The use of “fresh” unstented homograft valves for replacement of the aortic valve

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.

Preimplantation alteration of adenine nucleotides in cryopreserved heart valves

To assess the initial metabolic phase of cellular injury from cardiac valve processing, high-energy phosphate concentrations were analyzed in valve leaflets subsequent to critical processing steps. Using a porcine model, valves were processed in a manner identical to human homografts, with 58 randomly assigned to five groups representing distinct preparation phases. Group I (controls) sustained 40 minutes of warm ischemia concluded by liquid nitrogen immersion. Remaining groups similarly endured 40 minutes of ischemia, but were subsequently prepared according to stepwise design: II, warm ischemia + 24 hours of 4 degrees C ischemia; III, warm ischemia + 24 hours of 4 degrees C antibiotic disinfection; IV, warm ischemia + 24 hours at 4 degrees C (without antibiotics) + cryopreservation (-1 degrees C/min cryoprotected freezing); and V, warm ischemia+disinfection+cryopreservation. At each regimen's conclusion leaflet extracts were assayed by high-performance liquid chromatography for high-energy adenine nucleotides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate) and catabolites. A 47% and 86% decrease in cellular adenosine triphosphate level was observed in group III and group V leaflets, respectively. The level of total adenine nucleotides was maintained up to cryopreservation; thereafter a 74% decrease was noted. Catabolite analysis confirmed incomplete degradation of adenine nucleotides indicating cellular metabolic resilience throughout standard homograft preparation in valves previously exposed to 40 minutes of warm ischemia.

High energy phosphate depletion in leaflet matrix cells during processing of cryopreserved cardiac valves

Preimplantation preparation of cardiac valves includes three major steps: (1) harvesting with accompanying ischemia (warm time from cessation of donor heart beat), (2) antibiotic disinfection, and (3) controlled-rate cryopreservation. To define the interdependent injury effects of these manipulations on leaflet matrix cells and specifically the potential for prolonged harvest-related ischemia to predispose greater injury by the subsequent steps, 96 semilunar valves were harvested from pigs in a manner analogous to human heart valve retrievals and randomly allocated to study groups as follows: 48 control valves were exposed to increasing harvested-related ischemic times, (2, 6, 12, 24 hr) and immersed in liquid nitrogen to arrest metabolic activity (i.e., prior to cryopreservation) and conclude the ischemia; another 48 were similarly harvested, subjected to identical ischemic times, then disinfected in 4 degrees C RPMI medium with standard antibiotics for 24 hr and dimethylsulfoxide cryopreserved at -1 degrees C/min to -170 degrees C (i.e., formal cryopreservation protocol). At thawing, each valve was extracted in 12% trichloroacetic acid and assayed by high performance liquid chromatography for components of the adenine nucleotide pool including ATP, lower energy nucleotides (total adenine nucleotides, [TAN] = [ATP] + [ADP] + [AMP]), adenosine, and the diffusible purines. Results are reported as nanomoles metabolite/milligram of leaflet cell protein (Lowry) and reflect a maintenance of total high energy phosphates in the control groups (5.41 +/- 0.29 nmole TAN at 2 hr; 8.34 +/- 0.67 nmole TAN at 24 hr), which fell significantly in all cryopreserved groups (1.27 +/- 0.33 nmole TAN at 2 hr; 0.34 +/- 0.22 nmole TAN at 24 hr).(ABSTRACT TRUNCATED AT 250 WORDS)

Freehand homograft aortic valve replacement--the learning curve: a technical analysis of the first 31 patients

The technique for implanting the homograft aortic valve is significantly more complex than that of either the bioprosthetic or mechanical valve. During development of the procedure, errors of technique were committed; a critical analysis of the learning experience is presented. In the initial 31 patients, the following problems were encountered: mitral stenosis secondary to inadequate debulking of the homograft (1 patient), prolapse of a single homograft leaflet necessitating valve replacement three days later (1 patient), incorrect homograft orientation with torsion in a calcified aorta necessitating subsequent replacement (1 patient), and aortic sinus perforation (thawing injury) (1 patient). In addition, another 4 patients had diastolic murmurs thought to be secondary to inadequate tension setting of the homograft commissural posts. From this experience, several important technical considerations for homograft replacement of the aortic valve were noted: use of interrupted subannular sutures; careful inspection for aortic perforation (thawing); extensive trimming of the homograft septum and mitral remnant; orientation of the homograft to the recipient aorta to obtain the best commissural and sinus alignment; selection of another type of valve if the size of the recipient annulus is greater than 27 mm; retention of the homograft sinus, which orients to the recipient non-coronary sinus (for a calcified aorta); and exaggerated tension on the homograft commissural posts before initiation of the second suture line. There has been 1 hospital death and no late deaths. Adherence to rigid principles of technique has resulted in no further valve replacements and no incidences of valvular leakage at early or late follow-up.

