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Ann Thorac Surg 1996;62:1069-1075
© 1996 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Comparison of Techniques for Implantation of Aortic Valve Allografts

Joseph A. Dearani, MD, Thomas A. Orszulak, MD, Richard C. Daly, MD, Michael R. Phillips, MD, Fletcher A. Miller, MD, Gordon K. Danielson, MD, Hartzell V. Schaff, MD

Section of Cardiovascular Surgery, Mayo Clinic and Mayo Foundation, Rochester, Minnesota


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Background. Various implantation techniques for allograft aortic valve replacement have evolved over the years. Our objective was to examine the effects of different implantation methods on subsequent valve performance and durability.

Methods. Between May 1985 and January 1994, 137 patients underwent allograft aortic valve replacement. The first 59 aortic valve allografts were inserted by the freehand scalloped technique with removal of the aortic sinuses, and the last 78 valves were inserted by the cylinder technique, in which the aortic sinuses and sinotubular junction were retained. The mean age of the 91 men and 46 women was 53.7 years (range, 18 to 83 years). Preoperative diagnoses were aortic stenosis (n = 57), aortic regurgitation (AR, n = 40) and aortic stenosis/AR (n = 40); 27 patients had prior aortic valve operations and 1 patient had a previous heart transplantation. Active endocarditis was present in 29 patients. Associated procedures included coronary artery bypass (n = 33), ascending aneurysm repair (n = 4), left ventricular aneurysmectomy (n = 3), repair of atrial septal defect (n = 2), mitral valve repair or replacement (n = 6), and aortic root enlargement (n = 24). Follow-up was complete in 133 patients (97%) a mean of 4.9 years (range, 1 day to 9.8 years) after allograft aortic valve replacement.

Results. Operative mortality was 6.5% for all patients but only 1.9% for patients without infection having isolated aortic valve replacement. Early echocardiography (mean of 8.4 days postoperatively) demonstrated no AR or mild AR and a mean gradient of 10.6 ± 6.2 mm Hg in all patients. The cumulative risk of development of grade III or IV AR at 7 years postoperatively was 26.2% ± 6.3% in the scallop group and 12.4% ± 5.6% in the cylinder group (p = 0.4). Late postoperatively, transvalvular gradient by echocardiography was 13.1 ± 9.4 mm Hg, and was similar in the two study groups. Late AR led to reoperation in 13 patients (22%) who had initial implantation with the scallop method and only 4 patients (5.4%) who had the valve inserted with the cylinder method. However, because duration of follow-up was longer for patients in the scallop group, cumulative risk of reoperation was similar at 5 years postoperatively (scallop, 13.7% [95% confidence interval, 76.7% to 95.8%]; cylinder, 11.5% [95% confidence interval, 75.5% to 99.1%]).

Conclusions. The insertion of an aortic valve allograft as a cylinder, retaining the sinotubular junction, appears to result in less aortic regurgitation at 7 years postoperatively, and with additional follow-up may result in less reoperation for AR.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
See also page 1075.

With the availability of cryopreservation, allograft valves are being used for aortic valve replacement with increasing frequency, and good medium-term results have been reported [1]. Allograft aortic valves have numerous theoretical and practical advantages including low transvalvular gradients, resistance to infection when used for acute endocarditis, and the potential for greater durability compared with heterograft prostheses. Most studies of allograft valves have focused on the influence of sterilization and preservation methods on longevity of the valve. However, implantation method affects early outcome of allograft aortic valve replacement; indeed, others have commented on the "learning curve" of aortic valve replacement with allografts. Late integrity of allo-grafts may be influenced by implantation method if distortion of commissural alignment and height interferes with central apposition of cusps.

In our initial experience with allograft aortic valve replacement, we removed the sinus portions of the graft (scalloped graft). Subsequently, we used a partial scallop method with retention of the donor aorta in the noncoronary sinus. Believing that preservation of the sinus portions of the allograft might minimize spatial geometry of the commissures at the sinotubular ridge, we later implanted the allograft as an intraaortic cylinder. The purpose of this review was to examine the effects of different implantation techniques on subsequent valve performance and durability.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 Acknowledgments
 References
 
Patient Characteristics
Between May 1985 and January 1994, 2,637 patients underwent aortic valve replacement at the Mayo Clinic. Of these, 137 patients underwent cryopreserved allograft aortic valve replacement. Patient characteristics are shown in Table 1Go. Patients operated on for correction of complex congenital defects were excluded from this review. Concomitant procedures are depicted in Table 2Go. Reoperative procedures included secondary aortic valve replacement in 19 patients, tertiary aortic valve replacement in 4 patients, and quaternary aortic valve replacement in 4 patients. Prior aortic valve procedures performed were mechanical aortic valve replacement (n = 14), bioprosthetic aortic valve replacement (n = 8), and aortic valvotomy or decalcification (n = 5). One patient had undergone previous orthotopic heart transplantation.


