What is Aortic Stenosis
Aortic stenosis is the medical term used for a tight aortic valve. The aortic valve is the valve through which blood leaves the heart. A tight valve means greater stress on the heart and less blood to the body. The body needs blood to survive and the heart is responsible for pumping blood around the body. The main pumping chamber of the heart is called the left ventricle. Every time the left ventricle beats it pumps blood out to the body. To leave the heart though, the blood has to go through the aortic valve. The aortic valve is like a door that opens to allow blood to exit the heart and then closes to stop blood from leaking back in. In aortic stenosis the aortic valve is tight and cannot open properly. The tight valve means it’s harder for blood to leave the heart to reach the body where it is needed.
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How Does Aortic Stenosis Affect the Heart?
Significant aortic stenosis is a stress on the heart and can lead to symptoms and heart failure and when severe enough can lead to death. As we said above, the aortic valve is like the door that blood has to go through to get to the body. Imagine that door hardly opened. The body would still need the same amount of blood but the heart would have to work much harder to pump the blood through a tight valve. The heart adapts to this over time and the heart muscle becomes thicker, much in the same way a bodybuilder gets bigger muscles as they life heavier and heavier weights. Unfortunately a thick heart muscle has negative consequences. The heart that used to be able to fill with blood now finds that more difficult because it is so thick. This leads to congestion, and congestive heart failure. The pressures generated by this thick heart are very high, as this is required to allow blood to leave the severely tight valve and reach the body. This may lead to passing out and potentially fatal heart rhythms. Also at some point, the heart will be required to generate such high pressures that it simply gets overwhelmed and fails. At this point the pumping function of the heart can seriously deteriorate and the heart becomes very weak.
What Happens to the Valve In Aortic Stenosis?
In most cases of aortic stenosis the valve becomes thick and full of calcium which can result in severely restricted valve opening. Decades ago rheumatic fever was the most common cause of aortic stenosis. Rheumatic fever is now rare in the Western world but aortic stenosis is becoming more and more common. This is because people are living longer and longer. Over time the aortic valve is subject to damage and degeneration, wear and tear, almost like joints are more likely to pose a problem in the elderly. This degeneration of the valve results in a process called calcification, which is basically build up of calcium. This calcium build up causes the valve to become less and less mobile, restricting the ability of the valve to open. In severe aortic stenosis, the valve leaflets hardly move and the valve becomes very tight.
When Aortic Stenosis Becomes Dangerous
Severe aortic stenosis is dangerous, particularly when symptoms develop. Mild aortic stenosis, or aortic sclerosis is not a problem. The heart usually handles moderate aortic stenosis well unless there are other heart problems going on. Problems typically develop when there is severe aortic stenosis however. Although in many people the heart can handle severe aortic stenosis well for a while, at some point the stress will become too much. When patients with severe aortic stenosis develop symptoms or show signs of heart weakness, it’s time to do something. This is because the combination of severe aortic stenosis and symptoms results in a significantly reduced life expectancy. At this point it’s clearly time to fix the valve. Once chest pain, passing out, or heart failure develop, patients with severe aortic stenosis are not likely to survive more than a few years unless the aortic stenosis is treated.
Signs and Symptoms of Aortic Stenosis
Symptoms of aortic stenosis include fatigue, shortness of breath, chest pain, feeling dizzy and passing out. It’s rare to develop signs and symptoms of aortic stenosis unless the degree of aortic stenosis is severe. Commonly patients may presents with fatigue, the tight valve means it’s difficult to pump the amount of blood the body needs. Fatigue may mean slowing down, reduced levels of activity, or just less energy. Tasks that patients used to do may be much harder. Shortness of breath is another common complaint from patients with severe aortic stenosis. This is a sign if congestive heart failure. There may be swelling also. The high pressures generated by the heart in response to the tight valve may lead to chest pain, particularly on activity. Some patients experience passing out spells; this may be due to dangerous heart rhythms.
Grading Severity of Aortic Stenosis
Grading the severity of aortic stenosis can be challenging and best results are seen from dedicated valve specialists.
Although there are criteria for diagnosing aortic stenosis its important to realize that decision making in patients with aortic stenosis is complex. The tests used are not an exact science. Often tests are not accurate and a number of factors need to be taken in to account to come to a conclusion. Many patients with severe disease are misclassified as being less than severe. In the same way some patients have their symptoms attributed to aortic stenosis when in fact the valve is not the issue.
Normal Aortic Valve
As we stated above, aortic stenosis is a tight aortic valve. Every time blood leaves the heart it needs to go through the aortic valve. A normal aortic valve that opens fully provides no obstruction and allows as much blood as needed to leave the heart. Imagine the normal aortic valve area to be as big as the clock face of a medium sized wristwatch. This can be from 3 to 4 cm2 in area.
