Long-term follow-up of patients with the antibiotic-sterilized aortic homograft valve inserted freehand in the aortic position

Animal models for partial heart transplantation

BACKGROUND

Partial heart transplantation delivers growing heart valve implants by transplanting the part of the heart containing the necessary heart valve only. In contrast to heart transplantation, partial heart transplantation spares the native ventricles. This has important implications for partial heart transplant biology, including the allowable ischemia time, optimal graft preservation, primary graft dysfunction, immune rejection, and optimal immunosuppression.

AIMS

Exploration of partial heart transplant biology will depend on suitable animal models. Here we review our experience with partial heart transplantation in rodents, piglets, and non-human primates.

MATERIALS & METHODS

This review is based on our experience with partial heart transplantation using over 100 rodents, over 50 piglets and one baboon.

RESULTS

Suitable animal models for partial heart transplantation include rodent heterotopic partial heart transplantation, piglet orthotopic partial heart transplantation, and non-human primate partial heart xenotransplantation.

DISCUSSION

Rodent models are relatively cheap and offer extensive availability of research tools. However, rodent open-heart surgery is technically not feasible. This limits rodents to heterotopic partial heart transplant models. Piglets are comparable in size to children. This allows for open-heart surgery using clinical grade equipment for orthoptic partial heart transplantation. Piglets also grow rapidly, which is useful for studying partial heart transplant growth. Finally, nonhuman primates are immunologically most closely related to humans. Therefore, nonhuman primates are most suitable for studying partial heart transplant immunobiology and xenotransplantation.

CONCLUSIONS

Animal research is a privilege that is contingent on utilitarian ethics and the 3R principles of replacement, reduction and refinement. This privilege allows the research community to seek fundamental knowledge about partial heart transplantation, and to apply this knowledge to enhance the health of children who require partial heart transplants.

Early Experience with Homograft Valve Banking

Homograft cardiac valves have been shown to have several advantages over conventional prosthetic valves. From October 1993 through November 1996, 273 homografts (262 valved and 11 non-valved) were used in various procedures at the All India Institute of Medical Sciences, New Delhi, India. The recommendations of the American Association of Tissue Banks were followed for procurement, harvesting, and storage of the valves. One hundred and ninety-six hearts were procured yielding a total of 439 homograft valves; 192 were pulmonary homografts, 187 were aortic homografts, and 60 were mitral homografts. Eighty-five homografts were used in the Ross procedure, 64 were used in homograft replacement of the aortic valve, 28 were used in replacement of the mitral valve, 85 were used in various operations for heart disease as valved conduits, and 11 homografts were used as either non-valved conduits or for patch repair. One hundred and thirty-five homografts (31%) were discarded for various reasons. Our early experience of valve banking is discussed.

Allografts for aortic valve and root replacement: veni vidi vici?

Allografts were introduced in the early 1960s for the replacement of the aortic valve and regarded at the time as a close-to-perfect valve substitute. However, over the past 40 years it has become evident that not all of the high expectations could be met. This review summarizes the past 40 years of clinical experience with allografts for aortic valve replacement, describes the advantages and disadvantages of allografts compared with other aortic valve substitutes and their impact on patient prognosis, and discusses the future role of allografts for the replacement of the aortic valve or root.

Heart valve allograft decontamination with antibiotics: impact of the temperature of incubation on efficacy

Heart valve allografts are typically processed at 4°C in North America, including the step of antibiotic decontamination. In our own experience with heart valve banking, we often observe persistent positive cultures following decontamination at wet ice temperature. We hypothesized that warmer temperatures of incubation might increase the efficacy of the decontamination procedure. In a first series of experiments, 12 different bacterial species were grown overnight, frozen in standardized aliquots and used directly to inoculate antibiotic cocktail aliquots at 10⁵ colony-forming units (CFU)/ml. The antibiotic cocktail contains vancomycin (50 μg/ml), gentamicin (80 μg/ml) and cefoxitin (240 μg/ml) in Dulbecco's Modified Eagle's Medium. Inoculated aliquots were incubated at 4, 22 and 37°C and CFUs were determined at regular intervals up to 24 h post-inoculation. In a second set of experiments, 10 heart valves were spiked with 5000 CFU/ml and incubated with antibiotics at 4 and 37°C for 24 h. The final rinse solutions of these heart valves were filtered and tested for bacterial growth. After 24 h of incubation, CFUs of all 12 bacterial species were reduced by a factor of only one to two logs at 4°C whereas log reductions of 3.7 and 5.0 or higher were obtained at 22 and 37°C, respectively. Most microorganisms, including Staphylococcus epidermidis, Lactococcus lactis lactis and Propionibacterium acnes survived well the 24-h antibiotic treatment at 4°C (< 1 Log reduction). All 10 heart valves that were spiked with microorganisms had positive final rinse solutions after antibiotic soaking at 4°C, whereas 8 out of 10 cultures were negative when antibiotic decontamination was done at 37°C. These experiments show that a wet ice temperature greatly reduces the efficacy of the allograft decontamination process as microorganisms survived well to a 24-h 4°C antibiotic treatment. This could explain the high rate of positive post-processing cultures obtained with our routine tissue decontamination procedure. Increasing the decontamination temperature from 4 to 37°C may significantly reduce the incidence of post-disinfection bacterial contamination of heart valves.

Rheumatic heart disease in indigenous populations--New Zealand experience

Rheumatic fever continues unabated among the indigenous Māori and Pacific Island New Zealanders. Ethnic disparities have increased in the past decade. The major success story for disease control has been secondary penicillin prophylaxis with 28-day intramuscular benzathine penicillin with high penicillin delivery rates and low recurrence rates. A landmark study for primary prevention of acute rheumatic fever for group A streptococcal pharyngitis was published in 2009. New Zealand has helped establish the role of echocardiography in acute rheumatic fever, with subclinical carditis incorporated into guidelines as a major criterion of rheumatic fever in high prevalence regions. The rates of mitral valve repair for rheumatic heart disease (RHD) are currently greater than 90% in the children's cardiac unit but remain low in adult cardiac units in New Zealand. This is particularly relevant to women of child bearing age where New Zealand data has shown that pregnancy outcomes for mothers with prosthetic valves on warfarin are poor. There are new initiatives to prevent severe RHD using portable echocardiography by screening school aged children. The prevalence of definite RHD was 2.4% in a large cohort of socially disadvantaged children in South Auckland studied in 2007-2008. Cost benefit models of screening need to be developed. Ongoing research involves international consensus standardisation of RHD patterns, and the need to define the natural history of subclinical RHD.

