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.