Cardiac murmurs are caused by alterations in blood flow through the heart or its major outflow tracts which produce turbulence. It is important to record details of a murmur for comparison with later observations (possibly by a different clinician) which may in turn correlate with an altered clinical presentation. The criteria used to characterize a cardiac murmur are discussed in greater detail in site. It is important to realize that the intensity of a murmur does not necessarily correlate with the severity of the cardiac pathology responsible for its production or presence of congestive heart failure.
Timing (systolic, diastolic or continuous)
A pansystolic or holosystolic murmur extends throughout systole, that is between the first and second heart sounds; a diastolic murmur occurs after the second heart sound. A continuous murmur has both systolic and diastolic components.
The intensity of a murmur can be graded subjectively on a scale of 1-6 as follows:
Grade 1: Careful auscultation required; murmur barely audible.
Grade 2: Very soft murmur but heard immediately when the stethoscope is applied to the chest wall.
Grade 3: Murmur approximately the same intensity as normal heart sounds.
Grade 4: Louder than normal heart sounds but no precordial thrill.
Grade 5: Murmur can be heard with stethoscope barely touching chest wall; palpable precordial thrill present.
Grade 6: Murmur heard with stethoscope away from the animal’s chest.
High frequency ejection-type murmurs associated with aortic or pulmonic stenosis have a sharp, blowing quality compared to the low frequency, harsh regurgitant murmurs more typical of atrioventricular insufficiency. Other murmurs may be described as squeaky or musical.
The shape of a murmur refers to its modulation or quality. Does the murmur vary in intensity? A crescendo murmur is one which increases in intensity; a decrescendo murmur decreases in intensity. A crescendo-decrescendo murmur (diamond-shaped) murmur builds up to peak intensity and then falls away.
The capacity of a murmur to radiate to different areas of the thoracic cavity reflects its origin and pathogenesis. The murmurs of aortic or pulmonic stenosis often radiate to the thoracic inlet (in the case of aortic stenosis the murmur may radiate up the carotid arteries). Murmurs associated with severe mitral insufficiency radiate cranially and dorsally.