46: Bradyarrhythmias and Conduction Disturbances Flashcards
What is the definition of Bradyarrhythmias?
bradycardia (dog <60, cat <100) and associated with CS
What are the 2 groups of bradyarrhythmias (name 2 examples for each)
Impulse formation disturbances
* sinus arrest (e.g., SSS)
* atrial standstill
* sinus bradycardia
* sinus block
Impulse conduction disturbances
* Bundle branch block
* AV block
List 7 etiologies for bradyarrhythmias
- alteration in autonomic tone
- drug exposure
- electrolyte abnormalities
- trauma
- hypoxia
- inflammation or infiltration of the myocardium (–> fibrosis)
- degenerative disease of the conduction system
List 4 conditions that may lead to an increased vagal tone
- gastrointestinal
- respiratory
- neurologic
- ocular disease
explain “wandering pacemaker”
- 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
How can you differentiate sinus block from sinsu arrest on an ECG?
cannot be differentiated on an ECG
What is override suppression?
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
Name 3 drugs known to delay AV node conduction
- digozin
- Ca channel blockers
- beta-blockers
Define first degree AV block
all P waves a followed by a QRS complex, but there is a prolonged PR interval (>130 msec in dogs, >90 msec in cats)
Name 3 differential for etiologies of AV blocks
- AV node or myocardial fibrosis
- increased vagal tone
- drugs (digoxin, Ca channel blockers, beta-blockers)
What defines a high grade second degree AV block?
more atrial impulses fail to be conducted to the ventricles than are conducted
What is the Wenckebach’s phenomenom?
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
What is mobitz type II second degree AV block?
unexpected blocked P waves, PR intervals before and after block are identical
What is the typical location of the second degree mobitz type II AV block?
below the his bundle –> will cause bundle branch blocks and intraventricular conduction delays –> wide QRS complexes
When giving 0.04 mg/kg of atropin to a dog with second degree AV block, which mobitz type will respond/improve to atropine?
mobitz type I improves
mobitz type II does not improve
What is the normal range for escape rhythm/beat in dogs?
20-60 bpm
What is the normal rate for escape rhythm/beat in cats?
60-120 bpm
What breed is predisposed to persistent atrial standstill?
English Springer Spaniels
What is the most common differential for temporary atrial standstill?
hyperkalemia
What is the dose for atropine?
0.04 mg/kg IV
What is the dose for glycopyrrolate?
0.01 mg/kg IV
What are the side effects of parasympatholytics?
*mydriasis
* dry mouth
* constipation
* urinary retention
* neurologic signs
What type of drug is isoproterenol?
pure beta-agonist
* improves AV node and HIS-purkinje system conduction
* can cause resolution of AV block
* may increase escape rhythm
what limits the use of isoproterenol?
beta-2 stimulation will cause decrease in blood pressure
explain how to apply transcutaneous pacing
- 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
for temporary transvenous pacing, where should the bipolar lead be located
should end in the right ventricle
what does the sensitivity of a pacemaker refer to?
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
What is an adequate sensitivity for a transvenous pacemaker?
1.5 mV
