Exam #4: Equine Cardio Flashcards
Normal adult horse heart rate
26-50 bpm
Exercise max heart rate in horses
240 bpm - no time for diastolic filling = decreased CO
True or false - vagal arrhythmias are common and usually benign in horses
TRUE - horses have high vagal tone at rest
Normal foal heart rates from birth-2 months
- Birth = 40-80 bpm
- Next several hours = 120-150 bpm
- First week = 80-100 bpm
- Adult rate by 2 weeks (26-50 bpm)
What type of murmur occurs between S1 and S2, QRS and T?
Systolic murmur
What type of murmur occurs between S2 and S1 and T wave to QRS?
Diastolic murmur
What are the characteristics of vagal murmurs?
- Slow to normal HR (not tachycardic)
- Audible S4, S1, and S2
- Disappear if you increase the heart rate > 50 bpm
S1 heart sound indicates…
Closing of AV valves
S2 heart sound indicates…
Closing of semilunar valves
S3 heart sound indicates…
End of rapid diastolic filling
S4 heart sound indicates…
Atrial contraction
Bee-dum–bump indicates what and what makes it go away usually?
2nd degree AV block - goes away with sympathetic stimulation by raising the HR > 50 bpm
How can you differentiate A-fib from 2nd degree AV block or sinus arrhythmias?
No S4 with A-fib
True or false - being able to hear more than S1 and S2 in a horse is normal
TRUE
What can the base apex ECG lead system diagnose and not diagnose?
- Can dx arrhythmias
- Cannot dx enlargement patterns like conduction blocks, etc
What about the horse cardiac conduction system makes the ECG recordings different, compared to humans or small animals?
Purkinje fibers go deep into the ventricular myocardium, from endo to epicardium = FAST depolarization
ECG lead placement for lead I and II in the base apex system - WHERE DO WE PLACE THE ELECTRODES
- Lead I = negative right arm, positive left arm
- Lead II = negative right arm, positive left foot/leg
- Negative right arm (I, II) = 2/3 way down the jugular furrow
- Positive left arm (I) and positive left leg = caudal to left elbow
Normal P wave morphology on equine ECG
Notched, usually positive but complete inversion can occur
Wandering pacemaker = strange P wave morphology = normal in a high vagal tone horse
Normal QRS morphology on equine ECG
> > rS complex
- “r” = small positive deflection
- “S” = large negative deflection
Normal T wave morphology on equine ECG
- Uni or biphasic
- Positive, negative, or combo
- Normal as long as it doesn’t have a larger amplitude than QRS
- Ta = atrial repolarization (after P wave) = due to large muscular heart (may show up on ECG)
How do you measure HR in a horse on ECG? Normal? Bradycardic? Tachycardic?
> Count QRS complexes in 6 seconds, then multiply by 10
- Normal = 26-50 bpm
- Bradycardia = < 26 bpm
- Tacycardia = > 50 bpm
How do you determine if there’s a regular rhythm on ECG?
- P waves present?
- P wave for every QRS?
- QRS wave for every P wave?
- Atrial and ventricular rates are similar?
- Ectopic beats?
- Pattern to irregular rhythms, or is it irregularly irregular?
Difference between type I and type II second degree AV block on ECG? Which is normal and abnormal?
- Type I = variable PR intervals = NORMAL
- Type II = fixed PR intervals = ABNORMAL
Dx? Irregular rhythm, tachycardic, no P waves, normal QRS and T waves
A-FIB
Normal QRS and T = supraventricular in origin
What is the most common pathologic rhythm in horses?
A-FIB
Non-cardiac causes for equine arrhythmias (6)
1) Excitement
2) Fever
3) Toxemia/septicemia
4) Colic - vagal afferents lining the GI tract
5) Electrolyte abnormalities
6) Acid-base disorders
Pathologic arrhythmias in horses (7)
1) A-FIB
2) Atrial premature beats
3) Ventricular premature beats
4) Supraventricular tachycardia
5) Ventricular tachycardia
6) 2nd degree AV block type II
7) 3rd degree AV block
Mechanism of A-FIB in horses
> Uncoordinated depolarizations in the atria
- Can occur w/o atrial enlargement or pathologic heart disease
- Induced by autonomic NS imbalance
- Sympathetic tone on vagal tone
- Can occur in normal horses
- Persistent AF may result in heart disease
Characteristics of A-FIB
> Irregular, supraventricular, no P waves, tachycardic
- Ventricular response is usually normal (26-50 bpm)
- No S4 sounds audible
- See marked irregularity in the R-R intervals at rest
- May see variable QRS duration, amplitudes, and polarities
Causes of A-FIB
1) Idiopathic or “lone”
2) Underlying cardiac disease, Ex: myocardial, AV regurg, CHF
3) Electrolyte or acid-base abnormalities, Ex: racing (sweat), colic, other illness
4) Anesthetic drugs or tranquilizers
What breeds is A-FIB common in? (3)
- Thorougbreds
- Standardbreds
- Draft breeds
Diagnostic work-up for A-FIB
- CBC = looking for inflammation or infection
- Electrolytes, esp. K+, Ca++
- Venous blood gas concentrations = alkalosis that affects K+
- ECG
- Echo
- Cardiac troponin test for cardiac disease
What can happen with A-FIB progression if not treated?
