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Bradyarrhythmias Flashcards

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1
Q

What is the definition of Bradyarrhythmias?

A
  1. Slow rhythms (HR < 60/min in dogs, 100/min in cats)
  2. Cannot be linked to a normal physiologic response (e.g. sleep)
  3. Usually associated with clinical signs (e.g. lethargy, exercise intolerance, decreased appetite, R-CHF, syncope)

Bradyarrhythmias are characterized by a heart rate that is slower than normal and is not a result of physiological factors.

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2
Q

What are the two possible classifications of bradyarrhythmias based on?

A
  1. electrical impulse formation
  2. electrical impulse propagation

Classifying bradyarrhythmias helps in diagnosing the underlying issues with heart rhythms.

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3
Q

What are the types of abnormalities of electrical impulse formation?

A

a. Sinus bradycardia: decrease in impulse discharge rate from nodal cells
b. Sinus block
c. Sinus arrest

These abnormalities indicate issues with how the heart generates electrical impulses.

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4
Q

What are the types of abnormalities of electrical impulse propagation?

A

a. Bundle branch block
b. 1st, 2nd and 3rd degree AV blocks

Impulse propagation issues can lead to varying degrees of heart block, affecting heart function.

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5
Q

List 7 causes of bradyarrhythmias

A
  1. Alterations in autonomic tone
  2. Drugs
  3. Electrolyte abnormalities
  4. Trauma
  5. Hypoxia
  6. Inflammation or infiltration of myocardium
  7. degenerative age-related process
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6
Q

What causes sinus bradycardia?

A

Systemic disease causing increased vagal tone

Includes gastrointestinal, respiratory, neurologic, and ocular causes.

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7
Q

Name 3 respiratory causes of SB

A
  • Chronic upper airway obstruction in brachys
  • Pulmonary hypertension
  • Lung worms (cats)

These conditions can lead to increased vagal tone affecting heart rate.

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8
Q

Name 4 causes of secondary SB

A
  1. gastrointestinal
  2. Respiratory
  3. Neurological (increased ICP?)
  4. Ocular

Associated with systemic hypertension and abnormal breathing patterns.

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9
Q

What medications may be used to treat sinus bradycardie?

A

Parasympatholytic medications:

  • Atropine
  • Glycopyrrolate

These are parasympatholytic medications used to counteract vagal tone.

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10
Q

What can be seen on ECG with SB?

A
  • P waves + QRS complexes are associated
  • P waves positive in leads I, II, III and aVF –> origin of the electrical impulse in the dorsal region of the RA (sinus node)
  • Narrow QRS complexes: dogs 60ms, cats 40ms (unless BBB)

P waves are typically positive in leads I, II, III, and aVF, indicating the origin of the electrical impulse.

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11
Q

What indicates high vagal tone on an ECG? Explain this finding.

A

Wandering pacemaker = variation in amplitude of P wave in relatino to respiratory cycle

inspiration: faster HR + higher P wave
Expiration: slower HR + smaller P wave

Variation in the amplitude of the P wave in relation to the respiratory cycle.

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12
Q

What are the two types of bundle branch block (BBB) and their causes?

A
  • Right BBB: right-sided heart diseases or no underlying disease
  • Left BBB: extensive disruption of left ventricular myocardium (e.g., DCM, infiltrative disease)

DCM refers to dilated cardiomyopathy, while infiltrative diseases may include myocarditis or neoplasia.

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13
Q

What triggers vasovagal syncope?

A

Sudden increase in vagal tone –> transient extreme bradycardia –> collaps

  • Intense activity/excitement
  • Cough
  • Vomiting

These activities can lead to sudden increased vagal tone resulting in syncope.

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14
Q

What reflex is attributed to vasovagal syncope? Explain this reflex.

A

Bezold–Jarish reflex:

stimulation of intraventricular receptors (type C vagal fibers) during tachycardia + hypercontractile ventricle –> bradycardia, vasodilation and hypotension

This reflex involves stimulation of intraventricular receptors during tachycardia leading to bradycardia, vasodilation, and hypotension.

