Ann Thorac Surg 2005;79:757-766
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
CryoLife-O'Brien Stentless Valve: 10-Year Results of 402 Implants
Mark F. O'Brien, FRACSa,*,
Michael A.H. Gardner, FRACSa,
Bruce Garlick, FRACSa,
Homayoun Jalali, MDa,
Julie A. Gordon, RNa,
Sarah L. Whitehouse, PhDb,
Wendy E. Strugnell, BAppScc,
Richard Slaughter, FRANZCRc
a Department of Cardiac Surgery, Brisbane, Australia
c Department of Medical Imaging, The Prince Charles Hospital and St Andrew's War Memorial Hospital, Brisbane, Australia
b Orthopaedic Research and Statistics Unit, Queensland University of Technology, Brisbane, Australia
Accepted for publication August 23, 2004.
* Address reprint requests to Dr O'Brien, 37/3482 Main Beach Parade, Main Beach Qld 4217, Australia (E-mail: drmfobrien{at}bigpond.com).
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Abstract
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BACKGROUND: This truly stentless porcine valve is composite, without Dacron, and implanted supra-annularly. Ten-year analysis with magnetic resonance imaging is presented.
METHODS: From 1992 to 2002, 402 patients (mean 73.5 years) had aortic valve replacement. Associated procedures were required in 252 patients (63%). Serial echoes provided 1340 studies. Clinical follow-up was 100%. Magnetic resonance imaging focused on aortic annulus extensibility.
RESULTS: The 30-day mortality was 0.99% (4 deaths). Morbidity comprised thromboembolism (40 patients including 18 patients with permanent strokes); endocarditis (9 patients); and reoperation (9 patients [periprosthetic leak, 2; endocarditis, 5; technical needle damage, 1; and structural degeneration, 1]). Of 402 valves more than 10 years, five valves were explanted, one only for structural failure. Except for endocarditis (2 patients), no late deaths (69 patients, 1.5 months to 5.7 years) were valve related. Echocardiography demonstrated low gradients with good orifice areas, excellent ventricular regression (p = 0.0001 preoperative and postoperative comparisons) and late incompetence (mild in 45 patients and moderate in 9 patients). No living patient has severe incompetence. Magnetic resonance imaging demonstrated the annulus ‘expanding and relaxing’ throughout the cardiac cycle, the mean increase in cross-sectional area being 37%, resembling normal aortic root dynamics.
CONCLUSIONS: Elderly patients received this hemodynamically acceptable valve with its simple, supra-annular implantation and satisfactory mid-term morbid-free lifestyle to 10 years maximum follow-up. With only one structural failure, restoration of valve annular extensibility may have a favorable influence on long-term durability.
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Introduction
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| Dr O'Brien discloses that he has a financial relationship with CryoLife, Inc.
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The first clinically implanted porcine aortic valve xenografts in 1965 to 1969 were stentless [1–4], but the introduction of both a stent and glutaraldehyde preservation by Carpentier and colleagues [5] saw their rapid disappearance. Their revival by David and associates [6] in 1987 initiated the appearance of many designs with varying degrees of Dacron cloth support of either the whole porcine valve or partial Dacron support over the right coronary leaflet base, where, in the intact porcine animal, ventricular muscle gave support to this leaflet.
In 1991 the authors returned to the use of a composite trileaflet porcine valve constructed from three size-matched noncoronary leaflets [7] (CryoLife Inc., Atlanta, GA). Originally in 1967 to 1969 this same composite design, but formaldehyde preserved, had been used by us at The Prince Charles Hospital in 129 patients. From this experience [8], the concept of a composite valve, single suture line technique, and supra-annular implantation was established and proven to be reliable. However, the preservation solution proved inadequate. In the early 1970s the reoperation rate was 50% at 5 years. This poor valve durability was unacceptable. With the subsequent well-documented performance of glutaraldehyde preservation of porcine valves, the reintroduction of the composite valve appeared justified in the early 1990s [9].
