Cardiac Arrhythmia Flashcards
What does a atropine response test assess?
For bradycardia,
- there is a a response (ie. an increase in heart rate), then the bradycardia is vagal mediated
- if there is no change, then there is an intrinsic disturbance of impulse formation or conduction
How does the respiration cycle change heart rate?
heart slow down on expiration and speeds up on inhalation
seen in dogs mostly
What’s ventriculophasic sinus arrhythmia?
it’s when the P-P interval that flanks the QRS is shorter than the P-P interval during a block
- seen in high grade 2 or grade 3 AV block
- no clinical significance
- just need to know it’s not an atrial arrhythmia
How does a “wandering pacemaker” appear on ECG?
- variation in the height of the P wave
- constant P-R interval, constant QRS
- normal QRS
- slight variation in R-R interval
- if in conjunction is respiration sinus arrhythmia, the P wave is taller on inspiration, and shorter an expiration
What are some ECG differentials for wandering pacemaker?
- P pulmonale
- premature arterial complexes (PACs) –> but the P wave in a wandering pacemaker should not be so premature that it goes into the previous T wave, and the P wave will be taller (not shorter) with an increased heart rate (wandering pacemaker and resp sinus arrhythmia don’t occur at HR >150/min
How high is the high rate to constitute a tacycardia?
160/min
How is the ECG for a sinus tachycardia?
HR > 160/min
- normal P-QRS-T
- this indicates SA in origin
- may need vagal maneuver to detect the P/T waves
What are the 5 ECG changes that can be seen with a APC?
- premature sequence of P-QRS-T
- QRS = narrow, tall; comparable to sinus rhythm
- P wave has a different amplitude compared to sinus rhythm
- P-R interval is not the same as a sinus rhythm (shorter or longer)
- postextrasystolic pause
What are some differentials for atrial premature contractions?
structural abnormalities in the atria
- atrial distension
- atrial tumours, ex. hemangiosarcoma
- cats with hyperthyroidism
- digitalis toxicity and other toxicities
What’s the clinical implication of APC?
minor
- increases awareness of atrial abnormalities
How does atrial tachycardia looks like on ECG?
looks like a bunch of APC, with increased heart rate
How is atrial tachycardia treated?
- diltiazam
- propanolol
- phenylephrine
Long-term oral therapy:
- atenolol
diltiazem
What’s the clinical significance of atrial tachycardia?
depends on the underlying cause (similar to atrial premature contraction)
- more commonly seen in older dogs
- can lead to atrial fibrillation
What are the ECG characteristics of atrial flutter?
- rapid, rhythmic waves (flutter)
- doesn’t return to baseline
- normal, supraventricular QRS
- variable, irregularly irregular R-R interval
How is atrial flutter treated?
digoxin and diltiazem
What’s the clinical significance of atrial fibrillation?
- it’s a common arrhythmia
- 50% of dogs with DCM
What are the ECG features of atrial fibrillation?
- QRS = supraventricular
- irregularly irregularly R-R interval
- no visible P waves, replaced by f waves
What are some differentials for chaotic irregular rhythm on auscultation, coupled with pulse deficits?
- atrial fibrillation
- polymorphic ventricular tachycardia
- frequent VPCs or APCs
How can one make sure it’s afib + BBB and not vTach?
With vTach, there will be P waves
- a vagal maneuver will reduce the heart rate but won’t have an effect if it’s vTach
What’s the most likely cause of atrial fibrillation?
enlarged atria
What are some ddx for structurally normal atrial fibrillation (aka lone atrial fibrillation)?
- general anesthesia
- hypothyroidism
- pericardiocentesis (large, rapid volume)
- Gi disease
- volume overload
- commonly seen in giant breeds
How common is atrial fibrillation in cats?
less common than in dogs
- mostly with underlying structural defect –> atrial enlargement
- not any worse in outcome vs lone atrial fibrillation (as noted in dogs)
- can be normal in 20-25% of cats
How is atrial fibrillation treated?
digoxin and diltiazem
goal is so accept the atrial fibrillation, but slow down the ventricular/heart rate
How does atrial dissociation look like on ECG?
