Transcatheter valve replacement: resection and valved stent implantation in a beating heart

Native Aortic Valve Resection Using a Novel Blade-Based Device

OBJECTIVE

The aim of this study was to validate the use of a new resection device in patient candidates for surgical aortic valve replacement. We evaluated the efficacy of this new circular blade to resect the aortic valve and the efficacy to collect the debris during the resection.

METHODS

For this study, a single size instrument was used, with an external diameter of 22 mm, and patients were selected on the basis of the preoperative assessment of the aortic diameters.

RESULTS

From October 2018 to June 2019, 10 patient candidates for surgical aortic valve replacement were selected to undergo native aortic valve resection using a new device, before surgical valve implantation. The mean age of the patients was 74 ± 7.6 years, and 8 of 10 were male. The mean aortic annulus diameter, measured before the procedure, was 25.7 ± 1.57 mm. The resection was complete in 9 (90%) patients. In 1 patient, due to an imprecise positioning of the device, the valve resection was partial. None of the patients showed signs or symptoms due to debris embolism. In all patients, the postoperative course was uneventful.

CONCLUSIONS

These preliminary results show that resection of the aortic valve using a circular foldable blade is feasible. This prototype, used during conventional surgery even through a small incision, provided an efficient tool to easily resect the valve without debris release.

Endovascular resection of the native aortic valve before transcatheter aortic valve implantation: state of the art and review

Transcatheter aortic valve implantation was introduced into clinical practice in 2002 as a rescue approach in patients presenting with symptomatic severe aortic stenosis but not eligible for conventional aortic valve replacement. This technique allows implantation of a balloon expandable bioprosthesis without resection of the native aortic valve. Several complications are described as a consequence of the residual highly calcified valve being squeezed against the aortic wall by the stent of the implant. This can result in deformation of the metal stent and paravalvular leakage, risk of occlusion of the coronary ostia, or central and peripheral embolization of valvular debris. To avoid these complications, many authors suggest the possibility to resect and remove the native aortic valve before transcatheter aortic valve implantation. In this field, different authors have described possible techniques and different sources of energy to resect the calcified valve. In this article, we review the development of these experimental techniques and discuss future prospects in this field.

Comparison of different resection tools for human calcified aortic valves

OBJECTIVE

Symptomatic severe aortic valve stenosis is a disease primarily found in patients of advanced age. The standard therapy is the aortic valve replacement. Transcatheter aortic valve implantation (TAVI) is a treatment for patients ineligible for conventional aortic valve replacement. To minimize the incidence of TAVI-related complications, such as paravalvular leakage, pacemaker necessity, and ostial coronary occlusion, our research group works on the development of resection tools for aortic valves. The aim of this study was to investigate ex vivo different resection tools for human calcified aortic valves concerning cross-section morphology.

METHODS

With the use of 12 human calcified aortic leaflets, the effect of laser scalpel, punching device, and scissors on cross-section morphology was investigated. Scanning electron microscopy and histological analyses were applied to evaluate the cutting surface area.

RESULTS

The cross-section areas created by a laser scalpel were smooth, regular, and uniform, whereas these areas were rough, irregular, and inhomogeneous when using the scissors or the punching device. Quantitative analysis of the cutting edges demonstrated significant differences between the three resection tools. The best results were obtained for the laser scalpel compared with the punching device (P < 0.001) and for the laser scalpel compared with the scissors (P < 0.05), whereas the scissors compared with the punching device showed no significant differences (P > 0.05).

CONCLUSIONS

Laser cutting of human calcified aortic valves demonstrated the best results concerning homogeneous cross-section morphology compared with the punching device and the scissors and seems to be a promising tool for aortic valve resection during TAVI procedures in the future.

Resection of calcified aortic heart leaflets in vitro by Q-switched 2 µm microsecond laser radiation

BACKGROUND

Transcatheter aortic valve implantation (TAVI) can result in paravalvular leakage and stent deformation in the presence of severe calcification. This study was undertaken to determine the efficacy of laser-assisted resection of calcific aortic valve leaflets as a method to minimize the effects of calcium on perivalvular leakage during TAVI.

METHODS

A Q-switched Tm:YAG laser emitting at a wavelength of 2.01 μm was used to evaluate the cutting efficiency on highly calcified human aortic leaflets in vitro (N = 10). A pulse energy of 4.3 mJ, a pulse duration of 0.8-1 μs, and a repetition rate of 1 kHz were used. The radiation was transmitted via a 200 µm core diameter quartz fiber. Resection was performed in a fiber-tissue contact mode on water-covered samples in a dish. The remnant particles were analyzed with respect to quantity and size by light microscopy.

RESULTS

A resection rate of 40.4 ± 22.2 mg/min on highly calcified aortic leaflets was achieved. This corresponds to a cutting speed of approximately 1 cm/min; a laser dissection time of 3 min per leaflet is expected. The majority of the remnant particles (85.4%) were <6 μm in diameter, with only 0.1% exceeding 300 μm.

