Equine dysrhythmias Flashcards
Myocardial disease in horses causes
Dysrhythmias due to disruption of action potential propagation and abnormalities in contraction
Endocardial disease in horses causes
Murmurs, due to valvular regurgitation and jet lesions
List 4 ways that myocardial disease manifest
No clinical signs
poor performance- atrial fibrilation and ventricular premature depolarisation
Collapse- multiple ventricular premature depolarisations and Ventricular tachycardia
Death - Ventricular tachycardia progressing to Ventricular fibrillation
Describe how to diagnose cardiac dysrhythmias
ECG
evaluation of underlying cause using echocardiogram, blood tests ect
List the 4 conditions that may lead to myocardial dysfunction
Electrolyte abnormalities
Increased myocardial muscle mass
Increased chamber size
Myocarditis
Describe the Use of clinical pathology to evaluate the large animal myocardium
Sensitivity and specificity of these tests is questionable
-Proteins
- Enzymes
- Creatine kinase
List the bacteria that can cause myocarditis
Staph aureus
Strep equi
Clostridium chauvoei
Myocobacterium spp.
Secondary to sepsis, pericarditis, endocardititis
List the viral causes of mocarditis
FMD, EIA, EVA, EIV, AHS
Other than bacterial and viral what else can cause myocarditis in horses
Borrelia burgdorferi (Lyme disease)
Parasites- large strongyles, Toxoplasma, Sarcocystis
Thromboembolic disease
List the cardiomyopathies of large animals
Only DCM reported to be important (subacute to chronic, see a dilated ventricle)
Describe how we evaluate the myocardium using echocardiography
- Assessment of myocardial appearance (long/short axis views),
- Fractional shortening (at rest and following exercise to evaluate contractility),
Describe dobutamine atropine stress echocardiography
Causes a progressive increase in HR,
Allows function to be assessed as HR increases and how function is maintained,
Simulates exercise
Describe how myocardial biopsies can be performed
Can be done standing,
Ultrasound guided,
Biopsy instrument into heart via jugular vein
Describe a Standard equine ECG at rest
Complexes uniform, identical and at regular intervals
Describe how to assess an exercising equine ECG
Harder to assess, P and T waves are hard to see,
Assess the regularity of the R waves (downward projections)
Check intervals are regular and they look similar
What is the most common physiological dysrhythmia in horses
2nd degree AV block
considered normal in horses
what causes 2nd degree AV block
due to high vagal tone in autonomic control of the equine heart
describe what a 2nd degree AV block looks like on ECG
P wave not followed by a QRS complex (blocked by the AV node),
Are 2nd degree AV blocks of clinical concern
NO
will disappear when horse is stimulate
What is the most important cardiac dysrhythmia in the horse
Atrial fibrillation
why does Atrial fibrillation occur
- Lack of coordinated atrial electrical activity
- Can be triggered by electrolyte/acid-based imbalances, anaesthetic and drug administration (that causes bradycardia, exercise
List some horses which are more susceptible to atrial fibrilation
TBs, SBs, Draught horses- large horses
due to large atrial mass
List the clinical signs of atrial fibrillation
None- most
Exercise intolerance/poor performance
Epistaxis
RARE presentations:
Weakness/syncope
Myopathy
Colic
CHF
What are the 2 forms of atrial fibrillation
Paroxysmal
Sustained
What is the difference between paroxysmal and sustained atrial fibrillation
Paroxysmal - Lasts less than 24-48hrs and spontaneously converts back to sinus rhythm,
Sustained (lasts longer than 24-48hrs)
What can Paroxysmal atrial fibrillation be associated with
Potassium depletion (furosemide) and administration of bicarbonate
List the things seen on clincal exam in horses with atrial fibrillation
Irregularly irregular rhythm (less irregular with chronicity),
HR and pulse quality varies on intensity (booming S1 and no S4),
Usually a normal or decreased HR, occasionally increased if associated with heart failure,
Abnormally high heart rates at exercise (can be associated with VPDs, should perform an exercising ECG)
Describe how to diagnose atrial fibrillation
ausculatation and physical exam
resting ECG - confirms diagnosis
Further diagnostics PRIOR to attempting treatment
what is seen on ECG with atrial fibrillation
No P wave
normal QRS complexes
F (fibrillation) waves
How does the cause of atrial fibrillation being chamber enlargement affect diagnosis
Worse prognosis for return to sinus rhythm
Describe the pharmacological treatment of atrial fibrillation
Quinidine sulphate
Is a Negative inotrope
List the side effects of quinidine sulphate
Fatal dysrhythmias,
Colitis (drug irritant to mucosa),
Laminitis/nasal oedema/ataxia
Because of this need to be cautious when using
Describe the Cautious use of quinidine sulphate
Need repeated physical exam
Auscultation
Continuous ECG at the time and 24hrs after
Check acid base and electrolytes prior to treatment
Describe how to assess quinidine sulphate toxicity
by assessing prolongation of QRS complex (>25% of pretreatment value makes untoward effects more likely)
What is DC cardioversion
Wires into the heart of an anaesthetised horse,
Positioned using ultrasound and radiography,
Increase current to try and stop heart and convert to sinus rhythm
what does DC cardioversion treat
atrial fibrillation
Where are the two wires places in electrocardioversion
One wire in left pulmonary artery,
Other wire in right atrium
What is the Prognosis of paroxysmal atrial fibrillation
Excellent to good unless keeps recurring
what is the Prognosis of sustained atrial fibrillation with no cardiac disease
<3 months - good either technique (quinidine or DC cardioversion)
>3 months better with DC cardioversion,
Risk of re-fibrillation
what is the Prognosis of sustained atrial fibrillation with underlying cardiac disease
Average with DC conversion
More likely to re-fibrillate
what is the Prognosis of sustained atrial fibrillation with heart failure
Poor to grave, no treatment
What other dysrhythmias are seen in horses other than 2nd degree AV block and atrial fibrillation?
Atrial premature depolarisation
Ventricular premature depolarisation
Ventricular tachycardia
Third degree AV block
Asystole
Ventricular fibrillation
List the Dysrhythmias which are not compatible with life
Asystole = lack of electrical activity,
Ventricular fibrillation = unusual in horses, leads to sudden death
How can be treat ventricular dysrhythmias in horses
Lidocaine,
Magnesium,
Procainamide,
Amiodarone
When is pharmacological management of acute tachyarrythmias in the horse warranted
Evidence of poor cardiac function (clinical signs)
Poor perfusion/ evidence of this
Malignant arrythmia = HR over 100bpm, multiform or polymorphic complexes, R-on-T
What is the first line treatment for ventricular tachycardia
Lidocaine
List the CNS adverse events associated with lidocaine to treat ventricular dysrhythmias
Nystagmus, muscle twitching, disorientation, excitement, convulsions
when is magnesium used to treat ventricular dysrhythmias
if lidocaine treatment has failed
When when can lidocaine treatment of ventricular dysrhythmias not be as effective
in hypokalaemia
Describe what is seen on ECG with Torsades de pointes
Undulating baseline with no beginning or end to the complexes
basically looks wavy
what is the prognosis for a horse with Torsades de pointes on ECG
BAD
this rhythm is not associated with life
List 4 causes of bradyarrhythmias in the horse
Drugs,
Electrolyte derangements,
Intestinal disease,
Primary myocardial disease
Describe how we can manage bradyarrhythmia’s in horses
Relevance of 2nd degree AV block is unknown, likely require further investigation if persistent at exercise,
Anticholinergics = Glycopyrrolate, atropine, hyoscine (buscopan),
Ventricular pacemaker
