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SPV (St Jude Medical) is a porcine valve requiring two suture lines w11x. The stentless valves were compared with a stented pericardial valve (Mitroflow ; Sorin, ...
ARTICLE IN PRESS doi:10.1510/icvts.2009.230771

Interactive CardioVascular and Thoracic Surgery 10 (2010) 976–980 www.icvts.org

Institutional report - Valves

Aortic root distensibility and cross-sectional areas in stented and subcoronary stentless bioprostheses in pigs夞 Jonas Amstrup Fundera,*, Steffen Ringgaardb, Markus Winther Frosta, Per Wierupa, Kaj-Erik Klaaborga, Vibeke Hjortdala, Hans Nygaarda, John Michael Hasenkama Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Skejby, Brendstrupgaardsvej 100, DK-8200 Aarhus N, Denmark b MR Research Centre, Aarhus University Hospital, Skejby, Brendstrupgaardsvej, DK-8200 Aarhus N, Denmark

a

Received 18 December 2009; received in revised form 26 February 2010; accepted 3 March 2010

Abstract A flexible aortic root is essential for natural leaflet stress distribution. It is suggested that stentless bioprosthetic valves retain the flexibility of native valves. We investigated aortic root distensibility and cross-sectional area (CSA) in stentless (Solo䊛 , ns4; Toronto SPV䊛, ns7), stented (Mitroflow䊛 , ns8) and in native valves (ns8) in pigs. Magnetic resonance imaging was performed to assess aortic root areas. At the annular level the Solo䊛 valve had a larger CSA (2.83"0.26 cm2 ) than both the Mitroflow䊛 (2.24"0.23 cm2 ) and Toronto SPV䊛 (1.87"0.59 cm2 ) (Ps0.003; Ps0.01). At the sino-tubular junction the Mitroflow䊛 valve had a significantly larger CSA (2.96" 0.80 cm2) than the Toronto SPV䊛 (2.05"0.47 cm2 ; Ps0.02). At the annular level the percentage change in area between end-diastole and end-systole was lower for the Mitroflow䊛 than for all the other valves (Ps0.006). No difference was found between native and stentless valves. In conclusion, the Solo䊛 valve had a larger CSA at the annulus than both the Mitroflow䊛 and the Toronto SPV䊛 . However, the stentless valves had a smaller CSA at the sino-tubular junction than the Mitroflow䊛 . We, furthermore, found that implantation of stentless heart valves preserves aortic root distensibility at the annular level in pigs. 䊚 2010 Published by European Association for Cardio-Thoracic Surgery. All rights reserved. Keywords: Aortic valve replacement; Heart valve stentless; Heart valve bioprostheses; Magnetic resonance imaging

1. Introduction A flexible aortic root is essential for the smooth movement of aortic valve leaflets w1, 2x. To optimize valve durability, it would appear intuitive to utilize flexible bioprosthetic designs, which imitate the natural movements of the native aortic root. Stentless heart valves are flexible in nature and, moreover, make claims of lower transvalvular pressure differences, larger coronary blood flow, and a faster left ventricular mass regression in comparison to their stented counterparts w3–5x. Although only one in vivo measurement of flexibility has been made (in root implants only) w6x, flexible valve designs have been shown to mimic the natural movement pattern of the aortic root, resulting in a better stress distribution in the surrounding tissue w7, 8x. This results in an improved freedom from structural valve deterioration, as seen in an animal study where less calcification 夞 Presented at 19th World Congress – World Society of Cardio-Thoracic Surgeons, Buenos Aires 2009. Oral presentation. Financial support: This research was made possible by donations from: Lundbeck Fonden, Snederkermester Sophus Jacobsen og hustru Astrid Jacobsens Fond, Aarhus Universitetshospitals Forskningsinitiativ, D irektør Kurt Bønnelycke og hustru fru Grethe Bønnelyckes Fond, Else og Mogens WedellWedellsborgs Fond, Raimond og Dagmar Ringga ˚rd-Bohn’s Fond, and Kirsten Anthonius Mindelegat and Carl og Ellen Hertz’s Legat. The prostheses used in the study were donated by Sorin Biomedica and St Jude Medical and financial support was given from Vingmed Denmark and St Jude Medical. *Corresponding author. Tel.: q4589495481; fax: q4589496016. E-mail address: [email protected] (J.A. Funder). 䊚 2010 Published by European Association for Cardio-Thoracic Surgery