Previous reports have detailed the clinical performance of this stentless valve [7, 10–12] and the implementation techniques [13–16], which are very different when compared with those of other stentless valves. These details are not repeated except to briefly summarize several very important features. The very small 5-mm to 6-mm cuff of xenograft aortic wall distal to the valve hinge and the absence of a proximal cuff of this composite valve enable a simple, rapid single suture line implantation technique [14]. Because of this small aortic cuff no problems have been encountered with low-lying host coronary ostia. Additional advantages of the supra-annular placement have included good exposure for the small aortic root, provision of an effective central flow and nonobstructive orifice with low transvalvar gradients mimicking those of the homograft valve. The chosen valve size, being one size larger (ie, a 25-mm valve inserted in a 23-mm host annulus), allows for discrepancies of annular and sinotubular diameters.
The difference between supra-annular implantation and annular placement, which is pertinent to the understanding of the hemodynamic performance and of the magnetic resonance imaging (MRI) findings of restoration of annular extensibility, are demonstrated in Figure 1. The residual native annulus becomes subvalvar.
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Fig. 1. Supra-annular implantation (left) maximizes the effective orifice compared to the reduced orifice with the intra-annular implantation (right). With complete valve excision and thorough annular decalcification, the exposed annulus would appear capable of having its ability "to dilate" restored. (LV = left ventricle.)
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The purpose of this report is to update previous clinical appraisals of this valve now that maximum follow-up is more than 10 years. Second, we will emphasize the ease of technical implantation with the low early mortality and mid-term morbidity in an elderly patient population. Finally this report will focus on a novel postulation from MRI studies that the observed restoration of the extensibility of the aortic valve annulus following supra-annular implantation of a truly stentless device may favorably enhance long-term durability.
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Patients and Methods
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From December 30, 1992 to December 4, 2002, 402 patients received the CryoLife-O'Brien model 300 stentless porcine aortic xenograft for aortic valve replacement (AVR). All patients were either contacted by telephone or seen personally by a physician/cardiologist/surgeon; their records were perused from 2002 through June 2003. Although the follow-up was 100% complete and it has now entered its 12th year, this report focuses on the first 10-year analysis. All patient events up to and including the year of 2002 have been included in this analysis. The evaluation of patient progress and the definitions and assessment of morbid events have been conducted strictly in accordance with the Guidelines for Reporting Morbidity and Mortality after Cardiac Valvular Operations [17, 18]. The mean patient age was 73.5 years old (range 55 to 89 years old), males 58%, 73 patients (18.2%) being 80 years or older at the time of operation. Concomitant procedures were required in 252 patients (63%), most of whom (186 = 46%) were coronary artery bypass operations (CABG; 2.4 grafts/patient). Forty-two patients (10.4%) had left ventricular (LV) myomectomy. Although an intraoperative transoesophageal echocardiographic examination was used initially in this series, later on the transthoracic echocardiography performed at the prehospital or preoperative phase became sufficient. Subsequent echocardiographic examinations were conducted postoperatively at 4 to 5 days, at 6 months, at 1 year, and at 1 to 2 years thereafter. Late serial echocardiography included some 1340 studies over the 10 years in order to gain knowledge of the late valve function.
Magnetic Resonance Imaging
As an ongoing study, 10 patients who some years previously had received this stentless valve (range 2 to 11 years old; mean age 6 years old), were imaged to assess the change in the area of the aortic valve annulus throughout the cardiac cycle. MRI was performed on a 1.5 Tesla Signa Twinspeed system (GE Medical Systems, Milwaukee, WI) with a four-element cardiac phased array coil. Steady-state free precession imaging was used to identify the aortic valve annulus, which was seen as an area of low signal intensity beneath the valve (Fig 2). Electrocardiogram (ECG) gated cine phase contrast images with full R-R coverage were then obtained directly through the annulus, orthogonal to the left ventricular outflow tract (Fig 3). Image acquisition using a segmented k-space technique, occurred over approximately 16 cardiac cycles (depending on heart rate) to produce a single cine loop representing one cardiac cycle. Some through-plane motion was apparent because of the fixed imaging plane relative to cardiac motion but, due to the tubular nature of the annulus, this was thought not to introduce significant variation.
