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Eur J Cardiothorac Surg 2005;27:836-840
© 2005 Elsevier Science NL

Percutaneous aortic valve replacement: resection before implantation

René Quaden, Tim Attmann, Andreas Boening, Jochen Cremer, Georg Lutter*

Department of Cardiovascular Surgery, School of Medicine, Christian-Albrechts-University of Kiel, Arnold-Heller-Strasse 7, D-24105 Kiel, Germany

Received 4 September 2004; received in revised form 2 January 2005; accepted 12 January 2005.

* Corresponding author. Tel.: +49 431 597 4582; fax: +49 431 597 4402. (E-mail: lutter{at}kielheart.uni-kiel.de).


   Abstract
Top
 Abstract
1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Conclusions
 Appendix A. Conference...
 References
 
Objective: After transluminal endovascular implantation of a new valved stent, the aim of this study was to evaluate the feasibility of using a high-pressure water stream to endovascularly resect human calcified aortic valves. Methods: First, human calcified aortic valves were excised and then resected in vitro to determine optimal water jet parameters. Second, healthy porcine aortic valves were ablated in vitro to evaluate possible destruction to the surrounding anatomy. Third, resection was performed endoluminally by introducing microsystemic tools into the descending aorta, passing them through the arch and ascending aorta to the aortic valve in an in vitro porcine model. Macro- and micropathology of specimens were analyzed. Results: First, resection of human calcified valves took a mean of 6.0±2.4min per three leaflets at 150bar (n=17). The maximum size of the cut leaflets was 7.1±1.7mm. Second, resection of healthy porcine aortic valves at 60bar took 2.3±0.3min per three leaflets (n=10). Only the aortic annulus was moderately affected in six cases. Third, endoluminal resection via the descending aorta took 12.2±0.8min per three leaflets at 60bar (n=10). The aortic wall was affected in four cases, the aortic annulus and the coronary ostia only once. Microscopic analysis also revealed superficial lesions with a maximum lesion depth of 1200µm in one case, and an average of 580±145µm in subsequent lesions. The mitral valve and the left ventricular outflow tract were not affected. Conclusions: Percutaneous resection of heart valves is emerging as a promising auxiliary method for the resection of calcified aortic heart valves because they can be cut endoscopically. Nonetheless, before this resection tool can be clinically applied by surgeons to perform a true percutaneous valve replacement, an additional aortic valve resection chamber (already at the prototype stage) designed for capturing all debris, has to be established.

Key Words: Resection • Excision • Percutaneous valve replacement • Aortic valve • Endovascular • Transluminal


   1. Introduction
Top
 Abstract
 1. Introduction
2. Material and methods
 3. Results
 4. Discussion
 5. Conclusions
 Appendix A. Conference...
 References
 
Aortic valve replacement is generally performed by standardized cardiosurgical procedures, although endovascular procedures for valve replacement may provide an alternative to cardiac surgery in selected cases [1–5].

It would be especially advantageous if defective heart valves could be percutaneously removed [2,4]. The procedure would then be carried out endovascularly, using the vascular system to guide the appropriate operation devices to the aortic annulus, and then undertake percutaneous resection of the calcified aortic valve. There are three major reasons for performing resection before implantation [2,4]: the avoidance of any possible embolization, paravalvular leakage, and a small aortic valve area after sole valved stent implantation [3].

Initially, efforts were made to develop a transluminal technique for the resection of calcified aortic valves, testing a variety of different resection devices. Preliminary in vitro studies in our laboratory demonstrated the possibility of ablating human calcified aortic valves with three different types of lasers (CO2, Hol:YAG, and Erb:YAG lasers) [4]. However, the duration of the laser resection procedures proved unrealistic (≥1h), stimulating the search for new methods [2].

This report presents our initial experience with aortic valve resection in three in vitro porcine models using a high-pressure water stream scalpel.


   2. Material and methods
Top
 Abstract
 1. Introduction
 2. Material and methods
3. Results
 4. Discussion
 5. Conclusions
 Appendix A. Conference...
 References
 
A high-pressure water stream scalpel (Erbe®, Tübingen, Germany), with a maximum pressure of 150bar, was used for all resection studies (Fig. 1).



