How does decreased preload affect the murmur of aortic stenosis?

How does decreased preload affect the murmur of aortic stenosis?

• A. It shows little to no change with decreased preload
• B. It worsens with decreased preload
• C. It disappears with decreased preload
• D. It becomes holosystolic with decreased preload

Answer: (A)

The main idea here is that the murmur of a fixed outflow obstruction like aortic stenosis depends on how much blood is flowing across the narrowed valve, but small to moderate changes in preload don’t drastically alter that flow. In aortic stenosis, the turbulence causing the murmur comes from the high-velocity jet through the stenotic valve during systole. While preload (venous return) changes stroke volume and the amount of flow, the obstruction itself doesn’t change, so the intensity of the murmur remains largely the same with decreased preload. In contrast, other conditions with dynamic outflow obstructions show more pronounced changes with preload, but for aortic stenosis the murmur is relatively preload-insensitive.

The main idea here is that the murmur of a fixed outflow obstruction like aortic stenosis depends on how much blood is flowing across the narrowed valve, but small to moderate changes in preload don’t drastically alter that flow. In aortic stenosis, the turbulence causing the murmur comes from the high-velocity jet through the stenotic valve during systole. While preload (venous return) changes stroke volume and the amount of flow, the obstruction itself doesn’t change, so the intensity of the murmur remains largely the same with decreased preload. In contrast, other conditions with dynamic outflow obstructions show more pronounced changes with preload, but for aortic stenosis the murmur is relatively preload-insensitive.