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SMALL ANIMAL > 4.3.2: Dysrhythmias > Flashcards

4.3.2: Dysrhythmias Flashcards

1
Q

What is happening in the heart to produce each of the following:
* P wave
* QRS complex
* T wave

A
  • P wave is produced by atrial depolarization.
  • QRS complex by ventricular depolarization.
  • T wave by ventricular repolarization.
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2
Q
A

Ventricular tachycardia

Important to recognise as it is an emergency - requires treatment!

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3
Q

Dysrhythmia? Does it require treatment?

A

Persistent atrial standstill
* There are no P waves
* QRS complexes are narrow and upright
* This is always significant!
* Look for primary cause e.g. metabolic disease

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4
Q

Dysrhythmia? Does it require treatment?

A

3rd degree AV block
* P waves are unrelated to QRS complexes
* This means there is a block at the level of the AV node
* This animal is likely to have clinical signs and therefore require treatment

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5
Q

Primary causes of rhythm disturbances e.g. tachydysrhythmias

A
  • Structural heart disease
  • Systemic disease
  • SNS activation (-> leads to ventricular dysrhythmia)
  • Drugs and toxins
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6
Q

What are the classes of anti-dysrhythmic agents?

A
  • Class 1 - sodium channel blockers
  • Class 2 - beta blockers
  • Class 3 - potassium channel blockers
  • Class 4 - calcium channel blockers

Modern drugs may act via multiple mechanisms. This classification does not account for digoxin.

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7
Q

Class 1 drugs - Examples

A

Lidocaine, mexiletine

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8
Q

Class 2 drugs - Examples

A

Propanolol, atenolol

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9
Q

Class 3 drugs - Examples

A

Sotalol, amiodarone

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10
Q

Class 4 drugs - Examples

A

Diltiazem, verapamil

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11
Q

Supraventricular tachydysrhythmias cause what kind of QRS complex?

A

Narrow complexes

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12
Q

Ventricular tachydysrhythmias causes what type of QRS complex?

A

Wide complex

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13
Q

Which tachydysrhythmias cause narrow complexes and which cause wide complexes?

A
  • Supraventricular - narrow complex
  • Ventricular - wide complex
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14
Q

Should you treat supraventricular tachycardias/dysrhythmias? If so, when?

A
  • Treat any underlying primary condition especially congestive heart failure
  • Treat if there are clinical signs of poor output
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15
Q

What might you use to treat supraventricular tachycardias?

A
  • If patient is in heart failure: digoxin ± diltiazem (Ca channel blocker)
  • Sotalol (beta blocker)
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16
Q

Dysrhythmia? Does it require treatment?

A

Supraventricular tachycardia
* This is a fast one
* Treat the heart failure! Hopefully the rate will drop.
* If the animal is out of failure, but the rate is still too fast -> use diltiazem and/or digoxin

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17
Q

Dysrhythmia? Does it require treatment?

A

Supraventricular tachycardia
* This happened to be a primary SVT for which no cause was found
* The animal showed clinical signs
* The rate is over 300bpm so the signs are associated with poor output
* Treatment: must bring the rate down, try diltiazem ± solatol
* Vagal manoeuvre has debated efficacy

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18
Q

Dysrhythmia? How fast will it kill the animal?

A

Supraventricular tachycardia
* The animal won’t die for another few hours so you have time to find some drugs, don’t have to jump straight to a highly debatable vagal manoeuvre

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19
Q

Dysrhythmia? Does it need treatment?

A

2nd degree AV block
* There are P waves sometimes getting through to the ventricles and forming QRS complexes
* May need treatment - depends on clinical signs

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20
Q

What bradydysrhythmias are there and of these, which are likely to be clinically significant?

A
  • Variations on sinus arrhythmia -> not usually clinically significant
  • Sinus arrest, 2nd/3rd degree AV block -> usually clinically significant
  • Clinically significant bradydysrhythmias are usually those where the heart rate is very low
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21
Q

Why do ventricular tachydysrhythmias produce wide and bizarre QRS compexes?

A

In ventricular tachydysrhythmias, the electrical activity is conducted passively from cell to cell in a weird direction, hence the “wide and bizarre” presentation on ECG.

22
Q

Differentiate between supraventricular and ventricular tachydysrhythmias

A

Supraventricular: arise in or above the AVN. Usually produced narrow and upright QRS in Lead II.
Ventricular: arise from the ventricles, usually wide and bizarre QRS complexes in lead II.

23
Q

What is a high grade 2nd degree AV block? What would it look like on ECG?

A
  • This means lots and lots of P waves aren’t being conducted.
  • On ECG, we would see multiple P waves, then the occasional QRS complex when one of these P waves makes it through.
24
Q

What type of AV block is often seen in cats with cardiomyopathy?

A

3rd degree AV block

25
Q

Metabolic derangements can be the cause of rhythm disturbances. Abnormal levels of which electrolyte may lead to atrial standstill?

A

Hyperkalaemia can lead to atrial standstill

26
Q

Clinical signs of bradydysrhythmias

A
  • Weakness
  • Lethargy
  • Syncope
  • Sudden death (rare)
27
Q

Sick sinus syndrome

A

The SAN periodically decides it won’t fire.

28
Q

What are some possible primary causes of bradydysrhythmias?

A
  • Cardiomyopathy
  • Drug toxicity/effect e.g. digitalis/digoxin
  • AV node fibrosis
  • Endocarditis
  • Electrolyte imbalance
29
Q

Sinus arrhythmia is a function of ______ ______. This means that it can be abolished with…

A

Sinus arrhythmia is a function of PSNS tone. This means that it can be abolished by atropine (blocks the PSNS via muscarinic receptors) or exercise.

