Exam 4 - Cardiac Arrhythmias Flashcards
what does the p wave, pr interval, qrs complex, & t wave represent in an ecg?
p wave - atrial depolarization
pr interval - av nodal conduction
qrs complex - ventricular depolarization
t wave - atrial repolarization
what is the autonomic control over the SA node in regards to sympathetic & parasympathetic?
sympathetic - increases rate
parasympathetic - decreases rate
where is the location of the SA node?
located in the upper right atrium close to the cranial vena cava
what rate do the pacemakers set in the SA node?
70-160 bpm
what is the physiology of the SA node?
pacemaker cells spontaneously depolarize
where is the AV node located?
endocardial - interatrial septum near the junction of the atria and ventricles
what is the physiology the AV node is responsible for?
propagated depolarization from atrial myocardium with:
- pacemaker capability
- slows conduction: allows the atria to expel blood into the ventricles & protects ventricles from pathologic arrhythmias
- autonomic control: same as SA node
what on the ecg represents the av node?
pr segment
what is the action of the bundle of HIS & purkinje fibers?
bundle of HIS - conduct rapidly between the AV node & its branches
fascicular branches divide into left & right bundles
purkinje fibers - conduct rapidly through the ventricular endocardium
what on ecg represents the bundle of HIS/purkinje fibers?
QRS complex
what are the intrinsic pacing rates of the SA node, AV node, & bundle of HIS/purkinje fibers?
sa node: 70-160 bpm
av node: 40-60
bundle of HIS/purkinje fibers: 20-40
what pathologic conditions can affect conduction in the heart?
inflammation, infection/parasites, fibrosis, & infarction
what are the major differences between the effect of increased sympathetic & increased parasympathetic tone in regards to the cardiovascular system?
sympathetic:
- increases rate of SA node discharge
- increases speed of AV nodal conduction
- increased risk of ventricular arrhythmias
parasympathetic:
- decreases rate of SA node discharge
- decreased speed of AV nodal conduction
- ‘vagal maneuver’
why can a rapid heart rate result in a decreased cardiac output?
decreased diastolic filling will cause decreased stroke volume
why can a slow heart rate decrease cardiac output?
there is adequate but decreased overall output
what are some cardiac origins of arrhythmias?
structural - cardiomyopathy, valve disease, infectious (chagas, endocarditis), or inflammatory
what are the 3 big non-cardiac origins of arrhythmias?
hypoxia, pain, & electrolyte abnormalities (hyperthyroidism, hyperkalemia, medications, toxins)
why are cardiac arrhythmias of clinical importance?
can result in clinical decompensation through:
-decreased cardiac function, blood pressure, reduced tissue perfusion, limits exercise capacity, syncope, myocardial fibrillation, asystole, & sudden death
when would you treat cardiac arrhythmias?
clinical signs - weakness, collapse, cough, breathing difficulty
if the rhythm carries a risk of sudden death
what are the advantages & disadvantages of using an ecg for a patient with a cardiac arrhythmia?
advantages: immediate rate & rhythm diagnosis
disadvantages: short duration represents a fraction of the animal’s day & some arrhythmias are intermittent
when would you want to use a holter monitor for a patient with an arrhythmia?
ideal if you suspect an intermittent arrhythmia, screening for boxer ARVC & doberman DCM, & to assess the animal’s response to therapy
what are some indications for performing an ECG?
- suspect arrhythmia: abnormal auscultation or pulses, patient has a history of weakness/collapse
- screening: breed predisposition
- pre-anesthetic work up
- monitoring a sick patient with trauma or metabolic disease or one that is on anti-arrhythmic drug therapy
why would you run cardiac troponin I for a patient with an arrhythmia?
it is an indicator of myocardial damage
where can conduction go wrong?
-abnormal rate: too fast/slow
- abnormal conduction: SA node, AV node, bundles of HIS
- abnormal tissue generating beats: supraventricular or ventricular
what is the normal mechanism for initiating systole?
normal sinus rhythm - beats originate from the sinus node with a normal heart rate range
exercise may increase the rate & vagal stimulation may decrease the rate
what are some clinical signs of bradyarrhytmias?
weakness, collapse, signs of heart failure (ascites, pulmonary edema)
what are 3 common cardiac causes of bradyarrhythmias?