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  		Table 1. . Characteristics of Patients
 

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  		Table 2. . Allograft Aortic Valve Replacement and Associated Procedures
 
Aortic Valve Allograft and Technique of Implantation
The techniques of allograft implantation were dictated by the pathologic findings at operation, but two general methods have been employed. In our initial experience, allograft valves were prepared by removal of the sinuses (scalloped method), and the graft was inserted in the subcoronary position with two suture lines [2–4]. The lower suture line (continuous 4-0 Prolene or interrupted 4-0 Ethibond; Ethicon, Somerville, NJ) anchored the valve to the recipient aorta at or just proximal to the native valve annulus (Fig 1AGo). The upper suture line (continuous 4-0 Prolene) followed the U-shaped configuration of the allograft and anchored the allograft to the recipient aorta.



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  		Fig 1. . (A) Complete scallop implantation technique, demonstrating removal of all three aortic sinuses. (B) Partial scallop implantation technique. The left and right aortic sinuses are removed and the noncoronary sinus is maintained intact. (C) Cylinder implantation technique. All three aortic sinuses are left intact with minimal or no notching of the right sinus to accommodate the right coronary ostium. The left coronary ostium is usually reimplanted as a button. The wall noncoronary and minimally notched right sinus are tacked to the native aortic wall with Prolene suture to obliterate any potential space (not shown).

 
This method was altered in late 1987 similar to that described by Ross [5] and others [6–9], where the allograft was inserted as a partial cylinder or sleeve with scalloping of the left and right aortic sinuses but leaving the noncoronary sinus intact (Fig 1BGo). This technique was again altered shortly thereafter based on our technical manipulations and those of others [7, 10–12], where the allograft was inserted as a complete cylinder (retaining the allograft aortic sinuses) within the native aortic root (Fig 1CGo). Either the recipient coronary ostia were directly reimplanted into a buttonhole in the side of the donor graft at or near the site of the donor coronary ostium or, due to the natural distal location or elevation of the ostia, the distal suture line passed beneath the coronary ostia or required minimal notching of the allograft wall. In the partial scallop and cylinder method of implantation, the wall of the noncoronary sinus was tacked to the native aortic wall with 4-0 Prolene mattress sutures to obliterate any potential space. As more experience was obtained, the specifics of the distal suture line and handling of the coronary ostia were dictated by local patient characteristics and anatomy. More recently, we as well as others [13–15] have inserted the allograft as a "mini-root" replacement in selected cases of complex reoperations or endocarditis that necessitates native aortic root excision. In the present review, 52 patients (38%) underwent complete scallop implantation, 7 (5%) partial scallop, 68 (50%) cylinder, and 10 (7%) "mini-root" replacement. For the purpose of data analysis, the complete and partial scalloped insertions are grouped together, and the cylinder and root replacement insertions are grouped together.

The cryopreserved aortic allografts used in this study were supplied by Cryolife Cardiovascular, Inc (Marietta, GA), American Red Cross, and United Cryoinstitute. Procurement protocols were performed by each of their respective guidelines [9, 16].

Echocardiography
Preoperatively, patients were studied with echocardiography, cardiac catheterization, or both. Since 1988 intraoperative transesophageal echocardiography was used to assess operative results and to provide a baseline for subsequent studies. All patients underwent echocardiographic assessment of their valve before hospital dismissal. Echocardiographic determinations of mean and maximum gradients, as well as valve area calculations, were obtained using standard formulas [17–19]. These studies were repeated at approximately 1-year intervals. The most recent echocardiogram available in the patient's record was analyzed for late follow-up.

Follow-up
The 137 patients who have undergone cryopreserved allograft aortic valve replacement between May 1, 1985, and January 1, 1994, constitute the patient cohort. Follow-up data included the most recent clinic or personal physician visit, correspondence by mail questionnaire, or phone contact. Follow-up (97% complete) ranged from 1 day to 9.8 years (mean, 4.9 years) and totaled 654.8 patient-years. All review and patient contacts were coordinated by Dr Dearani.

Data Analysis
Survival and survivorship risk of late events was calculated using the Kaplan-Meier method [20]. Survivals presented in this report included patients who died (in the hospital) within 30 postoperative days. Cumulative risk of late events was calculated excluding patients who died within 30 postoperative days. Data are expressed as mean ± standard error of the mean. Values of p less than 0.05 were considered to be statistically significant.


