Historically 90% of Marfan’s deaths are related to ascending aortic disease. The mean survival of untreated patients is 40 years but the variance is large. The risk of Type A aortic dissection (splitting of the elastic layers of the wall of the aorta with tracking of blood within it) clearly increases with aortic root diameter but risk increases with aortic root diameter greater than 45mm and is higher in patients with a family history of aortic dissection. Beta-blocker medication can slow the rate of aortic dilatation and reduce the risk of dissection.
Echocardiographic evidence of mitral prolapse is seen in 75% of the patients with Marfan’s syndrome but a much smaller proportion will develop clinically important mitral regurgitation. The aortic root is the main site of dilatation and dissection and accounts for 90% of dissection but 10% can occur elsewhere, usually distal to the left subclavian artery and other parts of the aorta including the arch and other large elastic arteries can become dilated in patients with Marfan’s syndrome and occasionally dissect and rupture, although it is much less common than aortic root disease.
Surgical Options for Aortic Root Disease in Marfan’s Syndrome
The conventional surgical treatment is a composite aortic root replacement with mechanical valve (Bentall’s operation). This remains an option for the patient with severe aortic regurgitation and abnormal aortic valve leaflets. This is more common when the aortic root is dilated beyond 6cm in diameter and the valve leaflets have become severely stretched and damaged by the jet going through the leaflets. Aortic regurgitation is due to a combination of dilatation of the annulus that is the base of the valve and the sinotubular junction, which is the top of the valve. The vast majority of patients with Marfan’s syndrome have a normal trileaflet aortic valve and the actual tissue of the valve is not affected by Marfan’s disorder because it does not contain the elastic tissue, which the sinuses of Valsalva of the aorta contain.
A much more attractive option is the aortic valve sparing repair of the aortic root aneurysm (David I operation). The original procedure described by Tyrone David from Toronto, Canada, involves excision of all aortic sinus tissue, mobilisation of the coronary arteries and retention of the aortic valve leaflets themselves. The valve is then re-implanted within a Dacron tube graft of appropriate size and the coronary arteries are also re-implanted in the Dacron tube. This operation has the advantage of retaining the native aortic valve which means that anticoagulation is not necessary beyond antiplatelet treatment with Aspirin. The valve is silent and the haemodynamics are normal. This operation can be accomplished with a competent aortic valve in virtually all cases in which the valve is competent to start with and in cases where the aortic root is certainly less than 6cm in diameter and there is central regurgitation with normal aortic valve leaflets. The Dacron tube fully supports the aortic valve eliminating the weakness inherent in the Marfan’s tissue. The final decision as to whether the valve is suitable for repair can only be made at operation.
A further refinement of this approach is the use of a purpose made Dacron graft with a segment which mimics the sinuses of Valsalva of the normal aorta. That is to say that the segment in which the valve was re-implanted contains bulges. These bulges allow the aortic leaflets to open with the same flow characteristics of a normal aorta so that the eddy currents created around the leaflets effectively allow them to open to the fullest extent and to avoid contact with the wall of the Dacron conduit which may damage the leaflets.
The reported results of aortic valve sparing surgery by David’s group indicate that the survival is excellent and that after 10 years no re-operation had been required for aortic regurgitation. Patients with Marfan’s syndrome using the re-implantation technique in David’s series were almost all free of important regurgitation.
The use of the Valsalva prosthesis to carry out a valve sparing procedure has equivalent early results to the tube graft in terms of low operative risk and excellent valve competence and is, I believe, the current operation of choice for the suitable patient with Marfan aortic root dilatation.
Mitral valve prolapse is also common in Marfan’s syndrome, being present in approximately 75% of Marfan’s patients and a significant proportion of these go on to develop mitral regurgitation sufficient to warrant surgery. There is limited data about surgery for mitral valve disease in Marfan’s patients but the experience at several major centres would suggest that conventional mitral valve repair by an appropriately experienced surgeon can yield very good results with retention of the mitral valve, avoidance of anticoagulation and stable long-term outcome. Such techniques as Gore-Tex replacement of chordae tendinae (heart strings) and ring annuloplasty can stabilise the valve and stop progression of regurgitation.