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Fig. 2. The aortic valve annulus is seen as an area of low signal intensity beneath the valve on steady-state free precession imaging.
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Fig 3. (A) Phase contrast images are acquired directly through the annulus, orthogonal to the left ventricular outflow tract (white line); (B) resultant magnitude; and (C) phase images of the aortic valve annulus.
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Image analysis was performed on an Advantage Windows workstation using Medis flow analysis software. The mean cross-sectional areas and flow volumes were calculated and plotted (Fig 4) at 30 intervals throughout the cardiac cycle.
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Fig 4. The mean cross-sectional area of the aortic valve annulus (top) and the mean flow volumes (bottom) were calculated at 30 intervals throughout the cardiac cycle and plotted against each point of the cardiac cycle.
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Operative procedures remained essentially standardized throughout the 10 years. These include full median sternotomy, aortic cannulation, intermittent anti- and retrograde crystalloid cardioplegia, CO2 insufflation into the pericardial cavity during cardiopulmonary bypass, LV decompression through superior pulmonary vein cannulation, and distal CABG graft anastimoses before transverse aortotomy. Valve excision was followed by aggressive calcific debridement of the native valve annulus remnant. Although this area remains exposed to the blood stream with supravalvar implantation, care was taken to leave this annulus area reasonably "smooth" without obvious semiloose fragments or spicules of calcium. Measurement of both annular and sinotubular diameter (STD) dictated the selection of valve size (Table 1). With supravalvar implantation, using a single layer continuous 3-0 polypropylene suture, a valve of at least one size larger than the annulus was selected (ie, a 23-mm porcine valve for a 21-mm host annulus). If the STD was 29 mm and the valve annulus only 25 mm, a 29-mm valve would be implanted supra-annularly (ie, two sizes larger than the annulus diameter). Therefore, in assessing the level and importance of any gradient, appropriate analysis of echocardiographic transvalvar gradients demands recording of the host annulus diameter in addition to the larger porcine valve diameter. Table 1 outlines the sizes of the implanted porcine valve and host annulus.
Left ventricular myomectomy was carried out in 42 patients. The indication was made at operation rather than on any preoperative echo study. After native value excision, if the LV myocardium was prominent and the free edge of the anterior mitral valve leaflet was not readily visible through the aortic orifice, then longitudinal/vertical LV myomectomy was performed.
Institutional approval for the clinical use of this valve was obtained from The Prince Charles Hospital (October 14, 1992) and St Andrews Ethics Committee (1994). The Therapeutic Goods Administration of Australia (TGA) was notified according to the Clinical Trial Notification (CTN) category (November 17, 1992). All patients gave informed consent to their receiving this stentless valve.
Statistical Analysis
Outcomes were reported according to the guidelines for reporting valve-related mortality and morbidity [17]. Descriptive statistics were presented as mean ± standard deviation. Actuarial survival was calculated using the Kaplan-Meier method with 95% confidence limits. Data were collated using Microsoft Access (Microsoft Corp, Redmond, WA), and statistical analysis was performed using the SPSS statistical package (SPSS Inc, Chicago, IL).
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Results
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The mean follow-up of the patient cohort was 4.3 years (standard deviation [SD] 2.6 years, range 0 to 10.4 years). All but 4 patients survived (30-day hospital mortality was 0.99%). The early mortality was 0.6% for the 329 patients less than 80 years of age and 2.7% for the 73 patients greater than 80 years old. The four deaths were essentially valve unrelated (retroperitoneal hemorrhage from intraaortic balloon insertion on first day postoperative; aortic dissection from cardioplegic site on second day; ruptured spleen [patient fell out of bed] on third day; and sudden death at home [arrhythmia] on 29th day). Of 398 patients, late mortality has occurred in 69 patients (17.3% ranging from 39 days to 9.6 years after operation). Valve-related deaths have occurred in two unoperated late endocarditis patients, dying of multisystem failure, beyond surgical retrieval. Except for the debatable relationship that embolism has as a tissue-valve–related cause of death, all other reasons for death were readily explained on natural causes in this elderly patient cohort (eg, cancer, cerebrovascular accident, noncardiac induced renal failure, respiratory infections). The actuarial 8-year patient survival is 70.8% ± 7.1% (95% confidence limits [CL]; Fig 5) with thereafter, a less meaningful decline due to reduced patient numbers. Eight of a possible 14 patients who had their operation 11 years ago are still alive.
