Lecture 11: Approach to Cardiovascular Disease of the Horse Flashcards
Horses heart have a high resting vagal tone- what does that mean
high parasympathetic tone, little to no sympathetic tone at rest
horses high vagal tone predisposes them to __
arrhythmias
benign, vagally mediated arrhythmias should disappear during ___
exercise
what is a common sample of a vagally mediated arrhythmia that should disappear with exercise
2nd degree AV block
What is normal HR
26-50bpm
what is max HR during exercise
220-240
Horses have extensive ___branching that results in simultaneous depolarization of ___
purkinkje fiber branching, ventricles
QRS complex only useful for deterring __ and ___
rate and rhythm
T of F: QRS complex gives you info on size and ectopic focus
false
__-___ heart sounds can be auscultated in normal horse
2-4
what are the 4 heart sounds and which ones do you always hear
S1- AV valve closure (lub)
S2- semilunar valve closure (dub)
S3- ventricular filling
S4- atrial systole
what is a murmur
abnormal heart sound
if you have a murmur between S1 and S2 what type of murmur is it
systolic murmur
if you have a murmur between S2 and S3 what type is it
diastolic murmur
what 4 things do you characterize a murmur by
timing, shape, point of maximal intensity, intensity level
diastolic decrescendo murmur/ aortic regurgitation is common in ___
older geriatric horses
PDA is common in __
newborn foals
what is a grade 1 heart murmur
soft and not easily heard, localized
what is a grade 2 heart murmur
soft but easily heard, heard consistently over PMI
what is a grade 3 heart murmur
moderate intensity, heard immediately and consistently, small area of radiation
what is a grade 4 heart murmur
loud, audible over a wide area, no palpable thrill
what is a grade 5 heart murmur
loud, radiating, and with palpable thrill
what is a grade 6 heart murmur
loud with palpable thrill and audible with the stethoscope held slightly away from chest wall
what are some indications for performing an ECG
- Murmur
- Poor performance/ exercise intolerance
- Syncope
- Weakness
- Significant electrolyte imbalances
- Unexplained bradycardia or tachycardia
where are the leads placed for base-apex ECG
black lead- left fifth ICS at level of olecranon
Red lead- right jugular furrow 2/3 of the way from the mandible and thoracic inlet
White lead- right shoulder
what do P waves indicate, and what heart sound
atrial depolarization, S4: atrial systole
What does QRS indicate and what heart sound
ventricular depolarizaztion, S1 AV valve closure
what does the T wave indicate and what heart sounds
ventricular repolarization, S2 semilunar valve closure followed by S3 ventricular filling
normal or abnormal- identify problems if present
Red line is 10 seconds
Normal sinus rhythm
normal or abnormal- identify any problems- red line= 10 seconds
Sinus bradycardia: Atrial and ventricular rats <24
normal or abnormal, identify any problems. Red line = 10 seconds
Sinus tachycardia. Atrial and ventricular rates= 90
normal or abnormal- identify any problems. Red line =10 seconds
2nd degree AV block- no all P waves followed by QRS complex
are 2nd degree AV blocks always pathological?
no- they may disappear with exercise
normal or abnormal- identify problems if any. Red line= 10 seconds
Atrial fibrillation
are atrial fibrillations always pathological
yes
normal or abnormal- identify problems if any. Red line= 10 seconds
missing complex- problem with SA node
Dx: sinus block and sinus bradycardia
How do you measure atrial rate on ECG
count p waves over 10 seconds then multiply by 6
how do you measure ventricular rate on ECG
count QRS complex over 10 seconds and multiply by 6
what does an echocardiography tell us/measure
- Chamber size
- Wall thickness
- Valves
- Hemodynamics
what are some indications for cardiac work up in athletic horse
- Non-physiologic arrhythmia
- Murmur that increases in intensity over time
- 3/6 heart murmur with mitral or aortic regurg
- 4/6 heart murmur with tricuspid regurg
- Congenital heart disease (VSD)
- Continuous or systolic- diastolic murmurs
- Signs of myocardial disease
- Signs of CHF
horses with what conditions (3) should not be ridden
- Signs of CHF
- Signs of pulmonary hypertension
- Complex ventricular arrhythmias
a “lone” a-fib refers to an “a-fib” with no __
underlying cardiac disease
a-fib clinical signs only noted during __
strenous exercise
what is the likely cause of A-fib
random re-entry mechanism
how does a normal heart prevent re-entry mechanism
impulse generated and travels then refractory period occurs and impulse dies and another one can’t be regenerated
describe how re-entry occurs when the “path is longer”/heart is bigger
by the time the impulse returns to the heart, the refractory period has ended, impulse transmitted again
describe how re-entry occurs when an impulse travels slowly/slow heart rate
by the time the impulse returns the refractory period has ended, impulse transmitted again
what is the tx/protocol for atrial fibrillation
- ECG to confirm rhythm
- Echo to assess structure and hemodynamics
- Cardioversion
what is the drug of choice for cardiac conversion during A-fib
quinidine sulfate
What is quinidine sulfate and how does it work
class 1a anti-arrhythmic
