Wikipedia:Osmosis/Aortic valve diseases
Author: Tanner Marshall, MS
Editor: Rishi Desai, MD, MPH
The aortic valve is typically made up of three leaflets - the left, right, and posterior leaflet and it opens during systole to allow blood to be ejected to the body. During diastole, it closes, to allow the heart to fill with blood and get ready for another systole. If the aortic valve doesn’t open all the way, it gets harder to pump out to the body, and this is called aortic stenosis. If it doesn’t close all the way, then blood leaks back into the left ventricle, called aortic valve regurgitation or aortic insufficiency.
Usually, the aortic valve opens to about 3-4 cm2, but with stenosis it can become less than 1 cm2. This is usually caused by mechanical stress over time, which damages endothelial cells around the valves, causing fibrosis and calcification, which hardens the valve and makes it more difficult to open completely. This type usually shows up in late adulthood, with patients over 60 years old.
Similarly, patient that have a bicuspid valve, with two leaflets, as opposed to a tricuspid with three, are more at risk of fibrosis and calcification since the mechanical stress that’s usually distributed between three leaflets is now being split by two leaflets, and therefore they see more stress per leaflet. Another important cause of aortic stenosis is chronic rheumatic fever, which can cause repeated inflammation and repair, leading to fibrosis. In this case, the leaflets can actually fuse together, called commissural fusion, which can be an important distinction from the type caused by mechanical stress over time.
When the valve fuses together or hardens, it doesn’t open as easily, right? And so as the left ventricle contracts, it creates this high pressure that eventually pushes on the valve until it finally snaps open, causing a characteristic “ejection click”.
Since the blood has to flow through a narrow opening, there’s turbulence which creates noise or a murmur, which gets initially gets louder as more blood flows past the opening and then quieter as the amount of blood flowing subsides because less remains in the ventricle. This is called a crescendo-decrescendo murmur.
Since now it’s harder to open and push blood past this hardened valve, the left ventricle has to generate higher pressures each time it contracts to get the same amount of blood through. To accomplish this, the left ventricle can thicken its muscles, called concentric left ventricular hypertrophy. This happens because new sarcomeres are added in parallel to the existing ones.
Even though you have this bulked up ventricle, the heart still might struggle to get enough blood through the narrowed opening and the body, and ultimately to the vital organs, and that means that the person’s at risk of developing heart failure, and various symptoms related to whichever organ’s involved. For example, if there’s a reduction in blood flow to the brain, it could lead to syncope, and a reduction in blood flow through coronary arteries to the heart’s own myocardium could cause chest pain and angina. Patients might not initially experience symptoms at rest, only during exercise, because exercise requires more blood, right? And this heart isn’t able to increase blood flow through the small opening.
A final complication is called microangiopathic hemolytic anemia, which is essentially damage to red blood cells as they’re forced through the smaller valve, splitting them into smaller fragments called schistocytes, leading to hemoglobinuria, which is hemoglobin in the urine. Treatment is usually replacement of the valve, which often doesn’t happen until after the onset of symptoms.
Alright so that was aortic stenosis, what about aortic regurgitation? Well normally, right after the ventricle pumps blood out through the aortic valve, the valve shuts and remains shut until the ventricle fills again. With aortic regurgitation, or sometimes called aortic insufficiency, blood flows back from the aorta into the left ventricle during diastole, or during ventricular filling. About half of cases are caused by aortic root dilation. Which is where the root dilates, or gets bigger, and in doing so pulls apart the leaflets, making it harder for the valves to fit snugly together and close all the way and letting some blood flow backward. The vast majority, about 80% of aortic root dilations are idiopathic, which means that the cause is unknown. The remaining 20% of causes are things like aortic dissection, aneurysms, and syphilis, all of which can ultimately lead to a widened the aortic root. Besides root dilation, regurgitation may happen due to valvular damage, from something like infective endocarditis, a bacterial infection of the inner lining of the heart, or again from chronic rheumatic fever.
In this situation, the chronic inflammation leads to fibrosis, but instead of fusing the valve leaflets together, it makes it so that they don’t form a nice seal and instead let blood leak through. Patients with aortic regurgitation will have an early decrescendo diastolic murmur, caused by the blood flowing back through the valve.
Since blood’s leaking back from the aorta into the left ventricle, the left ventricular blood volume increases which increases the stroke volume or the amount that the left ventricle pumps out during contraction, or systole. More blood pumped out of the heart per squeeze, requires more pressure, so systolic blood pressure increases. During diastole, though, there’s less blood volume in the aorta since some has leaked back into the ventricle, which means that diastolic blood pressure decreases.
A higher systolic pressure and lower diastolic pressure means an increase in pulse pressure, which is just systolic pressure minus diastolic pressure. A large pulse pressure, meaning a large difference between systolic and diastolic pressure, is referred to as a hyperdynamic circulation.
Patients with a hyperdynamic circulation have bounding pulses, or water-hammer pulses because the blood (which is mostly composed of water) slams like a hammer against the walls of the arteries with each heartbeat.
These bounding pulses can be dramatic enough that they cause head bobbing that’s in tune with the heartbeat, as well as causing the capillary beds in the fingernails to pulsate, sometimes called Quincke’s sign.
Over time, the increase in blood volume in the left ventricle causes the chamber to grow larger, called eccentric ventricular hypertrophy. In this situation, new sarcomeres are added in series to existing ones. Just like aortic stenosis, treatment for aortic regurgitation is replacement of the valve after symptoms and left ventricular dysfunction develops.
SUMMARY
All right, as a quick recap…. Aortic stenosis happens if the aortic valve doesn’t open all the way, and aortic valve regurgitation happens if the valve doesn’t close all the way. Both can cause murmurs and hypertrophy of the left ventricle. Stenosis can also lead to heart failure and microangiopathic hemolytic anemia, while regurgitation can also cause hyperdynamic circulation. Treatment for both is replacement of the valve after symptoms have developed.
Sources
[edit]Goljan
Pathoma