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J Thorac Cardiovasc Surg 2008;135:1278-1279
© 2008 The American Association for Thoracic Surgery
Invited Commentary |
However, just as a movie critic needs to find something wrong with a movie to maintain credibility as a critic, I can't let you off scot-free. The positive aspects your study include the fact that it is a large study of more than 3000 patients who received a single type of valve with a mean follow-up of 5 years. A sophisticated statistical analysis (and thank you for the explanation of the Z value) to minimize confounding variables lends further clarity to the data. However, this is not a population with isolated pure aortic stenosis, with 56% of the patients having undergone concomitant coronary bypass surgery and 35% of patients also having aortic regurgitation, factors known to affect outcomes. In addition, only 13% of the patients were actually asymptomatic, yet significant management conclusions are drawn from this group.
My specific questions are as follows. First, you defined a small prosthesis as a patient–prosthesis Z value of –1.5, which corresponds to 1.5 standard deviations below normal valve size for patient body surface area. Why did you pick that Z value rather than perhaps 1 or 2?
Second, do you think that analysis of a population in whom more than half of the patients underwent coronary artery bypass grafting and one third of the patients had aortic regurgitation is valid for isolated pure aortic stenosis?
Third, we now make clinical decisions in patients with asymptomatic mitral regurgitation on the basis of an effective regurgitant orifice greater than 40. Surgeons are familiar with echocardiographic parameters of AV area, peak and mean gradients, jet velocity, and EF for making decisions. Should we now include an LV mass index of greater than 135 in men or greater than 100 in women as an indication for surgery in patients with critical aortic stenosis?
Four, as surgeons, we always want to know what to do different when we go home. We use the red, yellow, green charts to choose valve size now based on patient body surface area. Do your data mean that we should now ignore those color charts for elderly patients?
Fifth, you state that guidelines should be changed to recommend earlier AVR in asymptomatic patients, yet current guidelines, class IIb, already recommend AVR in asymptomatic patients with either an abnormal exercise test, likelihood of rapid progression based on age, calcification and coronary artery disease, or extremely severe aortic stenosis with a valve area of less than 0.6 cm2. How specifically would you recommend these current guidelines be changed?
Last, is it possible to come up with a patient management algorithm factoring in all the variables you have identified, including age, severity of aortic stenosis, LV dysfunction, LV mass index, to guide the timing of surgical interventions?
Dr Mihaljevic. The first question was why did we define a Z value of –1.5 as a cutoff? That was not truly a deliberate decision. That was a result of an observation that by the Z value of –1.5 and less, we noted the detrimental effects of the patient–prosthesis mismatch that truly affected the outcomes of our patients, in particular in those patients who had severe LV hypertrophy.
Your second question was whether we think that the analysis of the population in whom more than 50% of patients underwent coronary artery bypass grafting and one third of patients had severe aortic regurgitation is truly representative of typical patients with aortic stenosis. We think this is definitely the case. We purposely included these patients, because when patients present to a surgeon or a cardiologist with aortic stenosis, this is what typical patients look like. These are the patients who almost always have some degree of aortic regurgitation, but we were careful to exclude patients in whom the aortic regurgitation was a predominant pathology. Furthermore, it is just a reality that most of these patients will have coronary artery disease. The median age of patients in our study was 71 years, so those patients are most likely going to have coronary artery disease, and those are the patients we are going to see referred to us for aortic stenosis. We don't know if the coronary artery disease is present up front until they undergo a coronary angiogram. We are currently conducting a study in which we are particularly studying the effect of coronary artery disease in patients and their outcomes when they have severe aortic stenosis. Our preliminary findings show that the presence of coronary artery disease triggers the symptoms in patients with aortic stenosis much earlier in the course, and those patients almost never develop severe LV hypertrophy, because they become symptomatic much sooner in the course of their illness.
Your third question was regarding the echocardiographic parameters and whether we should use the LV mass index of greater than 135 as an indicator for surgery. I would absolutely concur with this statement. We as surgeons have to be familiar with new echocardiographic measurements, and just as you mentioned an example of mitral valve surgery, I think we have to pay particular attention to the ventricular effects of valvular heart disease. Ultimately all untreated patients with aortic stenosis die not because their aortic stenosis gets worse but because the effects of the aortic stenosis on the ventricle caused it to fail. The presence of severe LV hypertrophy should not any longer be viewed as a benign side effect of aortic stenosis, which will be reversed after we replace the AV, but a significant contributor in the pathology or bad outcomes of these patients even after a successful operation.
Your fourth question related to the sizes of the AV prostheses that should be used for elderly patients with severe aortic stenosis. As you saw from our presentation here, if we take a look at the entire population of patients with aortic stenosis and compare those who have severe patient–prosthesis mismatch with those who have prostheses that are larger than their anticipated AV area (standard AV area), their overall survival is fairly similar. When we look at patient–prosthesis mismatch, we have to look at the different ages of the patients undergoing operation, and in an elderly patient, the survival is truly not affected by a smaller prosthesis. So even implantation of a relatively small prosthesis was sufficient enough to relieve the gradient to the extent that it was beneficial to survival. If we take a look at our curves of survival of elderly patients, they benefited the most from AVR. Their survival is better than the expected survival of their matched cohorts, in contrast with our younger patients.
The fifth question is an important question about the current guidelines and class IIb indications for AVR for asymptomatic patients. In our opinion, some of these class IIb indications should be class I indications. For example, AV stenosis with an AV orifice area of –0.6 and a high gradient of 60 should truly be an indication for surgery based on our data. As you can see from the curves shown previously, patients with severe aortic stenosis and high gradients did poorly, even after initial successful surgery. If we take a critical look at the criteria that was used for the medical management, for example, of patients with asymptomatic aortic stenosis, all articles had a series with no more than 150 patients, with a follow-up that was not more than 1.5 to 2 years. The longest observed survival in patients with severe aortic stenosis who were asymptomatic and underwent medical management was 67% 1-year event-free survival. The survival of patients who undergo surgery in the same condition is approximately 10% to 15% better after the first year. Obviously, they lack long-term follow-up because most of the patients develop symptoms anyhow and undergo surgery.
We hope that this article is going to be a significant contribution to influence a change in the guidelines for treatment of patients with asymptomatic aortic stenosis.
Your last question was, is it possible to come up with a patient management algorithm to include all the risk factors and come up with a new management scheme? Yes, absolutely. What we have to take into consideration now is no longer only the AV orifice area and gradients but also the degree of the LV hypertrophy, the age of the patients, and the degree of the LV dysfunction at the time of surgery, which most of us have been doing intuitively.
Related Article
J. Thorac. Cardiovasc. Surg. 2008 135: 1270-1279.
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