of stentless valves was observed after a period of six months w9 x . We hypothesize that stentless valves remain flexible after implantation. This is especially important in subcoronary implantations, as the suture lines lie in close proximity to the leaflet attachment area. We aim to investigate aortic root distensibility as well as the aortic cross-sectional area (CSA) in two different subcoronary stentless valve types implanted in pigs. The Pericarbon Freedom Solo䊛 (Sorin, Italy) is a pericardial valve which requires a single suture line w10x and the Toronto SPV䊛 (St Jude Medical) is a porcine valve requiring two suture lines w11x. The stentless valves were compared with a stented pericardial valve (Mitroflow䊛; Sorin, Italy) and with native porcine valves in a porcine model using cardiac magnetic resonance imaging (MRI) (see Fig. 1). 2. Material and methods 2.1. Experimental animals The study was comprised of 38 Danish LandraceyYorkshire pigs, weighing 90 kg each. Immediately after the experiments, the pigs were euthanized under continued anesthesia. The experiments were conducted according to the guidelines and approval from the Danish Inspectorate of Animal Experimentation under the Danish Ministry of Justice.

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977 Editorial New Ideas Work in Progress Report Protocol

Fig. 1. The three artificial heart valves in the study. (a) Solo䊛 (Sorin) pericardial subcoronary stentless valve. It has a very thin sewing skirt causing limited obstruction in the aortic root. It is implanted supraannularly using a single suture line. (b) Toronto SPV䊛 (St Jude Medical) porcine subcoronary stentless valve. The valve, including part of the porcine vessel wall, is implanted inside the recipient root. It requires two suturelines with interrupted sutures annularly and a running suture line supraannularly. (c) Mitroflow䊛 (Sorin) pericardial stented valve. It is implanted supraannularly and the small sewing ring with tissue mounted outside the stent causes limited obstruction.

Institutional Report

2.2. Experimental procedure

ESCVS Article

Fig. 2. Twelve slices equally distributed around a rotation axis along the aortic root with an angle of 158. This produces 12 longitudinal images from which the analysis could be performed.

Follow-up Paper State-of-the-art

2.3. MRI protocol

Best Evidence Topic

Measurements were performed immediately postoperative using a Philips 1.5 Tesla Achieva MRI scanner (Philips Medical Systems, Best, Holland). The animals were continuously sedated with isoflurane and ventilated. They were examined in the right decubital position and a five-element cardiac coil was used for signal reception. Three electrocardiograms (ECG)-gated 2D cine scans were performed in order to determine the orientation of the aortic valve and root. The motion of the aortic root was examined during breath holds by a set of 12 longitudinal slices equally distributed around a rotation axis along the aortic root; i.e. the angle between each slice was 158 (Fig. 2). The locations of the slices were controlled on a transversal slice. The sequence was a balanced steady-state-freeprecession (B-SSFP) cine sequence with a slice thickness of 5 mm, field of view was 320=320 mm on a 160=160 matrix, TRyTE was 3.6y1.8 ms, and 40 cardiac phases were obtained.

Nomenclature Historical Pages

Fig. 3. MRI slice showing three aortic root levels: annulus, sino-tubular junction and ascending aorta. MRI, magnetic resonance imaging.

