Equine Cardiology Flashcards
What heart sounds can be heard in a normal equine heart?
Two to four can be heart in a normal equine heart
What is a gallop rhyth?
Three seperate beats heard
Typically this is pathological but can be normal in the horse
What are the two most important tests for evaluating an equine heart?
Ascultation and ultrasound
Why is radiology unhelpful?
The normal equine heart is usually too big to get an accurate picture of
Smaller foals you may be able to get a good picture of
Why is ECG less useful in the horse than in other animals?
The purkinje fiber arrangement is not linear in the horse making vector analysis less accurate
How does the depolarization work in a horse?
Depolarize more in a wringing motion so the heart twists from the apex to the base as opposed to a linear motion
Which lead position is the most helpful in equine patients and why?
Lead 1 since you are able to maximize focus on the ventricular septum
Where are the leads placed typically in the horse?
Left arm at the thorax at the 5th ICS at the level of the elboy and right arm at the jugular furrow
T/F: ECG is an effective test to assess chamber enlargement.
False- horse hearts depolarize weirdly so vector analysis isn’t accurate
How do P-waves typically appear in a horse?
Biphasic
How do QRS complexes typically appear in a horse?
negative deflection due to intraventricular septum depolarization
How do T-waves typically appear in a horse?
Large and spiked due to repolarization of a lot of myocardium at once
What areas are you able to feel a jugular pulse in a normal horse?
No higher than the junction of the middle and distal third of the neck and with the the head in neutral carriage position
If you are able to feel pulses in places other than normal, what are they most likely due to?
Valvular insufficiency causing blood to regurgitate back into the cranial vena cava and jugular veins
What is the most common physiologic arrhythmia in the horse?
2nd degree Mobitz type 1 AV block
aka Wenkenbach
Why can horses have a normal Wenkenbach arrhythmia?
Persistent high vagal tone so any changes in it cause issues in communication between AV and SA node
How does 2nd degree Mobitz type 1 AV block appear on an ECG?
Progressive prolongation of the PR interval until there is a drop in regular beat pattern
Why do horses typically not present with sinus arrhythmias?
Because sinus arrhythmias are caused by decreased vagal tone and horses live at a really high vagal tone normally
What is the most common pathological arrhythmia in the horse?
Atrial fibrillation
Why is a-fib common in horses?
Due to increased cardiac size and high vagal tone
Why does a-fib occur?
The atria are not synchronized exactly and will not be at the same phase of polarization
Typically this isn’t an issue in a normal horse but can be detrimental to an athlete
What are the two kinds of a-fib that can manifest in the horse?
Paroxysmal and sustained
What is paroxysmal a-fib?
Single episode of a-fib causing poor performance during periods of high heart rate
Very easy to miss
What is sustained a-fib?
Go into a-fib and stay in it
Much easier to diagnose and not necessarily associated with high heart rate
T/F: Most a-fib cases are associated with underlying cardiac pathology.
False- usually have nothing else wrong
T/F: Presence of a systemic abnormality predisposes animals to a-fib.
True- especially electrolyte abnormalities
What are the clinical signs of a-fib?
Exercise intolerance and poor performance
What are some systemic underlying causes of a-fib?
- EIPH
- Myopathies
- Colic
- Collapse
- CHF
What will a-fib sound like on auscultation?
Irregularly irregular
Tennis shoes in a dryer
What will pulses feel like with a-fib?
Variable strength with longer or shorter period due to erratic ventricular contraction and polarization
What do you look for on standard work ups to help diagnose any underlying causes of a-fib?
UA- fractional excretion
Blood- cardiac troponin-1 to assess for cardiac disease
What test is done to confirm a-fib?
ECG
What should be done to assess functionality of the heart in horses with a-fib?
Echocardiography to assess fractional shortening and diameter of chambers
What does treatment of a-fib depend on?
Heart rate and ultrasound foundings
What is the best case senario for treatment of a-fib?
Resolution spontaneously when not exercising
How do you treat an animal with a-fib with normal PE, HR
Quinidine PO
Can get complications if given IV
How do you treat an animal with a-fib with normal PE, HR>60bpm, and normal echo?
Digoxin first then quinidine
Digoxin first so that you bring the HR down to 60 then give quinidine
Why do you want to give digoxin prior to quinidine in higher HR with a-fib patients?
Quinidine is arrhythmogenic especially at higher heart rates
What qualifies as a complicated case of a-fib in a horse?
A-fib with underlying cardiac disease
Abnormal PE and abnormal echo
What is used to treat complicated cases of a-fib?