Homograft replacement of single aortic valve cusps: 22 years follow-up

Single aortic valve cusp replacement with fresh aortic homografts were performed in four patients from November 1966 to April 1970. All had preoperative aortic insufficiency due to destruction of a single cusp, with the remaining two cusps structurally and functionally intact. Replacement was performed using the noncoronary cusp from fresh aortic valve homografts. Patient one had homograft cusp replacement of the left coronary cusp at age 13 due to bacterial endocarditis. She recently underwent mitral valve replacement; study and inspection of the aortic valve showed it to be structurally and functionally intact 22 years following homograft cusp replacement. Patient two sustained a gunshot wound perforating his right coronary cusp. He underwent single cusp replacement in January 1967. Currently, he is asymptomatic and has been without evidence of significant aortic valve dysfunction for the past 21 years. Patient three had destruction of the noncoronary cusp due to endocarditis and had homograft cusp replacement in October 1967. Four and a half years later he developed recurrent endocarditis, presented with severe congestive heart failure due to aortic insufficiency, and died. Patient four had bacterial endocarditis affecting the right coronary cusp and had replacement in April 1970. In February 1980, he underwent aortic valve replacement for aortic stenosis. Inspection revealed calcification of the other two cusps with the homograft cusp structurally normal. In summary, follow-up of homograft replacement of single aortic valve cusps from 4 1/2 to 22 years, shows it to be a durable and feasible alternative to prosthetic valve replacement.

The Ross operation: the autologous pulmonary valve in the aortic position

Aortic valve replacement (AVR) with a pulmonary valve autograft (PVA) was first reported by Donald N. Ross (DNR) in 1967. The expectation of this procedure was to avoid degenerative changes seen in other biological tissue valves such as calcification, attenuation, and rupture of the leaflets. Recent reports by the original investigator's group have confirmed the lack of degenerative changes in PVA. To corroborate their conclusions, the fate of 12 patients undergoing AVR with PVA by one of us (LGL) has been ascertained. From March 1969 to June 1971, 12 patients underwent AVR with PVA. The right ventricular outflow tract (RVOT) was reconstructed with an aortic homograft valved conduit. The mean age was 42.7 years (range 21 to 52 years). The mean follow-up for 11 hospital survivors is 12.4 years. Three PVA have been replaced; one following infective endocarditis at 13 years, and two at 15 and 73 months due to technical malalignment. There was no evidence of PVA degeneration during histological examination of these explanted PVAs. Six patients are alive and retain the original PVA at 12 years (55%). This analysis corroborates the conclusions of the DNR report and strongly suggests an immunological mechanism in the process of calcification of other biological tissue valves. The Ross operation is advocated for AVR in young patients as valve durability is of paramount importance especially in this group.

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

A series of 252 isolated aortic homograft valves in 248 patients have been followed for 9 to 16.5 years (mean 10.8). The valves were sterilized in antibiotic solution and stored in a nutrient medium at 4 degrees C and were nonvital. There were 15 in-hospital deaths (6%) and a mortality of 2.7% in patients undergoing an elective first operation. Actuarial survival with the study valve in situ was 57% at 10 years and 38% at 14 years. Only 8.4% of the patients died late from homograft valve failure, chiefly because of failure to refer patients with endocarditis for reoperation or because reoperation was refused in elderly, frail subjects. Incompetence was the sole cause of valve failure and was due either to valve wear or endocarditis. Significant incompetence required reoperation. On actuarial analysis, freedom from significant incompetence for the entire group was 95% at 5 years, 78% at 10 years, and 42% at 14 years. Factors increasing the risk of significant incompetence due to valve wear on multivariate analysis were increasing donor valve age (greater than or equal to 55 years), recipient age (less than 15 years), and an aortic root diameter over 30 mm. Analysis of the patient group that excluded each of these variables (low-risk group), which comprised 61% of the study population, indicated freedom from significant incompetence due to valve wear of 98% at 5 years, 94% at 9 years, and 56% at 13 years.