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  		Fig. 1. The Erbe HydroJet® (I) with one of its application devices (II), the endoscope (Richard Wolf®) with a diameter of 5.0mm (III), and an endoscopic view onto a porcine aortic valve (IV).

 
2.1. Resection of human calcified aortic valve leaflets: resection protocol I
To obtain optimal water jet parameters in vitro, numerous pilot studies were performed. Leaflet size was measured and then the leaflets were stitched into a rubber band (diameter of 20mm, area of 16mm2) with 6.0 Prolene® (Fig. 2 I and II). Resection was performed endoluminally in a water-filled set up through an acrylic plastic tube (length 100mm, inner diameter 25mm). The rubber band with an institched highly calcified aortic valve was placed into the acrylic tube (Fig. 2 III). A polyethylene balloon was positioned just below the rubber band to close off the acrylic tube in one direction. A surgeon performed the resection (n=17) using a fine-control extended inflexible resection tool (length 200mm, outer diameter 1.5mm) with a pressure of 150bar (Figs. 1 and 2 IV).



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  		Fig. 2. For the resection of human calcified aortic leaflets (I), the cusps were fixed in a rubber band (II) and placed into an acrylic tube (III). Then, the calcified cusps were cut by the water jet scalpel. See Section 2.1, ((IVa) view from beneath before resection; (IVb) equal view during resection; (IVc) excised calcified cusp).

 
To produce leaflet fragments, which can be removed through a port, the leaflets were cut into fragments of 5.0mm in length. The duration of the water jet resection required for three leaflets, and the size of the excised fragments were recorded. Macropathology of specimens were analyzed and the resistance of the polyethylene balloons was checked.

2.2. Resection of healthy porcine aortic heart leaflets in a direct approach: resection protocol II
Ten porcine hearts supplied by a slaughterhouse were used to both ablate the leaflets and to evaluate potential damage caused by the resection method.

Before resection, the dimensions of healthy valves were on average: length 19.5±1.2mm; width 14.6±1.1mm; height 1.0±0.1mm.

The resection was performed directly on the aortic leaflets (90° angle), with a pressure of 60bar. After holding them in place by forceps, leaflets were excised completely 2mm from the aortic annulus. An inflated polyethylene balloon was positioned directly beneath the aortic valve to protect the subvalvular area. The aortic wall, the coronary ostia, the aortic annulus, the mitral valve, and the left ventricular outflow tract were macroscopically and microscopically analyzed for possible lesions (up to 40mm distance from aortic annulus in any direction).

2.3. Endoluminal resection performed via the descending aorta: resection protocol III
Endoluminal resection was performed by a surgeon on ten porcine hearts with an intact thoracic aorta (ascending, arch, and descending). The resection device was manually controlled by a flexible endoscope (outer diameter 5.0mm, length 600mm; Richard Wolf® GmbH, Knittlingen, Germany) with a fiber optic channel linked to a digital camera, three fiber optic channels for illumination, and a separate device channel for inserting instruments, especially the resection tool (Fig. 1). The distal part of the endoscope (40mm) was flexible in one plane for an angle of 130°/120° and in addition 120° rotatable.

The resection device, with an outer diameter of 1.5mm and a length of 2000mm, was positioned in situ. The endoscope was inserted into the descending aorta, pushed forward through the arch and the ascending aorta and placed, as guided by endoscopic visualization, directly above the aortic valve (5mm distance, Fig. 1 IV).

An assistant controlled a flexible catheter with a distally fitted grab (length 500mm, outer diameter 1.1mm) which was also inserted into the descending aorta. The grab was opened and closed by a proximal manual control. Leaflets were held in place by this tool and an inflated polyethylene balloon was placed (Fig. 3).



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  		Fig. 3. The endoscope with resection tools inside were inserted via the descending aorta to excise the aortic valve. A polyethylene balloon was placed directly beneath the aortic valve to protect the subvalvular structures (see Sections 2.2 and 2.3).

 
The ascending aorta was filled up with mains water. Preliminary studies indicated a need for combined water irrigation and suctioning of the half-closed resection chamber. Irrigation (water, 80ml/min) was applied through a 3.5mm port through the wall of the brachiocephalican truncus. Suction was applied at a vacuum of –800mbar.