Brief Case Report Communication

2.4. Data analysis The data were analyzed using custom-made software (Siswin, Denmark). On each longitudinal slice, three levels were identified: the annulus, the sino-tubular junction and

Negative Results

the ascending aorta. At each level the internal vessel wall was marked on both sides, giving a total of 24 marks (see Fig. 3). The marks were thus scattered around the internal diameter of the vessel and were then fitted to a plane. The marks were not fitted to a circle i.e. the original

Proposal for Bailout Procedure

Surgery was performed through a median sternotomy using cardiopulmonary bypass and cold crystalloid cardioplegia (Kardioplex, SAD). In the intervention animals a total transverse aortotomy was made and the native valve removed. An artificial heart valve size 21 (Freedom Solo䊛, Toronto SPV䊛 or Mitroflow䊛) was inserted according to the techniques recommended by the valve manufacturer (see Fig. 1). The aortotomy was closed with a single running suture. In the control animals (native valve), cardiac arrest was maintained for 20 min and no aortotomy was performed. After weaning from the heart-and-lung machine an immediate postoperative epicardial echocardiography was performed to disclose any valve insufficiency or paravalvular leak (Vivid 7 Dimensions 06, GE HealthCare, Horton, Norway) w12x.

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transversal shape was used for calculations. The internal area was calculated both at end-diastole and at endsystole. The percentage change in area (PCA) from enddiastole to end-systole was calculated while the area at end-systole was used as the CSA. Data were analyzed in a blinded fashion by a single investigator. However, identification of valve type (stented, stentless or native) was in most cases possible from the MRI images. 2.5. Statistics All data are reported as a mean"standard deviation (S.D.). We used Kruskal–Wallis (multiple groups) or Mann– Whitney (two groups) tests for establishing differences from the mean. A P-value of 0.05 was utilized for determining significance. 3. Results We obtained data from 27 pigs (71%) all of which showed competent valves on postoperative epicardial echocardiography (Mitroflow䊛: ns8; Solo䊛 : ns4; Toronto SPV䊛: ns7; Native: ns8). Proper fitting of valves into the aortic root was achieved in all cases. MRI examination revealed no differences between groups in stroke volume (Ps0.33), pulse frequency (Ps0.09) or cardiac output (Ps0.96) during MRI examination. Ten pigs died postoperatively from cardiac failure, bleeding or fatal arrhythmia (Mitroflow䊛: ns2; Solo䊛: ns7; Toronto SPV䊛 : ns1). None of the deaths were prosthesis related, apart from one case (Solo䊛) where a leaflet was caught in the suture line. One pig (Solo䊛) was excluded due to poor image quality. 3.1. Percentage change in area PCA values at the annular level for the Mitroflow䊛, Solo䊛, Toronto SPV䊛, and native valve were in respective order: –2.1 ("4.2), 11.6 ("10.5), 13.5 ("18.3), and 10.9 ("20.9) (Fig. 4). The Mitroflow䊛 valve had a significant lower PCA than the other valves (Ps0.006). No difference between the stentless valves or between the stentless and native valves was observed at this level. PCA values at the sino-tubular junction were, respectively: 9.8 ("10.8), 15.7 ("5.2), 17.0 ("18.3), and 11.7 ("7.2). There was no significant difference between the four groups. At the level of the ascending aorta, the following respective PCA values were observed: 12.1 ("8.5), 10.6 ("4.1), 18.5 ("21.0), and 15.2 ("11.9). There was no significant difference between the four groups. Exact differences in cm2 are given in Table 1. Table 1 Area change between end-diastole and end-systole (cm2)

Fig. 4. Percentage change in area (PCA) at the annular level, the sino-tubular junction and the ascending aorta. At the annular level the PCA of the Mitroflow䊛 valve is significantly lower than the three other valves (Ps0.006).

Mitroflow䊛 Solo䊛 Toronto SPV䊛 Native

Annulus

Sino-tubular junction

Ascending aorta

–0.05"0.10 0.28"0.23 0.24"0.27 0.31"0.32

0.28"0.32 0.32"0.15 0.28"0.25 0.37"0.23

0.31"0.20 0.31"0.13 0.32"0.26 0.48"0.40

Mean"S.D. S.D., standard deviation.

