Abstract
The 18F Direct Flow Medical (DFM) THV has conformable sealing rings, which minimizes aortic regurgitation and permits full hemodynamic assessment of valve performance prior to permanent implantation. During the DISCOVER trial, three patients who were at risk for receiving contrast media, two due to severe CKD and one due to a recent hyperthyroid reaction to contrast, underwent DFM implantation under fluoroscopic and transesophageal guidance without aortography during either positioning or to confirm the final position. Valve positioning was based on the optimal angiographic projection as calculated by the pre-procedural multislice CT scan. Precise optimization of valve position was performed to minimize transvalve gradient and aortic regurgitation. Prior to final implantation, transvalve hemodynamics were assessed invasively and by TEE. The post-procedure mean gradients were 7, 10, 11 mm Hg. The final AVA by echo was 1.70, 1.40 and 1.68 cm 2 . Total aortic regurgitation post-procedure was none or trace in all three patients. Total positioning and assessment of valve performance time was 4, 6, and 12 minutes. Contrast was only used to confirm successful percutaneous closure of the femoral access site. The total contrast dose was 5, 8, 12 cc. Baseline eGFR and creatinine was 28, 22, 74 mL/min/1.73 m 2 and 2.35, 2.98, and 1.03 mg/dL, respectively. Renal function was unchanged post-procedure: eGFR = 25, 35, and 96 mL/min/1.73 m 2 and creatinine = 2.58, 1.99, and 1.03 mg/dL, respectively. In conclusion, the DFM THV provides the ability to perform TAVI with minimal or no contrast. The precise and predictable implantation technique can be performed with fluoro and echo guidance.
The Direct Flow Medical Transcatheter Aortic Valve System (Direct Flow Medical Inc., Santa Rosa, CA) is the first transcatheter aortic valve implantation (TAVI) device that is not based on a metallic frame technology. The prosthesis incorporates inflatable rings which, during the procedure, are pressurized with saline and contrast solution, allowing for precise positioning, repositioning, and retrieval, if needed. Once inflated, the prosthesis is readily visible using standard non-contrast fluoroscopy and/or echocardiography such that injection of contrast media is not required during valve positioning or deployment. Fluoroscopic and echocardiographic assessment allows full evaluation of valvular performance.
The lack of dependence on contrast assessment protects the kidneys from contrast-induced nephropathy. The unique design in combination with advances in pre-procedural gated cardiac computer tomography (CT) evaluation presents the physician with the ability to perform TAVI using minimal contrast media, thus decreasing the risk of peri-procedural acute kidney injury.
Gated cardiac CT has emerged as an invaluable tool in the evaluation of patients for TAVI by providing accurate and highly reproducible measurements of the aortic valve and adjacent structures . In addition, the three-dimensional volume may be utilized to determine specific fluoroscopic implant projections . This is critical to avoid device malposition and device embolization . This pre-procedural planning allows the fluoroscopic view to be maintained perpendicular to the outflow of the aortic valve and in-plane with the annulus. This preparation decreases procedural time and contrast media required. In the setting of TAVI, the incidence of acute kidney injury (AKI) is about 20% . Although the cause of AKI is multi-factorial, contrast dose is a well-documented factor causing acute injury during angiographic procedures and is associated with a significant increase in morbidity and mortality . A reduction of the quantity of contrast administered or elimination of contrast would be advantageous in this population.
During the DISCOVER CE mark trial, a methodology was adopted for analyzing the pre-operative CT that generates a patient-specific perpendicularity curve. With this guidance, it is feasible to eliminate the use of angiographic contrast during the positioning and implantation of the DFM valve. Only after complete deployment and detachment, a small amount of contrast media (< 10 cc) is used to confirm vascular access closure. The DFM valve is a unique next-generation TAVI device that is comprised from a bovine pericardial tissue leaflet valve. The DFM system utilizes a formed in place support structure. It is designed with independently inflatable ventricular and aortic rings, which encircle and capture the native valve annulus thereby ensuring positive anchoring of the bioprosthesis ( Fig. 1 A ). The bioprosthesis is positioned using three independent positioning wires and valve positioning is performed in a completely controlled and relaxed manner as the DFM is fully functional during positioning. The correct final position is confirmed with a high level of certainty based on the fluoroscopic appearance of the inflated valve and its relationship with the native annulus in the valve plane as follows ( Fig. 1 B): 1) the ventricular ring of the DFM placed at the virtual basal ring and appearing as a straight line parallel to the valve plane; 2) complete circular inflation of both the aortic and ventricular rings, which appear linear in any view perpendicular to the valve plane and circular in the valve plane; 3) the inflated aortic ring above the native leaflets and expansion not hindered or impeded by the native leaflets; 4) a similar distance between the aortic and ventricular rings without compression of the waist of the valve; and 5) catheter measurement of valvular hemodynamics. There is also some tactile feedback when the ventricular ring is pulled into contact with the native annulus. The final position is then confirmed on TEE by: 1) visualization of the DFM bioprosthesis positioned in the native annulus and capturing the native leaflets below the aortic ring; 2) either complete absence or minimal residual aortic regurgitation; and 3) a low transvalvular aortic gradient (< 20 mm). As the valve is fully repositionable, the position can be changed if the valve is not in an optimal position. Finally, before polymer exchange of the DFM valve, which excludes further repositioning or retrieval of the valve, the stability of the final position is confirmed with a “push test,” i.e. pushing on the positioning wires to confirm that the prosthesis cannot be malpositioned ventricularly.