- Decreased diastolic perfusion of the atria = fibrosis
- Dilation = pull valves apart = valvular insufficiency
Options for treatment of acute A-FIB?
- CORRECT UNDERLYING ABNORMALITIES = lyte imbalances, dehydration
- Medical - quinidine or flecanide
- Cardioversion
What is the treatment of choice for lone/idiopathic A-FIB?
Quinidine- given orally (REQUIRES A STOMACH TUBE), treatment stops at conversion
Side effects of quinidine
- Skin - urticaria
- Nasal edema
- Colic and diarrhea (after several doses)
- Arrhythmias = after 4 or more doses, due to myocardial changes
Medical options (2) for acute A-FIB tx, similarities and differences
- Quinidine = oral w/ stomach tube
- Flecanide = used parenterally (not safe orally)
- Side effects = colic, diarrhea, arrhythmias, urticaria, nasal edema
What do you administer as an antidote in a flecanide or quinidine overdose?
Sodium bicarb (NaHCO3)
What drug do you use if the animal has a HR > 50 bpm, atrial enlargement, or failed to convert with quinidine for A-FIB?
Digoxin (SHOULD ECHO FIRST to determine atrial diameter)
*Increases vagal tone = slows HR and AV node conduction
Treatment of choice for A-FIB - those who are chronic and fail to respond to medical conversion, or have relapsed after conversion
> > Cardioversion
- Usually successful and has a return to athletic ability (even with chronic AF)
- High conversion rate and low relapse
- Requires general anesthesia
- Minimal complications
What drug might you try, to treat A-FIB, if quinidine or quinidine+digoxin doesn’t work?
Amiodarone
What drug can you use to control the heart rate with A-FIB, but doesn’t work to convert them?
Diltiazem - Ca++ channel blocker
True or false - audible S4, irregular rhythym, normal HR is indicative of a pathologic murmur/rhythm
FALSE - most likely a benign sinus rhythm (could still be A-FIB
Dx? Normal QRS and T waves, normal P waves, but a block in conduction
2nd degree AV block
True or false - horses with a-fib are usually asymptomatic at rest, but become symptomatic with exercise
True
What PE signs should you pay attention to with heart murmurs?
- Heart rate, rhythm, sounds audible (S4? Irregular rhythm?)
- Lung sounds for edema
- Mucous membranes (poor perfusion)
- Edema = generalized, pain, temperature
- Jugular vein distension or pulsations
- Strength of arterial pulses
- LN’s
- Tachycardia
- Muffled heart sounds
- Exercise intolerance, syncope, weakness
What heart disease/valve disease do we see water hammer pulses with?
Aortic insufficiency and leakage
How do you interpret if a murmur is pathologic or not?
- Clinical signs?
- Location in cardiac cycle - diastolic? systolic (more likely benign)?
- Intensity = higher = more pathologic
- Shape or frequency of murmur
- Radiation = more pathologic
- PMI
Which murmur sounds like a dive-bomber?
Aortic valve regurgitation
How do you determine if the murmur is systolic or diastolic?
- Palpate for a peripheral pulse = at the same time = systolic
- Look at a phonocardiogram
Differences between grades of murmurs
> Grades 1-6
- Grades 5 & 6 = palpable thrill
- Grade 4 = no thrill but loud and radiates
Are ejection murmurs systolic or diastolic?
Systolic
What shape are regurgitant murmurs?
Plateau
What shape are diastolic murmurs?
Decrescendo
Lesion if murmur is at the left apex
Mitral v. (point of elbow)
Lesion if murmur is at the left base
Aortic, pulmonic v. (underneath the triceps m)
Lesion if murmur is on the right side
Tricuspid
Also = PDA’s, VSD’s
What is the PMI and radiation with ejection murmurs (not usually pathologic)?
Localized (doesn’t radiate), usually at left base
What is the PMI and radiation with mitral valve regurgitation?
Radiation, usually left apex towards the base
Characteristics of functional/non-pathologic murmurs in horse?
- Low to moderate intensity (grade 1-3)
- Usually an ejection pattern, peaks in mid systole
- Usually localized at left heart base
- Ends before S2 (not diastolic)
- No radiation
- Normal HR
- Normal arterial and venous pulses
What is a common location for benign and functional heart murmurs?
Left base - localized, no radiation
Conditions/type of horse that functional murmurs are common in ? (3)
1) Foals
2) Fever
3) Anemia
What are characteristics of normal foal murmurs?
> Systolic for 2-4 months
- Heart base
- Continuous murmurs or heard on both sides of chest
- Low grade (should exam grades > 3)
- No cyanosis
Which foals should have cardiac work-ups, aka pathologic murmurs?
