Aortic root replacement with pulmonary autograft in children

Aortic root replacement with pulmonary autograft in children Between September 1988 and February 1993, 14 patients whose ages ranged from 3 months to 16 years (mean 11.1 ± 4.3 years) underwent replacement of the aortic root with the autologous pulmonary root for aortic valve disease. The follow-up was 4 years (cumulative total of 25.2 patient-years). There was no early mortality. Late mortality (one patient) was 7.1 % (95% confidence limits 0% to 21 %). This patient had juvenile rheumatoid arthritis and died of consequent congestive heart failure with autograft failure 6 months after operation. Event-free survival after 4 years was 78.6 % (95% confidence limits 50 % to 95 %). One patient was reoperated on because of autograft failure caused by a relapse of rheumatic fever. One patient operated on for critical neonatal aortic stenosis has subnormal exercise tolerance because of restrictive cardiomyopathy and pulmonary homograft regurgitation. The other 12 patients were in New York Heart Association functional class I at the end of follow-up. There was no prevalence of bacterial endocarditis. There were no signs of primary structural degeneration of the pulmonary autograft. During follow-up, in eight patients, increased anulus diameter of the pulmonary autograft could be demonstrated by precordial two-dimensional echocardiography, suggesting growth of the autograft. Our experience shows that aortic root replacement with the pulmonary autograft can be done with low mortality and morbidity in children with aortic valve disease. The operation seems to be contraindicated in children with juvenile rheumatoid arthritis because of the risk of recurrence of rheumatic disease in the autograft. The pulmonary autograft has also been shown to be susceptible to recurrence of rheumatic inflammation in children with a history of acute rheumatic fever. Despite pulmonary autograft replacement of the aortic valve in infants with critical valvular aortic stenosis and endocardial fibroelastosis, clinical results may be poor. Growth of the autograft is suggested by echocardiographic follow-up. We consider aortic root replacement with the pulmonary autograft the procedure of choice in children who require aortic valve replacement. (J THoRAe CARDIOVASC SURG 1994;107:367-73)

Paul H. Schoof, MD, Adri H. Cromme-Dijkhuis, MD, PhD, Ad J. J. C. Bogers, MD, PhD, Eric J. M. Thijssen, MD, Maarten Witsenburg, MD, PhD, John Hess, MD, PhD, and Egbert Bos, MD, PhD, Rotterdam. The Netherlands

Aortic valve replacement in children is reserved for patients with severe valve disease that is not amenable to repair by more conventional means like valvotomy or balloon valvuloplasty. Mechanical aortic valve replaceFrom the Departments of Cardiothoracic Surgery and Pediatric Cardiology, University Hospital Dijkzigt and Sophia Children's Hospital Rotterdam, The Netherlands. Received for publication March 25, 1993. Accepted for publication July 30, 1993. Address for reprints: P. H. Schoof, MD, Department of Cardiothoracic Surgery, de Weezenlanden Hospital. Groot Wezenland 20, 8011 JW Zwolle, The Netherlands. Copyright

C<';

1994 by Mosby-Year Book, Inc.

0022-5223/94 $1.00 +.10

12/1/50729

ment in the pediatric patient with a potentially long life span is especially hazardous because of the cumulative effects of valve-related complications like thromboembolism, hemorrhagic complications of anticoagulation, prosthetic valve endocarditis, and reoperation because of somatic growth. Therefore, mechanical aortic valve replacement in this group of patients is generally considered to be a palliative procedure.!" Bioprosthetic aortic valve replacement has the advantage that anticoagulation can be avoided, but accelerated valve degeneration makes the aortic valve bioprosthesis unsuitable in children.' Homograft aortic valve replacement also offers the advantages of a tissue valve to children, but homografts may show premature degeneration

367

The Journal of Thoracic and Cardiovascular Surgery February 1994

3 6 8 Schoof et al.

Table I. Indications for pulmonary autograft replacement of the aortic valve in children Age (yr)

Initial diagnosis

M

4

subVAS

2

M

II

VAS

3

F

13

VAS

4

F

12

VAS

CoA, subVAS

5

F

12

AR

Seropositive

Patient No.