Aortic valve and/or aortic root replacement using an aortic homograft

Aortic valve replacement using the homograft valve has a special place in the cardiac surgical practice although it has never been widely used, in part due to the lack of tissue donors but also due to the perceived difficulty of the procedure compared with aortic valve replacement using prosthetic devices and concerns regarding homograft valve failure. The principal indication for aortic valve replacement using a homograft aortic valve is for active aortic valve endocarditis (native or prosthetic) with or without perivalvular tissue destruction (abscess cavity, fistula, detachment of the anterior mitral valve leaflet from the aortic annulus). Since the homograft tissue is pliable and adaptable, it can be used to repair defects in complex cases with root destruction. A second interesting application of homograft aortic valve is in the treatment of small aortic root (in which replacement with a small prosthetic valve would produce an unacceptable orifice ratio and ultimately affect long-term outcome) and left ventricular outflow tract obstruction when the homograft aortic valve can be combined to the Konno procedure. Homograft aortic valve can be used in these cases without sacrifying the pulmonary valve to be used as aortic valve substitute (for instance in adolescents and young adults who do not want to undergo a 'two-valve' procedure like the Ross-Konno procedure). The most frequent operation technique is the cylindrical aortic root replacement, performed in a similar way than the classical Bentall procedure. This technique is the most easiest one and performed more frequently than the subcoronary implantation, which is substantially more demanding. Results from centres that have significant experience with homograft valve surgery report equivalent survival data. The University of Alabama had an 87% survival at 5 years in a 10-year period from 1981 to 1991. Of those who underwent isolated aortic valve replacement with a homograft, there was 99% survival at 30 days and 94% survival at 8 years. In the Mayo Clinic series, 82% were alive at 8 years. Like all tissue valves, homograft aortic valves may fail. An understanding of the mechanisms of homograft valve failure and the way in which these mechanisms interact has important surgical implications. Homograft aortic valves may develop progressive regurgitation as a result of a change in the mechanical properties of the leaflets over time.

Autografts, homografts, and xenografts: overview on stentless aortic valve surgery

Stentless valves, either human (autografts, homografts) or animal (porcine xenografts), were historically among the first substitutes to be used to replace the diseased aortic valve. Forty years after those pioneering days and 15 years after revival of such valves, stentless grafts have become a mainstay in aortic surgery. Although limitations associated with the use of autografts, homografts and xenografts remain, stentless valves have profoundly improved quality of life after aortic valve/root replacement. In addition, stentless surgery has greatly advanced the understanding of aortic root anatomy, physiology and pathology among surgeons.

Allograft tissue for use in valve replacement

Homograft or allograft tissue has been available for use as replacement for diseased valves or reconstruction of major vessels for decades. However, with respect to replacement of diseased valvular tissue the search for the ideal valve still continues. In this review we will discuss the clinical indications, surgical techniques, and outcome of aortic homografts.

Are allografts the biologic valve of choice for aortic valve replacement in nonelderly patients? Comparison of explantation for structural valve deterioration of allograft and pericardial prostheses

OBJECTIVE

To compare explantation for structural valve deterioration in nonelderly patients after aortic valve replacement with stented bovine pericardial and cryopreserved allograft valves.

METHODS

From 1981 to 1985, 478 patients received pericardial prostheses during premarket approval; from 1987 to 2000, 744 patients received cryopreserved allografts. Mean age of patients receiving allografts was 49 +/- 12 years, and that of those receiving pericardial prostheses was 65 +/- 11 years; pericardial valves were used in 138 patients younger than age 60. Mean follow-up was 15 +/- 5.1 years for pericardial valves (4674 patient-years of follow-up) and 5.6 +/- 3.1 years for allografts (3892 patient years of follow-up). Multivariable hazard function methodology, age-group stratification, and propensity matching were used to compare age-specific explantation for structural valve deterioration.

RESULTS

Ninety-five pericardial valves and 46 allografts were explanted, and structural valve deterioration was the mechanism of failure in 74% and 59%, respectively. The risk of structural valve deterioration increased with younger age at implantation for both allografts (P = .07) and pericardial valves (P < .0001), with a similar magnitude of effect in patients age 50 years or younger (P = .5), 50 to 60 years (P = .7), and greater than 60 years (P = .9) and in propensity-matched pairs (P = .2). Thus, pericardial valves were as durable as allografts at all adult ages.

CONCLUSIONS

Structural valve deterioration is the most frequent cause of valve-related reoperation after both pericardial and allograft aortic valve replacement and is similarly age dependent, suggesting that pericardial valves may be appropriate for nonelderly as well as older persons.

Surgical Treatment of Paraannular Aortic Abscess

BACKGROUND

Aortic valve endocarditis with paraannular abscess remains a challenging problem in the surgical treatment of native and prosthetic valve endocarditis. The purpose of this study is to evaluate the long-term outcome of surgical intervention for aortic paraannular abscess.

METHODS

From January 1989 to November 2004, 32 consecutive patients (24 men, 8 women) were studied. Mean age was 50.6 +/- 16.2 (range, 17-80) years. Twenty-four had native valve endocarditis and 8 had prosthetic valve endocarditis. Eight of 24 patients who suffered from native valve endocarditis had bicuspid valve endocarditis. The predominant microorganism was Streptococcus viridans. No microorganisms were identified in 11 patients. Most patients were desperately ill at the time of surgery. Repair was performed by aggressive eradication of infected tissue and reconstruction of the defect with autologous pericardium (n = 24), bovine pericardium (n = 3), Dacron patch (n = 4), and primary closure (n = 1).

RESULTS

Although postoperative complications were common, early mortality occurred in only 4 patients (12.5%). Operative survivors have been followed for 5 months to 16 years (mean, 92.7 months). There were 2 late deaths but all were noncardiac deaths. Five patients (15.6%) underwent reoperation at a mean of 55.4 months after the initial surgery. The actuarial survival at 1, 5, and 10 years was 87.4% +/- 5.9%, 83.2% +/- 6.9%, and 79.1% +/- 7.7%, respectively. The freedom from reoperation at 1, 5, and 10 years was 88.7% +/- 6.2%, 79.8% +/- 8.1% and 75.4% +/- 8.8%, respectively.

CONCLUSION

These data suggest that aggressive surgical intervention and meticulous antibiotic therapy for aortic valve endocarditis with paraannular abscess yields a high success rate with relatively low mortality and good long-term results.

Transcatheter placement of a low-profile biodegradable pulmonary valve made of small intestinal submucosa: A long-term study in a swine model

OBJECTIVE

We sought to investigate a placement of a percutaneous low-profile prosthetic valve constructed of small intestinal submucosa in the pulmonary position in a swine model.

METHODS

Twelve female farm pigs were stented at the native pulmonary valve to induce pulmonary insufficiency. Once right ventricular dilation occurred, the small intestinal submucosa valve was implanted. The pigs were followed up with transthoracic echocardiographic Doppler scanning. One animal died of heart failure before valve replacement. Animals were euthanized at 1 day, 1 month, 3 months, 6 months, and 12 months after valve implantation.

RESULTS

The small intestinal submucosa pulmonary valve showed effective reversal of pulmonary regurgitation. There were no misplacements during deployment. There were no embolizations. One-year echocardiographic follow-up showed minimal regurgitation and no stenosis for a valve/vessel ratio of 0.78 or greater. Histologic examination demonstrated intensive remodeling of the small intestinal submucosal valve. Within 1 month, the surface was covered by endothelium, and fibroblasts invaded the interior. Over the following months, the small intestinal submucosal valve remodeled without apparent graft rejection.