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15
Q

What ECG change can sometimes be seen after a vasovagal syncope?

A

paroxysmal AFib (spontaneously terminates after a few minutes)

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16
Q

What is sinus arrest?

A

Failure of the nodal pacemaker cells to depolarize and generate an impulse

Sinus arrest leads to a sudden and prolonged pause with no atrial activation or P wave on ECG.

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17
Q

What is sinus block?

A

Failure of an electrical impulse to leave the sinus node and propagate to the atrial myocardium

Sinus block can also result in a pause in atrial activity.

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18
Q

What happens during a sinus arrest?

A

Drop in CO from 6-8s pause leading to syncope

The lack of atrial activation can result in decreased cardiac output.

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19
Q

What characterizes sick sinus syndrome (SSS)?

A
  • disease of conduction system
  • Periods of normal sinus rhythm or sinus block interspersed with long sinus arrest/block –> junctional and ventricular pacemakers fail to initiate escape beat

These arrests can last up to 10-12 seconds.

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20
Q

What does the absence of an escape beat after a 3-4s pause in the face of sick sinus syndrome suggest?

A

It suggests that the issue is not limited to the sinus node but affects the entire conduction system

This indicates a more widespread conduction problem.

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21
Q

Is sick sinus syndrome associated with a high risk of death?

A

No, it is not associated with a high risk of death

However, the frequency of syncope can increase as the disease progresses.

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22
Q

What drug class can result in a prolongation of periods of asystole?

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A

Opioids –> can become hemodynamically unstable after sedation/GA –> pacing required

Patients can become hemodynamically unstable after sedation or under anesthesia.

23
Q

What breeds are commonly affected by sick sinus syndrome?

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A
  • Older miniature Schnauzers
  • West Highland White Terriers

These breeds are predisposed to this condition.

24
Q

What medications may sick sinus syndrome respond to?

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A

Parasympatholytic medication (atropine, glycopyrrolate)

Atropine 0.04mg/kg IV and glycopyrrolate 0.01mg/kg IV may be effective.