Extended aortic root replacement for treatment of left ventricular outflow tract obstruction

Recurrent tunnel stenosis of the left ventricular outflow tract following operation for subaortic stenosis and hypoplastic aortic annulus remain a challenge for pediatric cardiac surgeons. We have recently applied a new technique of extended aortic root replacement using an aortic allograft to treat three patients who had previously been operated upon for subaortic stenosis and three who had aortic stenosis with a hypoplastic aortic annulus. This new procedure combines the concept of aortoventriculoplasty with allograft aortic root replacement and coronary artery reimplantation. The valved aortic homograft is used in place of an aortic valve prosthesis and the attached anterior mitral leaflet augments the interventricular septum to relieve the subvalvular left ventricular outflow tract obstruction. The coronary ostia are then reimplanted into the allograft and distal graft to ascending aorta anastomosis completed. Allograft aortic tissue is then used to patch the right ventricular outflow tract. There have been no operative or late deaths. One patient developed Serratia marcescens mediastinitis but recovered uneventfully after mediastinal drainage. Two cases of transient complete heart block reversed spontaneously. A patient with type II hyperlipidemia developed postpericardiotomy syndrome early, which resolved but then required reoperation at six months for stenosis of the distal anastomosis and left main coronary stenosis, both thought to be complications of his underlying disease. Completely benign convalescence and early follow-up has occurred in the last two patients. This modified technique using aortic allograft was very helpful in treating these difficult problems, and the lack of mortality, limited morbidity, and good function results are encouraging.

Detection of deterioration or infection of homograft and porcine xenograft bioprosthetic valves in mitral and aortic positions by two-dimensional echocardiographic examination

Results of two-dimensional echocardiographic examinations were compared with angiographic, hemodynamic and surgical results in 44 patients with bioprosthetic valves in mitral and aortic positions who were undergoing elective or urgent reinvestigation 24 to 87 months (mean 34) after implantation. In these patients, there were 18 homograft aortic valves in the aortic position, 9 stent-mounted homograft aortic valves in the mitral position, 13 porcine xenograft valves in the mitral position and 12 in the aortic position. Poor cusp support, gross fluttering and prolapse of cusps behind or below the anulus identified aortic insufficiency by two-dimensional echocardiography in six patients with an aortic homograft and four patients were identified with insufficiency of a stent-mounted aortic homograft in the mitral position. Two-dimensional echocardiographic examination revealed mitral stenosis in three patients with a porcine xenograft valve in the mitral position and suggested mitral insufficiency in two others. Bacterial endocarditis on homograft or porcine xenograft valves was associated with easily imaged vegetations by two-dimensional echocardiography in 10 patients. Despite difficulties in imaging valve cusps, and the skill required to obtain good echocardiographic images of bioprosthetic valves, significant valve deterioration or infected prostheses were quite effectively imaged by two-dimensional echocardiography in this study.

Valvular heart disease: a perspective

Valve replacement has been one of the most important advances in the management of patients with valvular heart disease. The 10 and 15 year survival rate after isolated aortic and mitral valve replacement with the Starr-Edwards valve is 56 and 44%, respectively. At 5 and 7 years, survival with the Björk-Shiley, porcine bioprosthesis and the Starr-Edwards valve is similar. Patients operated on during the last 5 to 10 years have a much better survival rate than those operated on in the 1960s; therefore, the 10 and 15 year survival of those operated on recently should improve. All patients with a mechanical prosthesis need long-term anticoagulant therapy with drugs of the coumadin type. Porcine bioprostheses have a low failure rate up to 5 years after valve replacement; after this, valve failure occurs at an increasing rate, but the incidence at 10 and 15 years is not known. Valve replacement usually produces a marked improvement in the symptomatic status of the patient because of improved hemodynamics; ventricular function is improved in selected subsets of patients. The role of long-term vasodilator therapy has not been fully determined. Antibiotic prophylaxis for secondary prevention of rheumatic carditis and for prevention of infective endocarditis is important.

Homograft aortic valve replacement: seven years' experience with antibiotic-treated valves

One hundred and sixty-five patients had their aortic valve replaced with antibiotic-sterilised homograft. In all cases, a two-layered freehand technique of valve implantation was used. Tailoring (narrowing) of the annulus was required in 29 cases, and an aortic root gusset was used to enlarge the non-coronary sinus in 68 cases. There was an early mortality of 1.8% and late mortality of 2.4%. The actuarial survival rate was 95% at a maximum follow-up of seven years. The incidence of valvar regurgitation (early diastolic murmur) was 11.5% up to six months after operation and an additional 7.2% subsequent to this. Overall, it was trivial in 10.3%, mild in 7.8%, and moderate in 0.6%. Most valve regurgitation was non-progressive and actuarial analysis showed 74% regurgitation-free valves at the end of seven years. The age of the donor and the valve storage time showed some relationship to valve deterioration. Special attention has been paid to the control of hypertension to prevent accelerated graft degeneration. The results suggest that this has been successful. Anticoagulant therapy was not used and thromboembolism has not been seen in patients undergoing isolated aortic valve replacement. There was one case of miliary tuberculosis after homograft valve replacement but no pyogenic or fungal endocarditis occurred. No haemolysis, calcification, or valvar stenosis were observed. This series, followed for a maximum of seven years, shows excellent sustained valve performance and a very low incidence of important postoperative regurgitation, with 91.8% of the survivors symptom-free.