CONCLUSION

The small intestinal submucosa valve has the potential for graft longevity without the need for anticoagulation or immunosuppression. Histologic remodeling of the valve tissue provides a replacement capable of resembling a native valve that can be placed percutaneously with low-profile delivery systems.

Complex aortic valve repair as a durable and effective alternative to valve replacement in children with aortic valve disease

OBJECTIVE

This study was undertaken to determine the utility of aortic valve repair in children.

METHODS

A retrospective analysis was conducted on aortic valve surgery from 1973 to 2004 at Children's Hospital of Wisconsin.

RESULTS

Procedures were classified as simple repairs (blunt valvotomy, commissurotomy with or without thinning, n = 147), repair of aortic insufficiency with ventricular septal defect (n = 22), complex repairs (any combination of additional procedures including suspension of prolapsed leaflets, leaflet extensions, repair of torn or perforated leaflets, annuloplasty, reduction of sinus of Valsalva plasty, and concomitant repair of supravalvular or subvalvular stenosis, n = 57), and replacements (n = 57, 20 mechanical, 2 porcine, and 35 human valves). Freedoms from reintervention for simple repairs and repair of aortic insufficiency with ventricular septal defect at 10 years were 86% +/- 5% and 93.3% +/- 6%, respectively. For complex valve repair, freedoms from reintervention at 1, 5, and 10 years were 94% +/- 3%, 85% +/- 6%, and 44% +/- 15%, versus 96% +/- 3%, 77% +/- 9%, and 77% +/- 9% for valve replacement ( P = .3). At intermediate follow-up, patients with complex valve repair had a residual gradient of 20 +/- 21 mm Hg, and 94% were free of severe aortic insufficiency. Residual aortic stenosis ( P < .05) but not the preoperative diagnosis of combined aortic stenosis and insufficiency predicted the need for reintervention.

CONCLUSION

Freedom from reintervention after complex valve repairs was not different from that after valve replacement, with acceptable residual aortic stenosis and insufficiency. Simple repairs and repair of aortic insufficiency with ventricular septal defect yielded excellent long-term freedom from reintervention.

The Ross Operation: An Evaluation of a Single Institution's Experience

BACKGROUND

Pulmonary autograft aortic root replacement was used in adults. Risk factors for aortic valve incompetence (AI) and pulmonary homograft valve stenosis are identified.

METHODS

From February 1991 through May 2003, 103 patients, with a mean age of 35.2 +/- 9.5 years, underwent aortic root replacement with the pulmonary autograft. Annulus reinforcement (reduction annuloplasty or use of root ring) was carried out in 45 patients. In all but 1 patient, the right ventricular outflow tract was reconstructed with a cryopreserved pulmonary homograft. Mean follow-up duration was 6.0 +/- 2.8 years (range 0.3 to 11 years).

RESULTS

There were no hospital deaths. Overall patient survival was 98.9 +/- 1.0% at 1 year and 97.3 +/- 1.9% at 10 years. Autograft function follow-up resulted in 5 patients requiring reoperation for aortic incompetence. The univariate risk factors for aortic incompetence at discharge and during follow-up were respectively annulus reinforcement (p = 0.05) and bicuspic aortic valve (p = 0.05). Reoperation for homograft failure occurred in 1 patient. During follow-up, 24 patients (25.5%) developed homograft stenosis (gradient > 20 mm Hg). Univariate analysis indicated the diameter of the homograft (p = 0.001) as factor associated with stenosis during follow-up. Cox regression identified smaller diameter of the homograft (p = 0.001) and older age of donor (p = 0.002) as independent risk factor for the development of homograft stenosis.

CONCLUSIONS

The Ross operation can be performed with few complications. Although both the aortic autograft and the pulmonary homograft have limited durability, this has not yet resulted in considerable reoperation rates and associated morbidity and mortality.

Processing of cardiovascular allografts: effectiveness of European Homograft Bank (EHB) antimicrobial treatment (cool decontamination protocol with low concentration of antibiotics)

To assess the effectiveness of antimicrobial treatment by using cool decontamination protocol with low concentration of antibiotics during processing of cardiovascular allografts, 948 allografts processed during a 2-year period were analysed. Five hundred and fourty one donors aged <62 years were classified in: multiorgan donors (MOD) with non-transplantable hearts; recipients of cardiac transplantation (RHT); and non-beating heart cadavers with a warm ischemic time of less than 6 h (NBHD). During processing three samples for bacteriology testing were taken A (sampling before decontamination); B (sampling after decontamination); C (sampling on the final product). Samples A were positive in 348 cases (36.4%), respectively 36% for MOD, 21.6% for RHT and 78.1% for NBHD. All the allografts were immersed in a cocktail of four antibiotics at 4 degrees C. After exposure to antibiotics the rate of decontamination of those with A positive was 90.4, 92.5, 82.5% respectively for MOD, RHT, NBHD. At the end of processing, 57 allografts (6%) were positive in B and/or C, 15 allografts remained contaminated with the same bacteria as in A, 42 were contaminated during processing. The overall rate of sterility in the end of processing is 94% and for each group this is: 95.4% for MOD, 96.8% for RHT and 86.3% for NBHD. Analysis shows that there is no influence of time of exposure in AB in the rate of decontamination for MOD and RHT. The most predominant germ in contamination is Coagulase Negative Staphylococcus (CNS) (53.4% alone, 8.9% with other bacteria). 83.3% of MOD; 88.5% of RHT were contaminated with one germ, while 40.4% of NBHD were contaminated with more than one.

Allograft Aortic Valve Replacement in the Adult: A Review

Aortic valve replacement using an allograft has been used continuously for over 40 years. Its advantages are excellent haemodynamic function, low thrombogenicity, resistance to infection and avoidance of the complications of anticoagulation. The main concern is its long-term durability, with the high hazard phase for failure between 10 and 20 years. We have only recently been able to judge the true long-term behaviour of the contemporary allograft with two recently published series of patients having reached follow-up beyond 20 years in significant numbers. This review of allograft aortic valve replacement in the adult covers the areas of history, benefits, techniques of sterilisation and preservation, operative methods and outcomes.

Prognosis after aortic root replacement with cryopreserved allografts in adults

BACKGROUND

Aortic root replacement with cryopreserved allografts is associated with excellent hemodynamics, little endocarditis, low thromboembolic event rates, and no need for anticoagulation. There is, however, concern regarding the long-term durability of this valve substitute, especially in younger patients. Meta-analysis and microsimulation were used to calculate age-specific long-term prognosis after allograft aortic root replacement based on current evidence.

METHODS

Our center's experience with cryopreserved allograft aortic root replacement in 165 adult patients was combined in a meta-analysis with reported and individual results from four other hospitals. Using this information, the microsimulation model predicted age- and gender-specific total and reoperation-free and event-free life expectancy.

