Exam 2 - Equine Cardiology Flashcards
what is the maximum heart rate of a horse during exercise?
250 bpm
what may the client report in terms of cardiac history of their horse?
poor performance, exercise intolerance, lethargy, collapse (syncope), & lethargy
what may the veterinarian note as abnormal on the cardiac exam of a horse?
tachycardia, arrhythmia, murmur, abnormal pulses, venous distention/jugular pulses, & abnormal mucus membranes/CRT
what points do you listen to on the left side of the horse during cardiac evaluation?
pulmonic valve - 3rd intercostal space/rib
aortic valve - 4th intercostal space/rib
mitral valve - 5th intercostal space/rib
what points do you listen to on the right side of the horse during cardiac evaluation?
tricuspid valve - 4th intercostal space/rib
how many heart sounds can be heard in a healthy horse?
4
you are listening to a 15 year old Thoroughbred gelding and detect a diastolic murmur on the left side at approximately the 4th ICS. what do you expect is affected? do you think this is pathologic or innocent? why?
aortic valve - valvular disease
pathologic - degenerative or idiopathic
older horse - no other signs given, but could see bounding pulses if volume overload is present
what does s4 correspond with?
atrial contraction
what is the first sound heard in each cardiac cycle?
S4 - atrial contraction
where is S4 best heard?
best heard near the apex of the heart
in relation to an ecg, when does S1 occur?
conclusion of QRS complex
what does S1 correspond with in the cardiac cycle?
onset of ventricular contraction (systole) - closure of the AV valve
what are some causes for an accentuated S1 sound?
increased sympathetic tone
thin animal
anemia
fever
what are some causes for a diminished S1 sound?
obese animal
pleural/pericardial fluid
decreased contractility
where is S1 best heard?
apex of the heart
in terms of frequency & duration, how does S1 compare to S2?
S1 is lower in frequency & longer duration in sound
what does S2 correspond with in the cardiac cycle?
termination of systole - closure of semilunar valves
in relation to an ecg, when does S2 occur?
coincides with or comes just after the T wave
why can S2 sometimes be ‘split’?
the closure of the aortic & pulmonary valves isn’t simultaneous
where can S2 be heard best?
best heard at the base of the heart
what does S3 correspond with in the cardiac cycle?
early diastole - rapid/passive ventricular filling
where is S3 best heard?
best heard at the apex
what heart sound can sometimes sound like a ‘squeaky gate’?
S3
what is an ecg especially helpful for evaluating?
arrhythmias
what does an echocardiogram assess?
heart structure, contractions, valvular competence, evidence of pericardial effusion etc.
what lab tests may help when assessing cardiovascular health?
cardiac troponin I for inflammation
CBC/fibrinogen/SAA
chemistry panel - renal & muscular values
blood culture - endocarditis
what diagnostic test is critical for evaluating an arrhythmia?
ecg
where do you put the leads of an ecg on a horse for a standing base/apex reading?
positive over the left heart apex
negative in the right jugular furrow
how does an ecg of a horse differ from one in small animals?
P wave is often notched
QRS complex is mostly negative
why do horses get physiological arrhythmias?
result from high vagal tone
how can you test a horse for a suspected physiologic murmur?
can get rid of it by elevating the heart rate/sympathetic tone
excitement/fright, exercise, or vagolytic drugs
what is the most common physiological arrhythmia that occurs in >50% of horses at rest?
second degree AV block - usually wenckebach or type-1
T/F: a physiologic murmur is associated with clinical signs
false - no clinical signs
what murmur is shown on this ecg?
2nd degree av block - p wave missing a qrs complex
when do sinus arrhythmias often occur in horses?
often occurs during heart rate recovery following exercise
T/F: sinus arrhythmias are more common in dogs than horses, but more common in horses than cats
true
what is the single most common pathological arrhythmia of the horse?
atrial fibrillation
what is the most common atrial fibrillation type seen in horses?
lone ‘afib’
other than lone afib, what other types can occur?
paroxysmal, persistent, & permanent
what is the suggested cause of lone afib?
no underlying disease cause!!
high vagal tone & large atrial myocardial volume
apart from lone afib, what other etiologies may cause paroxysmal/persistent/permanent atrial fibrillation?
atrial chamber enlargement
electrolyte/acid base disturbance
atrial myocardial disease
myocarditis
what is the primary disease cause of afib in cattle?
gi disease
what horse breeds are most commonly affected by afib?
standardbreds, thoroughbreds, & draft breeds
T/F: horses with afib are often asymptomatic
true
what clinical signs may be seen in a horse with afib?
epistaxis & poor performance
‘shoes in a dryer’ describes what arrhythmia in horses?
afib
what will be heard upon auscultation of a horse with afib?
irregularly, irregular rhythm
variable intensity of the first & second heart sound
absence of the 4th heart sound
what arrhythmia is present on this ecg?
afib
what will be seen on ecg of a horse that has atrial fibrillation?
normal QRS-T morphology, but frequency is variable
no p waves
isoelectric line undulates - fibrillation/flutter waves, f waves
why would an echo be used on a horse with atrial fibrillation?
used to look for structural heart changes - determine prognosis
what is the major finding seen on an echo of a horse with atrial fibrillation?
large left atria!!
mild decrease in shortening fraction, loss of atrial contribution to ventricular filling, & absence of the 2nd atrial opening of the mitral valve
what medication is the most common treatment given for horses with atrial fibrillation?
quinidine sulfate - class 1a sodium channel blocker
how is quinidine sulfate dosed? what are the conditions that must be met to stop dosing?