- Intensity = grade > 3/6
- Cyanotic
- Premature or dysmature foals
- Murmur radiates over a large area and is present on both sides
- Marked tachycardia (> 100 bpm)
- Marked dyspnea or tachypnea
- Abnormal venous or arterial pulses
Most common foal congenital defects
PDA, VSD
Dx? systolic or continuous murmur, goes away within 3 days
PDA
Dx? PMI on right side, softer relative murmur on the left side (volume overloads, ejection murmur)
VSD
Dx? PMI at left heart base or right side, cyanotic foal
Tetralogy of Fallot
True or false - louder VSD’s are usually pathologically worse
FALSE
True or false - patent foramen ovale and ASD’s are commonly benign
TRUE
What should you always do if you suspect a congenital cardiac defect?
ECHO THE ANIMAL = may have other defects
When, in the cardiac cycle, do you hear mitral valve regurg?
Holosystolic - loudest at left apex
When, in the cardiac cycle, do you hear aortic valve regurg?
Holodiastolic - loudest at heart base
When, in the cardiac cycle, do you hear tricuspid valve regurg?
Holosystolic - loudest on right side
When, in the cardiac cycle, do you hear pericarditis?
Continuous
Which valve is most commonly affected with acquired degenerative valve disease?
Aortic»_space; mitral»_space; tricuspid
*More common in older horses (> 8 yo)
Clinical signs of decompensated heart disease
- Exercise intolerance
- Cough
- Changes in endurance
- Respiratory distress
- Tachycardia
- Weak pulses
- Loud murmur with radiation
- Peripheral edema
- Weight loss
- Hyponatremia, pre-renal azotemia
True or false? - Hyperkinetic pulses are compensated
True
Dx? Loud systolic plateau shaped murmur at left heat apex with radiation to the left base
Mitral valve regurg
Short and long term complications from mitral valve dz
- LA enlargement
- AF develops
- Left sided heart failure
- Decreased stroke volume = activate RAAS
- Eventual CHF
Dx? Divebomber, loud, holodiastolic murmur at heart base, bounding arterial pulses (LV overload)
Aortic valve disease
How do we monitor if the heart disease is decompensating?
> > Monitor HR
- Increase in resting heart rate = sustained 5 bpm or more
- Failure to return to resting heart rate within 20 min of exercise
Treatment of degenerative valve disease
> Prognosis is guarded
- Furosemide
- Digoxin if there is CHF
- ACE inhibitors aren’t very helpful
- Hydralazine = arterial dilator
Dx? Holosystolic plateau shaped murmur, fever, exercise intolerance, tachycardia, jugular venous pulsations, weight loss
Bacterial endocarditis
Three top etiologic agents for bacterial endocarditis
1) STREPTOCOCCUS
2) Trueperella pyogenes
3) E. coli
Clin path lab findings with bacterial endocarditis
- Neutrophilic leukocytosis
- Anemia of chronic infection
- Hyperproteinemia due to hyperglobulinemia
- Positive blood culture
Treatment of bacterial endocarditis
- ANTIBIOTIC based on C&S, frequently is a parenteral beta lactam
- Combine with RIFAMPIN
- For 4-6 weeks
Dx? Petechial hemorrhage, edema (commonly in head, neck, limbs), sloughing of the skin
Vasculitis
DDx for causes of peripheral edeam
- Heart disease
- Vasculitis
- Hypoproteinemia (liver disease)
- Trauma or injury
- Neoplasia
- Decreased activity “stocking up”
- Lymph system dysfunction = lymphadenopathy, lymphadenitis, lymphangitis, lymph obstruction
Characteristics that help you differentiate vasculitis from CHF or hypoproteinemia edema
- Localized
- Warm
- Non-pitting
- Painful
- Leakage of serum
- Evidence of petechial hemorrhage
Causes of vasculitis (6)
1) Purpura hemorrhagica = previous or constant exposure to Strep, vax after infection = immune complexes in endothelium
2) Equine infectious anemia
3) Equine viral anemia
4) Anaplasma phagocytophila
5) Allergic
6) Idiopathic
Diagnosis of purpura hemorrhagica
- Skin biopsy for immune complexes
- High Strep. equi titer
Diagnosis of equine infectious anemia
Coggins or ELISA
Diagnosis of equine viral arteritis
Virus neutralization, IHC, PCR
Diagnosis of equine granulocytic anaplasmosis (Anaplasma phagocytophilum)
- Morulae in neutrophils or eosinophils on peripheral blood smear
- PCR from buffy coat
Treatment of purpura hemorrhagica vasculitis
- Pencillin + corticosteroids
- Supportive care = hydrotherapy, bandaging
Treatment of Anaplasma phagocytophilum vasculitis
- Tetracyclines - oxytetracyclines + corticosteroids
- Supportive care = hydrotherapy, bandaging
What do we use in horses - prednisone or prednisolone?
Prednisolone