RESULTS

The pooled results comprised 629 patients with a total follow-up of 1860 patient-years (range 0 to 12.8 years). Annual risks were 0.6% for thromboembolism, 0.05% for bleeding, 0.5% for endocarditis, and 0.5% for nonstructural valve failure. Structural allograft failure requiring reoperation occurred in 15 patients, and a patient age-specific Weibull function was constructed accordingly. Calculated total life expectancy varied from 27 years in a 25-year-old to 12 years in a 65-year-old male; corresponding actual lifetime risk of reoperation was 89% and 35%, respectively.

CONCLUSIONS

Cryopreserved aortic allografts have an age-related limited durability. This results in a considerable lifetime risk of reoperation, especially in young patients. The combination of meta-analysis and microsimulation provides an appropriate tool for estimating individualized long-term outcome after aortic valve replacement and can be useful both for patient counseling and prognostic research purposes.

Aortic insufficiency: Indications for surgery in children

The goals of surgery in children with chronic aortic insufficiency are to prevent irreversible left ventricular dysfunction and to provide for long-term survival. In the past, surgical options included placement of a mechanical valve, a porcine bioprosthesis, or an aortic valve homograft. Complications from these options include thromboembolism, prosthetic valve endocarditis, limited durability, and lack of growth potential. The increasing utilization of the Ross procedure to treat chronic aortic insufficiency has led to new interest in the question of when to operate on a regurgitant aortic valve. This review focuses on the pathophysiology of aortic insufficiency and the invasive and noninvasive preoperative indices that may indicate the optimal time for aortic valve surgery in the pediatric population. Copyright 1998 by W.B. Saunders Company

Acute endocarditis treated with radical debridement and implantation of mechanical or stented bioprosthetic devices

BACKGROUND

Operation for active infective endocarditis carries high mortality and morbidity rates, especially when the annulus is involved. Overall the literature favors the use of autograft and homograft valves because of better resistance to infection. In our clinic during the last 5 years we used an aggressive surgical approach to infective endocarditis in combination with implantation of mechanical or stented bioprosthetic devices.

METHODS

From 1994 to 1999, 50 adults with aortic and/or mitral valve endocarditis underwent valve replacement. The median age of the 36 men and 14 women was 58 years (range, 17 to 78 years). All patients had active endocarditis at the time of operation. Native valve endocarditis was present in 48 patients and prosthetic valve endocarditis was present in 2 patients. The aortic valve was affected in 24 patients, the mitral valve in 21 patients, and both the aortic and mitral valves in 5 patients. Two of the patients with mitral endocarditis also had infection of the tricuspid valve. Annular destruction was present in 24 patients (48%). The patients were treated with radical excision of all infected tissue. The annular defects were closed, if possible, with direct sutures. Otherwise, a reconstruction was performed. Follow-up was 100% complete with a median follow-up period of 45 months (range, 6 to 66 months).

RESULTS

The procedures were performed without lethal bleeding complications. Early mortality was 12% and the actuarial survival at follow-up was 80%. In none of the patients who died was death related to the prosthetic valve or recurrence of the endocarditis. Only 1 patient (2%) developed recurrence of the infective endocarditis and was reoperated with a Ross procedure. Three and a half years later the patient developed severe valve insufficiency of the autograft and was operated again with implantation of a mechanical device.

CONCLUSIONS

Native and prosthetic valve endocarditis can be treated successfully with aggressive surgical debridement and implantation of mechanical or stented bioprosthetic devices with a low risk of recurrent endocarditis.

Long-term results after valvotomy for congenital aortic valvar stenosis in children

As interest increase in the Ross procedure performed as a therapeutic option for children with congenital aortic valvar stenosis, it becomes increasinly important to know the late results of aortic valvotomy in this population. We have therefore examined retrospectively the medical records of 121 consecutives survivors undergoing aortic valvotomy before 10 years of age between 1974 and 1992. The mean age at the first valvotomy was 29 months, with a range from 3 days to 10 years. The mean duration of follow up was 9.4 years, with a range from 1.6 to 22 years. Fifteen patients (12.3%; 70% CL: 10-16) died: 9 following reoperation, and 6 late after surgery. Death was related to the hearts in 86% of cases. The actuarial survival rate was 79% (70% CL: 72/84) at 10 years. Young age at the first valvotomy, and the number of procedures, emerged as risk factors of secondary mortality. Reoperations on the aortic valve, 73 in all, were required in 56 patients. The second procedure was done after a mean interval of 6 years, with a range from 1 day to 18 years. This was for restenosis in three-quarters of the cases. The aortic valve was replaced in 30 patients, at a mean of 9 years, and with a range from 9 months to 18 years, after the first procedure. The survival without replacement at 20 years was 29% (70% CL: 15-49). No factor was identified with a relationship either to reoperation or valvar replacement. Long term results after aortic valvotomy, therefore, show a high late mortality, frequent reinterventions, and an almost inescapable eventual need for valvar replacement. The ongoing use of the Ross operation is justified, even if longterm studies in children are still needed to validate its use.

Pulmonary homograft: should it be used in the aortic position?

OBJECTIVE

Retrospective analysis was performed to determine the suitability of pulmonary homograft as an aortic valve substitute.

METHODS

From January 1994 through June 1999, 147 patients (mean age, 32.2 +/- 17.3 years) underwent aortic valve replacement with either an aortic homograft (group 1: n = 103, 25 fresh antibiotic preserved and 78 cryopreserved) or a pulmonary homograft (group 2: n = 44, 11 antibiotic preserved and 33 cryopreserved). In group 1 a scalloped subcoronary technique was used in 64 patients, and a root replacement technique was used in 39 patients. In group 2 the scalloped subcoronary technique was used in 34 patients, and the root replacement technique was used in 10 patients.

RESULTS

There were 131 operative survivors (group 1 = 91; group 2 = 40). Follow-up ranged from 2 to 62 months. In group 1 none of the patients had significant aortic regurgitation during the hospital stay. Three patients (all having undergone the scalloped subcoronary technique) had moderate aortic regurgitation after 6 to 32 months. In group 2, 10 patients (9 having undergone the scalloped subcoronary technique and 1 having undergone the root replacement technique) developed significant regurgitation: 2 intraoperatively, 5 in the early postoperative period before discharge from the hospital, and 3 during late follow-up 6 to 12 months postoperatively. Among the various risk factors analyzed for overall homograft failure, use of a pulmonary homograft was the single independent predictor of valve failure (odds ratio, 8.6; 95% confidence interval, 1.9-39; P =.006).

CONCLUSION

Pulmonary homograft, when inserted by means of a scalloped subcoronary technique, is not a suitable aortic valve substitute.