PSNS: parasympathetic nervous system

30
Q

When might a supraventricular tachydysrhythmia not have a characteristic narrow upright QRS complex?

A

If there is a conduction abnormality/damage to the conducting system which means the impulses have to travel every which way.

31
Q

Describe the dysrhythmia shown here and suggest appropriate treatment (if needed)

A

3rd degree AV block
* P waves are unrelated to QRS complexes.
* Possible treatment: treat the primary causes e.g. electrolyte disorders, implant a pacemaker, use of parasympatholytic drugs (e.g. atropine) to rule out sinus rhythms

32
Q

Describe the dysrhythmia shown here and suggest appropriate treatment.

A

Supraventricular tachycardia
* Treat any underlying primary condition especially CHF
* Treat if there are clinical signs of poor output
* Anti-dysrhythmic drugs you could use: diltiazem (first line) ± solalol
* Beta blockers are not likely to be useful as dogs and cats don’t tolerate these very well and can worsen the heart failure by interfering with their compensatory mechanisms

33
Q

A patient presents with heart failure and a supraventricular tachycardia. Why is the heart rate important in this case and what are you going to treat this with?

A
  • Supraventricular tachycadia - patient’s heart rate is likely to exceed 200bpm
  • This very high HR will contribute to poor cardiac output so it is very important to slow this down
  • Treat the heart failure and hope the rhythm disturbance resolves (better oxygenation -> reduced SNS -> reduced rate and rhythm abnormality)
  • Try to get the HR less than 140bpm
  • If after treating the HR the rhythm is still fast -> First line treatment: diltiazem ± sotalol (some sources say digoxin)
34
Q

What is a primary supraventricular tachycardia? What will you treat it with?

A

Primary supraventricular tachycardia: rhythm disturbance for which we can find no primary cause (i.e. this isn’t occurring secondary to something else).
Treat with diltiazem (± sotalol if no response to diltiazem alone)

35
Q

What is the vagal manoeuvre? What is it used to treat and how effective is it?

A

Vagal manoeuvre: push the animals eyeballs in, massage the carotid sinus in the neck -> this is the equivalent of a precordial thump.
* Used to treat a fast supraventricular tachycardia.
* It may make the animal worse and there is very limited evidence for its success in the UK.

36
Q

When might we see ventricular premature complexes? What associated conditions may lead to them?

A
  • Often seen when inducing GA
  • May happen without associated disease in some individuals
  • May occur with structural cardiac disease, both congenital and acquired
  • May occur with drugs: anaesthetics, digitalis glycosides
  • May occur with hypoxia
  • May occur with high autonomic tone
  • May occur with systemic disease e.g. pyometra, sepsis -> there are so many cytokines that they disrupt cardiac function
37
Q

How do we treat ventricular dysrhythmias?

A
  • Treat the underlying primary condition
  • Indicaions for specific anti-dysrhythmic therapy: short coupling interval (R on T phenomen), clinical signs associated with the dysrhythmia
38
Q

An animal presents with a ventricular dysrhythmia. You treat the primary cause. When should you administer specific anti-dysrhythmic therapy?

A
  • If there is a short coupling interval (R on T phenomenon) as this will kill the animal
  • If there are clinical signs associated with the dysrhythmia
39
Q

Describe the dysrhythmia shown here and whether it should be treated with specific anti-dysrhythmic therapy.

A
  • We have sinus rhythm and ventricular rhythm (both are similar in this case)
  • If the animal is healthy and pink, without showing clinical signs due to this, we do not need to administer specific anti-dysrhythmic therapy
40
Q

Describe the dysrhythmia shown here and whether it requires treatment.

A

Very unstable ventricular rhythm
The complexes are almost on top of each other.
This requires treatment!

41
Q

Describe medical treatment of ventricular dysrhythmias

A
  • If critical -> IV lignocaine
  • If stable/episodic signs -> send home with sotalol
42
Q

When is specific anti-dysrhythmic therapy indicated?

A
  • When treatment of the dysrhythmia is likely to improve patient survival
  • When the patient is showing clinical signs related to the occurence of the dysrhythmia (often because heart rate is excessively fast/slow)
43
Q

1

A

Diltiazem/sotalol

44
Q

2

A

Verapamil

45
Q

3

A

Diltiazem ± digoxin

46
Q

4

A

Sotalol

47
Q

5

A

Lidocaine

48
Q

Timing of abnormal events is important. Which of the following is more dangerous and why?
a) Long pause, then ventricular escape complex
b) Early VPC lands on top of the preceding T wave

A

a) long pause, then ventricular escape complex -> this is good, because the ventricles are realising they received no stimulation and are depolarising
b) very early VPC lands on top of the preceding T wave -> this is dangerous because the ventricle is being asked to depolarise while it is repolarising. This make the ventricular very unstable and **likely to deteriorate. **

49
Q

What are other methods of controlling dysrhythmias, aside from medical therapy?

A
  • Pacing
  • Ablation with catheters
  • Implantable cardiovertors
50
Q

What do implantable cardiovertors do?

A

If patient enters ventricular tachycardia/fibrillation, they get shocked and rhythm returns to normal.

51
Q

Describe this arrhythmia and what we should do about this.

A

Sinus arrhythmia
* The dog was clinically normal.
* We could prove this was due to PSNS tone by exercising/giving atropine.
* But the animal is fine.

52
Q

Which abnormal finding is circled here? Does it need treatment?

A

Ventricular escape complex
May need treatment - this depends on clinical signs.
Treat any primary/associated disease. If still present/no primary disease but this still causes problems, consider pacemaker.

SMALL ANIMAL (90 decks)

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