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 Acknowledgments
 References
 
Patient Survival
Overall operative mortality (30-day or hospital mortality) was 6.5%; risk was 1.9% for patients without infection having isolated aortic valve replacement. The operative mortality was 6.8% for patients with the scalloped insertion (4 deaths) and, 6.4% for patients with the cylinder insertion (5 deaths). Causes of early mortality were sepsis/multiple organ failure in 4 patients, low cardiac output in 2 patients, respiratory failure in 2 patients, and stroke in 1 patient. There were no early deaths related to the allograft aortic valve replacement. At 8 years postoperatively the actuarial patient survival was 77.5% ± 5.5% for the scalloped group and 71.2% ± 8.1% for the cylinder group (p = 0.5) overall, and 80.3% ± 5.6% for the scalloped group and 82.1% ± 8.7% for the cylinder group (p = 0.9) in patients without endocarditis (Fig 2Go).



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  		Fig 2. . (A) Actuarial percent patient survival after allograft aortic valve replacement with the scallop (n = 58) and cylinder (n = 75) techniques, and (B) actuarial percent patient survival of patients without endocarditis after allograft aortic valve replacement with the scallop (n = 51) and cylinder (n = 53) techniques. The absolute numbers of patients surviving are indicated at 1, 4, and 7 years postoperatively. (C = cylinder; S = scallop.)

 
There have been a total of 18 late deaths, 9 each in the scalloped and cylinder groups (11 cardiac nonvalvular, 7 noncardiac).

Morbidity
There was one early complication related to the allograft aortic valve, which required reoperation 5 days postoperatively. The patient originally required a reduction aortoplasty to accommodate an allograft aortic valve (22 mm internal diameter) implanted as a cylinder. At the time of reoperation, the upper and lower suture lines anteriorly near the ventricular septum had dehisced, which was thought to be secondary to the small allograft in the relatively larger native aortic root. The allograft was removed and a St. Jude Medical (St. Paul, MN) 27-mm valve with pericardial root enlargement was performed, and the subsequent postoperative course was uneventful. Other causes of major morbidity are shown in Table 3Go. The high incidence of bleeding requiring reexploration and the high incidence of heart block requiring permanent pacemaker placement was due to the large number of patients with endocarditis and reoperative procedures. No endocarditis of the allograft developed during the follow-up period.


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  		Table 3. . Operative Morbidity
 
Aortic Valve Regurgitation
The cumulative risk of development of grade III or IV aortic regurgitation for all patients is shown in Figure 3AGo. The cumulative risk was 15.9% ± 5.2% (95% confidence limits) at 5 years postoperatively for the scallop group and 12.4% ± 5.6% for the cylinder group (p = 0.4). By 7 years postoperatively, the risk had increased in the scallop group to 26.2% ± 6.3% and was unchanged in the cylinder group. When patients with endocarditis were excluded, the cumulative risk at 5 years postoperatively was 15.1% ± 5.3% and 10.6% ± 6.2% for the scallop and cylinder groups, respectively (p = 0.3) (Fig 3BGo). At 7 years postoperatively the risk for the scallop group was 21.9% ± 6.1% and was unchanged in the cylinder group.



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  		Fig 3. . (A) Cumulative risk of the development of grade III or IV aortic regurgitation for all patients with the scallop (S; n = 54) or the cylinder (C; n = 70) technique, and (B) cumulative risk of development of grade III or IV aortic regurgitation for patients without endocarditis with the scallop (n = 49) or cylinder (n = 50) technique. The absolute numbers of patients at risk are indicated at 1, 4, and 7 years postoperatively.

 
The effect of allograft aortic valve replacement size on the subsequent development of aortic regurgitation was analyzed. The mean allograft size in the scallop and cylinder groups were 21.4 ± 1.7 and 22.3 ± 2.3 mm, respectively. Valve sizes were stratified into three groups: 17 to 20 mm (n = 27), 21 to 23 mm (n = 71), and 24 to 28 mm (n = 26). Cumulative risk of subsequent grade III or IV aortic regurgitation is depicted in Figure 4Go. Of the 26 patients with allograft aortic valve sizes of 24 to 28 mm, 20 had their implantations done as a cylinder.



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  		Fig 4. . Cumulative risk of development of grade III or IV aortic regurgitation based on allograft aortic valve size: 17 to 20 mm (s; n = 27), 21 to 23 mm (m; n = 71), or 24 to 28 mm (l; n = 26). The absolute numbers of patients at risk are indicated at 1, 4, and 7 years postoperatively.

 
At late follow-up there was no evidence of allograft valve stenosis in either the scallop or the cylinder implantations. The mean gradient was 13.1 ± 9.4 mm Hg, and the mean valve area was 1.7 ± 0.49 cm2.

