Equine cardiovascular system Flashcards
What is the difference between normal and abnormal jugular pulse?
Normal: lower third of neck
Abnormal: higher than lower one third when neck upright
Describe the four heart sounds in a horse
S1 (lub)- closure of AV valves, opening of semilunar valves, initial ejection of blood
S2 (dub)- closure of semilunar valves
S3 (ahh)- end of rapid filling phase
S4 (ba)- atrial contraction
What are normal heart sounds generated by?
Turbulence of blood
If cardiac sounds are absent or diminished, what could you suspect?
thick chest wall (draft horse), pericarditis, pulmonary consolidation, diaphragmatic hernia
What is the normal equine HR?
26-44 BPM
What is the preferred method of evaluating the equine heart?
Echocardiography
What are radiographs most helpful for?
Evaluation of extent of pulmonary involvement in suspected cardiac case
What is the automaticity order of the cardiac nodes?
SA node –> AV node –> HIS –> myocardial cells
What are three causes of changes in automaticity?
Alterations in autonomic nervous system tone
Alterations in electrolyte status
Presence of drugs/disease
What is ectopic foci?
Cells outside pacemaker centers developing membrane characteristics similar to those of pacemaker cells
What is torsades de pointes?
Atypical rapid ventricular tachycardia with periodic waxing and waning of amplitude of the QRS complexes on the ECG as well as rotation of the complexes about isoelectric line
Conduction through the AV node is profoundly affected by what?
Vagal tone- predominates at rest in horse
What is the most commonly used lead in equine?
Bipolar lead- base –> apex
How are the leads placed on the horse?
Positive lead on left thorax
negative lead on right jugular furrow
ground lead at any point away from heart
Electrocardiogram is most commonly used for what?
detection of dysrhythmias
T/F: It can be normal to see 1st degree AV block in a horse
TRUE
What is the most frequent manifestation of high vagal tone in the normal horse?
Second degree AV block
What is the difference in Mobitz type I and Mobitz type II?
Mobitz Type I (wekenbach)- gradual increase between S4 and S1 before beat dropped
Mobitz Type II- fixed interval between S4 and S1- PATHOLOGIC
What arrhythmia has complete AV dissociation and requires electrical pacing for the tx?
Third-degree AV block
What is the most common PATHOLOGIC arrhythmia of the horse?
Atrial fibrillation
Why are horses predisposed to developing A-fib in normal atrial tissue?
large atrial surface area
What are the two forms of A-fib?
Paroxysmal: occurs during race and can disappear with deceleration of HR (furosemide pre-race or oral bicarbonate pre-race can cause this)
Sustained
What is the treatment used if the HR <60
Quinidine therapy
What is the treatment used if the HR > 60
Digitalize first (digoxin)
What is the treatment used if HR > 60 and no underlying disease is found?
Digitalize first, then convert to quinidine once HR decreased
What is the treatment used if HR > 60 and underlying cardiac disease?
treat for heart disease
When would you use IV vs. oral quinidine?
IV- arrhythmia developed within 72 hours
Oral- arrhythmia persisting longer than 72 hours
What is the MOA of quinidine?
blocks fast inward Na current in myocardium causing increased myocardial refractory period and decreased conduction velocity
What is acute toxicity of quinidine treated with?
IV sodium bicarbonate- promotes quinidine binding and decreases amount of active drug
What is the maximum dose of quinidine that should NOT be exceeded?
12 mg/kg IV
How many VPCs are diagnostic of VT?
4+
What is the initial/most frequent used therapy for VT?
Lidocaine
What drug is used to treat refractory ventricular tachycardia?
Propafenone
What drug is used to treat life-threatening ventricular tachycardia or v-fib?
Bretylium tosylate