The leaflets were completely excised, 2mm from the aortic annulus. The duration of the water jet resection of the three leaflets, size of the fragments, resistance of the polyethylene balloon, and any complications noted in the surrounding tissue within 40mm of the annulus were protocolled. Macro- and micropathology of specimens were analyzed. The flexibility and guidance of the endoscope and microsystemic tools were also evaluated.


   3. Results
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
4. Discussion
 5. Conclusions
 Appendix A. Conference...
 References
 
3.1. Endoluminal resection of human calcified aortic valve leaflets: resection protocol I
The size of one leaflet before resection was in average 18mm in width, 7mm in length, and 2mm in height. The number of fragments and maximal fragment size per leaflet after excision, and the resection time are given in Table 1.


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  		Table 1. Results from resection protocol I
 
Endoluminal resection of human calcified aortic leaflets in the acrylic model proved successful. The HydroJet® proved comfortable to operate. On average, 0.6±0.6 securing balloons ruptured per three leaflets. Macroscopically the cut surface was clean, especially in calcified areas (Fig. 2 IVc).

3.2. Resection of healthy porcine aortic leaflets in a direct approach: resection protocol II
The procedure was easily performed and leaflets were ablated completely. Tissue in the vicinity of the aortic valve revealed small lesions. The aortic annulus was moderately affected in six cases, whereas the mitral valve and the coronary ostia remained untouched (Table 2). Micropathology of the affected aortic annuli demonstrated superficial lesions with a maximum lesion depth of 1400 and 1600µm in two cases, and an average of 460±215µm in the other four specimens. No dissection or penetration occurred. One securing balloon ruptured.


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  		Table 2. Results from resection protocol II
 
3.3. Endoluminal resection performed via the descending aorta: resection protocol III
Resection tool mobility proved to be smooth and regular: no increased resistance was detectable during the movement of the endoscopic tool through the aorta.

Before resection, the leaflets were measured and on average were the same size as those in protocol II. Endoluminal resection of three leaflets took 12.2±0.8min. Macroscopic examination revealed four superficial lesions in the aortic wall and one on the aortic annulus and the coronary ostium. Microscopic analysis demonstrated superficial lesions with a maximum lesion depth of 1200µm in one case, and an average of 580±145µm in subsequent specimens (Fig. 4). No dissection or penetration occurred. The mitral valve, and the left ventricular outflow tract remained unaffected (Table 3).



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  		Fig. 4. Macropathology (left) and micropathology (right) of a lesion due to resection into the aortic annulus (depth=700µm). The micropathology shows the endothelium (I), the resection lesion (II), the myocardial cell layer (III) and vacuolization due to the high water pressure (arrows).

 

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  		Table 3. Results from resection protocol III
 
The endoscope imaging allowed acceptable guidance during the resection procedure, and the application device worked precisely. The resection was performed carefully. Operating the grab presented difficulties with several attempts sometimes being required before leaflets were securely removed.


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
5. Conclusions
 Appendix A. Conference...
 References
 
Percutaneous valve replacement is a developmental concept using a biological heart valve mounted on an expandable stent, delivered percutaneously via standard catheter-based techniques and implanted in a diseased valve annulus [1,3], after the diseased valve has been dilated [3], or ablated [2,4], and removed.

4.1. Technical difficulties
The difficulties of establishing a safe and successful transluminal technique to replace a diseased valve are well known. Questions regarding valved stent preparation, its stable positioning, the maintenance of coronary flow in case of aortic valve placement [2,6], a feasible implantation technique without risk of emboli, and competence and durability of the valved stent are all encountered hurdles [4].

To overcome the high risk of embolization during the pre-dilation procedure of calcified aortic valves (which is necessary before sole valved stent implantation [3,4]) —endovascular resection of the diseased valve has been developed. Furthermore, after valved stent implantation paravalvular leakages and small aortic valve areas are often observed. These problems occur due to the fact that the diseased valve is not removed [3] and the ‘neo-annulus’ (calcified annulus after dilatation) is often asymmetric and still blocks the left outflow tract [4,7,8].