Pulmonary ventricular outflow reconstruction with a size-reduced cryopreserved pulmonary valve allograft: mid-term follow-up

Surgical reduction of pulmonary allografts is being performed because of the shortage of allografts of suitable size for pediatric use. However, the outcome of size-reduced pulmonary allografts for pulmonary conduits is unknown. In the present study, cryopreserved pulmonary allografts harvested from adults at the time of kidney donation were size-reduced and used in 4 children, 2 with pulmonary atresia and ventricular septal defect and 2 with atrioventricular discordance, pulmonary atresia and ventricular septal defect. They all had undergone right and/or left modified Blalock-Taussig shunt operations with a 5-mm synthetic graft prior to the reparative operations. They underwent definitive repair with a size-reduced cryopreserved pulmonary allograft valved conduit and were followed up for 2-5 years. Postoperative echocardiographic and cineangiographic assessments revealed excellent function of the pulmonary bicuspidalized valves with a minimal pressure gradient and no, or only trivial, regurgitation. Although the long-term result of a cryopreserved bicuspid pulmonary valved conduit remains unknown, the remodeled bicuspid pulmonary allograft conduits showed excellent hemodynamic characteristics in mid-term follow-up and appear to be a reasonable alternative to other types of conduits when an appropriate-sized allograft is not available.

Founder's Award, 25th Annual Meeting of the Society for Biomaterials, perspectives. Providence, RI, April 28-May 2, 1999. Tissue heart valves: current challenges and future research perspectives

Substitute heart valves composed of human or animal tissues have been used since the early 1960s, when aortic valves obtained fresh from human cadavers were transplanted to other individuals as allografts. Today, tissue valves are used in 40% or more of valve replacements worldwide, predominantly as stented porcine aortic valves (PAV) and bovine pericardial valves (BPV) preserved by glutaraldehyde (GLUT) (collectively termed bioprostheses). The principal disadvantage of tissue valves is progressive calcific and noncalcific deterioration, limiting durability. Native heart valves (typified by the aortic valve) are cellular and layered, with regional specializations of the extracellular matrix (ECM). These elements facilitate marked repetitive changes in shape and dimension throughout the cardiac cycle, effective stress transfer to the adjacent aortic wall, and ongoing repair of injury incurred during normal function. Although GLUT bioprostheses mimic natural aortic valve structure (a) their cells are nonviable and thereby incapable of normal turnover or remodeling ECM proteins; (b) their cuspal microstructure is locked into a configuration which is at best characteristic of one phase of the cardiac cycle (usually diastole); and (c) their mechanical properties are markedly different from those of natural aortic valve cusps. Consequently, tissue valves suffer a high rate of progressive and age-dependent structural valve deterioration resulting in stenosis or regurgitation (>50% of PAV overall fail within 10-15 years; the failure rate is nearly 100% in 5 years in those <35 years old but only 10% in 10 years in those >65). Two distinct processes-intrinsic calcification and noncalcific degradation of the ECM-account for structural valve deterioration. Calcification is a direct consequence of the inability of the nonviable cells of the GLUT-preserved tissue to maintain normally low intracellular calcium. Consequently, nucleation of calcium-phosphate crystals occurs at the phospholipid-rich membranes and their remnants. Collagen and elastin also calcify. Tissue valve mineralization has complex host, implant, and mechanical determinants. Noncalcific degradation in the absence of physiological repair mechanisms of the valvular structural matrix is increasingly being appreciated as a critical yet independent mechanism of valve deterioration. These degradation mechanisms are largely rationalized on the basis of the changes to natural valves when they are fabricated into a tissue valve (mentioned above), and the subsequent interactions with the physiologic environment that are induced following implantation. The "Holy Grail" is a nonobstructive, nonthrombogenic tissue valve which will last the lifetime of the patient (and potentially grow in maturing recipients). There is considerable activity in basic research, industrial development, and clinical investigation to improve tissue valves. Particularly exciting in concept, yet early in practice is tissue engineering, a technique in which an anatomically appropriate construct containing cells seeded on a resorbable scaffold is fabricated in vitro, then implanted. Remodeling in vivo, stimulated and guided by appropriate biological signals incorporated into the construct, is intended to recapitulate normal functional architecture.

A size-matching heterotopic aortic valve implantation model in the rat

BACKGROUND

Structural failure of cardiac valve allografts may be related to technical factors such as size mismatch, resulting in early intimal proliferation and fibrosis or immunological reactions against the transplanted valves, featuring lymphocytic infiltration.

OBJECTIVE

To develop a heterotopic aortic valve implantation model in the rat to study the immunological factors leading to graft failure in the setting of a technical adaptation for size mismatch.

METHODS

Syngeneic (WAG-WAG or DA-DA) and allogeneic (WAG-BN or WAG-DA) rat strain combinations were used to study the effect of the allogeneic response on valve properties. An end-to-side anastomosis was made between the U-shaped aortic root graft and the recipient's abdominal aorta to resolve the problems of size matching.

RESULTS

No animals suffered from ischemic or neurological complications during the study period. One hundred percent survival and patency of the aortic grafts were achieved at the end of a 21-day observation period. In the syngeneic group 9 of 10 valves were still competent when assessed during retrograde injection. In contrast, 2 of 10 allogeneic valve grafts were competent on postoperative Day 21. Microscopic evaluation revealed no fibrosis or intimal thickening in the syngeneic valve grafts while the allogeneic valve grafts demonstrated rejection-like morphology.

CONCLUSION

The absence of fibrosis and intimal thickening in the syngeneic transplanted valve grafts indicates that this implantation model is not influenced by nonimmunological-based structural changes. Therefore, this new model enables us to study the association between donor-directed immune responses and allograft degeneration in a technically unbiased manner.

Cryopreserved aortic allografts for aortic root reconstruction: a single institution's experience

BACKGROUND

An evaluation of early and long-term results of aortic root replacement with cryopreserved aortic allografts and echocardiographic follow-up of allograft valve function was performed.

METHODS

From September 1989 through May 1998, 132 patients aged 17 to 77 years (mean, 50.8 +/- 14.8 years) underwent freestanding aortic root replacement with a cryopreserved aortic allograft. Eighty-six (65.1%) patients had New York Heart Association class III or IV functional status before operation, and 27 (20.5%) patients underwent emergency operation. Fifty-nine (44.7%) patients had undergone previous cardiac operations. The cause of aortic disease was acute endocarditis in 63 (47.7%) patients, healed endocarditis in 15 (11.3%), degenerative in 20 (15.2%), congenital in 20 (15.2%), failed prosthesis in 10 (7.6%) and rheumatic in 4 (3.0%). Follow-up was complete, with a mean of 42 months.

RESULTS

There were 12 hospital deaths (9.1%; 70% confidence limits [CL], 6.6% and 11.6%); 9 of them were operated on for active endocarditis (p = 0.062). Multivariate analysis determined age older than 65 years (p = 0.012) and emergency operation (p = 0.009) as independent risk factors for hospital mortality. During follow-up, 6 (5.0%; 70% CL, 3.0% and 7.0%) patients died. Cumulative survival rate for the entire group was 81.8% +/- 5.4% at 8 years. Freedom from reoperation for structural valve failure was 100%, freedom from reoperation for any cause was 96.3% +/- 1.8% at 8 years. Freedom from endocarditis at 8 years was 97.9% +/- 1.4%. Follow-up of allograft valve function showed no or trivial aortic regurgitation in 97% of patients and absence of stenosis of the allograft in 100%.