22 mg/kg via NGT
conversion to a sinus rhythm, adverse or toxic effects occur, or a total or 4-6 doses
what is the downside of using quinidine for treating afib in horses?
narrow therapeutic index: 2-5ug/mL
what are some adverse effects caused by quinidine sulfate?
lethargy, colic, diarrhea, urticaria, laminitis, nasal edema, etc
what factors influence the prognosis of afib?
structural heart changes
duration greater than 3 months
higher heart rate: >60 bpm
murmur
associated cardiac disease
what is the recurrence rate of lone afib?
15-20%
what is the prognosis for afib in horses?
many may return to full performance
this is an echo showing an enlarged left atrium - what do you suspect?
afib
what does APC stand for?
atrial premature complex
what is an APC?
premature beat originating from the atrium
VPCs are linked to what other abnormal rhythm?
ventricular tachycardia
what are APCs/VPCs?
premature beats originating in the atrium or ventricles that interrupt an otherwise regular rhythm & may be followed by a compensatory cause
APCs may cause what other arrhythmias?
afib or flutter
T/F: in a horse with APCs/VPCs, cardiac output is usually not affected at rest
true
how are APCs/VPCs diagnosed?
ecg/exercising ecg
what arrhythmia is shown on this ecg?
APCs/VPCs
how are APCs/VPCs treated?
rest for 60-120 days
anti-inflammatories
anti-arrhythmic if cardiac output is affected at rest
what is ventricular tachycardia?
defined as an abnormal rhythm caused by 3 or more repetitive or linked VPCs
what are the main concerns if a horse has ventricular tachycardia?
collapse & sudden death
how is v tach diagnosed?
ecg
what may be heard upon auscultation & seen on physical exam in a horse with v tach?
rapid, usually regular rhythm, with variable intensity, & booming heart sounds (‘bruit de cannon’)
pulse deficits or bounding pulses
what arrhythmia is seen on this ecg?
ventricular tachycardia
what 4 medications are used to treat atrial arrhythmias?
- beta blockers - sotalol
- calcium channel blockers
- digoxin
- quinidine sulfate
what 5 drugs are used to treat ventricular arrhythmias?
- lidocaine
- magnesium sulfate
- beta blockers - sotalol
- procainamide
- quinidine sulfate
what is the definition of a murmur?
audible vibrations created by turbulent blood flow
what is the major difference between physiologic murmurs & pathologic murmurs?
pathologic murmurs are associated with structural abnormalities
what heart valves are typically involved in physiologic murmurs?
aortic or pulmonic
how are pathological murmurs diagnosed?
physical exam, echo, & doppler
how are pathological murmurs characterized?
point of maximal intensity, timing, longer duration, harsh/musical/widely radiating, and higher grade
if there is degenerative valvular disease/endocardiosis affecting the mitral valve, where would the murmur best be heard in regards to location & timing during the cardiac cycle? what is it associated with?
left apical systolic murmur
endocarditis
if there is degenerative valvular disease/endocardiosis affecting the aortic valve, where would the murmur best be heard in regards to location & timing during the cardiac cycle? what is it associated with?
left basilar diastolic murmur
may get bounding pulse with volume overload - older horses
if there is degenerative valvular disease/endocardiosis affecting the tricuspid valve, where would the murmur best be heard in regards to location & timing during the cardiac cycle? what is it associated with?
right 4th ICS systolic murmur
jugular pulsation
what horses can commonly have acquired valvular disease affecting the tricuspid valve?
thoroughbreds & racehorses
what is the prognosis of mild valvular disease?
mild regurgitation usually doesn’t not affect performance or heart function at rest
what is the prognosis of severe valvular disease?
may lead to exercise intolerance or heart failure
other than structural changes, what are some other causes of valvular disease?
chronic active infections - foot abscesses
neoplasia
ruptured chordae tendinae
endocarditis/myocarditis
what diagnostic test should be run on any neonatal foal that has a grade 3 or greater heart murmur?
echo
what is the most common cardiac congenital defect in foals?
ventricular septal defect
what is the prognosis of VSD?
prognosis depends on size
louder = smaller = better prognosis
what does a PDA sound like on cardiac auscultation?
continuous, machinery murmur
what does VSD sound like?
right-sided murmur - may hear on left
pansystolic
loud, harsh sound, grade 3 or higher
what is tetralogy of fallot?
what part of the heart is most commonly affected in bacterial endocarditis? how does it spread?