For example, a stented valve of 23mm (ignoring the mass of biological membrane and stent) could have a theoretical valve area of about 4.2cm2. In practical experience, implanting percutaneous valved stents (23mm) in chronic aortic stenosis reported by Cribier et al., the effective valve area is typically 1.7cm2, and the sonographic appearance of this implant indicates a small profile within the expanded plane of the sinuses clearly distant from and no conceivable threat to the coronary ostia. With knowledge of such generous performance margins, the a priori notion that the stent profile should fully efface the aortic valve ring to achieve an effective hemodynamic profile is obviously naive, and designers can use less demanding criteria in approaching aortic stenosis [7,8].

4.2. Resection chamber
A novel and challenging approach to overcoming the above mentioned problems is the in situ removal and resection of the diseased aortic valve by endovascular techniques in a non-beating heart and replacing it with the valved stent [2,4]. Such a catheter-based system provides a space between the mitral valve and the ascending aorta, wherein the calcified valve can be removed while preventing embolization by remnant particles using an aortic valve resection chamber (Fig. 5).



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  		Fig. 5. The aortic valve resection chamber is sealed by polyethylene balloons. The surgical instruments are inserted via the instrument channel. Two catheters with small sealing balloons provide the coronaries with cardioplegia and prevent coronary embolization during the resection process.

 
This aortic valve resection chamber will be the most challenging development for in vivo use [2]. The basic idea is to construct an operation chamber which is closed by two inflated sealing balloons. One is positioned above the aortic valve, the other subvalvular. In such a sealed chamber, no debris can escape. Before blood flow can be stopped in the aortic valve area, a femoro-femoral bypass must be established [2]. Coronary cardioplegia catheters will be blocked in the coronary ostia, and the heart vented in the left atrium. The two (cuff) sealing balloons will then be inflated; blood will be taken out of the chamber and the endoscopic guided ablation will commence. The debris will be suctioned out and the ablation chamber intermittently washed out.

4.3. Results of the study
This study introduces a new method for aortic valve resection using an endo-vascular approach which are the first steps toward percutaneous in vivo resection.

The feasibility of the high-pressure water stream scalpel was tested first on human calcified aortic leaflets (resection protocol I). A pressure of 150bar produced excellent resection results with a time of about 6min per three leaflets.

Nonetheless, a high-stream water stream scalpel with a pressure of 150bar was deemed capable of causing damage to the surrounding anatomical structures. As a result, resection protocol II was designed to evaluate the effect of water scalpels on the surrounding anatomical structures. The results indicated superficial lesions on the aortic annulus. The inflated polyethylene balloon proved effective in reducing damage to adjacent subvalvular structures.

The importance of resection protocol III was to check for possible damage and to analyze the flexibility and ease of guiding all three endoscopic tools via the descending aorta, through the arch and the ascending aorta to reach the aortic valve. The macro- and microscopic observations demonstrated small superficial lesions without penetration.

Insertion of the endoscope neither impaired handling nor increased resistance. Endoscopic pictures of the aortic valves were sharp. The grab catheter was less easy to manipulate under endoscopic view.

4.4. Limitations
Due to the fact that the materials and equipment were not designed for this new operation technique, limitations were observed. It would be helpful to have an endoscope, which can be controlled in any direction. The grab catheter was flexible without allowing guidance.

In addition, debris analysis was not mentioned in this study. The capture of all debris is very important for in vivo use to prevent embolization.


   5. Conclusions
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Conclusions
Appendix A. Conference...
 References
 
In conclusion, the use and feasibility of a high-pressure water stream scalpel as a new promising surgical method for endovascular resection of human calcified aortic valves have been evaluated.

The future of implanting aortic valves percutaneously in human subjects will depend on the development of a transluminal resection technique with a resection chamber to avoid emboli and an adequate circulatory support system.


   Appendix A. Conference discussion
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Conclusions
 Appendix A. Conference...
References
 
Dr H. Shennib (Montreal, Canada): There are some researchers that are advocating chemical ablation for aortic valve decalcification using chemical agents.

My question has to do with your choice of ablation technique; why did you choose the high pressure?

