Percutaneous treatment of aortic valve stenosis

The transapical technique

In the transapical technique, the valve delivery system is inserted via a small incision made between the ribs. The apex of the left ventricle is punctured with a needle, and the prosthetic valve is positioned within the stenotic aortic valve.^27,31–33 The main advantage of this approach is that it allows more direct access to the aortic valve and eliminates the need for a large peripheral vascular access site in patients with peripheral vascular disease, small tortuous vasculature, or a history of major vascular complications or vascular repairs.^31–33 Potential disadvantages are related to the left ventricular apical puncture and include adverse ventricular remodeling, left ventricular aneurysm or pseudoaneurysm, pericardial complications, pneumothorax, malignant ventricular arrhythmias, coronary artery injury, and the need for general anesthesia and chest tubes.^27,31–35

Common features of the three approaches

The three percutaneous approaches have certain final steps in common.^11,23,30,33 The position of final deployment of the prosthetic valve is determined by the patient’s native valvular structure and anatomy and is optimized by using fluoroscopic imaging of the native aortic valve calcification as an anatomical marker, along with guidance from supra-aortic angiography and transesophageal echocardiography.^11,23,30,33 Ideally, the aortic valve prosthesis is placed at mid-position in the patient’s aortic valve, taking care to not to impinge on the coronary ostia or to impede the motion of the anterior mitral leaflet.^11,23,30,33 In all three procedures, the prosthesis is then deployed by maximally inflating, rapidly deflating, and immediately withdrawing the delivery balloon. This final step is carried out during temporary high-rate right ventricular apical pacing, which produces ventricular tachycardia at 180 to 220 beats/min for up to 10 seconds.^11,23,30,33 This leads to an immediate decrease in stroke volume, resulting in minimal forward flow through the aortic valve, which in turn facilitates precise positioning of the prosthetic valve.

So far, only the Cribier-Edwards valve has been deployed via all three techniques. The CoreValve has been deployed only via the retrograde technique. The Edwards SAPIEN valve has been deployed with retrograde and transapical approaches (see www.edwards.com/Products/TranscatheterValves/SapienTHV.htm and www.corevalve.com for animations depicting these techniques).

EXPERIENCE WITH THE CRIBIER-EDWARDS VALVE

The Cribier-Edwards valve has three leaflets made from equine pericardial tissue sutured inside a balloon-expandable stainless steel 14-mm stent (Table 1).^11,23,33 With the use of a specially designed mechanical crimping device, the aortic valve prosthesis is mounted over a 3-cm-long balloon catheter, expandable to a diameter of 22 to 26 mm (NuMed Inc, Hopkinton, NY).^11,23,30,33

After this prosthesis was tested in animal models,^14,15 a trial for compassionate use in humans was begun, called the Initial Registry of Endovascular Implantation of Valves in Europe (I-REVIVE) trial. This trial was later continued as the Registry of Endovascular Critical Aortic Stenosis Treatment (RECAST) trial.²³ All patients were formally evaluated by two cardio-thoracic surgeons and were deemed inappropriate for surgical aortic valve replacement.²³

The success rate with the antegrade percutaneous approach was 85% (23 of 27 patients) and 57% for the retrograde approach (4 of 7 patients).^{11,23,30–33} Procedural limitations were migration or embolization of the prosthetic valve, failure to cross the stenotic aortic valve, and paravalvular aortic regurgitation.²³ Anatomic and functional success was evidenced by improvement in aortic valve area, increase in left ventricular ejection fraction, and improved New York Heart Association functional class, all of which were sustained at up to 24 months.²³

Webb et al¹¹ reported similar results with retrograde implantation of the Cribier-Edwards valve in a cohort of 50 patients.¹¹ The main difference between the two studies was the expected occurrence of aortofemoral complications with the retrograde approach.^11,26 Procedural success increased from 76% in the first 25 patients to 96% in the second 25, and the 30-day mortality rate fell from 16% to 8%, which reflected the learning curve. Importantly, no patients needed conversion to open surgery during the first 30 days, and at a median follow-up of 359 days 35 (81%) of 43 patients who underwent successful transcatheter aortic valve replacement were still alive.¹¹ Additionally, significant improvement was noted in left ventricular ejection fraction, mitral regurgitation, and New York Heart Association functional class, and these improvements persisted at 1 year.¹¹

Lichtenstein et al³¹ and Walther et al³² successfully implanted the Cribier-Edwards valve using the transapical approach in a very high-risk elderly population with poor functional class. All patients were deemed unsuitable for standard surgical valve replacement and also for percutaneous transfemoral aortic valve implantation because of severe aorto-iliac disease. In both studies, the short-term and mid-term results were encouraging.

These experiences with the Cribier-Edwards valve showed that device- and technique-related shortcomings could be addressed. To date, more than 500 percutaneous aortic valve replacement procedures have been done with the Cribier-Edwards valve worldwide, with a greater than 95% technical success rate in the latest cohorts.³⁶ Importantly, use of a larger (26-mm) prosthetic valve has been associated with a lower rate of prosthetic valve migration or embolization, and with a significantly lower rate of paravalvular aortic regurgitation.^11,23