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Fig 5. Actuarial patient survival expresses the number of patients at risk more than 10 years. The actual number of deaths more than 10 years and the actuarial freedom at 8 years is expressed with 95% confidence limits. (AVR = aortic valve replacement.)
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Table 2 summarizes the morbidity events of thromboembolism (56 episodes in 40 patients), endocarditis [9], paravalvar leaks [6], structural degeneration [1], and reoperation (9 from all causes).
Initially in this series, the first 83 patients were not temporarily warfarin anticoagulated during the initial postoperative weeks. Three patients, all in new early postoperative atrial fibrillation, sustained peripheral embolism (2 patients) or cerebral embolism (1 patient). Following this, all patients were anticoagulated for the first 6 to 12 weeks. Patients having a late thromboembolic event were medicated with warfarin or aspirin; there was no universal policy. Some patients who had a history of preoperative strokes eventually succumbed to late recurrent strokes, although 23 elderly patients had a total of 29 episodes categorized as either transient ischemic attacks (TIA) or reversible ischemic neurologic deficits (RIND). Patients were very closely questioned and a diagnosis made according to the well-established and recognized guidelines [17, 18]. This final subjective conclusion was often considered difficult. The actuarial 8-year freedom from thromboembolism of all types (82.1% ± 6.5%) and of thromboembolism causing permanent disability (90.0% ± 5.4%) are depicted in Figures 6 and 7.
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Fig 7. Actuarial freedom from thromboembolism (all grades of severity) causing a permanent disability (see Table 2). Depiction as in Figure 5.
*includes 1 death from mesenteric artery embolism. (AVR = aortic valve replacement.)
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Other morbid events include nine episodes of endocarditis (9 days to 5 years) over the 10 years of maximum follow-up. There were seven staphylococcal and two streptococcal infections. The event appearance comprised early endocarditis at 9 days in 1 patient and late infection at 5 months to 5 years in the remaining 8 patients. No patient, 5 years after AVR, sustained an infection. The actuarial freedom from the endocarditis was 97.1% ± 2.0% at 8 years (Fig 8). In 5 of 9 patients, the valve did not become dysfunctional, remaining completely competent on serial echocardiography. Of these 5 patients, 2 patients died of septicemia and multiorgan failure and 3 were medically cured of the acute endocarditis. One of the latter 3 patients sustained a ventricular septal defect (VSD) and another an expanding subvalvar abcess cavity as a result of the now sterile infection. Reoperations were performed, the VSD closed and the cavity patched. Both valves remained competent on the last echoes some 2 years after reoperation. Three patients required valve explantation in the acute phase of the endocarditis. One of 3 patients died of continuing septicemia and multiorgan failure after reoperation.
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Fig 8. Actuarial freedom from endocarditis. The nine episodes all occurred within the first 5 years after AVR (see Table 2). Depiction as in Figure 5. (AVR = aortic valve replacement.)
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Paravalvar leaks have not been a problem of recent years. However 2 patients did require reoperation. One patient obviously had too loose a suture and, at reoperation at 10 days, valve repair cured the problem. The other patient at 3 months returned with severe acute incompetence. At reoperation a 4-0 polypropylene suture had broken. A stronger suture along the disrupted segment was sufficient to repair the valve. A successful long-term outcome following both valve repairs has been verified by late echocardiography. Since these episodes, occurring early in this series, a stronger suture has been used (ie, 3-0 polypropylene [No 8936 on a small taper cut half-circle V5 needle; Ethicon, Somerville, NJ]). Four other patients without clinical murmurs of incompetence have presumed minor nonprogressive paravalvar leaks detected echocardiographically.
