Systolic ejection or midsystolic
murmurs are due to turbulent forward flow across the right and left
ventricular outflow tract, aortic or pulmonary valve, or through
the aorta or pulmonary artery.
Turbulence is produced by obstruction to blood flow, vascular
dilation, increase in the velocity of flow or a combination.
The ejection of blood begins after closure of the AV or
atrioventricular (mitral and tricuspid) valves and is preceded
by the time it takes for the ventricular pressures to sufficiently
exceed the aortic and pulmonary diastolic pressure and force open
the aortic and pulmonary valves. Because of this delay, there
is a silent interval between the first heart sound (S1 is produced
by closure of the AV valves) and onset of the murmur.
Since ejection ends before closure of the outflow or semilunar
(aortic or pulmonary) valve, there is another silent interval
between the end of the murmur and closure of the valve on the
side from which it originates. Thus, left sided murmurs will terminate
before closure of the aortic valve (A2 component of S2) while
right-sided murmurs will end before closure of the pulmonary valve
(P2 component of S2).
In contrast, the holosystolic murmur of mitral regurgitation
(MR) begins with S1 and continues throughout systole and up to
S2, without intervening silent intervals. Use the “play”
buttons on the above animation to toggle between an ejection and
a holosystolic murmur.
The ejection murmur first increases and then decreases in
intensity (known as a cresecendo-decrescendo pattern) to give it
a “diamond shaped” configuration. The overall intensity
of the murmur is proportional to the rate of ventricular ejection.
Also, the intensity of the murmur at any given point of ejection
is dependent upon flow at that specific time. Thus, if flow is highest
in early ejection, the intensity of the murmur will peak early.
In contrast, the murmur will peak late if flow is higher during
the later phase of ejection.