M/F

Previous procedures

Additional diagnosis

VAS

Enucleation subvalvular membrane Valvotomy, balloon valvoplasty Valvotomy, balloon valvoplasty CoA balloon dilation, valvotomy and resection of subvalvular membrane None

Diagnosis before intervention

re-AS re-AS AR re-AS

AR

JRA 6

M

12

VAS

AR

VAS

Valvotomy, balloon valvoplasty Valvotomy

7

F

12

8

M

8

VAS

Valvotomy

re-AS

9

M

12

VAS

re-AS

10

M

16

AR

Valvotomy, intraoperative balloon valvoplasty None

II

M

II

VAS

12

M

13

M

14

M

Previous rheumatic fever

re-AS

AR

Valvotomy, balloon valvoplasty

AR

VAS

ASD II, endocarditis

Balloon valvoplasty

AR

10

AR

Endocarditis

None

AR

15

VAS

Valvotomy, balloon valvoplasty

AR

0.25

Indication for operation

High peak gradient and syncope-like attacks Progressive ST-depression LV dilation, nonsustained VTs on exercise High peak gradient, LVH, ST-segment depression on exercise

Congestive heart failure and cardiorespiratory arrest Progressive LV dilation High peak gradient, grade II-Ill AR, repolarization disturbance on exercise ECG High peak gradient, grade III AR, progressive LV dilation High peak gradient, grade III AR Progressive LV dilation, decreased LV contractility, decreased exercise tolerance Progressive LV dilation, decreased LV contractility, repolarization disturbance on exercise ECG Myocardial ischemia with angina-like attacks and repolarization disturbance on ECG Progressive LV dilation. decreased exercise tolerance Progressive LV dilation, progressive repolarization disturbance on ECG

M, Male; F, female; sub VAS. subvalvular aortic stenosis; VAS, valvular aortic stenosis; re-AS, residual aortic stenosis; AR, aortic regurgitation; LV, left ventricular; VT, ventricular tachycardia; CoA, aortic coarctation; LVH, left ventricular hypertrophy; JRA, juvenilerheumatoid arthritis; ECG, electrocardiogram; ASD II, secundum atrial septal defect.

in infants and they are found to be subject to primary tissue failure leading to reoperation.v 6 Pulmonary autograft aortic valve replacement, first described by Ross? in 1967, may constitute an attractive solution. As a viable autologous transplant, the pulmonary autograft offers the advantages of the absence of primary tissue failure, the absence of the need for anticoagulation, and the potential of growth.v!'' In 1988, pulmonary autograft replacement of the aortic root was started in our institution. This report presents our results in patients less than 16 years old.

Patients and methods Between September 1988 and February 1993, 14 children (10 boys, 4 girls) underwent pulmonary autograft aortic root replacement. Mean age at operation was 11.1 ± 4.3 years

(range 3 months to 16 years). The indication for operation and the previously performed surgical procedures are described in Table I. In six patients the presenting diagnosis was restenosis of the aortic valve after open valvotomy, balloon valvoplasty, or enucleation of subvalvular membrane (Table I). One of these patients had a tunnel subaortic stenosis. In eight other patients the presenting diagnosis was aortic valve regurgitation, in five preceded by valvotomy or balloon valvuloplasty, or both (Table I). Three patients with aortic regurgitation exclusively had a history of previous infection. One of these patients had had acute rheumatic fever 10 and 8 years before operation. The second patient was a 3-month-old infant with critical aortic stenosis in whom successful balloon valvuloplasty of the aortic valve was done at 6 days of age and in whom aortic regurgitation subsequently developed as a result of endocarditis. The third patient was a 12-year-old girl with a 6-year history of seropositive juvenile rheumatoid arthritis in whom aortic valve regurgitation developed as a result of rheumatic valvulitis.

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Schoof et al.

