/glycopyr)
4. Drug administration - opiates, alpha-2, anti-arrhythmias, atropine