Reoperation
Seventeen patients came to reoperation for allograft failure due to structural deterioration; overall reoperation rate was 4%/patient-year (95% confidence interval, 2% to 6%). The reoperation rate was 5%/patient-year (95% confidence interval, 3% to 8%) for the scallop group and 2%/patient-year (95% confidence interval, 0.7% to 5%) for the cylinder group. Reoperation was required in 13 patients (22%) in the scallop group at a mean of 4.7 ± 2.6 years postoperatively and in 4 patients (5.4%) in the cylinder group at a mean of 2.1 ± 1.8 years postoperatively (p = 0.3). The cumulative risk of reoperation at 5 years postoperatively was 13.7% ± 4.8% in the scallop group and 11.5% ± 5.4% in the cylinder group (Fig 5AGo). At 7 years postoperatively the risk for the scallop group increased to 24.2% ± 6.1% and was unchanged in the cylinder group. When patients with endocarditis were excluded, the same relationship between the two groups was noted but with a slightly overall lower risk (Fig 5BGo).



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  		Fig 5. . (A) Cumulative risk of reoperation for all patients with the scallop (S; n = 54) or cylinder (C; n = 70) technique, and (B) cumulative risk of reoperation for patients without endocarditis with the scallop (n = 49) or cylinder (n = 50) technique. The absolute numbers of patients at risk are indicated at 1, 4, and 7 years postoperatively.

 

   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
Acknowledgments
 References
 
In the classic methods for allograft implantation described by Ross [21] and Barratt-Boyes [22], the sinus portions of the allograft are removed, and the surgeon then determines the proper position of each graft commissure within the recipient aorta. Malalignment of the commissures or splaying of the commissures, as might occur when the diameter of the sinotubular junction of the recipient is larger than that of the graft, may lead to malcoaptation of the central portions of the aortic valve cusps. Gross malcoaptation of allograft aortic valve cusps can cause early aortic valve regurgitation requiring reoperation. However, lesser degrees of central malcoaptation might also be expected to influence late outcome.

Normally, the closing edge of the aortic valve is a slightly thickened biscalloped ridge that is a few millimeters below the free edge. At the center of each cusp, the closing edge meets the free edge to form a small fibrous mound, the nodule of Arantius. During valve closure, apposing cusps contact one another along the closing edges and lunular surfaces, forming a competent seal. Centrally, the valve orifice is closed by interdigitation of the nodules of Arantius. Commissural malalignment may distort the cusps so that the closing edges do not make contact, and only the free edges of the cusps come together to prevent regurgitation. This results in a valve that is competent or has minimal leakage early after implantation but has abnormal stresses on the free edge of the cusps, which may lead to late cuspal prolapse and worsening regurgitation. Indeed, cuspal prolapse without calcification is the most common mode of late valve failure regardless of sterilization and preservation methods [23–31].

Thus, accurate sizing of the allograft and accurate positioning of the height and alignment of its commissures are prerequisites to good early and late valve function. This can be difficult when there is dilatation or asymmetric enlargement of the sinotubular ridge, which occurs commonly in patients with congenital aortic stenosis with bicuspid or unicuspid valves. Also, the sinus portion of the recipient aorta may be distorted because of preoperative endocarditis or prior operations.

The most important finding in this review was the divergence after 5 years of follow-up in curves plotting risks of aortic regurgitation and reoperation. These late complications indicating structural valve deterioration were substantially less frequent in valves implanted by the cylinder method compared with those inserted with the scallop technique. We believe that this is due to better cuspal apposition, and we speculate that additional follow-up will demonstrate that these differences are statistically significant.

There are several important limitations of this study, which should be acknowledged. First, patients in this review might not be comparable with those in other series of allograft aortic valve replacement. Our selectivity in using allograft valves is reflected in the fact that these prostheses accounted for only 5% of the 2,637 valves implanted during the study period. Compared with many others [1, 8, 14, 32], these patients were at higher risk for death and late valve complications because of number of prior and concomitant procedures and the high prevalence of active endocarditis preoperatively.

Second, we cannot separate the potential bias of additional experience from the method used; most patients having allograft valve implantation with the scallop technique were operated on in the earlier part of the study. Finally, we recognize that the lack of statistical significance should signal strong caution in concluding that the cylinder method is clearly superior to the scallop technique. Nevertheless, we believe that the differences between surgical methods in risks of aortic regurgitation and reoperation after 5 years postoperatively are sufficiently large to be important to surgeons who use allograft valves.


   Acknowledgments
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
References
 
We extend our appreciation to Duane M. Ilstrup and Betty J. Anderson for their expert assistance in statistical analysis.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 

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