Editorial Comment: Moderate aneuryms of the ascending aorta in stenotic bicuspid aortic valve - life threatening or merely an epiphenomenon?

Abstract

The current US guidelines for the diagnosis and management of patients with thoracic aortic disease recommend an operation for asymptomatic patients with bicuspid aortic valve (BAV) and aneurysm of the ascending aorta with a diameter of 4-5 cm [1]. With this recommendation, patients with BAV and ascending aortic aneurysms are treated following the same criteria as patients with Marfan syndrome. The guidelines categorize both diseases together as ‘Marfan syndrome or other genetically mediated disorders’. The background for this recommendation is growing evidence that BAV, the most common congenital abnormality, with an incidence of 1–2%, is related to a gene defect. For example, a mutation of the NOTCH1 gene is linked to development of BAV [2]. Therefore, systemically weakened aortic tissue will subsequently lead to an increased incidence of aortic aneurysm formation and aortic dissection in these patients. However, this recommendation carries a grade ‘C’ level of evidence. That means the recommendation is only based on the consensus opinion of experts, case studies or standards of care, but not on more appropriate methods of evidence-based medicine, such as randomized controlled trials. The paucity of studies in the literature to support the recommendation is evident. Girdauskas et al. recently questioned the theory that BAV is predominantly caused by an underlying genetic disorder [3]. In a review of the literature, they convincingly speculated that aneurysm formation in individuals with BAV may be related to abnormal haemodynamics more often than to a genetic disorder. They postulated the re-evaluation of the ‘genetic theory’ and asked for further studies aiming to determine the nature of aneurysm formation. This ‘haemodynamic theory’ would have an important impact on the treatment of this entity, because aortic valve replacement (AVR) aborts the asymmetric flow patterns in BAV, so that further dilatation of the ascending aorta becomes unlikely. However, there are controversial data in the literature demonstrating that acute aortic dissection and sudden death is significantly increased after AVR in patients with BAV compared with patients who have tricuspid aortic valves [4]. In this issue of the European Journal of Cardio-Thoracic Surgery, Girdauskas’s group add another piece of evidence to the puzzle, aiming to determine the best treatment of patients with stenotic BAV and moderate aneurysm of the ascending aorta [5]. They report on 153 consecutive patients with BAV stenosis and ascending aortic dilatation of 4–5 cm who underwent isolated AVR between 1995 and 2000. The concept was rather conservative, because 97% received mechanical valve prostheses and the ascending aorta was not replaced. The 30-day mortality was remarkably low, being 0.7%, and long-term survival was also favourable. Surprisingly, late aortic events were rare, and freedom from aortic intervention was 97 and 94% at 10 and 15 years, respectively, with only five patients (3%) requiring reoperation for progressive ascending aortic aneurysm. No aortic dissection or rupture occurred. Ascending aortic diameter was not found to be a predictor for adverse aortic events. Looking more closely at their report, a group of 21 young (mean age 41 years) and predominantly male (86%) patients with BAV and aortic valve insufficiency were treated in the same way as described. For these patients with the so-called ‘root phenotype’, adverse aortic events were significantly more often observed, at 24%, including two acute aortic dissections type A. These findings support the theory that abnormal haemodynamics are responsible, at least in part, for aortopathy in stenotic biscuspid valve disease. This entity is often called ‘poststenotic dilatation’. From these data, the aortopathy is sufficiently treated by AVR. Consequently, the current guidelines recommending ascending aortic replacement in patients with BAV and aneurysm of the ascending aorta with a diameter of 4– 5c m based on the ‘genetic theory’ need to be re-evaluated, and isolated AVR may be an option. The Bentall procedure with either mechanically or biologically valved conduits is considered a safe operation for BAV combined with an ascending aneurysm, with low early mortality in experienced centres [6]. However, a simple AVR results in better early outcomes than the Bentall procedure, with a 30-day mortality of 3 vs. 8% in Germany in 2010 [7]. Furthermore, adverse events and reoperation after conduit replacement are reported in all long-term studies, especially for biologically valved conduits [8], demonstrating that this strategy also is far from perfect. Supracoronary replacement of the ascending aorta can be an option in older patients with a preserved sinotubular junction and a ‘normal’ appearing aortic wall tissue. However, potentially