Murmurs are described by their timing in the cardiac cycle, intensity, shape, pitch, location, radiation and response to dynamic maneuvers. Using the aforementioned criteria, a clinician can accurately characterize the nature of a murmur and communicate their findings in a precise manner.
The timing of a murmur is crucial to accurate diagnosis. A murmur is either systolic, diastolic or continuous throughout systole and diastole. Remember: Systole occurs between the S1 and S2 heart sounds, while diastole occurs between S2 and S1.
With the knowledge of the possible cardiovascular conditions that cause systolic or diastolic murmurs, the clinician can narrow their differential diagnosis. Thus, it is important to remember which lesions result in systolic murmurs and which result in diastolic murmurs. Stenosis of the aortic or pulmonic valves will result in a systolic murmur, as blood is ejected through the narrowed orifice.
Conversely, regurgitation of the same valves will result in a diastolic murmur, as blood flows backward through the diseased valve when ventricular pressures drop during relaxation. Regarding the mitral and tricuspid valves, stenosis would result in a diastolic murmur and regurgitation a systolic murmur. Other murmurs will be discussed in their respective sections. A complete discussion of valvular heart disease is found elsewhere.
Once it is determined whether the murmur is systolic or diastolic, the timing of the murmur within systole or diastole also becomes important when characterizing murmur. Systolic murmurs can be classified as either midsystolic (aka systolic ejection murmurs or SEM), holosystolic (pansystolic), or late systolic. A midsystolic murmur begins just after the S1 heart sound and terminates just before the P2 heart sound, so S1 and S2 will be distinctly audible. Conversely, a holosystolic murmur begins with or immediately after the S1 heart sound and extends up to the S2, making them difficult, if not impossible, to hear. A mid-late systolic murmur begins significantly after S1 and may or may not extend up to the S2.
Systolic murmurs are graded on a scale of 6. This grading is, for the most part, subjective. Grade I murmurs may not be audible to the inexperienced examiner; however, grade 6 murmurs are heard even without the stethoscope on the chest and may even be visible.
Diastolic murmurs are graded on a scale of 4. This is a completely subjective grading scale. Once again, grade I murmurs may not be audible to some; however, grade IV murmurs are audible very easily.
The intensity of a murmur is primarily determined by the volume/velocity of blood flowing through a defect and the distance between the stethoscope and the lesion. For example, a very thin patient with severe aortic stenosis with a high pressure gradient across the valve (thus high velocity of blood flow) will have a loud murmur. Conversely, the exact same valvular lesion in a morbidly obese person or a person with severe COPD and a widened anterior-posterier chest diameter may be inaudible.
The shape of a murmur describes the change of intensity throughout the cardiac cycle. Murmurs are either crescendo, decrescendo, crescendo-decrescendo or uniform.
A murmur will be high-pitched if there is a large pressure gradient across the pathologic lesion, and low-pitched if the pressure gradient is low. For example, the murmur of aortic stenosis is high-pitched since there is usually a large pressure gradient between the LV and the aorta. Conversely, the murmur of mitral stenosis is low-pitched since there is a lower pressure gradient between the LA and the LV during diastole. Remember: High-pitched sounds are heard with the diaphragm of the stethoscope, while low-pitched sounds are heard with the bell.
The anatomic location where the murmur is best heard is an important factor in determining the etiology of the lesion. There are four main "listening posts" on the chest (see picture below).
A = aortic valve post (right upper-sternal border or RUSB)
P = pulmonic valve post (left upper-sternal border or LUSB)
T = tricuspid valve post (left lower-sternal border or LLSB)
M = mitral valve post (apex)
E = "Erb's point"
Note: Both the aortic and pulmonic listening posts are considered to be near the "base" of the heart.
In general, a murmur will be the most intense over whichever listening post corresponds to the diseased valve. Many murmurs will radiate to more than one listening post. For example, the murmur of aortic stenosis is best heard at the LUSB; however, it may radiate to the apex. This radiation of the AS murmur is called the "Gallavardin dissociation."
While murmurs are usually most intense at one specific listening post, they often radiate to other listening posts or areas of the body. For example, the murmur of aortic stenosis frequently radiates to the carotid arteries and the murmur of mitral regurgitation radiates to the left axillary region. It is often difficult to distinguish if one murmur is radiating to multiple sites, or if there are multiple murmurs present from many different causes. Dynamic auscultation and echocardiography is helpful in determining the exact lesion present.