Systolic and Diastolic Murmurs
Systolic murmurs occur between S1 and S2 (first and second heart sounds), and therefore are associated with mechanical systolic and ventricular ejection. Mid-systolic murmurs typically have a crescendo-decrescendo character, that is, they start softly and become loudest near mid-systole, followed by a decrease in sound intensity as shown in the figure to the right. This type of murmur is caused by either aortic or pulmonic valve stenosis. A second type of systolic murmur is holosystolic (sometimes called pansystolic) because the intensity is high throughout systole as shown in the figure. This type of murmur is caused by mitral or tricuspid regurgitation, or by a ventricular septal defect.
Diastolic murmurs occur after S2 and before S1; they are therefore associated with ventricular relaxation and filling. Such murmurs may be caused by aortic or pulmonic valve regurgitation. With outflow tract insufficiency, regurgitation begins immediately after S2 and quickly reaches maximal intensity, which then diminishes throughout diastole (descrescendo murmur) as shown in the figure to the right. A diastolic murmur may also be caused by mitral or tricuspid valve stenosis. With atrioventricular valve stenosis, the murmur is delayed beyond S2 when the ventricular pressure falls below atrial pressure and the atrioventricular valve opens. The sound is most intense early in diastole, then declines in intensity (descrescendo murmur). Near the end of diastole, atrial contraction can cause a brief increase in murmur intensity as shown in the bottom example in the figure.