Transapical off-pump removal of the native aortic valve: a proof-of-concept animal study

Testing of a novel percutaneous temporary aortic valve in a rabbit model of acute severe aortic regurgitation: an experimental study

PURPOSE

Device management of hemodynamic instability due to acute aortic regurgitation is not available. A novel, catheter-based, temporary aortic valve (TAV) has been in development. Early prototypes (balloon-based TAV) have undergone proof-of-concept studies in mathematical, bench and animal models. The redesigned membrane-based TAV prototype is evaluated in a rabbit model of acute severe aortic regurgitation.

METHODS

Acute aortic regurgitation was simulated by deploying a self-expanding endovascular stent across the aortic annulus. Eight rabbits of body weights ranging 4.9-5.4 kg were randomly assigned to two groups: those received additional hemodynamic support with the TAV prototype immediately after aortic regurgitation was induced versus no TAV support. The survival times of the two groups were compared.

RESULTS

Comparing the groups with TAV versus without TAV, the mean body weights were similar: 4.99 ± 0.06 vs. 5.10 ± 0.22 kg (p = 0.71). The mean stent sizes used to create acute aortic regurgitation were similar: 6.25 ± 0.50 vs. 6.75 ± 0.50 mm, respectively (p = 0.53). The mean survival times also did not differ significantly: 21.00 ± 15.41 vs. 8.25 ± 2.75 minutes, respectively (p = 0.45). A slight trend appeared to be in favor of longer survival in the TAV supported group.

CONCLUSIONS

In a rabbit model of acute massive aortic regurgitation, the use of the TAV support prototype did not hasten the animals' death, but rather survival may be enhanced by the use of the device. Future studies specifically designed to evaluate the efficacy of the TAV catheter can be valuable in this new technology.

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.

Qualitative coronary flow evaluation of a pre-clinical percutaneous temporary aortic valve

A published balloon-based percutaneous temporary aortic valve (TAV), with a specific fixed gap-to-aorta cross-sectional area ratio, was shown to provide haemodynamic support in acute aortic regurgitation (AR). The fixed gap of the balloon-TAV, however, limits the ability to optimize the gap size balancing coronary flow vs AR protection. Hence, a reduced diastolic gap may improve AR protection, but could reduce coronary flow and increase systolic TAV flow resistance. A new membrane-based TAV, which avoids these design limitations, could guide gap size optimization and advance the development into a pre-clinical tool. The re-designed TAV prototype has a membrane-cone collapsible in systole to reduce flow resistance and expands in diastole with a gap-to-aorta cross-sectional area ratio that can be tailored to optimize AR protection and coronary flow. Without the concern for systolic TAV flow resistance, a lower limit of the gap:aorta cross-sectional area ratio could be determined. The ability of the membrane-TAV design in determining an optimal gap:aorta ratio is tested in an in vitro flow chamber. Three prototypes with reducing gap:aorta cross-sectional area ratios (35%, 15%, 0%) were tested in a flow chamber of simulated acute severe AR. Correspondingly, increasing in forward cardiac output volumes, coronary flow:aortic regurgitant volume ratios and reduction in aortic regurgitant volumes were observed (p < 0.001) in the three models. The membrane-TAV concept contains a design feature for optimization of LV protection from acute AR and coronary perfusion by defining an optimal gap:aorta ratio. Along with the results from the balloon-TAV, a clinically useful percutaneous device for the management of acute severe aortic regurgitation is becoming possible.

Percutaneous temporary aortic valve: a hemodynamic support system for acute aortic insufficiency

A percutaneous temporary aortic valve hemodynamic support catheter is a device that can conceptually maintain stable hemodynamics when significant structural damage occurs to the native aortic valve ensuing acute severe aortic insufficiency. Applications may include a bridge to surgery in active aortic valve endocarditis and an option to allow for diseased valve resection prior to transcatheter aortic valve replacement. An early prototype has undergone successful fundamental mathematical, bench and animal proof-of-concept studies. Design, concept and early data are presented and discussed.

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.

Percutaneous aortic valve replacement. Part 3: Balloon counterpulsation of a novel temporary aortic valve

A previously published two-part study described an engineering design of a percutaneous aortic valve (PAV) replacement system, which utilizes a novel temporary aortic valve (TAV) support to improve procedural outcomes and safety. Conceptually, this investigational approach can promote accurate PAV placement, procedural hemodynamic stability, smaller catheter delivery system, reduction in PAV regurgitation, reduction in conduction and vascular complications. The balloon TAV can potentially facilitate the PAV replacement procedure by serving as the patient's surrogate aortic valve while the native valve is pretreated and replaced. The original TAV is designed to function with an effective aortic stenosis and insufficiency in moderate ranges, which lessens from the patient's more critical valve condition, should be well tolerated when the native valve becomes nonfunctional during the replacement process. Further optimization of the TAV's hemodynamic profile could further improve the system's overall performance and enhance the realization of a truly minimally invasive, cath lab-based PAV replacement procedure comparable to that of percutaneous coronary intervention. This study explores design permutations from the original published TAV, including varying the number of balloons and adding balloon counterpulsations, to improve upon its hemodynamic profile to better serve as the patient's surrogate valve and the overall PAV replacement procedure.

Qualitative haemodynamic validation of a percutaneous temporary aortic valve: a proof of concept study

The concept of temporary aortic valves has been suggested in the clinical settings of acute aortic regurgitation and transcatheter aortic valve replacement procedure (TAVR). In TAVR, suggestions have been made to pre-treat or remove the diseased aortic valve prior to implantation of the replacement valve. A successful temporary aortic valve must demonstrate the ability to prevent life-threatening haemodynamics of massive aortic regurgitation. A novel temporary aortic valve (TAV) design, comprised of inflatable balloon elements as a check-valve, can readily be deployed and retrieved via a catheter-system. A simple flow model is set up to test the TAV's performance in severe aortic regurgitation. With induced aortic regurgitation, placement of the TAV is found to increase the distal aortic diastolic pressure, to reduce the widened pulse pressure, to protect proximal aorta-left ventricle from diastolic pressure elevation and to reduce the aortic regurgitant volume. In conclusion, continued development of the TAV system can lead to a successful temporary aortic valve to be used in various appropriate clinical settings.

The future of new aortic valve replacement approaches

Aortic valve disease is a growing cause of mortality and morbidity, especially in developed countries. Whereas medical therapy is associated with an ominous prognosis, since the 1970s, surgical valve replacement has represented a standard therapy for fit patients. Indeed, this approach is safe and feasible in younger patients without comorbidities. However, in unfit patients, surgery may be associated with a very high risk. The advent of transcatheter valve replacement techniques, by means of percutaneous or transapical approaches, has been recently introduced into mainstream clinical practice and is likely to radically change the treatment of aortic valve disease. At present, further data are needed to thoroughly appraise the long-term risk–benefit balance of transcatheter valve replacement techniques. For this reason, it can only be considered for high surgical risk patients, but early results are so promising that in the future, transcatheter aortic valve implantation could became the first therapeutic choice, even for low-risk patients.