Mild Aortic Stenosis
Aortic stenosis is tightening of the aortic valve and mild aortic stenosis is a mild tightening. As we said above the usual aortic valve area is like a medium sized wristwatch around 3-4 cm2 in area. Generally, in mild aortic stenosis, the tight valve remains greater than 1.5-2 cm2. Interestingly, this means the valve isn’t really considered to have mild tightening until it reaches less than half its normal size. Mild aortic stenosis is not of any real significance and does not place strain on the heart or the body. When pressure measurements are taken across the valve in mild aortic stenosis using Doppler ultrasound, a mean gradient of less than 20mmHg across the aortic valve should be measured. We are able to measure the pressure difference across the valve because as the valve begins to tighten, the blood spurts through the valve at faster and faster speeds, much like when you put your thumb over the end of a garden hose. Doppler ultrasound can measure this speed and convert it into a pressure drop across the valve, which we can use to define how severe the valve stenosis has become.
Moderate Aortic Stenosis
In moderate aortic stenosis, the valve continues to get tighter. Generally in moderate aortic stenosis the valve area is in the 1 – 1.5 cm2 range. Moderate aortic stenosis is not usually of any significance and does not cause symptoms alone. It is handled well by the body. When pressure measurements are taken across the valve in mild aortic stenosis, a mean gradient of greater than 20mmHg but less than 40mmHg across the aortic valve should be noted.
Severe Aortic Stenosis
In severe aortic stenosis the aortic valve starts to get severely tight. The area of the aortic valve in aortic stenosis is generally less than 1 cm2. This is considered to be a severe obstruction to blood flow leaving the heart and places the heart under strain. Surprisingly patients can handle severe aortic stenosis well and if they have no symptoms this can simply be watched, albeit closely. Once symptoms develop however, the valve needs to be fixed, and relatively quickly. When pressure measurements are taken across the valve in severe aortic stenosis a mean gradient of greater than 40mmHg across the aortic valve should be noted.
Diagnosing Aortic Stenosis
Murmur – Patients with aortic stenosis will have a classic murmur when listened to with a stethoscope over the chest wall. It is a murmur that radiates up to the neck because that is the direction of the blood flowing through the valve as it enters the aorta through the diseased valve.
Pulses – Patients with aortic stenosis have a classic pulse waveform known as parvus et tardus. This means weak and late peaking. It is weak because it’s harder to pump as much blood through the diseased valve, and its late peaking because it takes longer to pump the blood through the tight valve.
Echocardiogram – This is the most important test in confirming the diagnosis and providing the critical information. The echocardiogram is the ultrasound scan test of the heart that gives us pictures of the valve and allows us to take measurements. This will show the tight valve and allow us to calculate a valve area based on pressure gradients through the valve. The echocardiogram also gives us information on the pumping function of the heart and the heart size. This test can also pick up other valve issues such as mitral regurgitation and tricuspid regurgitation. Patients may need a mitral valve repair or mitral valve replacement at the same time if they have a severely leaky mitral valve also.
Transesophageal Echocardiogram – This is an ultrasound scan of the heart, but in more detail, as the probe is passed in to the food pipe (esophagus) where it is close to the heart and can therefore give very clear pictures. This test is very useful in detailing structural heart disease. This allows us to see the valve in great detail and gives us information about other structures within the heart. Often when the normal echocardiogram findings are still unclear, the transesophageal echocardiogram can clarify the issue.
Heart Catheterization – In this test small tubes are passed up to the heart in order to gain information regarding heart pressures and also about the arteries that supply the heart with blood. In general most patients undergoing valve surgery will have a heart catheterization first to make sure no operation is required for the arteries either. Echocardiography is so good now that heart catheterization is rarely used to make a diagnosis of aortic stenosis, however in some complex cases, heart catheterization is used to confirm the diagnosis.
Treadmill Stress Testing – In some patients a treadmill exercise test is used to see the extent of symptoms or functional limitations caused by any aortic stenosis and potentially unmask symptoms patients didn’t know they had.
Stress Echocardiogram – In some cases the diagnosis of aortic stenosis is made difficult by either a weak heart pumping chamber or a small heart cavity. In these cases, standard testing may suggest a moderate tightening when in fact it is functionally severe. For this reason, in these patients, a chemical called dobutamine may be given to speed up the heart rate and the force of contraction, unmasking a severely tight valve of severe aortic stenosis. This is known as a dobutamine stress echocardiogram.
Medical Treatment of Aortic Stenosis
There is no medicine to treat significant aortic stenosis, it is a mechanical problem that requires a new valve to correct it. As things stand now, aortic stenosis is a problem of the valve itself and there is no medicine proven to prevent aortic stenosis or to reverse the valve tightening. For this reason valve replacement is the preferred treatment option. It’s important to make sure other cardiovascular risk factors are treated in patients with aortic stenosis for a number of reasons. Preventing the progression of other diseases such as artery diseases will improve outcomes. It’s also important to treat high blood pressures in this patient group.
When is it Time to Replace the Valve in Aortic Stenosis?
