ECG Part 3 - Common Cardiac Arrhythmias Flashcards
why do bradyarrhythmias often occur?
occur due to slow/absent sinoatrial node depolarization or atrioventricular node conduction
what is sinus bradycardia? what causes it? how is it treated?
depression of sinoatrial node depolarization
causes - high vagal tone, anesthetic/analgesic administration
treatment - treat underlying cause, give atropine if high vagal tone is suspected
what is a respiratory sinus arrhythmia?
arrhythmia normal to see in dogs & horses but rare in cats
sinoatrial node discharge varies based on the respiratory cycle, so increased heart rate on inspiration & decreased heart rate on expiration
what is the difference between intermittent & complete sinoatrial node block/arrest? what causes it?
intermittent = block
complete = arrest
cause - sinoatrial node fails to depolarize
what happens in sinus arrest caused by sick sinus syndrome?
with sinus arrest, the atrioventricular node takes over as the auxiliary/emergency pacemaker, so the heart rate is significantly slower than the normal sinus rhythm
no p waves are seen on ECG
in less severe cases - the sinoatrial node depolarization is slowed down & causes sinus bradycardia
how is sick sinus syndrome treated?
some cases will respond to treatment
parasympatholytic (atropine) or beta-adrenergic agonists (terbutaline or theophylline)
artificial pacemaker implantation needed for non-responsive clinical cases
what is atrioventricular block? what causes atrioventricular block?
atrial & ventricular contractions are not synchronized, on ecg the PP & PR intervals are regular but they are not the same & the PR interval varies due to 2 sites of impulse generation (SA node & AV node)
atrial action potential isn’t propagated to the ventricles, so the atria beat at a rate determined by the SA node while the ventricles beat at a rate of spontaneous atrioventricular node depolarization which is slower than the sinus rate
what is the mildest form of AV block?
1° AV block - SA node impulse is more slowly propagated by the AV node & the PR interval is prolonged
what type of av block is shown in the photo? how can you tell?
1° AV block -
what type of av block is shown in the photo? how can you tell?
2° AV block (mobitz I or wenckebach)
progressively prolonged PR interval before a blocked P wave
what type of av block is shown in the photo? how can you tell?
2° AV block (mobitz II) - ratio of P to QRS, look at the ratio (more commonly pathologic)
what type of av block is shown in the photo? how can you tell?
2° AV block (2:1 block) - compare P to QRS, this ratio is 2:1
what type of av block is shown in the photo? how can you tell?
3° AV block with junctional escape beats
ventricles beat at an escape rate, p waves/min are faster & QRS/min are slower & both are independent of each other
what is mobitz type I 2° AV block? what causes it? how is it treated?
progressively prolonged PR interval before a blocked P wave typically
causes - usually high vagal tone
treatment - usually none, common in fit horses (40%) that will go away with exercise
what is mobitz type II 2° AV block? what causes it?
progressively prolonged PR interval before the blocked P wave, describe it by a ratio of P to QRS, if > 3:1, considered to be high grade/advanced
causes - pathologic, not related to vagal tone
what is 3° AV block?
aka complete heart block
no impulses from the SA node are conducted through the AV node
ventricles beat at an escape rate of spontaneous AV depolarization
P waves/min are faster while QRS/min are slower & both are independent of each other
what are the 2 main reasons why we see tachyarrhythmias?
- more rapid SA node depolarization - increased sympathetic tone
- ectopic pacemaker - region of abnormal cardiac muscle that depolarizes spontaneously independent of the SA node in the atria/ventricles/SA node/AV node, or conduction pathway
what is supraventricular tachycardia a generalized term for?
sinus, atrial, & junctional tachycardia
what is sinus tachycardia? how does it look on ecg?
SA node depolarizes at an elevated rate often due to increased sympathetic tone such as excitement, exercise, & physiologic stress
normal ECG with a fast heart rate
what defines atrial tachycardia?
multiple atrial premature contractiosn
what is atrial tachycardia?
progression of atrial premature complexes
ectopic pacemaker in the atrium depolarizes independent of the SA node to produce the APC
singular APCs are random only conducted through the AV node if the node & ventricular myocardial cells are out of the refractory period
what is atrial flutter?
very rapid atrial tachycardia where the AV node conducts some but not all impulses & the ventricular rate is protected by the slowed transmission of the action potential through the AV node
what is atrial fibrillation?
continuous random atrial depolarization
what is the mechanism of atrial fibrillation?
no effective coordinated atrial depolarization, so no atrial contraction
AV node protects the ventricles by slowed depolarization & only conducting some atrial action potentials
what does atrial fibrillation look like on an ECG?
fibrillating baseline with no discernible p waves (called f waves instead)
QRS complexes are rapid & irregular based on when the beats get through the AV node, but the QRS complexes are still narrow & tall due to normal conduction through the AV pathway
what is the most common pathologic arrhythmia in horses? what causes it?
atrial fibrillation
can be secondary to underlying heart disease causing atrial enlargement or lone afib that occurs without any underlying cardiac disease
what is junctional tachycardia?
ectopic pacemaker in the AV node or the first part of the AV bundle
what are ventricular premature complexes?
ectopic foci in the ventricle depolarizes without atrial depolarization, so it isn’t related to p waves
not conducted through the normal bundle branches & purkinje fibers, so the shape of the complexes are wide & bizarre
what defines ventricular tachycardia?
more than 3 sequential VPCs
T/F: VPCs may occur singly with a normal heart rate or in groups of 2 or more
true
what does it mean if all VPCs look the same on an ECG? what if they all look different?
the same - likely from one focus
different appearance/polarity - suggestive of multiple ectopic foci
what is another name for benign ventricular tachycardia?
accelerated idioventricular rhythm
what are the 2 forms of vtach?
benign vtach & malignant vtach
what does benign vtach look like on an ECG? what causes it? how is it treated?
rate is typically less than 200 bpm
causes - commonly occurs secondarily to systemic disease such as trauma, GDV, & endotoxemia
only treat if causing hemodynamic instability!!!
what does malignant vtach look like on ECG? what animals do we see it in?
rate higher than 200 bpm
commonly seen in dogs with severe underlying cardiac disease & horses with myocarditis (DCM, arrhythmogenic right ventricular cardiomyopathy)
what is the risk that malignant vtach poses?
predisposes an animal to develop ventricular fibrillation causing a fatal arrhythmia & often results in sudden death