CONCLUSIONS

Aortic root replacement with cryopreserved aortic allografts can be performed with acceptable hospital mortality and long-term results. The durability of cryopreserved aortic allografts is good, and reoperation for structural valve failure is absent at 8 years.

Comparison of healing in fresh and preserved arterial allografts in the dog

The use of aortic allografts for the management of vascular prosthetic infections has recently been reintroduced. Impressive results have been obtained; however, the possibility of late degeneration remains a major concern. The healing behavior of aortic allografts, either fresh or preserved, in antibiotic-supplemented nutrient medium at 4 degrees C for 1 week and used as thoracic aorta substitutes in dogs was investigated after 6 months of implantation. Four dogs received a fresh aortic allograft from four different donors, and four dogs received a preserved allograft from two different donors. Autografts in two dogs were performed as controls. The in vivo investigation was conducted to describe (1) the histological characteristics of the arterial wall, (2) the macroscopic and thrombogenic aspect of the luminal surface, (3) the integrity of the endothelial lining by scanning electron microscopy, and (4) its biochemical function by prostacyclin (PGI2) and thromboxane A2 (TXA2) secretion. Immune-mediated reactions directed toward the grafts were measured by sequential screening of donor-specific serum antibody development. All donor-recipient pairs of dogs were major histocompatibility complex (MHC)-incompatible according to a mixed lymphocyte reaction (MLR) assay. From the results of this study we concluded that although preserved arterial allografts exhibited similar surface characteristics as those of fresh allografts in terms of re-endothelialization and long-term graft function, an elicited immune response, a degenerative process in the media, and a hyperplasic reaction in the intima could not be prevented using this method of preservation.

The effect of sizing on the in vitro hydrodynamic characteristics and leaflet motion of the Toronto SPV stentless valve

OBJECTIVES

We established an in vitro model to investigate the effects of valve sizing on the hemodynamic characteristics and leaflet motion of the Toronto SPV valve (St Jude Medical, Inc, St Paul, Minn).

METHODS

Nine valves were first implanted in fresh porcine aortic roots and then retested in glutaraldehyde-treated porcine aortic roots. Three valves were 1- to 2-mm oversized, 3 were 1- to 2-mm undersized, and there were 3 size-for-size implantations. The elasticities of the aortic roots and the composite roots were measured in the pressure range between 0 and 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and regurgitation were measured and the effective orifice area and performance index were calculated for each root. Leaflet motion was recorded on videotape.

RESULTS

The external diameter of the fresh root increased by 35% as the hydrostatic pressure rose from 0 to 120 mm Hg, as compared with 11% for the glutaraldehyde-treated root. Valve implantation in the fresh root reduced the distensibility to 22% but did not change distensibility in the glutaraldehyde-treated root. The effective orifice area was dependent on the valve size, with the transvalvular gradient decreasing as the valve size increased. For the same size of valve the hydrodynamic parameters were slightly better if the valve was undersized by 1 mm. A significant difference in favor of the undersized valves was found in open-leaflet bending deformation.

CONCLUSION

Leaflet motion of the stentless porcine aortic valve in vitro is improved if the valve is slightly undersized, and this may be beneficial to the long-term durability of the prosthesis.

Primary aortic valve replacement with allografts over twenty-five years: valve-related and procedure-related determinants of outcome

OBJECTIVES

Allografts offer many advantages over prosthetic valves, but allograft durability varies considerably.

METHODS

From 1969 through 1993, 618 patients aged 15 to 84 years underwent their first aortic valve replacement with an aortic allograft. Concomitant surgery included aortic root tailoring (n = 58), replacement or tailoring of the ascending aorta (n = 56), and coronary artery bypass grafting (n = 87). Allograft implantation was done by means of a "freehand" subcoronary technique (n = 551) or total root replacement (n = 67). The allografts were antibiotic sterilized (n = 479), cryopreserved (n = 12), or viable (unprocessed, harvested from brain-dead multiorgan donors or heart transplant recipients, n = 127). Maximum follow-up was 27.1 years.

RESULTS

Thirty-day mortality was 5.0%, and crude survival was 67% and 35% at 10 and 20 years. Ten- and 20-year rates of freedom from complications were as follows: endocarditis, 93% and 89%; primary tissue failure, 62% and 18%; and redo aortic valve replacement, 81% and 35%. Multivariable Cox analyses identified several valve- and procedure-related determinants: rising allograft donor age and antibiotic-sterilized allograft for mortality; donor more than 10 years older than patient for endocarditis; rising donor age minus patient age, rising implantation time (from harvest to aortic valve replacement), and donor age more than 65 years for tissue failure; and rising donor age minus patient age, young patient age, rising implantation time, and subcoronary implantation preceded by aortic root tailoring for redo aortic valve replacement. Estimated 10- and 20-year rates of freedom from tissue failure for a 70-year-old patient with a viable valve from a 30-year-old donor and no other risk factors were 91% and 64%; the figures were 71% and 20% if the donor age was 65 years. The rates of freedom from tissue failure for a 30-year-old patient with a 30-year-old donor were 82% and 39%; the figures were 49% and 3% with a 65-year-old donor. Beneficial influences of a viable valve were largely covered by short harvest time (no delay for allografts from brain dead organ donors or heart transplant recipients) and short implantation time.

CONCLUSIONS

Primary allograft aortic valve replacement can give acceptable results for up to 25 years. The late results can be improved by the use of a viable allograft, by matching patient and donor age, and by more liberal use of free root replacement with re-implantation of the coronary arteries rather than tailoring the root to accommodate a subcoronary implantation.

Endothelial prostacyclin (PGI-2) production of human and porcine valve allografts related to ischemic history

BACKGROUND

The significance of cellular viability in human valve allografts for functional clinical longevity continues to be debated. Meaningful tests for this biological entity are therefore in demand to quantify the relative merits of graft origin and procurement techniques. The valve leaflet endothelium is recognized as a particularly sensitive target to noxes and its continued ability to produce prostacyclin (PGI-2) after explantation has been suggested as indicating viability.

OBJECTIVE

Graft ischemic history and species differences were therefore studied in human and porcine valve leaflets by the measurement of endothelial prostacyclin production, post-explantational, basal and after stimulation with bradykinin.

METHODS

Four groups of aortic valve donors were established. Fresh human heart-beating donors (h-HBD), cadaveric human donors (h-NHBD) processed within 24 h, fresh porcine donors (p-HBD) and cadaveric porcine donors (p-NHBD) also processed within 24 h. Leaflets were separately incubated at 37 degrees C for successive periods of 30 min up to 5 h in Earle's Medium 199. After 240 min PGI-2 production was stimulated by 10 microM bradykinin. Postincubational release was stopped with indomethacin 10 microg/ml. Prostacyclin production was measured as 6-kPGF1a using an ELISA.