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Ascending aorta

2.24"0.23 2.83"0.26 1.87"0.59 4.68"0.82

2.96"0.80 2.30"0.46 2.05"0.47 3.50"0.41

3.18"0.58 3.19"0.34 2.64"0.62 3.54"0.66

Mean"S.D. S.D., standard deviation.

Follow-up Paper State-of-the-art Best Evidence Topic Nomenclature Historical Pages Brief Case Report Communication

The stentless Solo䊛 valve has a larger aortic CSA at the annulus than both the stented Mitroflow䊛 and the stentless Toronto SPV䊛. However, the stentless valves have a smaller CSA at the sino-tubular junction than the Mitroflow䊛, probably due to highly placed sutures inside the root. We, furthermore, found that implantation of stentless aortic heart valves preserves aortic root distensibility at the annular level in pigs, arguably resulting in diminished leaflet stress. If these acute observations speak for their long-term durability, the stentless single suture-line Solo䊛 valve should, therefore, be considered, since annular distensibility is preserved in combination with the larger

Negative Results

5. Conclusion

Proposal for Bailout Procedure

This study is the first to investigate aortic root distensibility after subcoronary stentless valve implantation. Using MRI analysis, we have shown that stentless valves retain the desired aortic root flexibility of native valves at the annular level, which stented valves cannot provide. In addition, the native and the Solo䊛 valves had a significantly larger CSA at the annular level compared to the stented valve and the Toronto SPV䊛. Effective orifice area has previously been reported larger in stentless valves when compared with stented valves w4, 5x. This was in concordance with our findings since the native and Solo䊛 valve had significantly larger CSAs at the annular level than the stented Mitroflow䊛. The notable exception, however, is the Toronto SPV䊛, which does not yield greater CSA values. This is well explained by the very design of the Toronto SPV䊛, where part of the porcine aortic vessel from donor animals is implanted inside the recipient lumen and, therefore, diminishes the orifice area. At the sino-tubular junction we found that native valve CSA was larger than that of the two stentless and, surprisingly, that the CSA of the Mitroflow䊛 valve was larger than that of the Toronto SPV䊛. This might be explained by the fact that the suture lines of the two stentless valves are placed higher in the root than the circular suture line of the Mitroflow䊛, resulting in a diminished tendency for the commissures to expand during systole. The distensibility of the aortic root varied depending on valve type. As anticipated, the native and stentless valves remained flexible at the annular level. The stented Mitroflow䊛, on the other hand, completely fixed the annulus. The recorded change in area at the annular level is slightly negative (–0.05 cm2) which quite likely is due to measurement variability.

ESCVS Article

4. Discussion

Institutional Report

Native valves yielded greater CSA values than artificial valves at the annular level (Ps0.0001). In addition, the Solo䊛 valve had a larger CSA than both the Mitroflow䊛 valve and the Toronto SPV䊛 (Ps0.008; Ps0.04). Differences in CSA between the Toronto SPV䊛 and Mitroflow䊛 valves at annular level were non-significant. At the sino-tubular junction CSA was greater for native valves than both the Solo䊛 valves and the Toronto SPV䊛 (Ps0.0006). Furthermore, the Mitroflow䊛 had a larger CSA than the Toronto SPV䊛 (Ps0.03). At the ascending aorta level no difference between the four groups was observed. Exact values are given in Table 2.

