By Francesco Maisano
The EVEREST trial results set the stage few months ago at ACC when Ted Feldman presented the first randomised trial comparing an interventional procedure to surgical treatment of mitral valve regurgitation (MR). The trial suggested that, in highly selected patients, MitraClip treatment (Abbott Vascular) is superior in safety and non-inferior in terms of efficacy, compared to surgery. The MitraClip is a percutaneously implantable device that reproduces the surgical Alfieri technique, by joining the leaflets at the site of regurgitation, creating a double orifice valve. MitraClip has received the CE mark in 2008 and it is widely available in Europe. To date, around 2,000 MitraClip implants have been performed worldwide mainly in high-risk patients.
Valve repair is the ideal treatment of MR: when performed early in patients with degenerative MR, it has low risk and can restore life expectancy. In experienced hands, it is durable and can be done safely and effectively with minimally invasive approaches. However, risk of surgery is higher in elderly patients, those with major comorbidities and with reduced left ventricular function. As a result, the Euro Heart Survey revealed that 50% of symptomatic patients with severe MR are denied surgery due to the risk of procedure.
Transcatheter interventions open a new perspective in this field. Besides the obvious reduction of invasiveness, the possibility of treating MR while the heart is beating offers the unique opportunity of guiding the procedures according to the physiological effect of the intervention. This is an advantage over surgery, where the procedure is performed under cardioplegic arrest. Surgery offers an unmatched anatomical visualisation of the lesions to allow precise anatomical reconstructions. But the functional result can be verified only after weaning from cardiopulmonary bypass. With the MitraClip, the implant is guided primarily by the dysfunction, rather than by the lesion. The haemodynamic effect of the implant is monitored live. Results can be optimised by relocating the implant until the intended haemodynamic effect is obtained. This feature is particularly effective in the setting of functional MR, where no valve lesions are involved in the mechanism of regurgitation and beating heart implantation and assessment are an absolute advantage.
The ACCESS post-market registry is actively enrolling patients undergoing MitraClip implantation in Europe. According to preliminary reports from the ACCESS registry, at least 70% of patients treated have functional MR, are high-risk surgical candidates (logistic Euroscore around 20%), with multiple comorbidities. Most patients have already received a CRT before they are referred to MR treatment. Compared to EVEREST, preliminary data suggest improved efficacy of the procedure, which is successfully completed in more than 95%, with almost all patients experiencing MR reduction. Although the real world population is at higher risk compared to EVEREST, still the procedure seems safer than surgery. Thirty days mortality is around 2%, and most patients are discharged home. Clinical improvement is evident and stable over time up to 12 months, with improved functional class and reduced hospitalisation rate. Further data are required to establish the exact role of MitraClip in clinical practice but the data are more than encouraging and the therapy has become a clinical option to treat heart failure patients, as well as selected high-risk patients with degenerative MR.
Beyond MitraClip, in the near future, we will witness the clinical introduction of new devices to enrich the treatment portfolio, the development of image guidance to safely and effectively plan and execute the procedures, and the evolution of new clinical trends and, potentially, updated guidelines.
The most desirable innovation in the field of MR devices will be annuloplasty. In surgical treatment of MR, annuloplasty is performed routinely in combination with any repair technique. Several concepts have been developed including coronary sinus remodeling, annular cinching, RF and HIFU remodeling, external compression and direct annuloplasty. Coronary sinus devices have been developed first, with the promise of an easy, safe and effective solution for mitral valve annuloplasty. Initial results have been discouraging due to less than expected safety as well as minimal and unpredictable efficacy, but more data from the trials could bring new lights in this category of devices. Among the various innovative technologies for annular remodeling, direct annuloplasty is the closest endovascular solution to surgical ring annuloplasty. There are three companies involved: Guided Delivery System, Mitralign and Valtech Cardio. The first two devices are delivered with a transarterial approach, retrogradely into the sub-annular region, while the latter is delivered from a standard transeptal approach. Annuloplasty devices could be involved in MR treatment either as a stand-alone procedure or in combination with leaflet repair. In this latter field, endovascular neochordae implantation offers a very efficacious solution for treatment of prolapsing lesions. Currently, only Neochord is involved in this area, with a transapical delivery system, but other devices are expected in the future. Neochordae implantation could offer early treatment of mitral valve prolapse, to gain prognostic benefit.
Finally, mitral valve implantation could become another alternative to treat MR when repair is not feasible. Transcatheter mitral valve implantation is probably the most challenging effort in the field with several companies involved, including Medtronic, Endovalve, CardiaQ and Mitraltech. Differently from aortic valve, the mitral devices will need to be much larger, and will not be implanted using radial force as fixation method since the valve is usually not calcified in case of MR, and because radial expansion of the valve would induce aortic valve deformations and outflow tract obstruction. In addition, while perivalvular leaks are negligible in case of aortic implants, in mitral position they would induce more serious consequences both in terms of degree of regurgitation and in terms of haemolysis.
All the above-mentioned programmes will strongly depend on development of intuitive and efficient imaging technologies to plan and guide the mitral interventions. Again, while TAVI can be performed in most cases solely on the basis of fluoroscopic imaging, mitral interventions will require far more advanced technologies, including 3D visualisation, robotic navigation, imaging fusion and tagging.
There is no doubt that transcatheter mitral valve interventions is the most innovative field in structural heart disease.
Francesco Maisano is director of Transcatheter Valve Treatment, San Raffaele Hospital, Milan, Italy