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OUR MISSION: TO REDUCE THE BURDEN OF CARDIOVASCULAR DISEASE
Dr. Otto addressed the issue of when to intervene in aortic stenosis. A previous study from Dusseldorf indicated that survival with aortic valve replacement was very much better than with medical therapy. There is not likely to be a randomised trial in the symptomatic patient with severe aortic stenosis. Therefore, the classic indication is a symptomatic patient with severe aortic stenosis. The next issue to address is what is severe aortic stenosis?
The definitions used have included a peak velocity of >4m/s, mean pressure gradient of >40mmHg and a valve area of <1.0cm², and both guidelines have used these similar criteria. However it is important that these criteria should be measured both correctly and accurately. Both velocity and mean gradient are very dependent on the blood flow across the valve. As a result, if the valve flow is increased, as with associated aortic regurgitation, both velocity and mean gradient will be higher, and will not necessarily indicate that aortic stenosis is severe. Velocity is also influenced by left ventricular systolic function, and thus in patients with reduced ejection fraction, the velocity and also mean gradient may be low in spite of the patient having severe aortic stenosis. The next issue that comes up are the symptoms relating to aortic stenosis, and how should symptoms be determined? Symptoms are obtained by a careful history and if there is a concern, exercise test can be performed, when it must be determined if symptoms occur and if blood pressure response is adequate. Exercise testing should not be done in symptomatic patients. More recently, BNP has been advocated for the assessment of the functional status. Patients with a bicuspid aortic valve have the problem of either aortic stenosis or aortic regurgitation, and a dilated ascending aorta. The dilated ascending aorta (≥4.5cm) is an indication for surgery, and could be combined with valve surgery if the valve lesion is severe. The asymptomatic patient poses a difficult problem, where one has to balance the risks versus the benefits. Another problem is the situation of the patient with severe aortic stenosis, but a low valve gradient. The gradient may be low because of small stroke volume or the presence of hypertension, and/or a reduced ejection fraction. A dobutamine stress test is usually advocated to separate severe aortic stenosis from non-severe aortic stenosis in this latter condition.
Dr. Eric Butchart discussed the choice of an appropriate prosthetic heart valve. The issues that have to be taken into account are manifold. Valve prothesis patient mismatch is associated with an increased operative mortality, especially in those with a reduced ejection fraction. Severe valve prosthesis patient mismatch is associated with increased morbidity and mortality. The usual choice is between a mechanical and a bio-prothesis. Mechanical valves are durable, with maximum documented follow up rate of up to 40 years, but have the disadvantage of requiring lifelong anticoagulation therapy. The bio-prosthesis has the disadvantage of structural valve deterioration. Moreover, the younger the patient, the higher the incidence of structural valve deterioration. For aortic replacement, the break-off point for structural valve deterioration of the aortic position is 60 to 65 years. Dr Butchart emphasised that frequently in the literature, structural valve deterioration has been judged by the need for re-operation, but the earliest manifestation of structural valve deterioration is documented very soon after valve replacement if the valve can be examined at pathology. By echocardiogram, structural valve deterioration can be demonstrated before the need for re-operation. The use of anticoagulation therapy is associated with an increased risk of bleeding. In older people, the risk of bleeding, even without anticoagulation therapy, is about 1.2% per year, and administration of anticoagulant therapy will increase that risk considerably, depending on associated conditions. Furthermore, even those who have a bio-prosthesis and do not need anticoagulation are at risk of atrial fibrillation, for which they would need anticoagulation therapy. The final consideration is the issue of quality of life and risk of re-operation. After successful valve replacement, the quality of life is initially similar with mechanical and bio-prosthetic valves. However, the development of structural valve deterioration, if not recognised and treated, may result in the demise of the patient. If re-operation is needed, the risks associated with the re-operation are higher than of the initial operation, but are very low in the asymptomatic or minimally symptomatic patient, but is increased considerably if they are severely symptomatic.
Dr. Mohr discussed the innovative new surgical approach of transapical aortic valve replacement. It has the advantage of avoiding a sternotomy and can be performed on a beating heart without the use of extracorporeal circulation. However, so far, he has placed wires in the femoral vessels to be used for emergency extracorporeal circulation, if needed. The first patient was treated in 2004, and lessons were learned. These were incorporated and the procedure was re-started in 2006, and many have been done worldwide. In Dr Mohr’s centre in Leipzig, 122 implantations have now been done, and are being used for patients at high risk for the standard procedure. The indications include symptomatic patients with severe aortic stenosis, those aged 75 years or older, and patients must have a ≥24mm annulus, and should be suitable for standard aortic valve replacement. In this series, the 30 day mortality was 6.5%, which compares with the predicted mortality by STS criteria of 20%. In addition, there is further 13.8% mortality during the first year. 4.7% of patients have needed immediate conversion to open heart surgery. The success rate is greater than 90% and is as safe as with MidCab. At one year, the re-operation rate was 1.6% and the actuarial survival was 74.4%. Prof. Mohr also described that they have developed a valve-in-a-valve (V-in-V) procedure that has been used in 1 patient so far to deal with a bio-prosthetic valve with structural valve deterioration.
Dr. Cribier provided an update on percutaneous valve replacement. A total of 700 patients have been treated worldwide with this technique. The valves that are available in the current ongoing studies include those of Edwards, (Cribier-Edwards / Edwards-Sapien) and CoreValves. It has been used in those who have a contraindication to surgical valve replacement or in those who are at very high risk for surgery. Initially, the antegrade approach was used in 36 patients, which required a transseptal puncture. The valve area was increased to 1.7cm², with an early increase in ejection fraction. The initial use was with a 23mm sized valve, which resulted in significant amounts of perivalvular regurgitation. A more promising strategy has been the use of the transfemoral retrograde approach. It has been used in patients 70 years of age or older, with a valve area of ≤0.6cm²/m², NYHA class 2 or greater, and those at very high risk, with an estimated risk of death by EuroScore of 20%, and an STS score of >10%, or in those with a contraindication to the traditional valve replacement. 214 such cases have been performed, with a success rate of >85%. The 30 day mortality ranged from 10 to 12%, comparing favourably to the predicted mortality of 31%. The myocardial infarction rate was 1%, and MACCE occurred in 13%. Currently, a problem associated with the transfemoral approach is the difficulty of using a large sized valve, because of arterial conditions. He mentioned that there are two studies in progress, namely PARTNER-EU, with a projected enrolment of 125 patients and the randomised trial PARTNER-US, with a projected enrolment of 600 patients.
Valve replacement for calcific severe aortic stenosis is the single most frequently performed procedure. As the population is ageing, its incidence is rising, and is has become a more and more important problem, even in those in their 80s and 90s. I personally would be very concerned with and would not perform an exercise test in a patient with severe aortic stenosis who is in an age group that has an increased probability of having associated coronary disease. The choice of valve replacement device has become much simpler now, with a choice of a mechanical valve or a stented bio-prosthesis in the vast majority of patients. The new procedures of transapical and percutaneous valve replacement are extremely exciting and require close cooperative efforts between the cardiac surgeon, cardiologist and anaesthesiologist. As time goes on, the proper role and timing of use of these new procedures will become clarified.
Aortic stenosis: an update Symposium
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