Dysrhythmias and poor performance Flashcards
Equien HR?
Resting: 2-42bpm
Can raise to 240 in exercising thoroughbred
Trot up to 140 in normal horse
when are dysrrhymias often seen?
during cool down when parasympathetic tone is highest
Common types of dysrhythmia?
When to investigate dysrhythmias?
- Vetting – always listen at rest prior to examination, straight after exercise and
during cooldown. - Heart rate or rhythm disturbance is detected by auscultation (often as part of a
routine clinical examination) - Relevant clinical signs of cardiac disease (CHF, oedema, cough)
- Client concerns
- Poor performance
- Collapse
How do we invesitgate?
ECG
How do we do ECG diagnostic?
- Exercising ECg often to decide if horse is at risk
- need to reach max exercise depending on breed and rq work
What does a normal equine ECG look like?
o P wave: large atria, often bifid
o QRS Complex: variation common
o T wave: changes during exercise
o PR interval
o RR interval
DESCRIBE 2nd ° Av block
o Common in fit/athletic horses at rest
o Due to high vagal tone
o Disappear with exercise/excitement or atropine administration
What primary cause of dysrhythmias?
isolated electrical disturbance
2ary causes of dysrhythmias?
- Structural heart disease
- Metabolic and endocrine disorders
- Systemic inflammation
- Hypotension, haemorrhage, anaemia and ischaemia
- Autonomic influences
- Toxicosis
- Drugs
Describe Atrial Fibrillation
o The most common cardiac dysrhythmia in horses
o Can be associated with poor performance and exercise intolerance
o Caused by irregular depolarization of the atrial myocytes
Clinical signs of AFib?
- Irregularly irregular rhythm -> intermittent long pauses with rapid runs
- Maybe no CLs
- Exercise intolerance (without cardiac structure change Afib will only affect performance in intense exercise)
- Signs of CHF
What are the two classifications of Atrial fibrillation?
- Lone atrial fibrillation
- Atrial fibrillation with concurrent cardiac dx
Describe lone atrial fibrillation?
- Irregular rhythm without evidence of cardiac disease
- Young athletic horses (4.9% of racehorses in Hong Kong)
- Sudden onset exercise intolerance
- Often develops during/immediately afterstrenuous exercise
- Revert to normal rhythm within 24h - 48h with no treatment
Describe Atrial fib with concurrent dx?
- Elderly horses with loud murmurs of MR
- Moderate to severe resting tachycardia with dysrhythmia: 50 bpm – 100 bpm
- Clinical signs of CHF: exercise intolerance, dyspnoea, oedema, weight loss, collapse
- Need further investigation and treatment
Diagnosis of A fib?
- PE & Hx
- Irregular heartbeat & pulse - ECg -> definitive diagnosis
- Echocardiography eval of underlying dx)
- Exercise ECG
Afib on Echo?
- Assess any regurg present?
- Assess structural abn
- Most likely atrial dilation
-> if structural abn -> tx likely unsuccessful
Exercising ECg for Afib - do we need to convert?
- If severe tachycardia present during exercise they are unsafe to ride as they
are an increased risk of sudden cardiac death - Assess for any ventricular tachycardia
- Must be done prior to commencing any treatment
Prognosis for Afib?
- HR >60 considered a poor prognostic marker
- Inc atrial flutter rate inc lieklihood of recurrence
- Atrial enlargement => poor prognostic marker
- Duration. foA-fib matters (remodelling of atria!)
- Lone A fib or recent onset = better prognosis
Treatement for Afib?
- conversion to normal sinus rhythm-> Exmaple: Transvenous electrical cardioversion (TVEC)
Describe TVEC?
- Widely performed in referral
- Cardioversion catheters placed in pulm artery and right atrium
- Synchronised electrical shock under GA
- Sotalol used prior to and after TVEC
Medical tx - Afib?
-> Quinidine sulphate
-> Amiodarone
Describe quinidie?
- Class IA anti-arrhythmic drug
- PO administration via NGT
- Repeat q2h until the rhythm converts to NSR
- Only applied in horses with no systemic illness
- Side effects: colic, diarrhea, tachycardia, urticaria, oedema of nasal mucosa, ventricular arrhythmias
Describe Amiodarone?
- Class III anti-arrhythmic drug
- IV CRI administration
What tx for cases showing signs of CHF at time of diagnosis?
o Supportive care before conversion trial
o Treatments to relieve signs of CHF: diuretics (e.g. furosemide)
o Improve ventricular response to fibrillating atria (e.g. digoxin)
o Conversion to NSR
o Poor prognosis though
Summarise approach to A fib?
DESCRIBE POST-NSR CONVERSION MONITORING?
- Echo & 24h holter post NSd conversion
- Anti-arrythmic drug (solatol) to prevent recurrence
- Rest -> 4 weeks + periodical auscultation
What causes primary tachyarrythmias?
Myocardial dx -> infectious, immune-M, toxic, nutritional, neoplastic ..
Tachyarrythmais can also be 2ary to what factors?
- Associated with non-cardiac causes
- Hypoxia (e.g. dynamic airway obstruction in athletic horses)
- Endotoxemia,septicemia, SIRS
- Electrolytes and/or acid-base imbalance
Describe Atrial PRemature contractions and wether to worry about them
- On auscultation there will be premature beats interrupting the NSR
- Rarely cause performance issues on their own
Biggest concern:
* Ability to incite a-fibrillation or a-flutter
What is Atrial premature contraction associated with?
o Often associated with primary myocardial disease
o Ectopic premature atrial activation
o Abnormal P with normal QRS-T
What abnormalities to note with premature atrial contractions?
- Change in P wave morphology
- QRS often normal BUT
- QRS can be wide and biazrre
Describe VPCs?
- On auscultation there will be premature beats interrupting the NSR
- Normally a compensatory pause following a VPC
- The abnormal beat will often sound loud
- Wide and bizarre QRS complex
What are VPCs associated with and what will we see?
o Often associated with secondary to other causes
o Abnormal QRS-T
o The more complex and variable the VPCs, the higher the risk
Management for tachyarrythmias?
o Primary goal istreating the underlying cause
- Often requires steroidal therapy
- Any infections treat those
o Anti-arrhythmic drugs
* Lidocaine and magnesium frequently used
* Beta-blockers can help
* Can consider digoxin if life threatening
Prognosis for tachyA?
- If lone VPC that is obliterated during exercise risk is small
- If occurring just after exercise can be associated with parasympathetic
tone and normal - If it occurs in exercise then serious concern
- Only consenting adults should ride these horses
Should. urest VPC?
yes at least >6months
Describe high degree heart blocks?
o High grade 2º AV block or 3º AV block can result in syncope and collapse
o More frequently seen in donkeys and mules
o Management: pacemaker
