Equine Cardiology: Heart Murmurs in Horses

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Questions and Answers

What primarily causes heart murmurs in horses?

Turbulent flow of blood (correct)

Abnormal heart structure

Increased blood pressure

Inflammation of cardiac tissue

Which type of heart murmur is typically considered to have no consequence?

Regurgitant murmurs

Continuous murmurs

Holosystolic murmurs

Physiologic murmurs (correct)

Which of the following conditions is of particular concern regarding prognosis and performance in horses?

Physiologic murmurs

Ventricular septal defect (correct)

Sinus bradycardia

Atrial fibrillation

What is the method primarily used to assess heart murmurs in horses?

Ultrasound (echocardiography) Signup and view all the answers

Which of the following heart conditions can be clinically concerning?

Atrial fibrillation Signup and view all the answers

What should be monitored annually in cases of aortic insufficiency?

Resting heart rate Signup and view all the answers

What does the presence of bounding pulses indicate in aortic insufficiency?

Severe regurgitation Signup and view all the answers

In which phase of the cardiac cycle does ventricular filling occur in aortic insufficiency?

Early diastole Signup and view all the answers

What may volume overload in aortic insufficiency lead to?

Mitral regurgitation Signup and view all the answers

Which echocardiographic finding suggests severe regurgitation in horses?

Multiple murmurs Signup and view all the answers

What is a key clinical sign of exercise-induced ventricular arrhythmias in horses with aortic insufficiency?

Collapse or sudden death Signup and view all the answers

Which of the following is a poor prognostic indicator for aortic insufficiency in horses?

Young age Signup and view all the answers

What should be performed in cases of suspected aortic insufficiency?

Echocardiography and ECG Signup and view all the answers

What is a characteristic feature of a ventricular septal defect (VSD) murmur?

It occurs throughout systole. Signup and view all the answers

What is the significance of a short murmur in veterinary cardiology?

It is usually not significant. Signup and view all the answers

Which of the following is true regarding the treatment of atrial fibrillation with quinidine sulphate?

It requires continuous ECG monitoring. Signup and view all the answers

What factor differentiates tricuspid regurgitation from a VSD murmur in terms of position?

Tricuspid regurgitation is heard lower than the VSD. Signup and view all the answers

What is the recommended follow-up after administering quinidine sulphate for atrial fibrillation?

Change the dosing schedule to every 6 hours after the first 5-6 doses. Signup and view all the answers

Which of the following conditions is commonly misinterpreted as significant dysrhythmia in horses?

2nd degree AV block. Signup and view all the answers

Which of the following murmurs is NOT considered significant in the context of equine heart conditions?

Short murmur. Signup and view all the answers

What does regular irregularity in heartbeats typically indicate in horses?

2nd degree AV block. Signup and view all the answers

What is the primary reason for the occurrence of valvular murmurs in horses?

Regurgitation of the valves Signup and view all the answers

Which of the following murmur types is considered potentially significant in horses?

Mitral regurgitation Signup and view all the answers

What is the common grade range for aortic flow murmurs in horses?

1-3/5 Signup and view all the answers

Which of the following statements about pulmonary valve murmurs in horses is correct?

They are rarely observed. Signup and view all the answers

What condition is associated with ventricular septal defect (VSD) murmurs in horses?

Congenital heart defect Signup and view all the answers

In a case of mitral insufficiency, which outcome is not predictable?

Rupture of the pulmonary artery Signup and view all the answers

Which heart murmur is generally NOT considered significant in horses?

Tricuspid valve murmurs Signup and view all the answers

What does the PMI (point of maximal intensity) of an aortic flow murmur typically indicate?

It is high, located under the triceps. Signup and view all the answers

Study Notes

Common Equine Cardiovascular Conditions

Equine cardiovascular conditions are frequently encountered in performance horses.
Heart murmurs can be caused by turbulent blood flow (rather than laminar flow) and can indicate underlying cardiac disease.
Some murmurs are benign ("functional"), while others signify cardiac abnormalities.
Valvular murmurs in horses are typically due to regurgitation, not stenosis.
Mitral and/or aortic valve regurgitation are the most significant valvular murmurs.
Ventricular septal defect (VSD) is another potentially significant murmur to consider.
Pulmonary and tricuspid valve murmurs are uncommonly concerning.