Pulmonary autograti root

Pulmonary homograft

369

Coronary anastomosis

Fig. 1. Current operative procedure of pulmonary autograft replacement of aortic root and orthotopic implantation of pulmonary homograft. Preoperative evaluation was done in all patients by means of a complete two-dimensional and color-coded Doppler echocardiographic study with M-mode and in nine patients by cardiac catheterization with angiography. In all patients the aortic and pulmonary valves were reassessed by means of epicardial echocardiography before the start of extracorporeal circulation. All operations were done with the use of cardiopulmonary bypass with moderate hypothermia using bicaval cannulation in 12 patients and single right atrial cannulation in 2 patients. At operation the aortic valve was inspected and crystalloid cardioplegic solution directly administered into the coronary orifices, supplemented with topical cardiac cooling. After excision of the aortic valve and the coronary orifices, the remaining aortic wall was removed up to the anatomic ventriculoaortic junction. The main pulmonary artery was transected just proximal to its bifurcation and through the right ventricular outflow tract leavinga ridge of supporting myocardial cuff (Fig. I). Care was taken not to damage the left anterior descending coronary artery or its first septal branch. The autograft was positioned in such a way that each coronary orifice faced a valve sinus. Continuous 5-0 polypropylene suture (Prolene; Ethicon, Inc., Somerville, N.J.) was used for both proximal and distal anastomoses except in one 3-month-old infant in whom absorbable monofilament 7-0 polydioxanone suture (PDS; Ethicon) was used. The coronary arteries were implanted with continuous 6-0 Prolene suture. The right ventricular outflow tract was reconstituted with a cryopreserved aortic homograft in 2 patients, a fresh wet-stored aortic homograft in I patient, and a cryopreserved pulmonary homograft in II patients. Size of the homografts at various ages ranged from 14 to 28 mm. The homografts were implanted with continuous 4-0 Prolene suture for the proximal and 5-0 Prolene suture for the distal suture line. Cryopreserved aortic and pulmonary homograft valves were obtained through Bio Implant Services, Leiden, The Netherlands, from the Heart Valve Bank, Dijkzigt University Hospital, Rotterdam, The Netherlands. One fresh, wet-stored aortic homograft was obtained from the National Heart Hospital homograft bank, London, United Kingdom. ABO cross-matching and HLA typing were not done routinely. Concomitant procedures consisted of resection of obstructing septal fibromuscular tissue in one patient with tunnel subaortic

stenosis and closure of a secundum-type atrial septal defect in another patient. Mean duration of cardiopulmonary bypass was 127 minutes (standard deviation 15.7;range 98 to 155 minutes). After operation all patients were reviewed every 6 months for assessment of their condition on the basis of history, physical examination, and electrocardiogram. Echocardiographic follow-up was done prospectively, according to a definite protocol, and videotaped. Measurements were made on-line and off-line. The longest follow-up was 4 years (mean 1.8 ± l.l). Where applicable, variables are presented as mean with I standard deviation and range. Proportion variables are given with 95% confidence limits (CL). Analysis of morbidity and mortality after the operation followed the guidelines formulated by Edmunds and associates. I I Actuarial analysis of survival and event-free survival (Fig. 2) was done according to the methods of Grunkemeier, Thomas, and Staff. 12

Results There was no early mortality in our series. Early morbidity was restricted to complete atrioventricular block in our first patient. This patient was a 4-year-old boy who underwent an enucleation of a subvalvular membrane at the age of 3 years. One year later he had syncope-like attacks caused by residual aortic stenosis at both the valvular and subvalvular level. At operation there was tunnel subaortic stenosis, and trimming of the septal fibromuscular tissue was done. After operation atrioventricular block had developed and a rate-responsive endocardial VVI pacemaker was implanted. He is in a clinically good condition 4 years after operation. In one patient rethoracotomy was done immediately after operation because of unexplained asystole. The postoperative course was uneventful and this patient is still in good condition. During the period of follow-up one patient died, giving a late mortality rate of7.! % (95% CL 0% to 21%). This patient was a l2-year-old girl with a 6-year history of

3 70

The Journal of Thoracic and Cardiovascular Surgery February 1994

Schoof et at.

?f. 100 CD

~

C

CD

>

CD Ul

C

CD

"@

Q.

a

90

20 10

~

0

CD

o,

78.6% _

1-..