mitral valve
aortic > tricuspid > pulmonic
hematogenous dissemination
what clinical signs are associated with bacterial endocarditis?
fever, weight loss, depression, murmur, tachycardia, & bacterial showering - affects other system
how is bacterial endocarditis diagnosed?
echo & blood culture
what is the prognosis of bacterial endocarditis if the mitral & aortic valves are involved? what about the tricuspid & pulmonic valve?
mitral valve & aortic valve - poor
tricuspid valve & pulmonic valve - guarded
what is the treatment for bacterial endocarditis?
long term IV & oral antibiotics, & antithrombotic agents
how is pericarditis diagnosed & treated?
pericardiocentesis with culture & lavage
antimicrobial therapy
what are the major clinical signs of pericarditis?
muffled heart sounds!!
fever, tachycardia, cardiac tamponade, & signs of right-sided heart failure
what is pericarditis?
effusive, fibrinous, or constrictive inflammation of the pericardial lining
what is the etiology of pericarditis?
viral - equine influenza virus & eastern tent caterpillar!!!!
others - EHV, EVA, streptococcus, actinobacillus, immune-mediated, & idiopathic
what toxins cause myocarditis?
monensin, oleander, white snake root, cantharidin, box elder, & snake bites
what is an infectious cause of myocarditis?
equine influenza virus
other than toxins & infectious causes, what else can cause myocarditis?
systemic disease/endotoxemia, electrolyte disturbances, colic, colitis, pleuropneumonia, metritis, & selenium deficiency
how is myocarditis diagnosed?
cardiac troponin 1!!!!
ecg for arrhythmia - APC/VPC/v tach
echo-dilation & reduced pump function
how is myocarditis treated?
treat the underlying/primary disease
anti-inflammatories, rest, & vitamin e
what is the treatment for congestive heart failure?
diuretics - furosemide
positive inotropes - digoxin
vasodilators - ace inhibitors
what is the prognosis of congestive heart failure?
poor to grave - 6 months even with therapy
how is congestive heart failure diagnosed in horses?
ecg & echo
T/F: murmurs may not be severe in congestive heart failure in horses
true
what causes aortic rupture?
during exercise or rest - usually vessel necrosis, but etiology unknown
collagen defect/idiopathic??
what breeds have a higher incidence of aortic rupture?
friesians
what is the cause of sudden cardiac death in horses?
in 1/3 of cases - undetermined causes
gi & respiratory diseases approximately 50% of cases
what heart sound is lost in a horse with atrial fibrillation?
S4
list what is happening in the cardiac cycle with each heart sound:
S1 -
S2 -
S3 -
S4 -
S1 - closure of the av valves, onset of ventricular contraction (systole)
S2 - closure of semi-lunar valves, termination of ventricular systole
S3 - rapid ventricular filling
S4 - atrial contraction
what is the first sound heard in each cardiac cycle?
S4 - atrial contraction
what is the most common physiologic arrhythmia? pathologic arrhythmia?
- 2nd degree av block
- atrial fibrillation
how would you treat this arrhythmia seen on ecg?
class 1a sodium channel blocker - quinidine sulfate
22mg/kg every 2 hours through an NG tube until there is a conversion to sinus rhythm, adverse effects are seen, or 4-6 doses are reached
narrow therapeutic index!!
what factors would improve the likelihood of successful treatment of this arrhythmia? what about the prognosis long term?
less than 4 weeks duration & low resting heart rate of the patient
better prognosis for shorter duration, no structural changes to the heart, no associated cardiac disease, and no murmur
list what valve would be associated with the murmur:
left sided systolic
left sided diastolic
right sided systolic
- left sided systolic - mitral valve
- left sided diastolic - aortic valve
- right sided systolic - tricuspid valve
the most common valvular disease in horses are acquired insufficiency/incompetency of what valves?
mitral, aortic, & tricuspid valves
you detect a machine-like murmur in a 48 hour old foal on your wellness check. Are you concerned? why or why not?
not yet - suspect PDA, should close by 96 hours after birth
what heart valve is most commonly affected by bacterial endocarditis?
mitral valve!!!
what do ‘muffled’ heart sounds indicate?
pericarditis - maybe pleural effusion
what are some common etiologies that result in muffled heart sounds?
EIV, eastern tent caterpillars, bacterial causes, & immune-mediated/idiopathic
what is a good diagnostic test for myocarditis?
cardiac troponin I test
you are listening to a horse that has a regular, dropped beat every 3-4 beats at rest. The heart rate is slow - 32bpm. what do you suspect to be the cause? how could you confirm your suspicion? should the
owner be concerned?
2nd-degree av block
exercise the horse to see if it persists
not really - not associated with clinical signs, result of high vagal tone
what arrhythmia commonly affects this breed?
atrial fibrillation - clydesdales
what lesion is seen here?
degenerative valvular disease/endocardiosis
what condition is seen on this ultrasound?
pericarditis - effusive, fibrinous, or constrictive inflammation of the pericardial lining
