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Ann Thorac Surg 1995;59:857-862
© 1995 The Society of Thoracic Surgeons

Comparison of Implantation Techniques Using Freestyle Stentless Porcine Aortic Valve

Department of Cardiothoracic Surgery, Bowman Gray School of Medicine, Winston-Salem, North Carolina, and Oxford Heart Centre, Oxford, England

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Stentless porcine aortic valves demonstrate superior hemodynamic performance when compared with their stented counterparts. The technical considerations for implanting these valves can be demanding. The Medtronic Freestyle aortic root bioprosthesis resembles an allograft, has zero-pressure--fixed leaflets treated with an antimineralization agent, and can be implanted using a variety of techniques. In this study of that valve, total root replacement (TRR) was compared with a partial scallop aortic inclusion technique (PSI). Implantations were performed in 75 patients (49 PSI and 26 TRR). There were no significant differences with respect to age, sex, or incidence of concomitant procedures. Mean aortic cross-clamp times were significantly less in the PSI group than in the TRR group (51.8 +/- 11.7 minutes versus 125.5 +/- 19.7 minutes; p = 0.0001). At discharge, mean systolic gradients seen on color-flow Doppler echocardiography were less in the TRR group than in the PSI group (6.17 +/- 3.66 versus 10.01 +/- 4.83 mm Hg; p = 0.014). Discharge echocardiography revealed trivial valve regurgitation in 8.3% of the TRR group and in 41.7% of the PSI group (p = 0.004). No patient experienced any significant valvular regurgitation on discharge echocardiography. We conclude that early experience with the Medtronic Freestyle aortic root bioprosthesis shows excellent short-term function regardless of implantation technique. Shorter cross-clamp times, comparable with those of stented valve procedures, occurred with PSI implantation. We anticipate that effects on long-term durability will be beneficial.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
See also page 862.

Stentless porcine aortic bioprostheses have potential advantages over conventional stented bioprostheses. Hemodynamic benefits have been demonstrated repeatedly [1–9]. Improved long-term durability can be anticipated based on the adverse effects of stent mounting reported with allograft valves [10–12].

The Medtronic Freestyle aortic root bioprosthesis (Medtronic Inc, Minneapolis, MN) was approved for investigational use by the Food and Drug Administration in July 1992. It has a stentless design analogous to an aortic allograft. The leaflets are treated with an antimineralization agent to inhibit calcification [13] and are fixed ``stress free'' to retain their structural integrity [14, 15]. The aortic wall is pressure-fixed for greater durability.

For many years, the use of allograft heart valves has been limited, not only by availability, but also by the technical demands required for competent valve implantation. Recent studies have evaluated the optimal technique of implanting aortic allografts and pulmonary autografts for aortic valve replacement [16–18]. In this article, we evaluated whether the same implantation concepts apply for this Freestyle bioprosthesis by comparing early results of a total root replacement (TRR) technique with those of a partial scallop aortic inclusion (PSI) technique.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Worldwide evaluation of the Freestyle porcine aortic root bioprosthesis began on July 1, 1992. This bioprosthesis can be inserted using a variety of techniques. To determine whether TRR or PSI has an advantage, two participating investigational centers, North Carolina Baptist Hospital and John Radcliff Hospital, pooled their data; that experience is presented here.

Seventy-five procedures were performed, 49 PSIs and 26 TRRs. The operation chosen was based on surgeon preference. The mean age in the TRR group was 71 +/- 6 years (range, 60 to 86 years). The mean age in the PSI group was 72 +/- 7 years (range, 44 to 86 years). Fifteen male and 11 female patients made up the TRR group; 31 male and 18 female patients made up the PSI group. Aortic valve lesion, cause, and implanted valve size are shown in Tables 1, 2, and 3, respectively. The incidence of concomitant procedures is shown in Table 4.

View larger version (21K): [in this window] [in a new window]   Fig 1. . The aorta is transected just above the sinotubular ridge.

View larger version (35K): [in this window] [in a new window]   Fig 2. . The coronary arteries are mobilized on generous buttons of aortic wall.

View larger version (22K): [in this window] [in a new window]   Fig 3. . The Freestyle aortic root bioprosthesis is attached to the heart with 28 to 35 simple interrupted sutures tied around a 1-mm strip of Teflon felt. The coronary arteries are sewn end-to-side to the corresponding sinus of Valsalva of the bioprosthesis with a continuous 5-0 polypropylene suture.

View larger version (33K): [in this window] [in a new window]   Fig 4. . A transverse aortotomy is made 2 to 5 mm above the sinotubular junction (inset). Strategic traction sutures are applied to display the valve and right coronary ostium.

View larger version (38K): [in this window] [in a new window]   Fig 5. . The inflow suture line is accomplished with 18 to 21 simple interrupted 2-0 braided Dacron sutures applied to maintain the inflow in a single plane.

View larger version (27K): [in this window] [in a new window]   Fig 6. . A U-shaped portion of the porcine aortic sinus is excised to remove the ligated porcine coronary artery directly adjacent to the human coronary ostium.

View larger version (31K): [in this window] [in a new window]   Fig 7. . The outflow suture line of the bioprosthesis is established with a single continuous double-armed suture of 4-0 polypropylene, which is begun by attaching the porcine commissure to the aortic wall between the left and right coronary cusps. The right coronary sinus outflow is attached first. The other arm of the suture then is taken beneath the left coronary ostium and continues until it meets the right arm above the noncoronary sinus.