Appears to have 2 rhythms: normal P-QRS-T, with (smaller) P waves that do not result in QRS
How is atrial dissociation treated?
No treatment required
- incidental, benign
What’s the most common arrhythmia?
VPC!
What are the hallmarks of premature ventricular contractions on ECG?
- shortened R-R interval
- wide bizarre QRS, no associated P wave
- different (often very large) T wave
What are 2 specific heart diseases in dogs that are almost exclusively arrhythmogenic and causes VPCs?
- Boxer cardiomyopathy (right ventricular cardiopathy)
- German Shepherd inherited sudden cardiac death –> most likely seen in young puppies. If they survive puppyhood, they will be ok
What’s the ECG characteristic of accelerated idioventricular rhythm?
Looks like ventricular tachycardia but slower
- same causes as VPCs
- Tx = correct underlying cause if possible
- antiarrhythmic meds only if tx for underlying cause is ineffective
What’s the clinical implication of ventricular fibrillation?
terminal/ fatal
- needs immediate treatment –> defibrillator, CPR
Ventricular escape rhythm is common in 3rd degree AV block. How should it be treated?
do NOT treat – it actually is life saving
What are some ECG characteristics of 3rd degree AV block?
complete dissociation
- P-P interval = consistent, but is not always followed by a QRS
- wide bizarre QRS
How severe in 3rd AV block in cats?
they can also have ventricular escape beats that makes the HR just a bit lower than a regular sinus rhythm - incidental finding
What’s the cause of AV blocks?
1st degree, and type I 2nd degree:
- most likely functional: high vagal tone, toxicosis, antiarrhythmics, alpha-2 agonist sedatives
type II 2nd degree and 3rd degree:
- can be functional, but often structural –> inflammatory or degenerativeW
What’s the treatment for AV blocks?
1st degree, and type I 2nd degree: none
type II 2nd degree and 3rd degree: pacemaker BUT may not be needed in cats with sufficient escape ventricular rhythm. Also doesn’t work if there is underlying structural cardiomyopathy (often seen in cats)
Which side is the bundle branch block benign?
Right bundle branch block = benign
left bundle branch block = L ventricular enlargement
What’s the ECG feature for atrial standstill?
lack of P wave, but constant R-R interval
- QRS = supraventricular
- low to normal rate
What are the top 3 ddx for atrial standstill?
- moderate to marked hyperkalemia
- atrial myopathy
- artifact
What’s electrical mechanical dissociation?
The electrical impulses are not translating into mechanical systole or diastole
- patient typically unconscious and hemodynamically unstable
- pre-terminal
- grave prognosis
How does extracellular potassium level effect the cardiac muscle action potential?
Potassium level influences the resting membrane potential.
1. Hypokalemia
- hyperpolarizes due to a greater difference between intracellular and extracellular K+ level
- prolongs repolarization –> increases risk of extrasystole
- Hyperkalemia
- faster repolarization = shorter Q-T interval, tented T wave
- sinus bradycardia. but this is often masked by concurrent conditions that often occur along side with hyperkalemia, so tachycardia might be noted –> heart rate therefore is not a reliable indication of potassium concentration
- bradycardia due to excitation suppression, atrial > ventricle
How does extracellular calcium level affect action potential?
it effects the threshold –> effects more profound in skeletal muscles/ other organs than the heart
Decreased calcium = decreased threshold –> easier to depolarize –> muscle fasciculation
- can prolong Q-T interval
Increased calcium = increased threshold –> harder to depolarize
- decreases Q-T interval
Describe ECG for sick sinus syndrome
simultaneous defect in SA node and AV conduction
- first or 2nd degree AV block
- prolonged sinus pauses
- bursts of supraventricular tachycardia or VPCs at variable rates
