Interventional cardiologist Dr. Martin Leon, of Columbia University and the Cardiovascular Research Foundation discussed the progress being made in transcatheter valves and related devices at the Innovations in Cardiovascular Interventions meeting in Tel Aviv in December 2011. In the past, he said, early TAVI prototypes relied heavily on operator creativity and off-the-shelf accessory devices. But as the field has evolved, each part of the procedure needs to be refined. Speaking at a session entitled "TAVR: Future Technology and Clinical Targets," Leon said, "Now, and especially in the future, all major and minor components of a TAVR system will be fully customized and designed for specific functional tasks. Moreover, adjunctive technology is being developed to enhance TAVR outcomes and reduce complications."
Transfemoral or Transapical: Which Is Better?
The start-ups profiled here are offering those adjunctive technologies to improve the management of the access sites, the two most common being transfemoral, generally the first-choice option, and transapical. (There are other methods, including the direct aortic, subclavian or axillary routes to the heart, but this article discusses only transfemoral and transapical approaches, which are the most widely used.)
Many considerations influence the choice of one route over the other. Probably most important is the skill set of the physician performing the procedure; interventional cardiologists generally prefer transfemoral access since it involves the catheter skills with which they are most experienced, and surgeons like the transapical approach because it requires their surgical skills. Transfemoral access provides access to the heart via a cut-down in the groin to gain entry to the femoral artery, through which the prosthetic valve is advanced on a guidewire over the aortic arch to the aortic valve. Transfemoral is the default option largely because it’s less invasive than transapical delivery, which requires an incision in the chest and the outer wall of the heart. There are other considerations; the quality of the patient’s vessels or his or her overall health status. The transfemoral approach is not feasible or is risky for patients with vessels that are too small, thin, fragile or tortuous for the large, stiff 18-24F delivery catheters or in patients with atherosclerotic or calcified vasculature. The transfemoral approach comes with certain risks of vascular complications: vessel perforations, the risk of dislodging embolic debris and complications of the vascular access site.
Because of those exclusions, in fact, 50% of TAVI procedures performed in Europe today employ the transapical route even though it is more invasive. Today’s transapical access methods require a mini-thoracotomy to access the chest space and a puncture in the apex of the left ventricle. The heart wall puncture is then dilated to allow the prosthetic valve to pass into the ventricular space. The transapical approach has demonstrated a reduced risk of stroke, generally attributed to the fact that the large diameter devices don’t travel through the vessels and over the aortic arch and thus don’t risk scraping off plaque, which can send embolic particles upstream to the brain.
The start-ups profiled here believe that improving access site management will go beyond procedural advantages to influence clinical outcomes. Better transapical access devices would provide a short and straight distance to the native annulus of the aortic and mitral valves, so it should be much easier to position the valves using this approach. The transapical route can also accommodate much larger heart valves because transfemoral access is limited by vessel size and quality. These are important features because improper valve positioning and insufficient valve size are two factors implicated in paravalvular leaks, a condition that increases mortality, and as noted, transapical access has the potential to improve upon both. But the transapical approach carries with it the increased risk resulting from its more invasive nature, along with the risk of access site bleeding. These disadvantages provide opportunities for device developers aiming to improve transapical procedures.
No matter which option is chosen, TAVI clinical practice is distinguished from other interventional or surgical procedures because of its emphasis on the need for the two groups of clinicians to operate as a team, since surgeons are sometimes required to do a cut-down in the femoral artery and manage it with sutures, and interventionalists sometimes need to lend their over-the-wire skills to surgeons advancing heart valves through the apex. (That’s why Edwards Lifesciences called its TAVI trial PARTNER.) The new access site management devices, by making access and closure safer, more reproducible and less dependent upon one specific skill set or the other, should help both groups of clinicians embrace this emerging hybrid practice area.