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
