Heart Murmur
Basic Information 
Definition
• Murmurs are audible vibrations heard during a normally silent part of the cardiac cycle. Blood flow through the heart is generally laminar, but a number of circumstances may alter the normal laminar flow, causing turbulent flow to develop. This may cause vibration of cardiac structures, resulting in a murmur that can be heard with a stethoscope. Turbulence is most likely generated when blood viscosity is low, when the blood flow velocity is high, or when the diameter of the blood vessel is large. Three different types of murmurs exist, two of which are not associated with cardiac abnormalities.
Functional murmur (systolic flow murmur, systolic ejection murmur): These benign murmurs are common in horses, especially in racehorses, because the large stroke volume and large diameters of the great vessels induce turbulent blood flow in aortic and pulmonary artery roots in early systole.
Physiologic murmur: A number of conditions such as anemia and endotoxemia can lead to altered blood viscosity as well as increased cardiac output, which induces turbulent blood flow, leading to a benign systolic murmur. This is quite often heard in horses presented with substantial hemorrhage, high fever, or colic.
Epidemiology
Species, Age, Sex
Whereas degenerative valvular diseases are often seen in older horses, clinically significant congenital cardiac diseases are often discovered in young animals.
Clinical Presentation
Disease Forms/Subtypes
As defined above, heart murmurs can be divided into three different types with functional and physiologic murmurs considered to be benign. Pathologic murmurs may or may not have a clinical effect on the horse. Therefore two fundamental questions should be answered: What is the source of the murmur, and what is its clinical significance?
History, Chief Complaint
• Heart murmur may be detected on routine examinations (eg, prepurchase examination, auscultation before sedation, vaccination or a general clinical examination) in otherwise healthy animals.
• Heart murmur may be detected in systemically ill patients (eg,. anemia, colic, endotoxemia). In this situation, it is important to rule out cardiac disease and to assess whether it is a physiologic murmur that will disappear after the primary disease has resolved.
• Heart murmurs detected in horses presented with signs of cardiac disease (eg, ventral edema, tachycardia, arrhythmia, tachypnea or dyspnea, exercise intolerance, or collapse).
Physical Exam Findings
• Before auscultation of the left hemithorax, palpation of the apex beat with the flat of the left hand should be performed because the point of maximal intensity (PMI) of the mitral valve is usually located in this area (apical area). The apical area lies above the point of the elbow at the caudal edge of the triceps musculature. In this region, the first (S1) and second (S2) heart sounds are of equal loudness. From this location, the stethoscope is advanced in a dorsocranial direction until S2 becomes more accentuated relative to S1 and the aortic and pulmonic valve area is identified (basal area).
• On the right hemithorax, the apex beat is rarely palpable unless the horse is thin and narrow chested or has enlargement of the right ventricle or atrium. The auscultation area is more cranially located compared with the apical area on the left side of the horse. Often the right forelimb should be placed cranial to the left forelimb to allow better access. The only valve auscultated on the right hemithorax is the tricuspid valve, and because of the anatomical location of the heart toward the left side of the thorax, the tricuspid valve may be difficult to hear in some horses.
• Murmurs are classified according to a number of different criteria.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