RESULTS

Initial PGI-2 production is significantly higher in porcine than in human grafts and in both species enhanced by previous warm ischemia. While baseline species differences disappear during progressive incubation, differences resulting from graft history are maintained. After PGI-2 stimulation species differences dominate again while ischemic history has no effect.

CONCLUSION

Ischemia and surgical manipulation are stimulators of endothelial PGI-2 production in both human and porcine allografts and, therefore, a correlation of this metabolic activity with cellular integrity may be misleading. Valid data are obtained only if the natural time-course and reaction to stimulation of PGI-2 production are duely recognized and species differences in the response to mechanical and ischemic stress are considered.

Aortic allograft implantation techniques: pathomorphology and regurgitant jet patterns by Doppler echocardiographic studies

BACKGROUND

The diagnosis of allograft-specific pathology by echocardiography has important consequences for patient counseling and research. This study describes the pathomorphologic findings and color Doppler jet patterns in a consecutive series of patients after allograft placement with either the subcoronary implantation or root replacement technique.

METHODS

From 1987 to July 1996, the subcoronary allograft implantation technique and root replacement technique were used in 82 patients and 70 patients, respectively. These patients comprised the study group.

RESULTS

The incidence of paravalvular leaks and eccentric regurgitant jets was higher with subcoronary implantation (41%) than with root replacement (11%). Patients with a subcoronary implanted allograft had a higher incidence of eccentric jets.

CONCLUSIONS

These findings support the concept of preservation of valve geometry after root replacement, as allograft-specific pathomorphologic abnormalities and eccentric jets are more common after subcoronary implantation of allografts. Learning effects, however, cannot be excluded as the cause of these abnormalities.

Role of intraoperative transesophageal echocardiography in determining aortic annulus diameter in homograft insertion

The sizing of aortic valve (AV) homografts for optimum function requires an accurate measurement of the aortic annulus. Typically, this measurement is obtained directly with sizers in the open aorta. We describe the use of intraoperative transesophageal echocardiography (IOTEE) to measure the aortic annulus and select the appropriate AV homograft before cardiopulmonary bypass and aortic cross-clamping. Thirty-two patients underwent AV homograft insertion between March 1993 and March 1996 and had IOTEE. There were 13 women and 19 men. Mean age was 58 +/- 14 years. IOTEE measurements were satisfactory in sizing in all patients, and no extraordinary surgical measures were necessary to insert the AV homografts. Early postoperative follow-up showed trivial or mild regurgitation of all homografts. Prebypass IOTEE is reliable in guiding the selection of optimal AV homografts.

Mid-term results of the Ross procedure

METHODS

Fifty patients underwent a Ross operation between June 1991 and October 1996. Preoperative diagnosis was: congenital aortic valve disease (31 patients), complex left ventricular outflow tract (LVOT) obstruction (11 patients), outgrowth of a small aortic valve prosthesis (five patients) and valve endocarditis (three patients). Half of the interventions were reoperations. All operations were root replacements. A pulmonary homograft was used in 45 patients. An aorticoventriculoplasty was combined with the root replacement in the 16 patients with LVOT obstruction and a too small aortic valve prosthesis. An enlargement or reduction plasty of the ascending aorta was necessary in seven patients.

RESULTS

The mean age was 20.9 years (range: 2.5-54 years). The mean follow up was 34.2 +/- 21 months and was 94% complete. Two patients died after 8 days (low cardiac output due to myocardial fibrosis) and 17.4 months (sudden death), respectively, resulting in a survival of 95 +/- 4% at 4 years. Those two deaths occurred in the group of patients undergoing Ross procedure and aorticoventriculoplasty. Two autografts were replaced after respectively 2 days (technical failure) and 44 months (progressive root dilatation) resulting in a reoperation-free incidence of 93 +/- 6% at 4 years. Other postoperative major complications occurred in six patients. All survivors had regular echo-Doppler examination. All autografts except one had a systolic gradient below 10 mmHg at the last examination. Thirty-four autografts had no leak, ten showed grade 1-2 regurgitation. Two patients showed a higher than grade 3 regurgitation: one leak remains stable with normal left ventricular dimensions and function, one autograft was replaced by a mechanical valve.

CONCLUSION

This experience demonstrates that the medium-term results of the Ross procedure are excellent even in complex LVOT obstructions.

Factors affecting the yield of cardiac valve allografts from living unrelated donors

OBJECTIVE

Allografts are the valve of choice for fertile women, patients with infective endocarditis and those with small aortic roots. However, the supply of valves is problematic and widespread usage is restricted by limited availability. Allograft valves are available from cadaveric donors and from the explanted hearts of transplant recipients. Potentially, hearts from these patients could be an excellent source of usable aortic and pulmonary valves. However, little information is available on the suitability of such donors, the procurement rate of allograft valves from this source, or the factors that limit the yield of implantable valves from explanted hearts.

METHOD

In order to examine some of these issues, we have carried out a retrospective study on the explanted hearts offered to the East Anglian Tissue Bank by Papworth hospital. Papworth hospital carries out approximately 90 heart and heart/lung transplants per year. Over a 2 year period, the tissue bank was offered 72 hearts from this programme.

RESULTS

Of the 72 hearts offered, 58 were accepted for subsequent dissection and further examination. A total of 14 hearts were refused. The main reasons for refusal were extensive cardiectomy trauma (4 hearts) and abnormal valve morphology (four hearts). Of the 116 valves from those hearts accepted for dissection, 55 valves were rejected upon further examination. Reasons for rejection included: cardiectomy trauma (26 valves), abnormal morphology (22 valves), procurement/dissection trauma (7 valves). Of the 61 valves banked, four were subsequently rejected due to positive or incomplete microbiology. Procurement trauma fell to 0% in the last 12 months of the study but cardiectomy trauma remained constant and was related to previous cardiac surgery. Overall, the yield of implantable valves was 0.8 valves/donor. However, the yield showed considerable variation, from 1.0 valves/donor for donors diagnosed as cardiomyopathy to 0.5 valves/donor for donors with ischaemic heart disease who had undergone previous cardiac surgery.

CONCLUSION

It is possible to predict the likely yield of explanted heart valves from different groups of heart transplant recipients, based on diagnosis and previous history. The yield of usable valves could be increased by avoidance of injury, both during cardiectomy and subsequent removal of the valves; this is achievable through appropriate training.

Metabolic detriment in donor heart valves induced by ischemia and cryopreservation

BACKGROUND

The injury resulting from postmortem ischemia is a critical deterrent to the availability of donor valves. Using the reduction of XTT-tetrazolium salt as a marker of metabolic sequelae, we assessed the injurious effect of ischemia and the metabolic sequelae in 156 porcine semilunar leaflets.