Digoxin and quinidine
What are the issues with quinidine in complicated a-fib cases?
Pro: maximizes cardiact output
Con: reduced efficacy due to underlying disease
T/F: Treatment often is not effective in complicated cases of a-fib.
True- not much you can do
What are some alternative therapies for treating a-fib?
Electrocardioversion or transvenous electrocardioversion- has to be under GA
No difference in long therm prognosis with electrical or chemical cardioversion
What is the most common issue with using digoxin and quinidine in the same animal?
Both highly protein bound so there is displacement when administering them at the same time which can lead to toxic levels free in circulation
What NSAID can also lead to protein binding issues in horses on digoxin/quinidine therapy?
Phenylbutazone
What are some signs of quinidine toxicity?
GIT, neurologic behavior signs, cardiac signs, some idiosyncratic reactions
What cardiac signs can be seen with quinidine toxicity?
Widening of QRS (~25%)
Can be prevented with dosage adjustment and regular ecg monitoring
What is an idiosyncratic reaction associated with quinidine in the horse?
Rapid supraventricular tachycardia
Prevent by giving a test dosage of quinidine prior to starting on therapeutic regimen
What is the test dosage typically given for quinidine?
5mg via nasogastric tube, recheck ecg 1 hours later then increase by 10g and check again
How to do treat rapid supraventricular tachycardia associated with idiosyncratic quinidine reaction in the horse?
Digoxin and sodium bicarb
What is the prognosis of a-fib in horses in general?
95% conversion rate
What is the prognosis of a-fib in horses with an HR
With a murmur of 1-3/6 and
What is the prognosis if there is a long duration of a-fib or concurrent cardiac disease?
80% conversion rate with 60% recurrence
Long term prognosis doesn’t change
What are ventricular premature contractions typically associated with in horses?
Metabolic disease
What are some potential causes for VPCs in horses?
- Electrolyte abnormalities
- Endotoxemia
- Myocardial Inflammation (strangles or influenza)
- Hypoxia
How do you treat VPCs in horses?
- Treat underlying disease
- Lidocaine (bolus or CRI drip)
What are the grades of physiologic murmurs in the equine heart?
Grade 3-4 left heart base systolic ejection murmor
What are physiologic murmurs created y?
- Reverberation of the great vessels
- Changes in viscosity like anemia or dehydration
How do you definitely differentiate physiological from pathological murmurs?
Ultrasound
What percentage of horses will have physiologic murmurs?
66%
Associated with rapid ejection of blood in early systole
T/F: Congenital cardiac murmurs are common in the horse and are typically extremely pathological.
False- they are very uncommon and typically only apparent when exercising the animal
What are the two most common congenital murmurs in the horse?
VSD ( most common) and PDA
What are the characteristics of VSDs?
Typically incidental but can impact performance
usually 3-4/6 coarse band shaped pan-systolic murmur
What are the characteristics of PDAs?
3-4/6 continuous machinery murmur over left heart base
What are the clinical signs of mitral valve insufficiency?
Variable depending on severity of dysfunction and purpose of the horse
Mild: Exercise intolerance
Severe: Sudden death, cordae tendinae rupture, acute decompensation and failure
T/F: Mitral insufficiency is the most likely valve dysfunction to lead to cardiac failure.
True
What is the typical pathophysiology of mitral insufficiency?
Degenerative or inflammatory lesion
What are typical findings of mitral insufficiency?
Grade 3 holosystolic or pan systolic band-shaped left 5th ICS murmur
What are complications associated with mitral insufficiency?
- Sudden death
- Cordae tendinae rupture
- Pulmonary artery rupture (death)
What is the prognosis of mitral insufficiency?
Prognosis worse for younger horses and athletes
How do you monitor mitral insufficiency?
Re-echo every 3 to 9 months to check progression
What kind of horses typically present with aortic insufficiency?
Older horses
If seen in younger is a cause for concern
What are the clinical signs of aortic insufficiency?
Often incidental associated with degeneration of the aortic valve (nodules, fibrous bands, plaques)
2-4/6 pan- holo- or early diastolic decrescendo left PMI 4th ICS Murmur loudest on the left but can be heard on right
What are some complications of aortic insufficiency?
Heart failure and aortic rupture
T/F: Vegetative and inflammatory valve diseases carry a better prognosis than degenerative ones.
False- carry a worse prognosis
T/F: Left sided overload has a poor prognosis especially if it is progressive.
True
Tricupid insufficiency, all the things
Thoroughbreds are increased risk
Typically only see exercise intolerance
Diagnosis: Right sided holo/pan-systolic murmur that radiates concentrically from PMI over tricuspid valve
What is the typical signalment of a vegetative endocarditis horse?