N=6

70 60 50 40 30

~ c

CD

91.7%

N=11

80

CD

Cl

N=14

Survival Event free survival 0

1 2 3 Time (years after operation)

4

Fig. 2. Survival and event-free survival after aortic root replacement with pulmonary autograft in children.

seropositive juvenile rheumatoid arthritis and severe aortic insufficiency caused by rheumatic valvulitis. At operation a macroscopically normal-looking pulmonary valve and root was used to replace the aortic root and fibrotic, retracted aortic valve. Six months after operation severe autograft failure developed with subsequent fatal congestive heart failure. At autopsy a dilated autograft anuIus with thickened and retracted valve cusps was found. Histologic study of the autograft showed destruction of the architecture with typical rheumatic features.l! The second autograft failure occurred in a 16-year-old boy with a history of acute rheumatic fever 10and 8 years before operation. After pulmonary autograft replacement of the aortic root for aortic valve regurgitation this patient was in good condition (New York Heart Association functional class I) for more than a year and had only mild to moderate autograft regurgitation on precordial echocardiographic follow-up. When he was 18 years old, his rheumatic fever antibiotic prophylaxis was discontinued. Two months later, readmission to the hospital was necessary because of fever, migrating arthritis, and a recent history of tonsillitis. High antistreptolysin titers confirmed a relapse of rheumatic fever. Initially progression of autograft regurgitation could not be demonstrated on precordial echocardiography. Treatment with diclofenac was instituted, whereupon fever and joint pains disappeared and the patient could be discharged from the hospital. At follow-up 3 months later, massive aortic regurgitation with cardiac failure had developed and subsequent operation was done. At operation a prolapse of predominantly the left coronary cusp of the autograft was found. All cusps were slightly thickened. The valve was excised and replaced by a 29 mm St. Jude Medical prosthesis (St. Jude Medical,

Inc., St. Paul, Minn.). Histologic study showed normal valve architecture with signs of active chronic inflammation with remarkable small-vessel proliferation compatible with the histopathologic diagnosis of acute rheumatic valvulitis. The postoperative course was uneventful. Salicylates were given for continuous rheumatic activity and monthly prophylaxis with long-acting penicillin was reinstituted. The patient was in good condition I month after the operation. Our youngest patient, who was 3 months old at operation, had a balloon valvuloplasty done for critical aortic stenosis at 6 days of age. There was a significant decrease of the systolic gradient over the aortic valve and minor aortic regurgitation after the procedure. During the following 3 months progressive aortic valve regurgitation developed and positive blood cultures proved endocarditis. After antibiotic treatment was started the child became ventilator-dependent because of heart failure. Replacement of the aortic root with the pulmonary autograft was done. At operation endocardial fibroelastosis of the interventricular septum was found. After successful operation the child was easily weaned from bypass and did well at short-term follow-up. However, I year after operation, dyspnea at rest developed and severely impaired left ventricular relaxation was found at echocardiography. At angiography, there was normal function of the pulmonary autograft with normal coronary arteries but important insufficiency of the pulmonary homograft. Treatment with diuretics and afterload reduction was instituted. All other patients (n = II) are in New York Heart Association functional class I, 2 months to 4 years after operation. None of them showed clinical signs of struc-. tural deterioration of the autograft. Neither bacterial

The Journal of Thoracic and Cardiovascular Surgery Volume 107, Number 2

Schoof et al. 3 7 1

E 35 E

....

Ql

Q)

31

E

ro 27

"0

Ql

>

""iii 23 >

.~

s: a.

19

Ol 0 "0

15

~

(ij

o

0

.s:::.

o

w

/

.>

11 11 0

0

5

10 Age (years)

15

20

Fig. 3. Echocardiographic enlargement of autograft in children after pulmonary autograft replacement of aortic valve.

endocarditis nor thromboembolic complications were evident. Event-free survival after 4 years, therefore, is 78.6% (95% CL 50% to 95%). The last echocardiographic study was done 4 weeks to 48 months after operation at the outpatient clinic and did not show a significant gradient across the left ventricular outflow tract in any of the patients. In all patients a grade 1 autograft central regurgitation could be demonstrated by color Doppler examination. Neither dilatation of the autograft root nor progressive valve incompetence was registered in any of the patients. At echocardiographic follow-up, in eight patients increased autograft anulus diameter was measured with equal valve competence (Fig. 3). There were no radiographic or echocardiographic signs of calcification or structural degeneration of the autograft. Discussion In children and young adults who require aortic valve replacement the pulmonary autograft seems to be an ideal substitute. It has all the advantages of a homograft valve in the aortic position and, moreover, it is a viable valve that grows with the patient.f 10, 14, 15 Long-term experience with pulmonary autograft replacement of the aortic valve has been associated with decreasing early mortality. Late mortality, which was caused by endocarditis or reoperation, is also decreasing during followUp.8 With Ross, Jackson, and Davies, 16 we think that root replacement is the preferred technique in children. In the small aortic anulus it is technically feasible to replace the complete root, and, with this technique, preservation of autograft growth potential is optimal. The relief of mul-