The actuarial 8-year freedom from reoperation due to all causes was 96.7% ± 2.3% (Fig 9) and the freedom from valve explantation was 97.8% ± 2.1% (Fig 10). Reoperation has been required for 9 patients with the explanting of 5 stentless valves (Table 2). Explantation has been for endocarditis at 1.5 years, 2 years, and 3.5 years after initial operation; for technical needle damage in a patient who had moderate incompetence on hospital discharge with subsequent progression until reoperation at 1.3 years, revealing an unusual square-shaped hole in the belly of the leaflet, which looked in all other respects normal; for structural degeneration at 5 years, the leaflet tearing away near one of but not at a commissure. There has been one structural valve failure in the 402 implants requiring reoperation over the 10 years. Therefore, the graphical depiction of the actuarial freedom from structural failure is unnecessary and not presented. An interesting observation has been made that this composite stentless valve, in the absence of endocarditis, is very easy to remove. The host aortic sinus wall attachment to the small rim of glutaraldehyde preserved xenograft wall is very easily separated with forceps alone once in the correct plane and after the knots of the continuous suture are cut. There has been no obvious macroscopic calcification detected in the xenograft wall of any of these explants (note, except for a diluted ether wash, this valve has no anticalcium agent in the preservation protocol).
Echocardiography (conventional transthoracic) revealed that most patients, in the late postoperative phase, had a nil or trivial degree of nonprogressive incompetence (Table 3). No living patient at last review during 2002 to 2003 had severe valve incompetence.
Transvalvar gradients and effective orifice areas have been almost but not quite as good as the homograft valve [9]. For example, at 6 months postimplant stentless valve for a 21-mm host annulus, the mean gradient is of the order of 9.8 mm Hg and orifice area 1.56 cm2; for a 27-mm host annulus, the mean gradient is 7.3 mm Hg and the orifice area 2.7 cm2. Left ventricular mass regression has been previously reported [19]; comparison of preoperative and postoperative regression was significant (p = 0.0001). The mean of the mean and peak transvalvar gradients from the large number of echoes are summarized in Table 4. A similar analysis of those 42 patients who had an associated LV myomectomy is presented in Table 5. The gradients were similar to those patients who did not receive a myomectomy. All 42 patients survived and clearly experienced a very smooth immediate postoperative course. In fact it was a subjective clinical impression, over the years, that not only these patients, but virtually all stentless valve patients, had good postoperative progress without low cardiac output states. The MRI studies with annular extensibility may be an explanation for this observation. Some years ago, more esoteric echocardiography studies suggested interesting observations of the aortic root postimplant. Analysis by three-dimension or four-dimensional echocardiography demonstrated dynamic changes in the size of the aortic root and valve annulus during the cardiac cycle. In retrospect, these findings confirmed the more recent accurate and readily documented MRI studies.
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Table 4. Transthoracic Echocardiographic Transvalvar Gradients in the Late Postoperative Studies in Patients in Table 3
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Magnetic resonance imaging studies demonstrated significant variation in the cross-sectional area of the aortic annulus throughout the cardiac cycle at rest in all 10 patients so far examined. The mean increase in cross sectional area of the aortic orifice was 37% of the smallest area in diastole. This would appear possible if, at operation, the calcified native valve is excised, the annulus aggressively decalcified and the valve implanted supra-annularly. The MR images demonstrated the ability of this valve annulus to "expand and relax" significantly throughout the cardiac cycle. Peak flow volumes corresponding to peak ejection during ventricular systole occurred just before maximal annular dilation (Fig 4).
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Comment
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The long-term durability of this stentless xenograft beyond 10 years is still unknown. This present review of the CryoLife-O'Brien valve to the beginning of the 11th year shows promise with only one reoperation for structural failure so far. Because the use of this valve has been largely confined to elderly patients, future analyses of both patient survival and valve durability will be influenced by the competing risk of death due to natural causes. The immediate results are very good with less than 1% early mortality in 402 patients who, at this age with 63% requiring associated procedures, would be classed as a moderately high-risk group.
