Midsystolic murmurs — also known as systolic ejection murmurs, or SEM — include the murmurs of aortic stenosis, pulmonic stenosis, hypertrophic obstructive cardiomyopathy and atrial septal defects.
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. The term midsystolic is preferred to SEM, since many lesions that produce midsystolic murmurs are unrelated to systolic ejection.
Aortic stenosis (AS)
The classic murmur of aortic stenosis is a high-pitched, crescendo-decrescendo ("diamond shaped"), midsystolic murmur located at the aortic listening post and radiating toward the neck.
The radiation of the aortic stenosis murmur is often mistaken for a carotid bruit. The aortic stenosis murmur is also well known to radiate to the cardiac apex on occasion, making it difficult to distinguish if mitral regurgitation is also present. This radiation of the aortic stenosis murmur to the apex is known as "Gallavardin dissociation." It requires dynamic auscultation or echocardiography to determine if coexisting mitral regurgitation is the cause of the apical murmur in a patient with aortic stenosis.
The intensity of the murmur of aortic stenosis is not a good indicator of the severity of disease. As aortic stenosis worsens, the LV begins to fail and the ejection fraction declines to the point where sufficient force to create turbulent flow is no longer produced, resulting in a decrease in the intensity of the murmur.
While the intensity of the murmur may not be an accurate determinant of the severity of aortic stenosis, the shape of the murmur can be very helpful. As aortic stenosis worsens, it takes longer for blood to eject through the valve, so the peak of the crescendo-decrescendo murmur moves to later in systole. Thus, mild aortic stenosis would have an early peaking murmur while the murmur of severe aortic stenosis peaks later in systole.
Remember from the heart sounds section that the delay in aortic valve closure can cause a paradoxically split S2 heart sound, and as the aortic valve becomes more heavily calcified, the intensity of the S2 heart sound declines. Also, in patients with bicuspid aortic valves, an ejection click may be heard just before the murmur begins.
Pulmonic stenosis (PS)
The murmur of pulmonic stenosis is very similar to that of aortic stenosis. It is a midsystolic, high-pitched, crescendo-decrescendo murmur heard best at the pulmonic listening post and radiating slightly toward the neck. However, the murmur of pulmonic stenosis does not radiate as widely as that of aortic stenosis. The murmur of pulmonic stenosis peaks early if the disease is mild and peaks later as the disease progresses. Also, the murmur of pulmonic stenosis demonstrates increased intensity during inspiration due to the increased venous return to the right heart, resulting in greater flow across the pulmonic valve.
While the murmur of aortic stenosis extends up to the A2 heart sound, the murmur of pulmonic stenosis extends through the A2 sound up to the P2 heart sound. Severe pulmonic stenosis results in decreased mobility of the pulmonic valve leaflets, and thus a softer P2 sound. Also, as the pulmonic stenosis worsens, the closure of the pulmonic valve is delayed, since more time is required to eject blood through the stenotic valve, resulting in a widely split S2 heart sound that still exhibits inspiratory delay. Note that the murmur of an atrial septal defect (see below) is also midsystolic; however, it has a fixed split S2.
Atrial septal defect (ASD)
The murmur produced by an atrial septal defect is due to increased flow through the pulmonic valve, thus it is remarkably similar to that of pulmonic stenosis. The difference lies in the intensity and splitting pattern of the S2 heart sound. The intensity of S2 should remain unchanged and may, in fact, be accentuated if pulmonary hypertension develops. The S2 is fixed-split in a person with an ASD. This differs from the widened-split S2 that is seen in severe pulmonic stenosis. Also, the murmur of an ASD does not increase in intensity with inspiration.
Hypertrophic obstructive cardiomyopathy (HOCM)
The murmur of hypertrophic obstructive cardiomyopathy is important to detect due to its clinical implications (see hypertrophic obstructive cardiomyopathy review). The murmur is a high-pitched, crescendo-decrescendo, mid-systolic murmur heard best at the left lower sternal border. The murmur of HOCM does not radiate to the carotids like that of AS. The important auscultatory features of HOCM that distinguish it from AS relate to dynamic auscultation (see below).
Holotsystolic murmurs are also known as pansystolic and include the murmurs of mitral regurgitation (MR), tricuspid regurgitation (TR), and ventricular septal defects (VSD). Since the intensity of these murmurs is high immediately after the onset of S1 and it extends to just before the S2, often the S1 and S2 sounds are overwhelmed by the murmur and may be difficult to hear.
Mitral regurgitation (MR)
The murmur of mitral regurgitation is described as a high-pitched, "blowing" holosystolic murmur best heard at the apex. The direction of radiation of the murmur depends on the nature of the mitral valve disease; however, it usually radiates to the axilla. The intensity of the murmur of MR does not increase with inspiration, which helps to distinguish it from the murmur of tricuspid regurgitation.
Tricuspid regurgitation (TR)
The murmur of tricuspid regurgitation is similar to that of mitral regurgitation. It is a high-pitched, holosystolic murmur. However, it is best heard at the left lower sternal border and it radiates to the right lower sternal border. The intensity significantly increases with inspiration, which helps to distinguish it from mitral regurgitation. This inspiratory enhancement of the tricuspid regurgitation murmur is called "Carvallo's sign."
Ventricular septal defect (VSD)
A ventricular septal defect produces yet another holosystolic murmur. Blood abnormally flows from the LV (high pressure) to the RV (low pressure), creating turbulent blood flow and a holosystolic murmur heard best at "Erb's point." The smaller the ventricular septal defect, the louder the murmur.
Late Systolic Murmurs
The murmur of mitral or tricuspid valve prolapse is the only significant late systolic murmur. Tricuspid valve prolapse is relatively rare and usually not clinically significant.
Mitral valve prolapse (MVP)
Mitral valve prolapse produces a mid-systolic click usually followed by a uniform, high-pitched murmur. The murmur is actually due to mitral regurgitation that accompanies the mitral valve prolapse, thus it is heard best at the cardiac apex. Mitral valve prolapse responds to dynamic auscultation.
Summary of Systolic Murmurs