Most often
What is the pathogenesis of vegetative endocarditis?
o Endothelial damage
o History of trauma to the endocardium or valve (Polyethylene catheter placed across the valvular surface )
o fibrinous clot formation of vegetation
o Bacteria able to adhere to endothelial damage – need bacteria from circulation
(Subclinical abscesses in the heart or Catheters)
o Local clotting activated
What are the clinical signs of vegetative endocarditis?
Fever of unknown origin, tachycardia, murmur
Fever typically presenting complaint
How do you diagnose vegetative endocarditis?
o CBC + Chem: Hyperproteinemia – Hyperglobulinemia with hyperfibrinogenemia, Leukocytosis – mature neutrophilia, Non-regenerative anemia
o Blood Culture
o Echocardiography (ECG)- Detect arrhythmias secondary to myocardial pathology (Most commonly APCs and atrial fibrilation)
o Electrocardiogram
What are the common organism isolates of vegetative endocarditis?
Strep, Actinobacillus equili, E. coli
Are blood cultures always useful for diagnosing vegetative endocarditis?
No, commonly come up negative even if present
How do you treat vegetative endocarditis?
Antimicrobials for 4-6wks (Typically KOen and gentamicin IV)
Flunixin and asprin
When should you recheck blood culture?
60 days after stopping treatment
Only if primary blood cultures came up positive
What are some causes of heart failure in the horse?
o Mitral Insufficiency
o Vegetative endocarditis
o Pericarditis
o Toxicities
T/F: Heart failure is unusual in horses
True
What two drugs are cardiotoxic in the horse and what animals are they typically used in?
- Monensin in cattle feed
- Lasalocid in poultry feed
What is the typical signalment for pericarditis in the horse?
No particular signalment
Food animals typically a result of hardware disease
What are the typical causes of pericarditis in a horse?
Typically infectious process with concurrent history of respiratory disease
- Viral respiratory disease
- Pleuropneumonia
- Sepsis
What are the two types of pericarditis found in the horse?
Effusive and constrictive (fibrinous)
What kind of fluid is typically found in effusive pericarditis?
Transudate
Typically a result of viral respiratory disease
What typically causes constrictive pericarditis?
Pleuropneumonia cases due to fibrin being laid down on the myocardium
What typically causes heart failure in constrictive pericarditis cases?
Pre-load issues- cannot acquire enough volume to maintain CO
Typically signs of right heart failure appear first
What conditions can cause a mix of constrictive and effusive pericarditis?
Pleuropneumonia and sepsis
What are some clinical signs of acute pericarditis?
o Ventral edema o Distended jugular/veins o Poor pulses o Weakness o Listlessness o Syncope o Fever
Typical signs of infection
What are the CBC and Chem findings in a horse with pericarditis?
Anemia, leukocytosis, hyperfibrinogenemia, elevated creatinine, hyponatremia, hyperkalemia, increased CVP
When should ECG be used especially in pericarditis cases?
When draining pericardial fluid
ECG will go nuts if you accidentally poke the myocardium
How do you treat effusive pericarditis?
Pericardiocentesis
How do you treat constrictive pericarditis?
Pericardiocentesis and pericardectomy
Typically done under GA
What are two main causes of endo/myocardial lesions?
Hypoxia/ischemia and toxins
How do you treat heart failure in a horse?
Furosemide, Digoxin, Enalaprin, Hydralazine
Just like everything else….
What is the history of a horse with suspected ionophore toxicity?
Ingestion of cattle or poultry feed
What are the clinical signs of ionophore toxicity?
o Colic: restlessness, anorexia, profuse sweating
o Reluctance to move, pyrexia, muscle trembling
o Hind limb weakness
o Arrhythmias most likely to develop within first few days to weeks of ingestion
What is the typical cause of death with ionophore toxicity?
Fatal arrhythmia
How long should horses be monitored after recovering from ionophore toxicity?
At least a year
How do you treat ionophore toxicity in horses?
Maybe vit E and Selenium
Nasogastric intubation and activated charcoal administration if recently ingested
Stall rest and balanced electrolyte fluids
T/F: Digoxin is contraindicated in monensin toxicosis.
True- can cause a massive Ca influx and cause more myocardial necrosis
What is prognosis based on with monensin toxicity?
Fractional shortening on echo
30-40% good prognosis
10%-20% grave prognosis but will have residual myocardial issues
T/F: Myocardial enzymes are not good prognostic indicators for survival or severity of myocardial damage.
True