25
What medications may be used to increase HR in sick sinus syndrome?
* Terbutaline * aminophylline ## Footnote These medications can help manage bradycardia.
26
What is bradycardia-tachycardia syndrome?
A variant of sick sinus syndrome characterized by paroxysmal atrial tachycardia followed by temporary failure of sinus rhythm ## Footnote This reflects an exaggerated normal physiological response of the sinus node.
27
What is "overdrive suppression" in relation to bradycardia-tachycardia syndrome in SSS?
An exaggerated response of the sinus node to the effect of a tachyarrhythmia ## Footnote This can lead to failure of the sinus rhythm to resume after tachycardia terminates.
28
Name 5 causes of AV blocks
1. Myocardial fibrosis 2. Inflammation 3. Infiltration 4. Drug toxicity 5. Age-related fibrodegenerative disease (most common)
29
Name 3 drugs that can cause AV blocks
1. Calcium channel blocker 2. B-blocker 3. Digoxin
30
What are the clinical signs of AV blocks?
Signs of Low CO: 1. syncope (most often in paroxysmal 2nd degree AV block due to abrupt drop in HR) 2. CHF 3. weakness
31
What is a 1st degree AV Block? Name possible 3 causes.
= Prolongation of PR invertal, but all atrial impulses are conducted dogs: > 130ms Cats: > 90ms 1. AV node fibrosis 2. increased vagal tone 3. Drugs that delay AV node conduction (Digoxin, b-blockers. calcium channel blockers)
32
What is a 2nd degree AV Block? What is considered a high grade 2nd degree AV Block?
= some P waves are not followed by QRS complex High grade = more atrial impulses fail to be conducted than are conducted
33
Can an increased vagal tone cause a 2nd degree AV block?
Yes
34
Describe the 2 different types of 2nd degree AV Block
1. Mobitz type I (Wenckebach) = Progressive increase in PR interval duration ending by a blocked P wave - usually benign, improves with atropin 2. Mobitz type II = unexpected occurence of blocked P waves, but otherwise identical PR intervals - no improvement with atropin, more likely to worsen + cause clinical signs
35
What is the meaning of a wide QRS complexes of conducted beats in a dog with 2nd degree AV block Mobitz type II?
area of block is below His bundle --> BBB + intraventricular conduction delays
36
Desceribe a 3rd degree AV block and its clinical consequence. What can we see on ECG?
- absence of conducted P waves to the ventricles - independent atrial and ventricular activities - Electrical activation of the ventricles is dependent on an escape rhythm beyond the site of block --> dramatic reduction in CO --> atrial rate increases in response (as under control of adrenergic tone) ECG: - wide and bizarre QRS - slow rates: dogs 20-60/min; cats: 60-140/min - Regular ventricular rate unless ventricular premature beats originating from ischemic myocardium - P-waves and QRS are not associated
37
Whar role does cTnI play in the face of a 3rd degree AV block?
Mild elevation is common marked increase --> myocarditis
38
What is atrial standstill?
= absence of atrial electrical activity on surface ECG --> abasence of P waves
39
What is often the underlying cause of atrial standstill in dogs?
- usually associated with an atrial myopathy - Rare (more prevalent in English springer spaniel) - Young dogs - Genetic or inflammatory process involved - Guarded long-term prognosis ECG: absence of P-waves = inability of sinus impulse to leave sinus node because of extensive replacement fibrosis and lack of functioning myocytes rate: 20-60/min
40
What electrolyte disturbance can mimic atrial standstill?
Hyperkalemia not a true standstill as electrical impulse still originates in sinus node and propagates to the AV node via preferential conduction pathways --> AV node and ventricule remain under control of sinus node --> HR can still be modulated by variations in autonomic tone on sinus node firing rate - Absence of P-waves resembles failure of the sinus impulses to propagate to the rest of the atrial myocardium because of alteration of myocyte membrane potential by elevated K+ concentration
41
What is the atropine response test used for?
Sick sinus syndrome and sinus bradycardia ## Footnote Atropine is administered at a dose of 0.04mg/kg.
42
What constitutes an appropriate response to atropine in the atropine response test?
50% to 100% increase in HR from baseline 15min after IV or 30min after SC administration ## Footnote ECG should be obtained 15 minutes after IV or 30 minutes after SC administration.
43
List 5 side effects of atropine.
* Mydriasis * Dry mouth * Constipation * Urinary retention * Neurologic signs
44
What is the role of sympathomimetic inotropes?
Increase HR by b-adrenergic stimulation
45
What are the effects of B2 and alpha adrenergic stimulation?
* B2: systemic vasodilation * Alpha: vasoconstriction
46
What is isoproterenol classified as and what is it used for?
Pure b agonist --> Improves conduction in AV node and His-Purkinje system --> partial or complete resolution of AV block May also increase rate of ventricular escape rhythm in complete AV block (limited success)
47
What happens to blood pressure with isoproterenol administration?
Causes significant decrease in BP via B2 stimulation
48
Name 4 drugs commonly used to treat bradyarrhythmias
1. Parasympatholytics (atropin) 2. Sympathomimetic inotropes - B2 agonist (dobutamine, dopamin, isoproterenol) 3. Terbutalin (Selective B2 agonist) 4. Aminophylline (Phosphodiesterase inhibitor)
49
What effect does aminophylline have besides being a bronchodilator?
Mild chronotropic effect
50
What are the indications for using a pacemaker?
Acute onset of AV block causing frequent syncope and severe bradyarrhythmia associated with hemodynamic instability (during GA)
51
What is transcutaneous pacing?
Via adhesive pads with pacing electrodes and use of external defibrillator
52
What are the pros and cons of transcutaneous pacing?
* Pros: quick + effective * Cons: discomfort from local skeletal muscle stimulation, requires deep sedation or GA
53
What are the two types

Cardiovascular (21 decks)

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