Design of Sapien XT valve and technical tips - By Dr Shahid Merchant
Introduction : Transfemoral aortic valve implantation (TAVI) may offer clinical benefit to patients not well suited to conventional surgery. New developments in delivery systems and valve technologies make the procedure safer, thereby paving the way for a broader application of Transfemoral aortic valve implantation.
Patients with severe symptomatic aortic stenosis are eligible for transarterial aortic valve replacement if the risk of conventional open-heart aortic valve replacement is considered excessive by a consensus group of cardiogists and heart surgeons. A minimal femoral arterial diameter of 7 mm for the 22 F and 8 mm for the 24 F Retroflex 3 system and 6 mm for the 18 F and 6.5 mm for the 19 F Nova flex system is required.
Introduction : Transfemoral aortic valve implantation (TAVI) may offer clinical benefit to patients not well suited to conventional surgery. New developments in delivery systems and valve technologies make the procedure safer, thereby paving the way for a broader application of Transfemoral aortic valve implantation.
Patients with severe symptomatic aortic stenosis are eligible for transarterial aortic valve replacement if the risk of conventional open-heart aortic valve replacement is considered excessive by a consensus group of cardiogists and heart surgeons. A minimal femoral arterial diameter of 7 mm for the 22 F and 8 mm for the 24 F Retroflex 3 system and 6 mm for the 18 F and 6.5 mm for the 19 F Nova flex system is required.
Procedure : is done under local anaesthesia and mild sedation. A percutaneous femoral arterial sheath allows introduction of the delivery system into the descending aorta. Flexion of the delivery catheter tip facilities atraumatic passage through the aortic arch and stenotic native valve. The delivery catheter is withdrawn to the ascending aorta to fully expose the deployment balloon during expansion. The valve is deployed during rapid pacing. Finally the delivery system is retrieved and femoral access site closed either utilizing previously inserted percutaneous sutures (ProGlide TM Prostar ) or by surgical cutdown.
Sapien XT valve : The valve consists of bovine pericardial leaflets, a cobalt-chromium frame and a sealing cuff on the inflow aspect of the stent to prevent paravalvular regurgitation. The bovine pericardium utilized undergoes a proprietary anti-calcification treatment (Thermafix Tm ).
New scallop-shaped leaflets are attached to the frame in a crown-like manner. The redesigned frame incorporates a more open design and a reduction in strut thickness. Stainless steel utilized in the SAPIEN valve is now replaced with a stronger cobalt-chromium alloy.
The design and the material allow for tighter crimping of the valve, without loss of stability or radial force. The SAPIEN XT aortic valve is available in four sizes: 20, 23, 26, and 29 mm external diameter valves. It is slightly longer that the previous SAPIEN valve.
New scallop-shaped leaflets are attached to the frame in a crown-like manner. The redesigned frame incorporates a more open design and a reduction in strut thickness. Stainless steel utilized in the SAPIEN valve is now replaced with a stronger cobalt-chromium alloy.
The design and the material allow for tighter crimping of the valve, without loss of stability or radial force. The SAPIEN XT aortic valve is available in four sizes: 20, 23, 26, and 29 mm external diameter valves. It is slightly longer that the previous SAPIEN valve.
Novaflex delivery system : The system allows for a reduction in sheath size to 18 French (for the 23 mm valve; 19 French for the 26 mm valve). The smaller diameter allows use in patients with smaller diameter ilofemoral arteries: 6 mm for the 18 French and 6.5 mm arterial diameter for the 19 French systems.
The delivery catheter incorporates an outer deflectable catheter and an inner balloon catheter with a tapered crossing tip. The valve itself is crimped on the inner catheter proximal to the inflatable balloon. This reduces the maximal diameter of the delivery catheter and allows for a reduction in sheath size. Once the delivery catheter and prosthesis have been passed through the femoral sheath, the inner balloon catheter is withdrawn back into the outer catheter while maintaining wire position. The outer catheter then advances the prosthesis distally on the inner catheter shaft and onto the balloon. Optimal alignment of the stent on the balloon is indicated when the frame is positioned between the two fluoroscopic markers. Imaging in a fluoroscopic view perpendicular to the markers is important for accurate positioning. Advancing the prosthesis too distally is prevented by a slightly larger distal tip of the balloon catheter. Fine adjustment is achieved by turning a valve alignment wheel situated on the handle of the delivery system.
Balloon expansion generally begins distal (ventricular) to the prosthesis first, followed by expansion proximal (aortic) to the prosthesis and finally by expansion of the central portion of the balloon. The result is initial expansion of the prosthesis within the left ventricular outflow tract (LVOT).
The delivery catheter incorporates an outer deflectable catheter and an inner balloon catheter with a tapered crossing tip. The valve itself is crimped on the inner catheter proximal to the inflatable balloon. This reduces the maximal diameter of the delivery catheter and allows for a reduction in sheath size. Once the delivery catheter and prosthesis have been passed through the femoral sheath, the inner balloon catheter is withdrawn back into the outer catheter while maintaining wire position. The outer catheter then advances the prosthesis distally on the inner catheter shaft and onto the balloon. Optimal alignment of the stent on the balloon is indicated when the frame is positioned between the two fluoroscopic markers. Imaging in a fluoroscopic view perpendicular to the markers is important for accurate positioning. Advancing the prosthesis too distally is prevented by a slightly larger distal tip of the balloon catheter. Fine adjustment is achieved by turning a valve alignment wheel situated on the handle of the delivery system.
Balloon expansion generally begins distal (ventricular) to the prosthesis first, followed by expansion proximal (aortic) to the prosthesis and finally by expansion of the central portion of the balloon. The result is initial expansion of the prosthesis within the left ventricular outflow tract (LVOT).
SAPIEN XT valve on the Novaflex delivery system : This allows a further reduction in internal sheath diameter to 18 French and 19 French, respectively. The absence of major vascular complications and major bleeds is encouraging.
The new design tends to result in balloon expansion being initiated distally (ventricular). As the prosthesis expands distally, it first contacts the outflow tract, rather that the leaflets. Subsequently, proximal (aortic) expansion is less likely to result in movement in the direction of blood flow and the native leaflets. Presumably more rapid balloon inflation due to the larger inflation lumen helps.
The new design tends to result in balloon expansion being initiated distally (ventricular). As the prosthesis expands distally, it first contacts the outflow tract, rather that the leaflets. Subsequently, proximal (aortic) expansion is less likely to result in movement in the direction of blood flow and the native leaflets. Presumably more rapid balloon inflation due to the larger inflation lumen helps.
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