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Bicuspid aortic valve (BAV) is present in around 1-2% of the population. Up to 80% of the patients will experience aortic dilatation. Incidence increases with age, and of course, this is accompanied by an increased incidence of aortic dissection. Depending on the fusion of the commissure, several types of BAV can be distinguished, namely R-L and R-NBAV corresponding respectively to the fusion of the right and left, and right and non coronary cusp, as the 2 most frequent forms of BAV.
Three types of aortopathy associated with BAV have been described. Type 1 aortopathy is dilatation of the tubular or ascending aorta. In type 2, the dilatation of the ascending aorta extends to the aortic arch, whereas on the contrary, in type 3, the dilatation is only located at the level of the aortic root mimicking a Marfan lesion. Type 3 seems to be more frequent in patients with R-L BAV.
4D MRI enables visualization of the aortic flow pattern. BAV patients will present different aortic flow according to the type of BAV. BAV have asymmetric opening compared to a normal tricuspid aortic valve. This increases the flow angle between the valve and the aorta. Thus, the jet hits the aortic wall and this will increase the rotation of the flow. The flow inside the aortic root can be described as right handed or left handed according to the rotation of the flow. This abnormal flow pattern increases the shear stress on the aortic wall. The shear stress could be described as “the friction of the blood against the aortic wall”, and increased shear stress promotes aortic dilatation. When we look at the architecture of the aortic wall from a histological point of view in the area of increased shear stress, we may find some alteration of the structure of the wall that is not present in the area without increased shear stress.
According to all these studies, patients with increased risk of aortic growth are:
More studies in the future will certainly help to identify the clinical risk factors and translate into clinical practice for the follow up of patients with BAV.
The relations between the aorta and BAV can be summarized in 6 take home messages:
Marfan disease had a prevalence of around 1/4000 persons. It is characterized by a triple organ involvement, namely: ocular (lens dislocation), cardiovascular (aortic root dilatation), and musculo- skeletal. It is a genetic disease related in most cases to a mutation of the Fibrillin 1 gene. For Marfan disease, things are clear - surgery can cure the root dilatation and medical treatment with beta blockers or angiotensin-receptor blockers can be used to prevent aortic dilatation. Moreover, the disease can be studied with animal models (mouse). There is no animal model for bicuspid aortic valve.
If we look at long term (25 years) population survival studies, we can see that patients with BAV have a better survival than Marfan patients. Aortic aneurysm will develop in 26% ± 4% of patients at 25 years, and 0.5% ± 0.4% of patients will have a dissection. Thus, the risk of aortic dissection is 0.03%/patient/year, which is quite low. The IRAD registry showed that the risk of aortic dissection in BAV is far lower than the risk in Marfan patients, but still greater than in the general population. A study published in Heart in 2014 demonstrated that 43% of patients with BAV do not have dilated aortic root.
American guidelines recommend surgery if the dimension of the aortic root exceeds 55 mm, except for Marfan patients and BAV patients with risk factors or rapid growth of the aortic root. Recent guidelines suggest to index measurement to body surface. ESC guidelines recommend intervention for aortic root dimensions of 55 mm, and 50 mm for BAV with risk factors. This threshold could be lowered to 45 mm in the case of an indication for aortic valve replacement surgery. Indeed, there is a risk of aortic root dilatation long after aortic valve replacement
Don’t forget that some people may have a dissection with a lower aortic root diameter.
The risk factors for aortic root dilatation (and dissection) are: smoking, uncontrolled hypertension, aortic coarctation, family history of aortic dissection, or rapid growth of the aorta but also root phenotype.
Hypertension in patients with BAV should be treated intensively, and the preferred treatment will be ACE or ARB inhibitors. Patients with BAV and aortic coarctation more frequently have complications regarding the aortic valve. Thus, it is mandatory when treating a patient with BAV to investigate the aortic arch but also to look at the abdominal aortic flow.
The root is not the ascending aorta. Measurement must be performed at the right position and avoiding oblique axis: sinus, sino-tubular junction, ascending aorta. It is not always easy to be perfectly aligned with echo. CT and MRI can be very useful, not only for the root, but also for their capacity to visualize the whole aorta. When looking at the changes in dimensions over time, it is critical to use the same technique, same measurement and same aortic level, otherwise you will have misleading data. Echo measurements using the leading edge to leading edge technique are comparable to CT and MRI inner wall to inner wall measurement in end-diastole.
First degree relatives of a patient with BAV should be screened for the presence of BAV.
What the surgeon needs to know about the aorta before aortic valve surgery (G Teixido Tura, Barcelona, ES)
Depending on the extent of the aortic lesion, different types of surgery can be envisaged. It is recommended to replace the root at the time of aortic valve replacement if the root exceeds 45 mm, and especially if the patient has risk factors for aortic dilatation, such as hypertension, tobacco smoking…
Aortic regurgitation must be analysed and classified according to the mechanisms causing it. There are 3 main mechanisms:
Type 3 is a relative contra-indication to repair of the valve. After aortic repair, it is possible to predict the outcome of the valve-sparing procedure. Residual leaks (especially if eccentric), coaptation below the annulus, coaptation length below 4 mm, are all predictors of poor outcome of the repair. The choice between valve repair and valve replacement must be oriented according to the patient’s age, comorbidities and lifestyle. Valve repair will be preferred in young, active patients, with a favorable valve lesion, and if pregnancies are planned.
When a TAVI procedure is being contemplated, it is important to have a look at the morphology of the annulus. The problem is not only the size or shape of the annulus, but also the presence and location of the calcifications. Most of the time, the annulus is oval or elliptical, and during systole, the annulus becomes less elliptical. Biplane TEE imaging makes it possible to be well aligned with the aortic annulus. CT is also very useful to measure the annulus and to quantify calcification burden. However, there are some pitfalls, especially in patients with arrhythmia (e.g. motion artefacts).
TAVI is not only about sizing the annulus. You must also have a look at the aspect of the septum. A “bulging” septum may lead to malpositioning of the implanted aortic valve.
It is also important to know where calcifications are located. During valve inflation, there is some risk of rupture of the annulus. The risk factors for aortic root lesions are severely calcified root, and bulky leaflets.
The position and height of the coronary ostia must be assessed before valve implantation to avoid any coronary occlusion after valve deployment. Finally, the sino-tubular junction and ascending aorta must also be analysed before the procedure specifically for the presence and location of calcifications.
Complications of TAVI procedures, such as peri-aortic hematoma must be recognized.
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