Cardiology Flashcards
What would you find on physical exam that would be indicative of mild cardiovascular disease
no clinical signs
reduced exercise tolerance
What clinical signs would you find on physical exam for moderate cardiovascular disease?
- tachycardia
- tachypnea
- dyspnea post exercise
- abnormal arterial pulse
- jugular distension
- edema over ventral abdomen- dependent edema in the intradermal space
- edema in distal limbs
- pathological arrhythmias.
Physical exam findings indicative of severe cardiac disease
- cool extremities
- weight loss over time
- reduced capillary refil time
- cough (left-sided failure)
- dyspnea at rest
- collapse
normal resting heart rate in horses
20-40 bpm
All 4 heart sounds are often present
Explain S4 on auscultation
Atrial sound (Ba)
- Low frequency
- arises from the ventricular vibrations set up when pressure wave caused by atrial contraction reaches the ventricles
- Occurs immediately prior to S1
- Arrhythmias
- Isolated S4 in 2nd degree A-V block
- Absent in sinoatrial block
- immediately precedes “lub” (S1)
S1 on Auscultation
“Lub”
- Arises from the ventricle after AV valve closure
- Split S1 is rarely heard in horses
S2 on auscultation
Sound 2- “dub”
- Sharp and clear
- Sound is made by the closure of the semi-lunar valvaes and rapid reversal of blood flow
- A split S2 is uncommon and is often confused with S2-S3 associations
S3 on Auscultation
- Made by early, rapid ventricular filling
- Heard in about 30-50% of horses
- Heard chiefly on the left side of horse
- .14-.17 seconds after onset of S2
What are ascultation sites for cardiac evaluation.
where can you hear S2 and S1 the loudest?
Mitral valve 5-6 intercostal space. S1 can be heard the loudest here
Aortic valve 4-5 intercostal space located dorsally in comparison to the others. S2 can be heard the loudest here
Pulmonic valve 3-4 intercostal space located behind the limb.
Origin of the P-wave on Electrocardiography
Depolarization with a wave spreading from the S-A node across the right atrium. the interatrial septum and then the left atrium
The P- wave is often bifid at rest
- first small “hump” represents right atrial depolarization
Origin of the QRS complex on electrocardiography
- Depolarization not as a wavefront across the chambers due to the complexity of the conducting system. Reflects the His-purkinje system
- Vector analysis of equine QRS is NOT valid. many of the dipoles cancel each other out
T wave Electrocardiography wave origins
Repolarization of the ventricles
- equine T-wave is very labile- may change shape while watching ECG, this occurs with a change in heart rate.
Cannot be used to assess “heart strain”
What part of the cardiac cycle is associated with Systole?
- QRS complex - T wave.
- Lub- Dub
- Lub- AV valve closure
- Dub- Closure of semilunar valves.
- The time between Lub and Dub should be silent.
If worried about performance horses and cardiovascular abnormalities, what tests should you perform
- Echocardiography used to identify arrhythmias
- Exercise testing- cardiac evaluation should be performed at or immediately after expected level of exercise.
- Heart function changes rapidly with cessation of exercise, but assessment of HR and rhythm difficult at intense exercise.
Wandering pacemaker
not clinically significant
P-wave shape may change from beat to beat, but the rhythm is regular
Reflects changing sites within the S-A node for impulse generation
Premature sinus beats
- P waves earlier than normal, but of normal conformation
- normal QRS
- All 4 heart sounds often present
- often disappears with exercise
- Occasional one is not significant
- if found frequent, myocardial disease is suggested
- Rest these horses and reevaluate in 4-6 months.
Premature atrial beats
Premature sinus beat (Early P waves) with ABNORMALLY shaped P wave.
- if frequent, suggests myocardial disaese
Describe a Sino-atrial block
No P-wave and a twice normal diastolic pause
This pause is silent
More common in ponies
Abolished by Exercise
Vagally mediated
Describe Sinus bradycardia
Atrial Arrhythmia
This is very rare- mostly in ponies
- very slow irregular atrial rhythm
reduced exercise or even lethargy
may resolve with rest.
Describe Post exercise sinus arrhythmias
Common after light trotting exercise in fit horses
As the heart rate slows, there are sudden pauses, and then a gradual return tothe pre-pause rate
Not usually significant, and can be abolished by more rigorous exercise
-Possibly vegally mediated.
Describe Atrial fibrilation
- Large horses (rare in ponies and foals)
- variable signs
On auscultation
- NO atrial sounds (S4)
- Irregularly spaced group of irregular beats
Heart rate 30-40 or up to 80-100
-May have pulse deficits.
Treatment for Atrial fibrilation
Best done early in the disease
-Oral quinidine is the drug of choice, administer via nasogastric tube
Warning- toxicosis can develop if you exceed 90 grams/day in 1000lb horse
First degree AV block
Common finding
Increase in P-Rinterval at rest
As P-R interval increases, so does the S4-S1 interval
This finding is not clinically significant
Describe an Second degree (partial) Atrio-ventricular block
verry common in fit, large horses
- Mobitz I - gradual increases in the P-R interval, then impulse blocked at A-V node
- Movitz II - may have no apparent increase in P-R interval with spontaneous occasional block at the A-V node
- Can detect on auscultation: diastolic pause twice the normal length with S4 in the middle of the pause
can be induced by Alpha 2 agonists such as xylazine and detomadine