tiple level stenosis of the left ventricular outflow tract is more easily done, thereby avoiding Konno-like procedures.l? Moreover the normal pulmonary valve is marginally larger than the normal aortic valve, a difference that may be accentuated in congenital obstruction of the left ventricular outflow tract in which instances root replacement is the technique of choice.l'' Although no long-term results of the root replacement technique have yet been documented, the midterm results are good. 19 No early deaths occurred in our group of patients, although a greater risk of operative death has been reported in association with this technique, as a result of intraoperative hemorrhage or difficulties with coronary anasto-

moses.!?

Echocardiographic enlargement of the autograft has been proportional to the growth of the patient and developed without increase of regurgitation. Although this may represent true growth of the autograft, simple dilatation may also playa role (Fig. 3). Autograft anulus enlargement with preserved function could also be demonstrated in children studied by Gerosa and Elkins and their associates.?: 14 Autograft growth could also experimentally be proved in puppies in whom the pulmonary root was not transplanted to the aortic position but reimplanted orthotopically.P Endocarditis of the autograft is reported to occur with an incidence of 1.8% per patient-year and it was the only reason for reoperation on the pulmonary autograft in the series of Gerosa and associates.!" In all patients of that series (n = 5) the infection occurred after 4 years or more. We did not observe any endocarditis in our group of patients with 4 years offollow-up. It was also not observed

3 7 2 Schoof et al.

in the Oklahoma group of children (n = 51) with 5 years of follow-up.? Another reason may be that we exclusively used the root replacement technique, which was also used by the Oklahoma group in 22 of their patients, whereas the patients in the series of Gerosa and associates'" in whom endocarditis developed, had the autograft implanted in the subcoronary position. This may cause more disturbed flow in the left ventricular outflow tract predisposing to the development of endocarditis. Another major difference in these studies is the consistent use of cryopreserved homografts for reconstruction of the right ventricular outflow tract in most of our patients and the Oklahoma group of patients" and the predominant use of fresh, antibiotic-sterilized homografts in the study of Gerosa and associates.!" Two of our patients had a history of rheumatic aortic valve disease. One of them had seropositivejuvenile rheumatoid arthritis, which is a relatively uncommon form of childhood arthritis that often causes severe destruction of joints associated with considerable functional disability? 1 Cardiac involvement in juvenile rheumatoid arthritis is unusual,22but cardiovascular disease accounts for 25% of all deaths caused by rheumatoid disease.P Aortic regurgitation in these patients appears to show a particularly aggressive course.21 Our patient with active juvenile rheumatoid arthritis had the regurgitant aortic valve replaced by a normal pulmonary autograft root. Postoperatively this patient had a recurrence of rheumatoid autograft valvulitis in the initially normal pulmonary autograft, which led to fatal congestive heart failure. The recurrence of the rheumatic valvular disease in the autograft may be a result of high flow-induced shear stress of the valve in the aortic position. 13 Acute rheumatic fever is an autoimmune disease in which invasive streptococcal infection evokesan antibody response by the host, and this antibody attacks antigenically similar host tissues.i" Contrary to the aggressive course of aortic regurgitation in juvenile rheumatoid arthritis, after rheumatic fever, aortic regurgitation usually remains mild for many years and even severe regurgitation may be tolerated for a decade or more without symptoms." Our second patient with rheumatic aortic valve disease had acute rheumatic fever 10 and 8 years before autograft aortic valve replacement. One year after operation the autograft had to be replaced by a mechanical prosthesis because of massive regurgitation after a relapse of acute rheumatic fever that developed 2 months after discontinuation of antibiotic prophylaxis for rheumatic fever. The highest prevalence of acute rheumatic fever is in children 5 to 14 years old and mainly in thirdworld countries. 26,27 In this young rheumatic patient population prosthetic valve replacement represents a difficult problem because of the necessity of permanent

