Heart Murmurs

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On auscultation, heart murmurs are sounds that signify abnormal turbulent blood flow in the heart or surrounding blood vessels.

Murmurs can arise from any of the following conditions:
1. Increased Blood Volume
2. Increased Blood Flow Velocity
3. Valve Regurgitation
4. Decreased Blood Viscosity

Types of Heart Murmurs

1. Systolic Heart Murmurs

This is the most common type of murmur among small animal patients and occurs during systole.

Functional Murmurs

(Occur without a pathological condition involved).

These include:

'Innocent Murmurs' - e.g. young animals with temporary murmurs
Physiologic/Flow Murmurs - e.g. athletic animals especially thoroughbred horses; conditions such as anaemia, fever, peripheral arteriovenous fistula
Aortic flow murmurs - these are the most common in young animals, particularly young fit thoroughbred horses.

Valve regurgitations in horses can be functional or pathological. (Endocardiosis is the most common form of older equine valve pathology.)

Pathological Murmurs

Include atrioventricular valve insufficiency, semilunar valve stenosis and cardiac shunting (e.g. PDA, VSD).

2. Diastolic Heart Murmurs

These are uncommon in small animals and they occur during diastole.

Functional Murmurs

(Occur without a pathological condition involved). These include Physiologic/Flow Murmurs (e.g. athletic animals especially thoroughbred horses) and Ventricular (mitral and tricuspid) flow murmurs, which are less common in young fit thoroughbred horses compared with aortic flow murmurs, but their presence can still be seen in normal horses.

Pathological Murmurs

Include atrioventricular valve stenosis, semilunar valve insufficiency and cardiac shunting (e.g. PDA).

3. Continuous Heart Murmurs

Are also called machinery murmurs and occur continuously throughout systole and diastole.

Pathological Murmurs

These can occur in cardiac shunting and is characteristic for a PDA.

Description of Heart Murmurs

1. Timing/Duration (Systolic, Diastolic, Continuous)

2. Location (Point of Maximal Intensity; Left Side: Heart Base (Semilunar Valves), Heart Apex (Mitral Valve); Right Side: Tricuspid Valve)

3. Intensity (Grading of Heart Murmur is on a scale 1-6)

4. Shape (Description from phonocardiogram:e.g. Holosystolic, Crescendo-decrescendo, Systolic decrescendo, Diastolic decrescendo, Continuous aka Machinery)

5. Sound (Quality & Pitch: High Pitch usually indicates ejection murmurs; Low Pitch usually indicates regurgitant flow murmurs)

6. Radiation (Description based on how far the murmur sound spreads from its point of maximal intensity. e.g. Aortic murmurs radiate up carotid arteries)

Heart Murmur Grading Scale

To listen to gradings and examples of canine cardiac murmurs visit the heartsound library.

Grade Description
Barely audible (need ideal conditions to hear)
Clearly audible at point of maximal intensity
Clearly audible (as loud as S1 & S2; +/- radiation)
Loud (louder than S1 & S2; - precordial thrill; radiation over thorax)
Loud (louder than S1 & S2; + precordial thrill)
Very loud (audible with stethoscope lifted off chest; + precordial thrill)

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