Equine Cardiac Arrhythmias Flashcards
What is the most common cardiovascular cause of poor performance? In what horses is it most common?
atrial fibrillation (ALWAYS PATHOLOGIC)
large breeds —> Warmbloods, Thoroughbreds
(not commonly seen in ponies)
What is atrial fibrillation?
multiples points in the atria are sending out impulses, which overtake the rhythm of the sinoatrial node
What are the 2 most common causes of poor performance in horses with atrial fibrillation?
- unable to efficiently push blood to ventricles during diastole
- disproportionately high heart rate at exercise makes the horse fatigue more quickly
How does atrial fibrillation affect horses at rest?
often tolerated at rest
- causes increased heart rate during exercise (walk, trot, gallop)
What is seen on physical exam in horses with atrial fibrillation?
- variable pulse quality
- irregularly irregular rhythm on auscultation and pulse palpation (chaotic!)
What are 2 characteristics of atrial fibrillation on ECG?
- P waves replaced by F waves that are randomly at different shapes and amplitudes
- irregular R-R interval with consistent QRS complexes
What is most commonly seen on cardiac ultrasounds in patients with atrial fibrillation? What laboratory tests are most commonly done?
enlarges atrial diameter and inefficient contractions
- CBC/chem: inflammation, electrolytes
- fractional excretions
- cardiac enzymes
What drug is associated with causing atrial fibrillation?
Furosemide —> diuretic that decreases potassium
When is treatment for atrial fibrillation done? How does signalment determine affect treatment?
if AF is present for >48-72 hours and a full cardiac exam was performed to search for causes
- easier to defibrillate younger horses
- if horses are only on pasture, it may not be necessary to treat since it is well tolerated at rest
How is atrial fibrillation medically managed? What are 7 associated side effects?
Quinidine sulfate by NG tube
- congestion/edema of mucous membranes
- colic
- ataxia
- laminitis
- urticaria
- tachycardia
- collapse/sudden death
What factors are considered before treatment for atrial fibrillation?
- HISTORY: duration of fibrillation
- PE: HR at rest
- ECG: presence/absence of other arrhythmias
- US: enlarged atrium
- effect of exercise
What alternative treatment is available for atrial fibrillation?
transvenous electric cardioversion, where electrodes are placed in the pulmonary artery and atrium and deliver electric shocks
What is atrial premature contraction?
one random point in the atria makes its own impulse, which overpowers the sinoatrial node, causing contraction of the atria before they are ready
What are the most common consequences of atrial premature contraction?
depends on underlying cause and number of APCs
- none
- exercise intolerance
- atrial fibrillation
What is heard on auscultation in patients with atrial premature contraction?
irregularly irregular rhythm where the regular rhythm is interrupted by a premature beat
What 2 things are observed on ECGs in patients with atrial premature contraction?
- ectopic premature P causes shortened P-P or R-R intervals
- normal QRS morphology
What are some signs of physiologic atrial premature contractions?
- rare at rest
- vanishes with exercise
- rare after exercise
What are 5 signs of pathologic atrial premature contractions? How is it treated?
- frequent at rest
- with episodes of tachycardia
- poor performance
- leads to fibrillation or flutter
- with other signs of cardiac disease
rest are corticosteroids
What causes sinus arrhythmia? Where does it originate?
changes in vagal tone (not common in horses)
SA node
When is the appearance of sinus arrhythmia most common?
- frequent, transient
- most commonly seen AFTER exercise, with a heart rate of 130-150 bpm
What is heard on auscultation in patients with sinus arrhythmia?
cyclic irregularity that disappears with exercise
What is seen on ECGs in patients with sinus arrhythmia?
cyclic changes in R-R interval, with normal QRS complexes
How are HR, exercise, and clinical signs affected by physiologic AV blocks?
- HR = low at rest
- block disappears with exercise
- no clinical signs
commonly physiologic in athletic horses, there is an advantage to having a slow resting HR and being able to ramp it up during exercise
How are HR, exercise, and clinical signs affected by pathologic AV blocks?
- HR = inappropriately low
- block persists with exercise
- exercise intolerance, ataxia, syncope, collapse, unexplained trauma
What is the most common etiology of second degree AV blocks? Where does it originate?
high vagal tone, common in athletic horses (most commonly disappears with exercise)
partial conduction at AV node
What is the most common physiologic arrhythmia in horses?
second degree AV block
What is heard on auscultation in patients with second degree AV blocks?
- regularly irregular rhythm with slow to normal HR
- diastolic pause where S4 is audible
What is characteristic of ECGs of second degree AV blocks?
not every P wave if followed by QRS complexes —> normal propagation in atrium, but AV node doesn’t let it through
- QRS complexes are normal and preceded by P waves
- disappears with exercise
What is an advanced second degree AV block? Complete block?
numerous P waves without QRS complexes
dissociation between atria and ventricles
What are 4 treatment options for second degree AV blocks?
- treat primary cause or disease
- sympathomimetics (vagolytics)
- glucocorticoids
- temporary or permanent transvenous pacemaker
What is ventricular premature contraction? What consequences are associated?
one random point in the ventricle makes its own impulse, causing ventricles to contract before they are ready
- none
- exercise intolerance
- collapse
What is heard on auscultation in patients with ventricular premature contraction?
- HR normal or tachycardia
- irregularly irregular rhythm (not as chaotic as A fib)
What are 2 characteristics of ECGs in ventricular premature contraction?
- shortened QRS intervals not preceded by P waves
- followed by compensatory pause to protect the heart from other impulses
What is characteristic of physiologic ventricular premature contraction? Pathologic?
rare at rest, vanishes with exercise, or rare after exercise
- frequent at rest
- with episodes of tachycardia
- poor performance
- leads to ventricular tachycardia
- other signs of cardiac disease
What is characteristic of ventricular tachycardia on ECG? What is heard on auscultation?
> 4 successive ventricular premature contractions
rapid (ir)regular rhythm with cardiac sounds of variable intensity
How does the type of ventricular tachycardia affect prognosis?
uniform > multiform > R on T > Torsades > fibrillation
What are 5 treatment options for ventricular tachycardia?
- lidocaine
- quinidine
- magnesium sulfate
- phenytoin
- propanolol
Exercise ECG:
increased HR causes P waves to not be seen —> may not be pathologic, software is used to determine changes
What is seen on this ECG?
AV block
- irregular P waves not followed by QRS complexes
- sudden drop in HR to 32
What is seen on this ECG?
atrial fibrillation
- F waves
What is seen on this ECG?
2 VPCs
- narrow and tall QRS complexes
What is seen on this ECG?
a. second degree AV block
b. ventricular premature contraction with compensatory pause
c. atrial fibrillation
d. atrial flutter
C - F waves + irregular spacing between QRS complex
A regularly irregular rhythm at rest most likely corresponds to which arrhythmia?
a. sinus arrhythmia
b. second degree AV block
c. third degree AV block
d. sinoatrial block
B - usually irregular
(A fib is irregularly irregular)
What is the most common pathologic arrhythmia in horses?
a. atrial tachycardia
b. premature supraventricular contraction
c. atrial fibrillation
d. second degree AV block
C - persists and affects performance
What are some factors that you should assess before treating horses with atrial fibrillation?
- HISTORY: knowing when it started, prior episodes
- SIGNALMENT: young horses easier to treat
- PE: normal HR at rest