CONCLUSIONS

The Q-switched Tm:YAG laser system showed promising results in cutting calcified aortic valves, by transmitting sufficient energy through a small flexible fiber. Catheter-based removal of aortic valve calcification may help to improve TAVI technology.

Transcatheter Valve Replacement: New concepts for Microsurgery inside the Heart

Objective

Transcatheter aortic valve implantation gained clinical relevance with an impressive and peerless power; however, the procedure induces unsolved complications such as paravalvular leakage, occlusion of coronary ostia, and vascular complications. The safe removal of bulky calcified valves will improve the outcome, well known through the open surgical procedure. In this article, a new stapler-based resection and implantation device as well as a new approach for valve isolation during normal heart cycle without extracorporeal circulation will be analyzed.

Methods

First, a novel stapler-based instrument for transapical aortic valve replacement [removal and implantation; stapler-based aortic valve replacement (StapAVR)] was constructed and analyzed in an aortic debris model. Artificial aortic valves (N = 20), containing fluorescent granules to simulate the calcification, were placed into an aortic model in anatomical supine position (DP) and right-sided lateral position (RP). With the StapAVR, resection before implantation was performed in a water-filled basin. Black light was used for debris visualization. The procedures have been digitally recorded and analyzed due to procedural times, and the debris amount in thoracic side branches. Second, an enhanced prototype of the pulmonary valve isolation chamber (PVIC) was analyzed in porcine in vitro (n = 10) and in vivo models (n = 1). This PVIC contains a microaxial pump (Impella; Abiomed, Aachen, Germany) in the central bypass channel. It was deployed through the right ventricular wall. Once the PVIC was in place, the pump was started before isolating the valve. The complete hemodynamic monitoring was digitally recorded.

Results

The deployment of the StapAVR in the correct position and the valve resection time took a mean (SD) of 95.8 (19) seconds in DP and 90.1 (18) seconds in RP. Fluorescent debris was found: in the left coronary artery, 22% in DP and 7% in RP; in the ascending aorta, 0% in DP and 11% in RP; in the aortic bulbous, 5% in DP and 10% in RP; in the left ventricle, 8% in DP and 14% in RP; in the brachiocephalic trunk, 4% in DP and 9% in RP; and in the descending aorta, 46% in DP and 1% in RP. Consecutive valved stent implantation was performed without complications. The PVIC deployment time in vivo was 5 minutes, replacements included. The total valve isolation time was 21 minutes, with a mean (SD) bypass flow of 2.1 (0.4) L/min. The oxygen saturation showed a median of 91% (range, 83%–97%), and the median arterial blood pressure was 69 mm Hg (systolic; range, 47–120 mm Hg) and 40mm Hg (diastolic; range, 32–56 mm Hg) without the use of inotropes or vasopressors. Electrocardiogram confirmed sinus rhythm during isolation.

Conclusions

The resection of the artificial valves followed by valved stent implantation was possible with the StapAVR. In vivo, the procedure will be carried out under rapid pacing and sudden vacuum; however, the results of this in vitro debris model underline the need for isolation or filter devices during transcatheter aortic valve implantation to avoid embolization. Secondly, the use of the pump-advanced PVIC showed stable heart function for 21 minutes under isolated pulmonary valve conditions. This time will be adequate to remove bulky calcifications and to implant a valved stent. Improvements of both prototypes are ongoing. Nevertheless, the presented concepts showed promising application possibilities in the future.

Transcatheter aortic valve replacement: transapical resection of the aortic valve in vivo

The resection of pulmonary valves has already been demonstrated in an experimental beating-heart model. The aim of this study was to analyse the transapical laser-assisted resection of aortic valves in an in vivo porcine model in a non-beating heart. The resection was performed in a porcine model (n = 10) using a Thullium:YAG laser. After establishing a standard extracorporeal circulatory support, the aortic valve isolation chamber (AVIC) system was inserted transapically. The resection of the aortic leaflets was carried out step-by-step in the arrested heart. The AVIC implantation, the resection process, and the gross anatomy of intracardiac lesions were analysed. The procedure for installing the AVIC took 5.8 ± 1.5 min. A sealed chamber was achieved in 9/10 cases. The resection of the valves was performed in 8/10 and completed in 7/10 cases. The resection took, on average, 7.4 ± 2.7 min/cusp. In 9/10 cases, the sealing was sufficient. Gross anatomy and histological analysis demonstrated only superficial damage to the surrounding tissue. In this study, the in vivo on-pump isolation of the left ventricular outflow tract and the laser resection of the native aortic valve could be demonstrated successfully. Nevertheless, this model is the next step towards a beating-heart resection of the aortic valve using the isolation chamber.