- sinus node dysfunction - sinus arrest, sick sinus syndrome
- av block
- atrial standstill - hyperkalemia
what are some non-cardiac causes of bradyarrhythmias?
hyperkalemia, excessive vagal tone (gi disease, pancreatitis, CNS), hypothermia, & medications such as opioids, beta/calcium blockers
what is the treatment for bradyarrhythmias?
atropine response test & treat the underlying cause
what breeds are predisposed to developing sick sinus syndrome?
mini schnauzer, cocker spaniel, & westies
what is sick sinus syndrome?
sinus node dysfunction +/- av nodal involvement with inappropriate bradycardia/tachycardia/sinus arrest
what is the treatment for sick sinus syndrome?
is tachycardia/bradycardia causing clinical signs - consider holter
pacemaker +/- anti-arrhythmics
what is sinus arrest?
no sinus node activity > 2 r-r intervals
what is seen on this ecg?
sinus arrest
what conditions can result in hyperkalemia causing atrial standstill?
urinary blockage/rupture, iatrogenic, addisonian crisis
what is the treatment for atrial standstill caused by hyperkalemia?
manage the hyperkalemia
what does this ecg show?
atrial standstill - no p wave & slow rate
what breed is associated with muscular dystrophy causing atrial standstill?
english springer spaniel
what is the treatment for muscular dystrophy causing atrial standstill?
pacemaker
what do av blocks affect on ecg?
the p-r interval
what are the 3 types of av block?
- 1st degree: slow av conduction
- 2nd degree: interrupted AV conduction
- 3rd degree: incomplete AV conduction
what is 1st degree av block caused by?
increased vagal tone, drugs, & av nodal disease
how is 1st degree av block diagnosed?
ecg
what is seen on this ecg?
1st degree av block - prolonged p-r interval characteristic of slow av conduction
what is the characteristic finding of type I 2nd degree av block?
prolongation of p-r interval until p wave isn’t conducted
what causes 2nd degree av block?
increased vagal tone, drugs, & av nodal disease
what is seen on this ecg?
type I 2nd degree av block
what is the characteristic finding of type II 2nd degree av block?
some p waves conduct & others don’t & sometimes there is a pattern
what causes type II 2nd degree av block?
increased vagal tone, drugs, & av nodal disease
what is seen on this ecg?
type II 2nd degree av block
what is seen on this ecg?
3rd degree av block
what characteristics are seen on ecg of 3rd degree av block?
complete failure of av node to conduct, some portion of the conduction system must take over & you see escape complexes with a slow heart rate, & no associated between p waves & qrs complex
what are the clinical signs associated with av block?
collapse or fainting, heart failure, forward failure: weakness/lethargy
what diagnostics are run for av block?
atropine response test
what is the treatment for av block?
address the underlying cause & pacemaker if clinical signs & there isn’t a response to atropine
how is the atropine response test performed?
give 0.04 mg/kg atropine IV & wait for the anticipated response in 5-10 minutes
- heart rate increases to > 160 bpm without further block = secondary to high vagal tone
- heart rate doesn’t increase or only slightly does & block persists = av nodal disease
what is supraventricular tachycardia?
intermittent or continuous impulses originating from the atrial myocardium or av node
what are some examples of supraventricular tachycardias?
atrial fibrillation, atrial flutter, atrial tachycardia, & av nodal reentrant
what are the ecg characteristics of atrial fibrillation?
no p waves & irregular rhythm
what are the causes of atrial fibrillation?
primary, lone atrial fibrillation in giant breeds
secondary to significant structural heart disease
what is ventricular tachycardia?
intermittent or continuous impulses originating from the ventricular myocardium
what is seen on this ecg?
ventricular tachycardia - PVC, wide & bizarre qrs
when do you treat ventricular tachycardia?
heart rate is > 180, can lead to decompensation
hemodynamically unstable
complex: multiform, sustained, r on t