And in your opinion, from experience or literature review, how do you compare high-pressure ablation with other means of ablating the aortic valve?

Dr Quaden: In a previous study, we tried other ablation techniques, and we used several lasers and mechanical methods, such as graspers or shavers. But this study showed that all these approaches were not useful for doing the ablation percutaneously in this ablation chamber and it took too much time with the lasers we used.

The HydroJet offers better procedure times. The calcified leaflets were cut in 2minutes per leaflet, and this worked precisely, and so we used it for all subsequent ablation studies.

Dr L. von Segesser (Lausanne, Switzerland): Do you think that in all cases the leaflets have to be removed for percutaneous valve replacement?

Dr Quaden: I think that the future prospect is that it should only be used in special cases, especially when the patient cannot be operated with conventional surgical procedures.

Dr von Segesser: And another question. The calcium you placed, where did you put it? Because we know from the clinical setting that usually it's very close to the aortic wall or even penetrating into the septum, so how is the cutting of the calcium going?

Dr Quaden: We try to cut the calcified leaflets that are 1–2mm distance from the aortic annulus.

Dr G. Lutter (Kiel, Germany): You asked whether you have to take out all of the calcified valve. And up to now, it's pre-dilated and then a valve stent is implanted. If you look at the data, you will find that they produce a neo-annulus. This annulus is not symmetric, and therefore you always find paravalvular leakage in most of the cases, about 80%. To prevent any neurological deficits and to get an overall true replacement, you need to have an optimal ablation beforehand.


   Acknowledgments
 
Georg Lutter and his project percutaneous valve replacement are supported by the German Research Foundation (Grant LU 663/4-1, LU 663/4-2).


   Footnotes
 
{star} Presented at the joint 18th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 12th Annual Meeting of the European Society of Thoracic Surgeons, Leipzig, Germany, September 12–15, 2004.


   References
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Conclusions
 Appendix A. Conference...
 References
 

  1. Bonhoeffer P, Boudjemline Y, Qureshi SA, Le Bidois J, Iserin L, Acar P, Merckx J, Kachaner J, Sidi D. Percutaneous insertion of the pulmonary valve. J Am Coll Cardiol 2002;39:1664-1669.[Abstract/Free Full Text]
  2. Lutter G, Kuklinski D, Berg G, Von Samson P, Martin J, Handke M, Uhrmeister P, Beyersdorf F. Percutaneous aortic valve replacement: an experimental study. I. Studies on implantation. J Thorac Cardiovasc Surg 2002;123:768-776.[Abstract/Free Full Text]
  3. Cribier A, Eltchaninoff H, Tron C, Bauer F, Agatiello C, Sebagh L, Bash A, Nusimovici D, Litzler PY, Bessou JP, Leon MB. Early experience with percutaneous transcatheter implantation of heart valve prosthesis for the treatment of end-stage inoperable patients with calcific aortic stenosis. J Am Coll Cardiol 2004;43:698-703.[Abstract/Free Full Text]
  4. Lutter G, Ardehali R, Cremer J, Bonhoeffer P. Percutaneous valve replacement: current state and future prospects. Ann Thorac Surg 2004;78:2199-2206.[Abstract/Free Full Text]
  5. Zhou JQ, Corno AF, Huber CH, Tozzi P, von Segesser LK. Self-expandable valved stent of large size: off-bypass implantation in pulmonary position. Eur J Cardiothorac Surg 2003;24:212-216.[Abstract/Free Full Text]
  6. Huber CH, Tozzi P, Corno AF, Marty B, Ruchat P, Gersbach P, Nasratulla M, von Segesser LK. Do valved stents compromise coronary flow?. Eur J Cardiothorac Surg 2004;5:754-759.
  7. Robicsek F, Harbold Jr NB, Daugherty HK, Cook JW, Selle JG, Hess PJ, Gallagher JJ. Balloon valvuloplasty in calcified aortic stenosis: a cause for caution and alarm. Ann Thorac Surg 1988;45:515-525.[Abstract]
  8. Fish RD. Percutaneous heart valve replacement. Enthusiasm tempered. Circulation 2004;110:1876-1878.[Free Full Text]



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