The Journal of Thoracic and Cardiovascular Surgery February 1994

anticoagulation. This favors the use of other surgical techniques and makes pulmonary autograft replacement of the aortic valve an attractive operation in this group of patients. The history of our patient, however, demonstrates the possibility of recurrence of rheumatic inflammation of the pulmonary autograft if the antibiotic prophylaxis is discontinued. Postoperative continuation of this prophylaxis seems crucial in these patients. One of our patients was an infant with critical aortic stenosis. The clinical presentation and the result of surgical treatment of this anomaly are vastly different from obstruction of the left ventricular outflow tract in older children. 28,29 Early surgical mortality rates of up to 50% have been reported for infants.P In infants with critical aortic stenosis, early replacement of the aortic root with a pulmonary autograft may achieve the best conservation of left ventricular function.'! We performed this operation in a 3-month-old infant in whom successful balloon dilation of the aortic valve with subsequent endocarditis led to massive regurgitation. At operation, endocardial fibroelastosis of the interventricular septum was found, which was not registered on preoperative precordial echocardiography. One year after operation heart failure developed and cardiac catheterization was done. A poorly relaxing but good contractile left ventricle was found with normal autograft function and significant regurgitation of the pulmonary homograft. Probably, in this patient, the poor clinical outcome was due to preexistent left ventricular restrictive cardiomyopathy with endocardial fibroelastosis. Another considerable problem in this child was the early failure of the pulmonary homograft. Early failures of homografts in infants have been reported before' and may turn out to be of major concern especially in infants or neonates who have pulmonary autograft replacement of the aortic valve. Ziemer'? operated on a neonate with critical aortic stenosis in whom the aortic root was replaced by a pulmonary autograft. This child had some regurgitation of the autograft valve after 2.5 years and had the pulmonary homograft replaced because of anastomotic stenosis. In our series the actuarial freedom from death (one late death) and all other valve-related complications (one reoperation for autograft failure and one homograft failure) at 4 years after operation (Fig. 2) is 78.6% (95% CL 50% to 95%). We conclude that pulmonary autograft root replacement for aortic valve disease in children can be done with low mortality and morbidity. The operation seems to be contraindicated in patients with juvenile rheumatoid arthritis because of the risk of recurrence of rheumatic disease in the autograft. The pulmonary autograft is also susceptible to recurrence of rheumatic inflammation in patients with a history of acute rheumatic fever. Despite replacement of the aortic root with

The Journal of Thoracic and Cardiovascular Surgery Volume 107, Number 2

the pulmonary autograft in infants with critical valvular aortic stenosis and endocardial fibroelastosis, clinical results may be poor. There is echocardiographic suggestion of growth of the autograft during follow-up. We consider aortic root replacement with the pulmonary autograft the procedure of choice in children who require aortic valve replacement.

I. 2.

3.

4.

5.

6.

7. 8.

9.

10.

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12.

13.

14.