Protocol

3.2. Aortic CSA

Work in Progress Report

Sino-tubular junction

New Ideas

Mitroflow䊛 Solo䊛 Toronto SPV䊛 Native

Annulus

To our knowledge, only one study has previously investigated aortic root distensibility in stentless valves using MRI w6x. The Freestyle (Medtronic) valve implanted as a full root was compared with homografts, finding no differences between the two. They performed their measurements as short axis slices just above the coronary ostia, and measured a percentage change in radius around 9–10% which is in agreement with our findings. One should, however, have through-plane-motion in mind when using short-axis scans. As pigs have a smaller intersubject variability than humans, it was possible to use the same size valve in all experiments. This strengthens our conclusions. MRI makes it possible to investigate the root at different levels in a much more exact manner than ultrasound. Through-planemotion and inaccurate slicing of the aorta can be a problem in MRI, but it was limited using the ‘12 longitudinal radial slices’ MRI method. Still, flow artifacts occurred during peak systole, rendering many of these images uninterpretable. Previous studies have shown that the aortic root area at peak systole is even larger than at end-systole w1, 13x. We chose not to make an aortotomy in our control animals, in order to compare the artificial valves to the natural root. This could, of course, have an impact on the distensibility at the level of the ascending aorta. On the other hand, no difference in the distensibility at this level was observed, and it thus seems that the suture line is rather distensible. It should be remembered that single suture lines were utilized in this experiment; a double suture line may be less flexible. Our mortality rate is in accordance with those of previous studies w14, 15x. The mortality rate was highest in the Solo䊛 valve group. However, most of the deaths were not prosthesis related (cardiac failure, bleeding, arrhythmia). In one case (Solo䊛 valve) a leaflet was caught in the suture line resulting in valve insufficiency and cardiac failure – a surgical technical error. Since most of the deaths were not attributed to the implanted valve we do not consider the high mortality in the Solo䊛 group as an indicator of inferior performance compared with the other two valves. Further research is necessary in order to clarify the distensibility changes on a longer term. Scar tissue formation may influence the aortic root flexibility as will the abatement of aortic root edema. Finally, human studies are ultimately required in order to identify the relevance of a flexible valve when implanted into an often stiff and calcified aortic root.

Editorial

Table 2 Aortic cross-sectional area at end-systole (cm2)

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orifice areas. Long-term studies are needed to confirm these findings.

w12x

Acknowledgements w13x

We are indebted to Niels Trolle Andersen for guidance in statistical matters and Tanja Thomsen for skillful help with the experiments. We are furthermore grateful to the following: Henrik Jensen, Peter Agger, Eva Nielsen, Marianne Bjerre, Jesper Hønge and Erik Hansen.

w14x

w15x

Insights into valvular pathology. Expert Rev Medical Devices 2006;3:453– 462. Smerup M, Pedersen TF, Nyboe C, Funder JA, Christensen TD, Nielsen SL, Hjortdal VE, Hasenkam JM. A long-term porcine model for evaluation of prosthetic heart valves. Heart Surg Forum 2004;7:E259–E264. Lansac E, Lim HS, Shomura Y, Lim KH, Rice NT, Goetz W, Acar C, Duran CM. A four-dimensional study of the aortic root dynamics. Eur J Cardiothorac Surg 2002;22:497–503. Vrandecic M, Fantini FA, Filho BG, de Oliveira OC, da Costa IM, Vrandecic E. Retrospective clinical analysis of stented vs. stentless porcine aortic bioprostheses. Eur J Cardiothorac Surg 2000;18:46–53. Nyboe C, Funder JA, Smerup MH, Nygaard H, Hasenkam JM. Turbulent stress measurements downstream of three bileaflet heart valve designs in pigs. Eur J Cardiothorac Surg 2006;29:1008–1013.

