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.
(Occur without a pathological condition involved).
- '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.)
2. Diastolic Heart Murmurs
These are uncommon in small animals and they occur during diastole.
(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.
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.
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.
|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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