Learning Objectives

Students should understand the causes of heart murmurs in horses.
Students should be able to differentiate clinically concerning and non-concerning heart murmurs.
Students should understand the prognostic implications of valvular regurgitation and ventricular septal defect (VSD) regarding performance.
Students should be able to differentiate common equine dysrhythmias, identifying those of clinical concern.
Students should be able to diagnose atrial fibrillation in horses.

Heart Murmurs

A heart murmur is an abnormal sound heard during the cardiac cycle.
Murmurs result from turbulent blood flow.
Murmurs can be detected through auscultation and further assessed (if needed) through echocardiography.
Some murmurs are physiological (no consequence) and others are pathological (affect cardiac output).

Equine Murmurs - General Rules

Valvular murmurs in horses are generally due to regurgitation.
Pulmonary valve murmurs are rare.
Tricuspid valve murmurs are rarely significant.

3 Potentially Significant Murmurs

Valvular murmurs are typically due to regurgitation, not stenosis.
Pulmonary valve murmurs are rare.
Tricuspid valve murmurs are rarely significant.
Mitral and aortic regurgitation are potentially significant; VSD is another.

Auscultation: 3 Pairs of Murmurs

This table differentiates between unimportant and potentially important murmurs based on location and characteristics

MURMUR	UNIMPORTANT	POTENTIALLY IMPORTANT
LEFT systolic	Aortic ejection	Mitral insufficiency
LEFT diastolic	Ventricular filling	Aortic insufficiency
Right systolic	Tricuspid insufficiency	Ventricular septal defect (VSD)

Aortic Flow

Typically short (in early systole), high-pitched sound.
Grade 1-3/5 or equivalent.
PMI (point of maximal impulse) is high and under triceps.
The sound is localized.

Mitral Regurgitation

Murmur occurs throughout systole.
Grade is 1-5/5 or equivalent.
PMI is often low.
Radiates caudorsally.

Ventricular Filling

This is an early diastolic murmur described as a "squeak,"
Grade is 1-2/5 or equivalent
The sound is low in pitch, located towards the apex.
The murmur is localized.

Aortic Regurgitation

The murmur occurs throughout diastole.
Grade is 1-5/5.
The sound is high-pitched located under triceps.
It radiates caudoventrally.

Aortic Insufficiency - Clinical Significance

Typically found in older horses.
Commonly not clinically significant.
Self-limiting through increased contractility.
Bounding pulses indicate severe regurgitation
Volume overload can lead to mitral regurgitation.
Susceptible to exercise-induced ventricular arrhythmias (VPCs).

Tricuspid Regurgitation

Murmur occurs throughout systole.
Grade is 1-5/5 or equivalent.
Located high under the triceps.

Ventricular Septal Defect - Clinical Significance

Often located below aortic/tricuspid valves.
Characterized by left-to-right flow.
Small defects (< 2.5 cm) are well-tolerated.
Larger defects reduce cardiac output, causing volume overload.
Generally not progressive in adult horses
In foals/young horses, careful assessment is required,

Murmurs Summary

This table summarizes the different types of murmurs, their location, timing, intensity, and grade.

Category	Side	Timing	Duration	Intensity	Grade
Aortic flow	L	Syst	short	high	1–2
Mitral regurgitation	L	Syst	pan/holo	low	1–5
Ventricular filling	L	Diast	short	low	1–2
Aortic regurgitation	L	Diast	pan/holo	high	1–5
Tricuspid regurgitation	R	Syst	pan/holo	high	1–5
Ventricular septal defect (VSD)	R	Syst	pan/holo	low	3–5

Dysrhythmias

Abnormalities of the cardiac rhythm.
Can or cannot impact cardiac output.
Detected through auscultation, supplemented by electrocardiography (ECG).
Bradydysrhythmias involve delayed or absent regular beats.
Tachydsrhythmias feature premature or earlier-than-expected beats.