References w1x Lansac E, Lim HS, Shomura Y, Lim KH, Rice NT, Goetz WA, Duran CM. Aortic root dynamics are asymmetric. J Heart Valve Dis 2005;14:400– 407. w2x Robicsek F, Thubrikar M. Loss of sinus compliance, cause of degenerative aortic valve disease, and early failure of biological valves. Z Kardiol 2000;89:104–106. w3x Bakhtiary F, Abolmaali N, Dzemali O, Wittlinger T, Doss M, Moritz A, Kleine P. Impact of mechanical and biological aortic valve replacement on coronary perfusion: a prospective, randomized study. J Heart Valve Dis 2006;15:5–11. w4x Borger MA, Carson SM, Ivanov J, Rao V, Scully HE, Feindel CM, David TE. Stentless aortic valves are hemodynamically superior to stented valves during mid-term follow-up: a large retrospective study. Ann Thorac Surg 2005;80:2180–2185. w5x Perez dA, Lees B, Flather M, Nugara F, Husebye T, Jasinski M, Cisowski M, Khan M, Henein M, Gaer J, Guvendik L, Bochenek A, Wos S, Lie M, Van Nooten G, Pennell D, Pepper J. Randomized comparison of stentless versus stented valves for aortic stenosis: effects on left ventricular mass. Circulation 2005;112:2696–2702. w6x Melina G, Rajappan K, Amrani M, Khaghani A, Pennell DJ, Yacoub MH. Aortic distensibility after aortic root replacement assessed with cardiovascular magnetic resonance. J Heart Valve Dis 2002;11:67–74. w7x Robicsek F, Thubrikar M. Role of sinus wall compliance in aortic leaflet function. Am J Cardiol 1999;84:944–946. w8x De Hart J, Baaijens FP, Peters GW, Schreurs PJ. A computational fluidstructure interaction analysis of a fiber-reinforced stentless aortic valve. J Biomech 2003;36:699–712. w9x Hazekamp MG, Goffin YA, Huysmans HA. The value of the stentless biovalve prosthesis. An experimental study. Eur J Cardiothorac Surg 1993;7:514–519. w10x Repossini A, Kotelnikov I, Bouchikihi R, Torre T, Passaretti B, Parodi O, Arena V. Single-suture line placement of a pericardial stentless valve. J Thorac Cardiovasc Surg 2005;130:1265–1269. w11x Skowasch D, Steinmetz M, Nickenig G, Bauriedel G. Is the degeneration of aortic valve bioprostheses similar to that of native aortic valves?

eComment: Aortic root distensibility in bioprostheses Authors: Leo A. Bokeria, Bakoulev Center for Cardiovascular Surgery RAMS, Rublyovskoye Shosse 135, 121552 Moscow, Russia; Dmitry V. Britikov, Maxim A. Sazonenkov doi:10.1510/icvts.2009.230771A Systolic aortic root distensibility augments the orifice area at the level of the aortic annulus. It reduces leaflet stress by blood stream and partially influences the bioprosthesis durability. Therefore, aortic root biomechanics research after implantation of various types of bioprostheses is of great importance. The presented data w1x allow one to prefer a bioprosthesis Solo (Sorin, Italy) for its near-natural systolic distension, both at the level of the aortic annulus and at the sinotubular junction. This movement is due to the curved line of proximal valve anastomosis. Excessive extensibility at both levels of the Toronto SPV (St Jude Medical) bioprosthesis can be the reason for the development of the late insufficiency. Extensive motion at the level of aortic annulus is doubtful because of the circular proximal suture line. The presence of the stent in the Mitroflow (Sorin, Italy) valve makes systolic aortic annulus extension impossible. Probably the left ventricular outflow tract (LVOT) extension was observed in this case. In our clinic, the stented xenopericardial bioprostheses BioLAB have been applied with good late results. Bioprostheses BioLAB were implanted in aortic position in 108 patients. At a follow-up of nine years, four reoperations (infective endocarditis) were required. We did not register any systolic expansion at the aortic annulus level. From the point of view of the laminar stream, we assume the auto- and allografts are most successful. They are also capable of aortic root distensibility because of the stretching of three arches of proximal suture line. Reference w1x Funder JA, Ringgaard S, Frost MW, Wierup P, Klaaborg KE, Hjortdal V, Nygaard H, Hasenkam JM. Aortic root distensibility and cross section areas in stented and subcoronary stentless bioprostheses in pigs. Interact CardioVasc Thorac Surg 2010;10:976–980.