Blocks fast sodium channels, increase duration of action potential and lengthen effective refractory period
how do you administer quinidine sulfate and what dose and when do you stop
22mg/kg q2hr via nasogastric tube until
1. Conversion to sinus rhythm
2. Development of toxic side effects
3. Max 6 doses
what drug may be useful for short duration a-fib <2 weeks
quinidine gluconate
if a patients heart rate is greater than 60 with A-fib treat first with __
digoxin
With a-fib, digoxin is indicated to slow to slow ventricular rate < 60bpm prior to __therapy
quinidine
how does digoxin work
- Positive ions trope- inhibition of Na/K ATPase- increase contractility
- Negative chronotrope- increases vagal tone
valvular heart disease is secondary to __, ___, ___, __
infection, inflammation, degenerative disease, trauma
what are the most common organisms cultured from valvular heart disease
actinobacillus, streptococcus
__valve disease is the most common cause of HF in horses
mitral valve disease
Aortic insufficiency very common in __
older horses
18yr old Arabian gelding presented with depression, breathing very hard, P=64, R=48, grade 5/6 heart murmur, crackles on thoracic auscultation. The following ECG and echo were obtained- what is wrong
ECG: sinus tachycardia
Echo: ruptured chordae tendinae of mitral valve
what are some appropriate treatments for CHF
- Digoxin
- Diuretics/ furosemide
- ACE inhibitors- benazepril
what are the appropriate tx for myocardial disease
- Gastric lavage, absorbants
- Corticosteroids
- Antibiotics
- Rest
- Management of HF
ionospheres are commonly added to cattle feed to prevent coccidiosis, toxic to horses at __% of cattle dose
10%
ionophore toxicity affects what
cardiac myocytes, myonecrosis
ionophore toxicity decreases __ function
systolic function
what are some clinical signs of ionophore toxicity
weakness, sweating, colic, tachycardia, tachypnea, muffled heart sounds, arrhythmias
t or f: ionophore toxicity is often fatal
true
what is tx for ionophore toxicity
activated charcoal, supportive care
what are cardiac troponins
molecules of contractile mechanism in skeletal, cardiac muscle
troponins complex are made up of __, __, __ proteins
I, T, C proteins
cardiac troponins (cTnI) often measure in horses with __
myocardial damage
what are some causes of pericardial disease
infectious, immune mediated, neoplastic
what is the most common bacteria isolated in pericardial disease
actinobacillus equuli
what is tx for pericardial disease
pericardiocentesis, pericardial lavage, antibiotics, supportive care
what is prognosis for pericardial disease caused by actinobacillus equuli
guarded prognosis
what is tx for pericardial disease caused by actinobacillus equuli
- Hospitalization
- Long term antibiotics- ampicillin and rifampin
- Supportive care
aortic root rupture results in ___
sudden death
what is classic presentation of aortic root rupture
older breeding stallion
aortic root rupture occurs in higher incidence in what breed
friesian horses
you are the owner of a successful racetrack practice. Speedy, a 4 years old thoroughbred stallion, presents with a history of decreased performance in his last few races. On your initial physical exam you find temperature of 100.2 F, respiratory rate of 20, heart rate of 52 and a heart rhythm that was irregularly irregular.
What is most likely cause:
A. Ventricular tachycardia
B. Ventricular fibrillation
C. Atrial fibrillation
D. 2nd degree AV block
C. Atrial fibrillation
you are called out to do a wellness visit on 28yr old Morgan gelding, Tex who spends time as a pasture ornament. In the course of your physical exam you note a heart rate of 44 and grade 2/6 diastolic decrescendo murmur at the left fourth intercostal space
Which of the following do you tell the client:
A. Its a tricuspid insufficiency, recommend an echo
B. It’s mitral valve insufficiency, recommend an ECG
C. It’s pulmonary stenosis, recommend an echo
D. It’s aortic regurgitation, recommend a recheck at next visit
D
dx ECG
Sinus bradycardia- every P wave followed by QRS but HR <26bpm
dx ECG
Sinus Tachycardia- every P wave followed by QRS, but HR >50bpm
dx ECG
sinus arrhythmia- RR intervals irregular, but every P wave followed by QRS
dx ECG
sinus block- RR interval equal to 2 normal RR intervals
dx ECG
atrial premature contraction- P wave occurs prematurely and followed by normal QRS-T complex
dx ECG
atrial fibrillation- P waves absent, f-waves present. Normal QRS but RR intervals irregular
dx ECG
2nd degre AV block- P wave not followed by QRS complex
dx ECG
Third degree AV block- no relationship between P waves and QRS, PP intervals regular. First QRS complex is escape beat
dx ECG
Premature ventricular contraction- no P wave before QRS. T wave is positive deflection. Short RR interval. also 2nd degree AV block following
Dx ECG
Ventricular tachycardia- two VPCs followed by normal P-QRS-T
dx ECG
Ventricular fibrillation- no normal QRS or T-waves
dx ECG
Muscle tremor causing sharp narrow deflections
dx ECG
ECG during exercise- T waves are large and in opposite polarity to QRS, P waves no longer visible as they are incorporated in preceding T waves
if the SA node doesn’t fire what is missing from ECG
p wave
if AV node doesn’t conduct what is missing from ECG
QRS