Common Dysrhythmias

2nd degree atrioventricular (AV) block.
Atrial fibrillation.

Occasional dysrhythmias

Atrial fibrillation

Uncommon dysrhythmias

Premature supraventricular (atrial) contractions
Premature ventricular contractions

Rare Dysrhythmias

Advanced 2nd degree AV block
3rd degree AV block
Sinoatrial block
Ventricular fibrillation

2nd Degree AV Block - Physiologic

Very common, usually not a problem.
Caused by high vagal tone at the AV node.
Usually resolves with exercise or excitement.
Heart rate is low-to-normal (24-36 bpm) with regular diastolic pauses.
Audible S4 during diastolic pause.

Normal Sinus Rhythm

Regular heart rhythm.
Demonstrates consistent PQRST complexes, reflecting normal electrical conduction through the heart.

Pathologic AV Block

Rarely seen, but possible cause of exercise intolerance or collapse.
Results from AV node scar tissue or inflammation.
Characterized by several consecutive blocked beats.
A 3rd-degree block indicates independent atrial and ventricular contraction.

Premature Depolarisations

Occasional premature beats are usually normal .
More frequent premature beats are associated with exercise intolerance.
Premature ventricular contractions (PVCs) occur earlier than expected.
These premature beats can be preceded by a compensatory pause.
Irregularly irregular heart rhythm may be indicative.
Characteristics of premature depolarizations may differ depending on the causative origin (supraventricular or ventricular)
Supraventricular premature beats are preceded by an early p-wave.
Ventricular premature beats are not preceded by a preceding p-wave.

Atrial Fibrillation

Most common cardiac dysrhythmia.
Loss of atrial contractions replaced by random ventricular contractions.
Characterized by an irregular heart rhythm.
Can be permanent or intermittent (paroxysmal).
High heart rates can lead to decreased cardiac output and poor ventricular filling.
Large heart mass may predispose to atrial fibrillation.
Less common in ponies .
Cardiac failure and atrial enlargement can cause secondary atrial fibrillation with tachycardia.

Atrial Fibrillation - Functional Effect

Atrial contraction loss directly impacts cardiac output.
Normal heart rate at lower rates; decreased filling efficiency at higher rates.
Exercise can trigger serious arrhythmias.

Diastolic Ventricular Filling

Ventricular filling is efficient during low heart rates due to passive filling.
High heart rates require atrial contraction to provide active filling.

Treatment of Atrial Fibrillation

Treatments are generally costly and carry risk.
Factors influencing treatment necessity include cause, horse type, and disease duration.

Atrial Fibrillation - Medical Treatment

Quinidine sulfate (22 mg/kg every 2 hours) for up to 6 doses.
Not an entirely safe treatment; intensive ECG monitoring.
Do not move the horse during treatment due to low blood pressure.
Stomach tube should remain in place.
Widening of QRS by more than 25% warrants cessation of quinidine.
Watch for adverse side effects like diarrhea, depression, hives, and death.

Atrial Fibrillation - Transvenous Electrocardioversion (TVEC)

Alternative treatment option at specialized centers.
Greater success rate compared to quinidine.

Summary points (Murmurs)

Short murmurs are typically insignificant
Murmurs lasting throughout systole or diastole are potentially significant(except tricuspid murmurs).
A normal resting heart rate is reassuring.
Only 3 murmurs are crucial: left pan/holo-systolic mitral regurgitation, left pan/holo-diastolic aortic regurgitation, and right pan/holo-systolic VSD.

Summary points (Dysrhythmias)

2nd degree AV block (common) or atrial fibrillation are common horse dysrhythmias.
Regular irregularity suggestive of 2nd degree AV block.
Random irregularity points to atrial fibrillation (more problematic for athletic horses).
Other rare causes might present.

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Description

Test your knowledge on the causes, assessment methods, and implications of heart murmurs in horses. This quiz covers crucial aspects of equine cardiac health, including specific conditions and echocardiographic findings. Understand the significance of various symptoms and how they relate to horse performance.