46: Bradyarrhythmias and Conduction Disturbances

Question 1

What is the definition of Bradyarrhythmias?

Answer 1

bradycardia (dog <60, cat <100) and associated with CS

Question 2

What are the 2 groups of bradyarrhythmias (name 2 examples for each)

Answer 2

Impulse formation disturbances
* sinus arrest (e.g., SSS)
* atrial standstill
* sinus bradycardia
* sinus block
Impulse conduction disturbances
* Bundle branch block
* AV block

Question 3

List 7 etiologies for bradyarrhythmias

Answer 3

1. alteration in autonomic tone
2. drug exposure
3. electrolyte abnormalities
4. trauma
5. hypoxia
6. inflammation or infiltration of the myocardium (–> fibrosis)
7. degenerative disease of the conduction system

Question 4

List 4 conditions that may lead to an increased vagal tone

Answer 4

• gastrointestinal
• respiratory
• neurologic
• ocular disease

Question 5

explain “wandering pacemaker”

Answer 5

• usually from marked vagal tone
• alterations in P wave amplitude in relation to the respiratory cycle
• due to impulse originating from different locations within the atrium

Question 6

How can you differentiate sinus block from sinsu arrest on an ECG?

Answer 6

cannot be differentiated on an ECG

Question 7

What is override suppression?

Answer 7

when a pacemaker cell (e.g., SA node) suppresses other pacemakre sites
* this other pacemaker will be depolarized at a higher frequency than its intrinsic rate –> override

Question 8

Name 3 drugs known to delay AV node conduction

Answer 8

• digozin
• Ca channel blockers
• beta-blockers

Question 9

Define first degree AV block

Answer 9

all P waves a followed by a QRS complex, but there is a prolonged PR interval (>130 msec in dogs, >90 msec in cats)

Question 10

Name 3 differential for etiologies of AV blocks

Answer 10

• AV node or myocardial fibrosis
• increased vagal tone
• drugs (digoxin, Ca channel blockers, beta-blockers)

Question 11

What defines a high grade second degree AV block?

Answer 11

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

Question 12

What is the Wenckebach’s phenomenom?

Answer 12

Mobitz type 1 second degree AV block
progressive prolongation in the PR interval until finally P wave is blocked and not followed by QRS complex

Question 13

What is mobitz type II second degree AV block?

Answer 13

unexpected blocked P waves, PR intervals before and after block are identical

Question 14

What is the typical location of the second degree mobitz type II AV block?

Answer 14

below the his bundle –> will cause bundle branch blocks and intraventricular conduction delays –> wide QRS complexes

Question 15

When giving 0.04 mg/kg of atropin to a dog with second degree AV block, which mobitz type will respond/improve to atropine?

Answer 15

mobitz type I improves
mobitz type II does not improve

Question 16

What is the normal range for escape rhythm/beat in dogs?

Answer 16

20-60 bpm

Question 17

What is the normal rate for escape rhythm/beat in cats?

Answer 17

60-120 bpm

Question 18

What breed is predisposed to persistent atrial standstill?

Answer 18

English Springer Spaniels

Question 19

What is the most common differential for temporary atrial standstill?

Answer 19

hyperkalemia

Question 20

What is the dose for atropine?

Answer 20

0.04 mg/kg IV

Question 21

What is the dose for glycopyrrolate?

Answer 21

0.01 mg/kg IV

Question 22

What are the side effects of parasympatholytics?

Answer 22

*mydriasis
* dry mouth
* constipation
* urinary retention
* neurologic signs

Question 23

What type of drug is isoproterenol?

Answer 23

pure beta-agonist
* improves AV node and HIS-purkinje system conduction
* can cause resolution of AV block
* may increase escape rhythm

Question 24

what limits the use of isoproterenol?

Answer 24

beta-2 stimulation will cause decrease in blood pressure

Question 25

explain how to apply transcutaneous pacing

Answer 25

• external defibrillators often have this function
• apply patches to the skin on 3rd to 5th costocondral function or over palpable apex beat (on either side of the thorax) –> bandage around chest to hold in place
• set pacing rate and gradually increase current until ventricular cpature is achieved –> want to see QRS complexes and palpable femoral pulses
• painful –> skeletal muscles will be stimulated too –> need anesthesia

Question 26

for temporary transvenous pacing, where should the bipolar lead be located

Answer 26

should end in the right ventricle

Question 27

what does the sensitivity of a pacemaker refer to?

Answer 27

level of minimum voltage of electrical potential the pacemaker will detect and therefore not initiate beat
* don’t want to be not sensitive enough and won’t detect actual QRS complexes
* don’t want to be too sensitive –> will detect T waves as beat

Question 28

What is an adequate sensitivity for a transvenous pacemaker?

Answer 28

1.5 mV