Bicuspid aortic stenosis: TAVI’s next challenge

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Didier Tchetche

Most of the initial registries, and the large randomised trials, for transcatheter aortic valve implantation (TAVI) excluded patients with bicuspid aortic valves. The presence of a bicuspid aortic valve has historically been seen as a potential contraindication to TAVI because of perceived risks of malpositioning, elliptical deployment, moderate-to-severe aortic regurgitation and potentially accelerated leaflet degeneration. However, given that TAVI is now being explored in lower risk populations1–3 and that these populations are more likely to include patients with bicuspid valves, the evidence base for TAVI in these types of valves is starting to build.

The bicuspid aortic valve remains the most common congenital valvular abnormality, affecting 0.5 % to 2% of the general population with approximately 50% of surgical aortic valve replacement procedures being performed in adults with bicuspid valves.4 As the trend, with ongoing randomised trials, towards using TAVI in low-risk and younger patients continues, the proportion of patients with bicuspid valves undergoing TAVI is likely to increase. Therefore, there has been growing interest about the safety and efficiency of TAVI in these patients. Mylotte et al reported, in 2014, data for 139 bicuspid valve patients who underwent TAVI with first-generation devices. This study highlighted the complexity of performing the procedure in such patients, with high rates of malposition, use of multiple transcatheter heart valves and relatively high rates of moderate-to-severe residual aortic regurgitation.5 More recently, a larger registry, led by Yoon, gathered the data for 561 bicuspid valve patients. Compared with tricuspid aortic valve patients, bicuspid patients had more frequent bailout surgery and had significantly lower device success rates. However, Yoon et al used second-generation devices—featuring repositionability, sealing properties and more accurate deployment—and found that they yielded better outcomes than did first-generation devices.6 Although the higher need for a permanent pacemaker after TAVI in patients with bicuspid valves (compared with tricuspid valves), even with second-generation devices, is a still matter of concern.

Additionally, identifying bicuspid valves remains difficult; particularly in patients with extremely calcified anatomies. The diagnosis relies on the combination of echocardiography, mainly transoesophageal, and multislice computed tomography (MSCT). MSCT—which has become the method of choice—is used to diagnose bicuspid valve and its type (Sievers 0, 1 or 2), analyse the aortic root anatomy, and characterise the calcium load and distribution.

There is a lack of consensus concerning the sizing methodology for TAVI in this area. Recent focus has been put on supra-annular sizing, in combination with the dimension of the aortic annulus. The intercommissural distance (ICD), measured 4–8 mm above the annular plane, could provide a reliable estimation of the maximum diameter achievable by a specific TAVI device once deployed in a bicuspid valve. Given the constraint associated with calcified bicuspid valve leaflets, avoidance of aggressive oversizing is largely being recommended. The optimal annulus/device or ICD/device ratios remain unclear. Dedicated registries, focusing on comparison of pre- and post TAVI bicuspid valve MSCT are ongoing.

As illustrated by various studies, deployment of TAVI devices in bicuspid is challenging. The choice of device type depends on the preferences of the individual heart team. Second-generation devices seem to share equivalent outcomes. Predilataton is advocated, eventually combined with contrast injection (balloon angiography), to guide sizing in grey zones when MSCT does not provide enough information for clear-cut decisions. High implants are considered, with minimal protrusion within the left ventricle outflow tract. It is recommended to land the device across the aortic annulus to maximise the anchoring (annulus and leaflets) and decrease the risk of moderate-to-severe paravalvular regurgitation. Deep implants should be avoided to prevent a need for a permanent pacemaker. Fast-pacing (90–120bpm) may be considered when using self-expanding device for enhanced stability. Postdilatation should be carried-out if necessary to decrease device ellipticity, paravalvular regurgitation or high residual gradient.

In conclusion, TAVI in bicuspid valves requires a perfect understanding of the anatomy of the patient. MSCT is the basis of the diagnosis and anatomic evaluation. Specific sizing rules need to be defined in this challenging scenario. Large prospective registries and long follow-ups are required to explore the outcomes.

References

  1. Reardon et al. N Engl J Med 2017; 376: 1321–31.
  2. Leon et al. N Engl J Med 2016; 374: 1609–20.
  3. Adams et al. N Engl J Med 2014; 371: 967–68.
  4. Roberts et al. Medicine (Baltimore) 2012; 91: 287–308.
  5. Mylotte et al. J Am Coll Cardiol 2014; 64: 2330–39.
  6. Yoon et al. J Am Coll Cardiol 2017; 69: 2579–89.

Didier Tchetche is at Groupe Cardiovasculaire Interventionnel, Clinique Pasteur, Toulouse, France

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