150. What causes a III/VI crescendo-decrescendo murmur heard at the right upper sternal border that peaks early in systole and does not change with handgrip?

This is a describes the murmur of mild 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 AS murmur is often mistaken for a carotid bruit. The AS 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 AS 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 AS.
    The intensity of the murmur of AS is not a good indicator as to the severity of disease. As AS worsens, the left ventricle 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 AS, the shape of the murmur can be very helpful. As AS 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 AS would have an early peaking murmur while the murmur of severe AS peaks later in systole.