Chapter 46 - bradyarrhythmias & conduction disturbances

Question 1

Definition of bradyarrhythmia

Answer 1

bradycardia (<60 in dogs, <100 in cats) + clinical signs

Question 2

Clinical signs of bradyarrhythmias

Answer 2

lethargy
decreased appetite
exercise intolerance
CHF
syncope

Question 3

length of asystolic pause required for syncope

Answer 3

6-8s

Question 4

causes of bradyarrhythmias

Answer 4

alterations in autonomic tone
drug exposure
electrolyte abnormalities
trauma
hypoxia
inflammation
infiltration of the myocardium
degenerative disease of the conduction system

Question 5

list 4 body systems that cause increased vagal tone in disease

Answer 5

respiratory
gastrointestinal
neurological
ocular

Question 6

common breeds with SSS

Answer 6

miniature schnauzers

terriers

Question 7

drug class to avoid with SSS

Answer 7

opioids often prolong periods of asystole

Question 8

causes of 1st degree AV block

Answer 8

AV node fibrosis
increased vagal tone
drugs that delay AV node conduction (digoxin, calcium channel blockers, B-blockers)

Question 9

Describe Mobitz type I 2nd degree AV block, give alternate name, clinical significance

Answer 9

progressive lengthening of PR intervals before dropped beats w/ normal QRS complexes, Wenckeback’s phenomenon, combo of AV node fibrosis and progressive increase in vagal tone, usually benign

Question 10

Describe Mobitz type II 2nd degree AV block, clinical significance

Answer 10

unexpected occurrence of blocked P waves, normal PR intervals before and after, QRS complexes usually widened (block is below His bundle - bundle branch blocks, intraventricular conduction delays). more likely to worsen and become clinical

Question 11

What test can you use to differentiate between Mobitz type I & II?

Answer 11

atropine 0.04mg/kg IV - type I usually improves, type II is unchanged or worse

Question 12

define ‘high grade’ 2nd degree AV block

Answer 12

more atrial impulses fail to be conducted to the ventricles than are conducted

Question 13

ECG features of 3rd degree/complete AV block

Answer 13

RR and PP intervals are regular, no relationship between Ps & Rs, atrial rate usually elevated (in response to increased adrenergic tone from decreased CO), QRS complexes generally wide & bizarre, 20-60bpm in dogs, 60-120bpm in cats, ventricular rate regular except in presence of ischemic myocardium

Question 14

causes of 3rd deg AV block

Answer 14

myocardial fibrosis (most common cause in dogs)
inflammation/infiltration of the myocaidium
drug toxicity (digoxin, calcium channel blockers, B-blockers)
structural heart disease (most common cause in cats)

Question 15

two categories of atrial standstill?

Answer 15

temporary (more common), persistent (rare)

Question 16

what breed is predisposed to persistent atrial standstill? prognosis?

Answer 16

English Springer Spaniels (also predisposed to developing AV block), usually when young. generally a significant myocardial pathologic condition is present, long-term prognosis is guarded

Question 17

ECG characteristics of persistent atrial standstill?

Answer 17

lack of P waves, regular ventricular or AV nodal escape at 20-60bpm in dogs

Question 18

most common cause of temporary atrial standstill?

Answer 18

hyperkalemia (>5.5-6mmol/L) - can also see narrow & tall T waves (peaked), QRS complexes widen)

Question 19

Side effects of atropine/glycopyrrolate use

Answer 19

Opposite of SLUDS
dry mouth
dry eyes
urine retention
constipation

occasionally neurologic signs

Question 20

which syndrome matches which therapeutic drug? list MOA

1. vagally induced bradyarrhythmias
2. B-blocker overdose
3. AV block
4. SSS (besides atropine)

Answer 20

1. atropine = anticholinergic (muscarinic)
2. dop/dobut = catecholamines (also calcium, atropine, vasopressin, glucagon, insulin, IV lipids etc)
3. isoproterenol = pure beta agonist
4. terbutaline = selective B2 agonist or aminophylline = non-selective phosphodiesterase inhibitor & non-selective adenosine receptor antagonist

Question 21

What landmarks do you use to place transcutaneous pacing pads?

Answer 21

3rd-5th costochondral junction (or over palpable apex beat) bilaterally

Question 22

drawback of transcutaneous pacing?

Answer 22

painful skeletal muscle stimulation + movement = GA