INTRODUCTION

Transcatheter aortic valve implantation (TAVI) emerged in 2002 as a minimally invasive treatment of native aortic valve stenosis in patients at high surgical risk for conventional open surgery^[1]. The adaptation of this technique, performing the implantation of a transcatheter prosthesis inside a bioprosthesis, became known as valve-in-valve (VIV) procedure and allows the treatment of patients with bioprosthetic valve dysfunction, commonly observed about 10 years after implantation^[2,3].

VIV procedures frequently result in reduced effective orifice area and prosthesis-patient mismatch, especially when implanted in small bioprosthetic valves (sizes 19-21 mm)^[4]. When the post- TAVI gradient is > 20 mmHg, it is related to increased mortality in one year after the procedure^[5]. Bioprosthetic ring fracture using a transcatheter non-compliant high-pressure balloon may increase the valve diameter and therefore its effective orifice area, reducing the gradient without related annular or aortic root rupture, coronary occlusion, or need for pacemaker. In a series with 75 cases submitted to this technique, only two patients presented transcatheter prosthesis insufficiency, resolved with the implantation of a new transcatheter valve^[6-8].

Due to the great variety of bioprostheses available in the market, with different types of structures, some ex vivo tests have evaluated the possibility of ring fracture and the pressure required for it, if it occurs^[9]. However, these studies did not include prostheses produced in Brazil. The resulting information is of great importance in the preoperative evaluation of VIV procedures, since some brands do not suffer fractures or may require too high pressures.

METHODS

The experiment was approved by the ethical committee of the Universidade Federal de São Paulo (number 2686290917). According to the Agência Nacional de Vigilância Sanitária (or Anvisa) electronic query system^[10], three Brazilian industries currently produce aortic bioprostheses: Braile Biomédica, Cardioprótese, and Labcor. The experiment was based on the original description of the technique^[11] and used one model of each bioprosthesis of nominal sizes 19 and 21 mm (external diameter) of each company. Also, Atlas Gold PTA balloons (Bard Peripheral Vascular Inc.) of 20- and 22-mm diameters were used, aiming a diameter 1 mm larger than the external diameter of the prosthesis to which it was intended. The balloon was introduced in the prosthesis to be fractured, and the balloon insufflation line was connected to one of the paths of a three-way stopcock. The other two paths were connected to an insufflator and a 60-ml capacity syringe, both filled with 0.9% saline solution.

With the stopcock path open to the syringe, the balloon was inflated manually until resistance was reached. Then, the stopcock was opened for the inflator line and the inflation proceeded. Prosthetic ring fracture was characterized by an abrupt drop in the pressure recorded on the inflator manometer, often accompanied by a characteristic high-pitched sound. The pressure at the time of fracture was recorded. Photographs and radiographs (superior-inferior projection) were taken to compare the appearance of the structure before and after the maneuver. Finally, the lining of the prosthesis rings was removed for evaluation and photographic documentation.

RESULTS

In the experiments performed, all the prostheses were fractured at the first attempt, except the 19-mm Braile prosthesis, which required two attempts with a 20-mm balloon, because the first balloon was ruptured around 24 atm. The ring fracture with the second balloon occurred at 25 atm. It was observed that the pressure required for fracture of the prostheses produced by Braile, with metallic rings, was higher than the breaking pressure of the other models (Table 1).

Table 1 - Pressures (in atm) at which fracture occurred in each bioprosthesis model studied after application of radial force by a high-pressure non-compliant balloon, sizes 20 or 22 mm.

The photographs and radiographs before the test allow the identification of the metallic ring in the models manufactured by Braile (Figures 1 and 2). After fracture, in all prostheses it was possible to evidence the site of the ring discontinuity, characterized by local deformity, which was more evident in the model with metallic ring (Figures 3 to 6).

Fig. 1 - Photographs of the prostheses used in the test in their upper, lower, and lateral aspects.

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Fig. 1 - Photographs of the prostheses used in the test in their upper, lower, and lateral aspects.

Fig. 2 - Radiography of the prostheses used in the test. Superior - inferior and lateral projections.

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Fig. 2 - Radiography of the prostheses used in the test. Superior - inferior and lateral projections.

Fig. 3 - Braile prosthesis after fracture, sizes 19 mm and 21 mm. Radiography (superior-inferior projection) and photographs (intact lining and dissected lining). Arrow corresponding to the fracture site.

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Fig. 3 - Braile prosthesis after fracture, sizes 19 mm and 21 mm. Radiography (superior-inferior projection) and photographs (intact lining and dissected lining). Arrow corresponding to the fracture site.

Fig. 4 - Labcor Dokimos prosthesis after fracture, sizes 19 mm and 21 mm. Radiography (superior-inferior projection) and photographs (intact lining and dissected lining). Arrow corresponding to the fracture site.

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Fig. 4 - Labcor Dokimos prosthesis after fracture, sizes 19 mm and 21 mm. Radiography (superior-inferior projection) and photographs (intact lining and dissected lining). Arrow corresponding to the fracture site.

Fig. 5 - Labcor TLPB prosthesis after fracture, sizes 19 mm and 21mm Radiography (superior-inferior projection) and photographs (intact lining and dissected lining). Arrow corresponding to the fracture site.

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Fig. 5 - Labcor TLPB prosthesis after fracture, sizes 19 mm and 21mm Radiography (superior-inferior projection) and photographs (intact lining and dissected lining). Arrow corresponding to the fracture site.

Fig. 6 - Cardioprótese Premium prosthesis after fracture, sizes 19mm and 21mm. Radiography (superior-inferior projection) and photographs (intact lining and dissected lining). Arrow corresponding to the fracture site.

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Fig. 6 - Cardioprótese Premium prosthesis after fracture, sizes 19mm and 21mm. Radiography (superior-inferior projection) and photographs (intact lining and dissected lining). Arrow corresponding to the fracture site.

A slight deformity in the ring structure was identified on palpation, keeping the Dacron reinforcement intact; no spicules were observed. After removing the Dacron lining and exposing the fracture site, linear discontinuity of the ring and absence of fragments were observed.

DISCUSSION

In the present work it was evaluated - for the first time in an ex vivo test - the possibility of ring fracture of aortic bioprostheses manufactured in Brazil, when submitted to radial force by a high-pressure non-compliant balloon.

In VIV procedures, the use of strategies that reduce the postoperative transvalvular gradient aiming at values < 20 mmHg have an impact on symptom improvement, prosthesis durability, and mortality reduction^[5]. The knowledge of the size of the dysfunctional prosthesis that receives the transcatheter prosthesis inside is part of the surgical planning, as well as the knowledge about the possibility of fracture in case of high postoperative gradient.

In several studies with ex vivo tests for ring fracture of bioprostheses^[9,11,12], it was observed that the presence of metallic reinforcement in some models of prostheses made them unbreakable (e.g., St. Jude Trifecta and Medtronic Hancock II) or demanded a greater pressure for fracture. Because of this, in patients who need small-sized surgical prostheses (19 or 21 mm), if it is not possible to perform an aortic annulus enlargement technique, it should be considered to avoid the implantation of valves with metallic reinforcement, which may be difficult or impossible to fracture during VIV procedures.

CONCLUSION

The present study revealed that the aortic bioprostheses produced by Brazilian companies, in a bench test, can be fractured using a non-compliant high-pressure balloon. However, this result does not allow the recommendation of the technique of ring fracture of bioprostheses in humans, and new studies must be done to warrant its security in vivo. The information obtained could assist in the planning of valve ring fracture in VIV procedures in patients with aortic valve bioprostheses.