Unit 1 - Cardiology (intro to Atrial arrhythmias) Flashcards
What physical exam findings are associated with mild cases of cardiovascular disease?
no clinical signs, reduced exercise tolerance
What physical exam findings are associated with moderate cases of cardiovascular disease?
tachycardia, tachypnea, dyspnea post exercise, abnormal arterial pulse, jugular distention, edema over ventral abdomen, edema in the distal limbs, and pathologic arrhythmias
What physical exam findings are associated with severe cardiovascular disease?
cool extremities, weight loss, reduced capillary refill time, cough, dyspnea at rest, and collapse
What are the reasons for evaluating for cardiovascular disease?
obvious signs of heart disease, poor athletic performance, pre-purchase examination, insurance examination
What are the components of a cardiac evaluation?
auscultaion, ECG, echo, and exercise testing
What is the normal resting heart rate of the horse?
20-40 beats per minute
What is S1?
sound 1 - the lub followed by systole
What is S2?
sound 2 - the dub followed by diastole
What is S4?
the atrial sound
What makes the atrial sound?
it arises from ventricular vibrations set up when pressure wave caused by the atrial contraction reaches the ventricle
When arrythmia is an isolated S4 associated with?
2nd (and 3rd) degree A-V block
When is S4 absent?
in a sinoatrial block
What does S4 immediately preceed?
lub
When and where does S1 come from?
It arises mostly from the ventricle, after AV valve closure
What does the atrial-S1 interval depend on?
the P-Q interval
What is S2 made by?
closure of semi-lunar valves and rapid reversal of blood flow
What is S3 made by?
early, rapid ventricular filling
Where anatomically is S3 heard? In what percent of horses?
left side, 30-50%
What are the semi-lunar valves?
aortic and pulmonic valves
Where is S1 the loudest on auscultation?
over the mitral valve - in the intercostal space between ribs 5 and 6, right at the caudal edge of the triceos
Where is S2 the loudest on auscultation?
over the aortic valve - in the intercostal space between ribs 4 and 5
What makes the P wave on an ECG?
right atrial depolarization with a wave spreading from the S-A node across the right atrium, the interatrial septum, and then the left atrium
At rest, how does the P wave appear?
it is often bifid
What does the first small ‘hump’ of the p-wave represent?
mostly right atrial depolarization
Is the QRS wave due depolarization as a wavefront like the p wave is?
No, the depolarization is NOT as a wavefront across the chambers due to much branching of the conducting system
QRS at body surface reflects about ___ of the depolarization of the myocardial mass.
20%
What causes the T wave?
repolarization of the ventricles
The equine T-wave is very ____.
labile
The T-wave changes polarity with ______.
heart rate
What can the T-wave not be used to assess?
heart strain
What is ECG only useful for determining?
arrhythmias
A.
bifid P wave
B.
diastole
C.
S4 - ba
D.
QRS complex
E.
systole
F.
S1 - lub
G.
T-wave
H.
Diastole
I.
S2 - dub
J.
S3 - ah
If a murmur is heard at E, what type of murmur is it?
a systolic murmur
If a murmur is heard at B or H, what type of murmur is it?
a diastolic murmur
Where will a atrial arrythmia be heard?
at S4
Is systole A or B? Diastole?
Systole is A, diastole is B
What depth is required for echo in horses? What size transducer?
a depth of 30 centimeters, 3.5 mHz transducer
What is echocardiography useful in detecting?
congenital anomalies
When should exercise testing take place?
cardiac evaluation should be performed at or immediately after expected level of exercise
What are the types of atrial arrhythmias?
wandering pacemaker, premature sinus beats, premature atrial beats, sino-atrial block, sinus bradycardia, post exercise sinus arrhythmia, and atrial fibrillation
Is wandering pacemaker a true arrhythmia?
not really, it is an ECG finding
How does a wandering pacemaker present on ECG?
the p-wave shape may change from beat to beat, but the rhythm is regular
Is wandering pacemaker clinically significant?
no
How do premature sinus beat arrythmias present on ECG?
P waves are earlier than normal, but of normal conformation. The QRS wave is normal
When do premature sinus beats disappear?
with exercise
When do premature sinus beats suggest myocardial disease?
when there are frequent ones - it is not significant if there is one occasionally every 5 minutes
What is the recommended treatment for horses that have frequent premature sinus beats?
to rest the horses and reevaluate in 4-6 months
How do premature atrial beats appear on ECG?
the same as premature sinus beats, but the P waves are of abnormal conformation
What causes the abnormal conformation of P waves in premature atrial beat arrhythmias?
there is an ectopic focus in the atrial muscle
When do premature atrial beats suggest myocardial disease? Treatment?
If they are very frequent, it suggests myocardial disease. Rest these horses, and then reevaluate in 4-6 months.
How do sino-atrial blocks appear on ECG?
There is no P-wave and a twice normal diastolic pause (2 dubs)
What horses are sino-atrial blocks more common in?
ponies
What abolishes sino-atrial block?
exercise
What mediates sino-atrial block?
it is vagally mediated
Is sino-atrial block clinically significant?
not usually
What horses typically have sinus bradycardia?
mostly ponies - it is rare
How does sinus bradycardia present?
as a very slow irregular atrial rhythm
What clinical signs are associated with sinus bradycardia?
reduced exercise or even lethargy
What may reslove sinus bradycardia?
rest
When are post exercise sinus arrhythmias common?
after light trotting exercise in fit horses
How do post-exercise sinus arrhythmias occur?
As the heart rate slows, there are sudden pauses, and then a gradual return to the pre-pause rate
Are post-exercise sinus arrhythmias significant? How can they be abolished?
Not usually significant, abolished by more rigorous exercise
What clinical signs are associated with atrial fibrilation?
they are variable - they could have none up to heart failure, they may have pulse deficits
On auscultation, how does atrial fibrilation sound?
there are no atrial sounds, irregularly spaced group of irregular beats, S1 and S2 vary in intensity due to variable ventricular filling
What heart rate is associated with atrial fibrilation?
the heart rate can range from 30-40 up to 80-100
What treatment is recommended for atrial fibrillation?
It is best if it is done early in the disease - oral quinidine is a drug of choice
How is oral quinidine administered?
via a nasogastric tube
What is the protocol for oral quinidine treatment for atrial fibrillation?
Give a test dose of 5 grams on day 1, if no adverse reaction then proceed to day 2
On day 2, give 20 grams as a start up dosage and give an additional 10 grams every 2 hours (make sure to perform an ECG before giving each dose)
What dosage should you not exceed for oral quinidine per day?
do not exceed 90 grams/day in a 1000 pound horse
What toxic signs are associated with atrial fibrillation treatment of quinidine?
Depression (often), tachycardia, diarrhea (often), colic (often), urticaria, nasal edema, weakness, ataxia, and death
Aside from oral quinidine, what can be used to treat atrial fibrillation?
IV quinidine (expensive and risky), Digoxin (if heartrate is greater than 60 bpm), and electrical cardioversion (shocking)
