Sinus Arrhythmias Flashcards
What is an arrhythmia?
abnormality in the rate, regularity, or site of origin of the cardiac impulse
- normal sequence of activation of the atria and ventricles is altered
What are the 3 possible origins of arrhythmic beats?
- atrial: positive deflection of P waves with constant PR interval and normal QRS duration
- junctional: negative deflection of P waves or no P waves with a normally conducted short QRS (unless BBB)
- ventricular: no P waves, wide/bizarre QRS that can be negative or positive
What are the 4 major deviations for normal rate of automaticity?
- too fast = tachycardia
- too slow = bradycardia
- too irritable = premature
- absent = block
What is the expected rate of automaticity of the SA node/atrial conduction tissue, AV junction/His bundle, and bundle branches/Purkinje fibers?
70-160 bpm
40-60 bpm
20-40 bpm
(whatever site fires fastest will drive the HR)
What allows ideal interpretation of ECGs?
right lateral recumbency with proper leads
- read lead II!
What are 4 possible artifacts that may look like arrhythmias on ECGs?
- 60 cycle electrical interference
- shivering or motion
- panting
- petting or tapping head
What is likely happening on this ECG?
panting artifact
What is likely happening on this ECG?
electrical interference
What is likely happening on this ECG?
breathing artifact
What is likely happening on this ECG?
purring artifact
What are the 5 general steps to reviewing ECGs?
- calculate HR
- assess rhythm - do all complexes look the same, are intervals regular?
- identify P waves - are they positive, in normal shape and location?
- assess QRS shape and duration
- assess relationship between P and QRS complexes - should be one P for every QRS
Reviewing ECGs:
What to evaluate on an ECG:
What is normal sinus rhythm?
beat initiated by the SA node, resulting in normal rhythm, and an upright P wave
What are 4 ECG features of sinus rhythm?
- regular rhythm
- very similar RR intervals
- positive P waves on lead II
- P-QRS complexes normal with constant PR
What is occurring in this ECG?
normal sinus rhythm
What is sinus arrhythmia?
an irregular heartbeat originating from an irregular rate in the SA node, commonly associated with respiration due to vagal tone
How does sinus arrhythmia appear on ECGs? In what 3 patients is this most commonly seen?
- HR increases with inspiration
- HR decreases with expiration
- there is a normal P with every QRS, but PP and RR intervals vary (regularly irregular)
- dogs that are fit
- brachycephalics
- patients with respiratory disease
Is treatment necessary for sinus arrhythmias?
NO —> helps rule out lung disease over cardiac disease (more likely lung disease if this is present)
- Atropine can reverse it, but it is not commonly necessary
What is occurring in these ECGs?
sinus arrhythmia
- HR increases with inspiration
- HR decreases with expiration
What is occurring in this ECG?
sinus arrhythmia
- HR increases with inspiration
- HR decreases with expiration
What is a wandering atrial pacemaker?
mixed sinus and atrial rhythm —> P waves come from outside the SA node, but still within the atria, resulting in different shapes of the P waves closer to the QRS complex
- high vagal tone is common, so it is often seen with sinus arrhythmia
What are the 2 major signs of wandering atrial pacemakers on ECG? Is treatment necessary?
- variable morphology/amplitude of P waves (negative = junctional)
- variable PR interval (often decreased)
NO —> typically no hemodynamic consequences
What is occurring in this ECG?
wandering atrial pacemaker
- abnormal P wave morphology
- rest of waves are normal
What is sinus bradycardia? How do they compare in dogs and cats?
very slow and infrequent complexes, but normal PQRST
- DOGS = < 70 bpm; can be normal in larger breeds (no treatment necessary)
- CATS = < 120 bpm; NEVER normal in cats
What are some physiological causes of sinus bradycardia in dogs and cats?
ELEVATED VAGAL TONE
- vomiting
- intubation
- increased CNS pressure
- ocular disease, increased IOP
- hypothermia
- hypothyroidism
- good conditioning
- respiratory disease
What are some pathological causes of sinus bradycardia in dogs and cats?
- systemic disease with toxicity (renal failure)
- impending cardiac arrest
- CNS disease
- HYPERKALEMIA
What are some drugs that can cause sinus bradycardia in dogs and cats?
- phenothiazines
- propanolol
- morphine
- anesthetics
- calcium channel blockers
What is occurring in this ECG?
sinus bradycardia
What are some clinical signs of sinus bradycardia?
weakness, lethargy, collapse
- treatment only necessary if clinical
What is occurring in this ECG?
sinus bradycardia
What arrhythmia is commonly associated with sinus bradycardia? Why? How is it differentiated from a VPC?
ventricular escape beats
ventricular pacemakers take over to create a beat since there was no P wave
it is not premature
What is occurring in this ECG?
ventricular escape beat
- wide/bizarre QRS complex
When are escape beats seen? What is seen on ECG?
decreased heartbeat (sinus bradycardia, AV block) where the heart will rescue itself by having another pacemaker take over, either from the AV node, junction, or ventricles
seen following a pause longer than the normal sinus cycle length (RR interval)
What is the difference between a junctional and ventricular escape?
JUNCTIONAL = no P wave associated, long pause, normal QRS complexes
VENTRICULAR = no P wave, long pause, more wide and bizarre QRS complex
What is considered sinus tachycardia in dogs and cats? What is seen on ECGs?
- DOGS = > 160 bpm
- CATS = > 240 bpm
normal PQRST with high HR with little response to vagal maneuvers —> P wave can get hidden
Is treatment needed for sinus tachycardia?
not always - typically physiologic
- sustained = treat underlying cause
What is occurring in this ECG?
sinus tachycardia
What are some physiological, pathological, and drug-induced causes of sinus tachycardia?
PHYSIOLOGICAL - elevated sympathetic tone caused by stress, pain, anxiety, hypovolemia, or toxicities
PATHOLOGICAL - fever, hyperthyroidism, shock, anemia, infection, CHF, hypoxia
DRUGS - Atropine, Epinephrine, Vasodilators (hypotension increases HR)
(treat underlying cause!)
What is indicative of sinus arrest/block on ECG? What is the most common cause?
disease in the sinus node or very high vagal tone cause the absence of sinus activity for > 2 RR intervals
pathologic > physiologic —> drug-induced (anesthetics), sinus nodal disease (sick sinus syndrome) > vagal mediation (brachycephalic)
What is commonly also seen with sinus arrest/block? What is the most common clinical sign?
escape beats
signs of weakness/collapse, prolonged periods where there is a low heart rate
What is occurring in this ECG?
sinus arrest/block
What treatments are indicated for sinus arrhythmia, bradycardia, tachycardia, and arrest?
SINUS ARRHYTHMIA - physiologic, no treatment needed
SINUS BRADYCARDIA - look into stopping drugs/treating diseases that cause increased vagal tone; can eliminate with Atropine, Glycopyrrolate, or catecholamines; run the dog and see if it resolves
SINUS TACHYCARDIA - treat underlying cause of increased sympathetic tone; can slow sinus rate with Atenolol/Esmolol or vagal manuever but rarely indicated
SINUS ARREST - high vagal tone = parasympatholytics, sinus nodal disease or sick sinus syndrome = pacemaker