REFERENCES Dunn JM. Porcine valve durability in children. Ann Thorac Surg 1981;32:357-68. Milano A, Vouhe PR, Baillot-Vernant F, et al. Late results after left-sided cardiac valve replacement in children. J THORAC CARDIOVASC SURG 1986;92:218-25. Schaff HV, Danielson GK, Di Donato RM, et al. Late results after Starr-Edwards valve replacement in children. J THORAC CARDIOVASC SURG 1984;88:583-9. Williams WG, Pollack JC, Geiss DM, et al. Experience with aortic and mitral valve replacement in children. J THORAC CARDIOVASC SURG 1981;81:326-33. Clarke R. Extended aortic root replacement with cryopreserved allografts: Do they hold up? Ann Thorac Surg 1991; 52:669-75. Matsuki 0, Robles A, Gibbs S, Boddnar E, Ross DN. Long-term performance of 555 aortic homografts in the aortic position. Ann Thorac Surg 1988;46:187-91. Ross DN. Replacement of the aortic and mitral valve with a pulmonary autograft. Lancet 1967;2:956-8. Ross DN, Jackson M, Davies J. The pulmonary autograft: a permanent aortic valve. Eur J Cardiothorac Surg 1992; 6:113-7. Elkins RC, Santangelo K, Randolph JD, et al. Pulmonary autograft replacement in children: The ideal solution? Ann Surg 1992;3:363-71. Gerosa G, McKay R, Ross DN. Replacement of the aortic valve or root with pulmonary autograft in children. Ann Thorac Surg 1991;51:424-9. Edmunds LH Jr, Clark RE, Cohn LH, et al. Guidelines for reporting morbidity and mortality after cardiac valvular operations. Ann Thorac Surg 1988;46:257-9. Grunkemeier GL, Thomas DR, Starr A. Statistical considerations in the analysis of time-related events. Am J Cardiol 1977;39:257-8. Suylen van RJ, Schoof PH, Bos E, et al. Pulmonary autograft failure after aortic root replacement in a patient with juvenile rheumatoid arthritis. Eur J Cardiothorac Surg 1992;6:571-2. Gerosa G, McKay R, Davies J, Ross DN. Comparison of the aortic homograft and the pulmonary autograft for aortic valve or root replacement in children. J THORAC CARDlOVASC SURG 1991;102:51-61.

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15. Santangelo K, Elkins RC, Stelzer P, et al. Normal left ventricular function following pulmonary autograft replacement of the aortic valve in children. J Cardiac Surg 1991; 6(Suppl):633-7. 16. Ross DN, Jackson M, Davies J. Pulmonary autograft aortic valve replacement: long term results. J Cardiac Surg 1991;6(Suppl):529-33. 17. Ross DN. Homograft aortic root replacement [Commentary]. Ann Thorac Surg 1991;52:674. 18. McKay R, Ross DN. Experience with pulmonary autograft for aortic stenosis [Commentary]. Ann Thorac Surg 1991; 52:674-5. 19. Elkins RC, Santangelo K, Stelzer P, et al. Pulmonary autograft replacement of the aortic valve: an evolution of technique. J Cardiac Surg 1992;7:108-16. 20. Murata H. A study of autologous pulmonary valve replantation [in Japanese]. Nippon Geka Gakkai Zasshi 1984; 32:144-53. 21. Leak AM, Miller-Craig MW, Ansell BM. Aortic regurgitation in seropositive juvenile arthritis. Ann Rheum Dis 1981;40:229-34. 22. Brewer EJ. Juvenile arthritis: cardiac involvement. Arthritis Rheum 1977;20:2231-6. 23. Iveson JMI, Pomerance A. Cardiac involvement in rheumatoid disease. Clin Rheum Dis 1977;3:467-500. 24. Kaplan MH. Rheumaticfever, rheumatic heart disease and the streptococcal connection: the role of streptococcal antigens crossreactive with heart tissue. Rev Infect Dis 1979; 1:988-96. 25. Reichek N, Shelburne JC, Perloff JK. Clinical aspects of rheumatic valvular disease: aortic regurgitation. Prog Cardiovasc Dis 1973;15:518-23. 26. Annegers JF, Pillman NL, Weidman WH, et al. Rheumatic fever in Rochester, Minnesota, 1935-1978. Mayo Clin Proc 1982;57:753-7. 27. Gordis L, Lilienfeld A, Rodriguez R. Studies in the epidemiology and preventability of rheumatic fever-II: socioeconomic factors and the incidence of acute attacks. J Chronic Dis 1969;21:655-66. 28. Hastreiter AR, Oshima M, Miller RA, et al. Congenital aortic stenosis in infancy. Circulation 1963;28:I084-95. 29. Lakier JB, Lewis AB, Heymann MA, et al. Isolated aortic stenosis in the neonate: natural history and hemodynamic considerations. Circulation 1974;50:801-8. 30. Sandor G, Olley P, Trusler G, et al. Long-term follow up of patients after valvotomy for congenital valvular stenosis in children. J THORAC CARDIOVASC SURG 1980;80:171-6. 31. McKay R, Smith A, Leung M, et al. Morphology of the ventriculoaortic junction in critical aortic stenosis. J THORAC CARDIOVASC SURG 1992;104:434-42. 32. Ziemer G. Discussion of Ross et al.8