METHODS

The leaflets were randomly allocated to noncryoprocessed (n = 72) or cryoprocessed (n = 72) groups. At each preservation temperature of 4 degrees C, 24 degrees C, or 37 degrees C, 24 leaflets each were exposed to one of four storage periods of 9, 17, 30, or 60 hours. Twelve fresh aortic leaflets served as baseline reference samples.

RESULTS

There was a progressive loss in the metabolic functioning of valve leaflet cells in both noncryopreserved and cryopreserved tissue as the storage times increased. Cryopreserved tissue showed a greater loss of function than noncryopreserved tissue did. The metabolic injury was mainly a consequence of cryoprocessing. The greatest loss in metabolic functioning occurred in the valves stored for 60 hours. The least favorable combination of variables was cryopreservation and a precryopreservation storage time of 60 hours.

CONCLUSIONS

We conclude that 30- to 60-hour delays do not have a significant metabolic effect on cardiac leaflets. Thus it may be possible to safely extend the permissible ischemic periods after organ harvest.

Identification of host and donor cells in porcine homograft heart valve explants by fluorescence in situ hybridization

The pathogenesis of the primary tissue degeneration that limits the life-span of aortic and pulmonary homografts has still not been revealed. Histopathological studies on homograft explants have not given definitive insight into the eventual fate of donor cells, nor have they demonstrated the assumed importance of host cell ingrowth into the graft tissue. In this experimental study, fluorescence in situ hybridization (FISH) is introduced as a new approach to examine the distribution of host and donor cells in homograft explants. Aortic valve replacement was performed with a cryopreserved porcine aortic homograft in three pigs; donor and recipient were of opposite sex. After 4 months, the grafts were explanted and examined by FISH using a biotinylated porcine Y-chromosome-specific library probe. Following probe detection with FITC-conjugated avidin, a clear distinction could be made between cells of host and donor origin without distorting the histological integrity of the explants. There was ingrowth of donor cells into the graft aortic wall and into the valve leaflet, to some extent. In all explants, remaining donor cells were present, though decreased in number. The introduction of FISH in homograft heart valve research provides a powerful tool to study the fate of recipient and donor cellular elements in situ, and may therefore contribute to a better understanding of the histopathological processes that take place in transplanted homograft valves.

A new model for heterotopic aortic valve transplantation

A new model for heterotopic aortic valve transplantation in the rat is described. A composite allograft with an intact aortic valve and partial mitral valve was harvested from 4-month-old (400-450 g) Long-Evans rats and grafted heterotopically into the abdominal aorta of 4-week-old (80-100 g) rats with an optimal size match. At the end of a 1-month observation period, all experimental animals were alive and all showed 100% patency of the aortic valve allografts on microscopic evaluation after death (n=40). Unlike previously used methods, the proposed model allows for the preservation of all three aortic valve cusps and a more remote placement of the anastomotic suture line from the aortic valve annulus. The use of younger recipient rats improves size match and amplifies allograft calcification. The purpose of this study was to provide an animal model to evaluate modalities of preservation and chemical treatment for aortic valves used as allografts or bioprosthesis.

Prediction of Homograft Aortic Valve Size by Transthoracic and Transesophageal Two-Dimensional Echocardiography

To avoid the problem of patient valve mismatch we assessed the reliability of echocardiographic measurements in selecting an appropriate-sized homograft aortic valve. Preoperative transthoracic echocardiography (TTE) was performed in 26 consecutive patients undergoing aortic valve replacement with a cryopreserved human homograft; 19 of the patients also had intraoperative transesophageal echocardiography (TTE). The diameters of left ventricular outflow tract (LVOT), aortic annulus, sinuses of Valsalva, and ascending aorta were measured by the same technique in all patients. There was a strong correlation between LVOT diameter measured by intraoperative TEE and homograft aortic valve size selected by the surgeon (r = 0.91, P < 0.001). A good correlation was also found between LVOT measured by preoperative TTE and the homograft valve size (r = 0.82, P = 0.001). The correlation between the homograft aortic valve size and the diameter of aortic annulus was less optimal; the correlation was poor for the diameter of aorta measured at the level of the sinuses of Valsalva and ascending aorta. Measurement of the LVOT diameter by intraoperative TEE and preoperative TTE is reliable and clinically useful for the preparation of homograft aortic valves and selection of proper size, particularly in those patients undergoing repeat aortic valve replacement, with heavily calcified aortic valve or with ascending aortic aneurysm.

Pulmonary autograft implantation in the dilated aortic annulus

The application of the pulmonary autograft (Ross) procedure in the treatment of dilated aortic annulus is still controversial, because technical errors of implantation are more likely to occur as the host annular diameter increases. The Ross procedure was successfully employed in a 28-year-old woman with a dilated aortic annulus after simple annular plication. The annulus was plicated beneath the three commissures where the pulmonary autograft was subsequently attached. The diameter of the annulus was reduced from 32 to 26 mm. This technique may provide a number of advantages compared with aortic valve replacement, especially for women of child-bearing age.

Accuracy of transesophageal echocardiography in preoperative determination of aortic anulus size during valve replacement

This prospective, blinded study evaluated the accuracy of transesophageal (TEE) and transthoracic echocardiography in predicting the size of the surgical aortic valve anulus in 20 consecutive patients undergoing aortic valve replacement. TEE was highly accurate in predicting surgical aortic valve anulus size (r = 0.98; p < 0.00001). The standard error of the TEE estimate of the size of the obturator anulus was only 0.04 mm, and in all cases the TEE estimate was within 1 mm of the direct surgical measurement. Both biplane and multiplane TEE probes were equally accurate and this accuracy was maintained over a wide range of sizes of surgical aortic anulus. Transthoracic echocardiography appeared less accurate in predicting anulus size (r = 0.64; p < 0.08). Therefore TEE can be used routinely for selection and preparation of aortic allografts before sternotomy, potentially reducing cardiopulmonary bypass pump time by 10 to 30 minutes and ensuring optimal size matching of the donor-recipient anulus.

A new experimental model for simultaneous evaluation of aortic and pulmonary allograft performance in a composite graft

A model was developed in pigs for simultaneous evaluation of aortic and pulmonary allograft performance in a composite graft. The composite graft consisted of vascular prosthesis and aortic and pulmonary allografts. Following antibiotic preservation, it was anastomosed to the recipient's thoracic descending aorta by an extrapleural approach without using cardiopulmonary bypass. Aortic blood flow was completely diverted into the composite graft. All 12 recipient pigs recovered well, 4 of which were assigned for the initial study to design the suitable experimental schedule. Calcification readily occurred in the aortic allografts and aneurysmal dilatation without calcification developed in the pulmonary allografts. These morphological findings were consistent with those of previous reports. This model has several benefits. First, aortic and pulmonary allograft conduits can be implanted and evaluated simultaneously under the same conditions by making a composite graft. Second, the magnitude of the operation is minimum, and postoperative circulatory and respiratory management is uncomplicated. Third, wound infection rarely occurs, because the skin incision is made on the back. These preliminary studies suggest that this model will allow future study concerning aortic and pulmonary allograft conduits under different conditions.