In general, in significant aortic stenosis, once symptoms develop or there is evidence of heart stress, its time to replace the valve. The answer is simple: in patients with severe aortic stenosis, once symptoms develop its time to replace the valve. Those symptoms were described a little earlier in this article. In patients with evidence of a weak heart due to the diseased aortic valve, the valve should be replaced even if there are no symptoms. In some cases, when the valve is very severely tight, a case can be made for replacing the valve even in the absence of symptoms.
Another time when the valve would be replaced before symptoms is when patients are undergoing cardiac surgery for some other reason and there is moderate or severe aortic stenosis. Although patients with severe aortic stenosis and no symptoms may be watched without valve replacement, it’s important to watch this group closely because if symptoms develop and they are not treated soon enough outcomes can be poor unless the aortic valve is replaced.
Why Don’t We Just Operate On Everyone With Aortic Stenosis?
In order for a treatment to be justifiable, the risk of the treatment has to be less than simply leaving the disease alone. This needs to take in to account both the short term and the long-term outcomes. In patients with less than severe aortic stenosis its very unlikely the condition will pose a risk. While it is obvious that patients with severe aortic stenosis and symptoms need to have their valve replaced, the situation is less clear in patients with aortic stenosis and no symptoms.
Let me walk you through some of the facts that help influence this decision. The chance of dying due to surgery for aortic valve replacement is around 2.5 %. This includes all patients, from the highest of the high risk to the lowest of the low risk. If we take a 70-year-old patient for example, with no other illness that is coming simply for what we would consider a low risk valve replacement, the chance of dying due to valve surgery is now less than 1%.
This is where it gets interesting. The risk of dying due to the severe aortic stenosis if we were to do nothing is around 0.5 – 1% per year. This approaches the risk of a low risk surgery and so in some circumstances it may be reasonable to consider valve surgery despite the lack of symptoms. On the other hand, in a high risk patient, where the risk of surgery is higher than the risk of simply watching the aortic stenosis, the risk of aortic valve replacement cannot be justified.
In centers of excellence, attention can be paid to risk factors in patients with no symptoms to see who is potentially in a higher risk group. These include patients with abnormal exercise tests, severely thick hearts, very calcified valves, and very tight valves. In patients with one or more of these risk factors it may be reasonable to perform aortic valve replacement in centers of excellence with known good outcomes.
Aortic Valve Replacement Surgery and TAVR procedure
Traditional Open Heart Surgery
Open heart surgery is the traditional method of replacing the aortic valve. The patient is put to sleep under anesthetic and the chest opened down the middle. This is called a sternotomy. Many of you may be familiar with the sternotomy scar that is the scar that runs down the middle of the top half of the chest. In this procedure the heart is placed on a heart lung bypass machine and the heart is stopped. The diseased aortic valve is then replaced with a new aortic valve. The heart is then restarted and the patient taken off the heart lung bypass machine. The in hospital stay will be in the region of a week. By this time most patients will be walking.
Mini Aortic Valve Surgery
This is still open-heart surgery however the incision made on the chest is much smaller than the traditional one. It is just a few inches long. The advantages to a mini approach are a much smaller scar and less trauma with faster healing times. Mini aortic valve replacement is generally the method of choice for the patients of established experts in valve surgery.
Transcatheter Aortic Valve Replacement (TAVR) – The New Revolution
TAVR also known as TAVI or transcatheter aortic valve replacement, is the revolutionary new method of replacing the aortic valve. With TAVR, the procedure is performed without having to place the patient on a heart lung machine. Most TAVR procedures are performed through small tubes that are inserted in to the arteries of the leg. The valve is passed up to the heart through these tubes and placed inside the diseased valve. The valve is then expanded in to place, crushing the old valve out the way and leaving the new valve functioning nicely. The TAVR procedure is outlined in detail in this linked article. In the few patients where TAVR cannot be performed through the arteries of the leg because they are too small or too diseased, then the TAVR is performed through a small incision on the chest wall. Incredibly, in expert centers, some TAVR patients are sent home in as little as 1-2 days after the procedure. Even more incredible is that we are beginning to perform TAVR procedures in patients without even having to put them to sleep.
Ensuring the Best Outcomes – Centers of Excellence
In patients with aortic stenosis, the key is to go to centers of excellence such as Princeton Baptist Medical Center where experts who live and breathe heart valve disease manage the condition. This ensures a number of things. First and foremost is a correct diagnosis and accurate assessment of the severity of the disease. Often this requires the expertise of dedicated imaging experts with expertise in advanced techniques such as cardiac CT scanning and 3D-echocardiography. Expert centers will have the entire range of treatment options available from standard, to mini, to TAVR, to ensure that the appropriate treatment is selected for each patient rather than simply a second best option because that’s all that is available at that place. This way low risk patients are ensured to remain at low risk and the highest risk patients that would have had no option previously are given good options. Expert centers ensure that experienced operators will perform procedures in top class facilities. Centers of excellence ensure no shortcuts are taken and that complication rates remain low. Heart surgery and procedures are a high stakes game. Even in the most routine of cases, unexpected things can happen and situations become critical. It simply makes sense to be in the right place with the right people in that event.