In this paper, we utilized a perpendicularity curve derived from analysis of pre-procedural CT data in order to perform a TAVI procedure with the DFM valve with minimal contrast. We also present the data of an initial case series of patients treated with minimal contrast injected only to evaluate the success of percutaneous large-bore closure.
1
Case presentation
An 82-yr-old male was referred for severe symptomatic aortic stenosis (mean gradient 65 mm Hg, aortic valve area 0.78 cm 2 ) associated with moderate–severe aortic regurgitation. He had a previous history of hypertension, chronic atrial fibrillation, chronic obstructive pulmonary disease and chronic kidney disease (stage 4). The ejection fraction was normal. He was evaluated by a local Heart Team, which concluded that he was at high risk for conventional surgery (EuroScore 18%, STS score 10%) and that TAVI was appropriate. However, a major concern was the risk of AKI after the procedure due to the baseline serum creatinine value of 2.35 mg/dL with an eGFR of 18.9 mL/min. As part of the pre-procedural evaluation, a MDCT was performed which confirmed that the ilio-femoral vessels were suitable for transfemoral TAVI. The aortic annulus dimensions were 20.1 × 27.9 mm with a mean diameter of 24.0 mm and 24.5 mm calculated from the perimeter. The patient was scheduled for transfemoral implantation of a 25-mm DFM valve.
The perpendicularity curve was calculated from an analysis of the pre-procedural CT to ensure that the valve plane was perpendicular during deployment without the need for contrast. The CT analysis involved performing one tilt of the AP axis and one tilt of the lateral axis in the 3D CT reconstruction in order to bring the originally axial view plane into the position and double-oblique view orientation of the valve plane. These two tilt angles are selected carefully to bring the lowest hinge point of each of the three coronary cusps into the valve plane view. Once determined, the valve plane orientation is confirmed by scrolling distally to verify that all three leaflets appear in view immediately and simultaneously. Returning to the valve plane, the major and minor annulus dimensions and the circumference are measured. The two tilt angles needed to rotate the axial plane into the valve plane are used to recreate the valve plane orientation geometrically and calculate the C-arm positions that will be in-line with it. Based on the perpendicularity curve generated by plotting the results of these calculations, the angiographic projection selected was LAO 16°/CRA 5° ( Fig. 2 ).
Left femoral access was obtained for crossover and balloon-assisted closure of the large-bore access as per our standard practice . Right femoral artery puncture was performed utilizing angiographic markers and the height of the femoral artery bifurcation on the pre-procedural CT and a Prostar XL closure device was placed. Balloon aortic valvuloplasty was performed with a 23-mm balloon utilizing standard techniques. The DFM delivery catheter was then advanced and the outer sheath retracted to expose the prosthesis. The ventricular ring of the valve was inflated in the left ventricular outflow tract with a contrast–saline mixture through the positioning wires of the delivery system. A pigtail catheter was placed in the non-coronary cusp (NCC) via the left femoral access, in order to mark the position the lowest point of this cusp. From this point, the operator draws an imaginary line to touch the lowest point of the left coronary cusp (LCC). The angulation of this line is based on the valve plane from the pre-procedural CT ( Fig. 3 ). The bioprosthesis is then positioned using the three independent positioning wires by first pulling up the inner curve (LCC) side of the prosthesis to the virtual basal ring and then pulling up the outer curve (NCC) side into position so that the ventricular ring appears as a straight line parallel to the valve plane ( Fig. 4 A ). Once positioned, the aortic ring is inflated and an optimal position of the DFM valve is confirmed by the symmetric and circular inflation of the aortic ring above the calcified native leaflets ( Fig. 4 B). An optimal anatomical position was evaluated by TEE ( Fig. 5 A ). Hemodynamics were confirmed by the invasive transvalvular mean gradient of 4.9 mm Hg and no paravalvular leak on TEE ( Fig. 5 B and C). The contrast–saline mixture was then exchanged for a polymer through the positioning wires via a closed loop system that maintains 12 atm of pressure in the bioprosthesis. The polymer solidifies to provide the permanent support structure to fixate the valve in position. The positioning wires are then detached and the delivery system removed. The femoral access was closed percutaneously and 4 cc of diluted contrast injected locally via crossover from the left femoral access to confirm adequate hemostasis. This was the only contrast given during the entire TAVI procedure. The patient had an uneventful post-operative course and was discharged home at day 5 with a serum creatinine of 1.40 mg/dL.