Statistical Analysis
Data forms at each clinical and echocardiographic evaluation were sent to the study director at Medtronic, Inc, and placed in the Freestyle database. Categoric data were analyzed with the Pearson ² test. Continuous data were evaluated with the Wilcoxon rank-sum test and corroborated with the t test. In addition, possible differences between the two procedures with respect to continuous hemodynamic data (mean systolic gradient, effective orifice area, and cardiac output) were evaluated with a generalized linear model with valve size being taken into account.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
There were no differences in age, sex, or incidence of concomitant procedures between the two groups. The 30-day operative mortality also was similar in the two groups, being 4.1% for the PSI group, 3.8% for the TRR group, and 4.0% overall.

A significantly shorter mean aortic cross-clamp time was noted in the PSI group (51.8 +/- 11.7 minutes) than in the TRR group (125.5 +/- 19.7 minutes). This difference occurred whether a concomitant procedure was performed (64.6 +/- 11.3 versus 133.2 +/- 23.3 minutes) or not (46.2 +/- 6.1 versus 118.9 +/- 13.8 minutes) (p = 0.0001).

The mean systolic gradients were excellent in all patients postoperatively (Table 5); however, at discharge a significantly smaller mean systolic gradient was detected in the TRR group (6.17 +/- 3.66 mm Hg) than in the PSI group (10.01 +/- 4.83 mm Hg) (p = 0.014). This difference no longer existed at the 3- to 6-month interval (4.65 +/- 2.62 versus 5.83 +/- 3.19 mm Hg; p = 0.443).

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

A major drawback to an unstented porcine xenograft is the complexity of the technical demands required for inserting a competent aortic valve. Similar technical demands have been addressed for aortic valve replacement with the aortic allograft [17] and the pulmonary autograft [18–20]. The trend in many of these studies has been to use a root replacement procedure to ensure implantation of a competent valve. The design of many stentless porcine valves limits the implantation technique to the traditional subcoronary implantation described by Ross [21] and Barratt-Boyes [22] for aortic allograft valve replacement. The Freestyle aortic root bioprosthesis consists of the entire porcine aortic root; therefore, all techniques described for allograft insertion potentially can be applied to this valve. We compared the advantages of a PSI technique with those of a TRR.

Both techniques proved to be quite satisfactory. With each technique, the gradients generated were comparable with those of other stentless valves [1–9] and superior to those of mechanical valves and stented xenografts [23]. There were no instances in which significant aortic insufficiency was detected after Freestyle aortic valve replacement regardless of the implantation technique used.

Specific advantages of the PSI technique included short aortic cross-clamp times comparable with those typically noted when a routine stented bioprosthesis is implanted. The transverse incision above the sinus rim retains the spatial orientation of the aortic root. This facilitates positioning of the commissures of the Freestyle stentless bioprosthesis. The glutaraldehyde-stiffened aortic wall of the prosthesis also makes this maneuver easier than it is with an aortic allograft or a pulmonary autograft.

The TRR took longer to perform but also had some specific advantages. It can be used regardless of the aortic root pathology and thus was particularly suited for the older patient with a small aortic annulus (19 to 20 mm) at one end of the spectrum or in annuloaortic ectasia at the other. Because the porcine aortic sinuses are left intact and thus are free to distend, the commissures cannot be malaligned, and leaflet coaptation thereby is optimized. This is exemplified in the low incidence of any discernable aortic regurgitation in patients who received a TRR. It is hoped that the increased degree of difficulty in redoing a TRR, should that become necessary, will be minimized by using generous buttons of aortic wall around the coronary arteries at the time of their implantation during the primary operation.

An interesting finding in the echocardiographic hemodynamic data was the decrease in gradients noted in the PSI technique at the 3- to 6-month interval. Similar findings also occurred with the Toronto stentless porcine valve [9]. Resolution of perivalvular hematoma or remodeling of the aortic root after insertion are possible explanations. Nonetheless, by 3 to 6 months postoperatively, there were no discernible differences in transvalvular gradients between the two implantation techniques.

In addition to being an entire aortic root bioprosthesis analogous to an aortic allograft, the Freestyle valve has other unique features. The leaflets are fixed at zero pressure and thus retain their structural integrity [15]. The leaflets also are treated with the antimineralization agent 2-aminooleic acid. Enhanced durability may be anticipated by inhibition of leaflet calcification [13]. For technical ease of implantation, a Dacron covering along the inflow aspect of the bioprosthesis facilitates placement of the proximal row of sutures.

The Medtronic Freestyle aortic root bioprosthesis provides a useful addition to the available prostheses for treating patients with aortic valvular heart disease. Both techniques of insertion described here provided excellent short-term results. Transvalvular gradients were very low, and there was no significant aortic regurgitation after implantation. This prosthesis also can be used to treat a wide array of aortic root pathology.

Superior hemodynamics and the potential increased longevity of this bioprosthesis (due to zero-pressure fixation, antimineralization treatment, and the absence of a rigid stent) warrant its continued clinical investigation. Long-term follow-up may reveal whether TRR or PSI preferentially improves durability.

	Acknowledgments

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
We thank Annemarie Beery for her excellent illustrations and Judith T. MacMillan for her editorial assistance.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Presented at the Forty-first Annual Meeting of the Southern Thoracic Surgical Association, Marco Island, FL, Nov 10--12, 1994.

Address reprint requests to Dr Kon, Department of Cardiothoracic Surgery, Bowman Gray School of Medicine, Medical Center Blvd, Winston-Salem, NC 27103.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment Acknowledgments References

 

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Neal D. Kon Stephen Westaby Ravi Pillai Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kon, N. D. Articles by Cordell, A. R. Search for Related Content PubMed PubMed Citation Articles by Kon, N. D. Articles by Cordell, A. R. Related Collections Related Article