David and coworkers [20, 21] described a case-controlled patient study with an actuarial survival at 8 years of 91% ± 4% with the Toronto SPV patient group and of 69% ± 8% for the Hancock (Medtronic, Minneapolis, MN) stented porcine xenograft group (p = 0.0006). The study was perhaps flawed by dissimilar groups and by the individual fact that the stentless valve group seemed to be inexplicably immune to the usual expected natural causes of death in any elderly patient group. Del Rizzo and coworkers [22] analyzed survival with patients receiving either the Medtronic Freestyle stentless valve (Minneapolis, MN) or the Hancock II porcine valve. Of interest was the significant advantage of the stentless valve in patients younger than 60 years old; the probability of death was fivefold greater with the Hancock than Freestyle valves. With advancing age the benefits of stentless valves were diminished.
In this study of 402 patients, a significant morbid event occurred in 35 patients (8.7%): 22 thromboembolism; 9 endocarditis; and 4 reoperations – excluding those for acute endocarditis. The interesting observation with endocarditis is made that the actual infection may occur more on the native host annulus, where turbulence is maximum and speed of flow greatest, than primarily on the supra-annular xenograft. In support of this observation is that in the endocarditis patients all but 4 of the 9 continued to have a competent valve and 4 of the 9 were medically cured of the infection without replacement of the valve.
The incidence of thromboembolic events may seem high. The data collection has been assiduous and may, in comparison with other studies, tend to overestimate the overall incidence of thromboembolism, especially by including all "suggestive" TIA events. During data collection in our institutions, the determination of a higher incidence of thromoembolic events may likely be overestimated as our many published clinical homograft analyses always had a patient thromboembolic incidence, unlike that of many similar publications by others. It is considered that a stentless tissue valve is unlikely to be the primary site of thromboemboli especially in this elderly group of patients, prone to innate carotid and cerebrovascular disease and to developing early and late postoperative arrhythmias. Forty-six percent of patients required CABG for coronary arteriosclerosis. Except in the presence of endocarditis, thrombus on any stentless tissue valve has not been seen by the surgical authors. However, although the stentless valve itself may be exonerated as the likely focus of thrombus giving rise to an embolic episode, the possibility does exist, especially with supra-annular xenograft valve implantation, that the subvalvar area (ie, the actual denuded native valve annulus), may be a primary thrombotic site. No early or late echocardiographic studies have suggested thrombus in these denuded areas. In addition, an early higher incidence of thromboembolism has not been found. Of the 40 patients who sustained thromboembolism, four episodes were early (less than 1 month after operation), and all of these were transient ischemic episodes. Because thromboembolism in this patient study has been more of a late phenomenon than an early event, the denuded native valve annulus site is far less an important cause of thromboembolism. Of equal interest is the observation that of the 42 patients who had a myomectomy, only 1 patient (at 16 days postoperative) had a TIA episode. Of this group, a further 6 patients suffered a late thromboembolic episode (4 months to 6.3 years).
The details of serial echocardiography have previously been documented [10]. They have not changed over time and hence are not repeated in this presentation except to state that 94% of patients have either nil, trivial, or mild degree of incompetence on echocardiography across time. In addition, echo studies have shown no dilatation of the aortic root in this elderly patient cohort. Therefore, no sinotubular diameter changes have been observed and no specific surgical sinotubular fixation techniques have been necessary in retrospect. Progression of incompetence has been rare and cannot be attributed to any root dimensional changes. An interesting comparison of hemodynamics and LV mass regression between the CryoLife-O'Brien stentless and the supra-annular Carpentier-Edwards stented porcine valve (Edwards Life Sciences, Irvine, CA) has been reported from our institution by Thomson and colleagues [19]. Briefly, at 6 months the mean gradients were lower (p = 0.001), the effective orifice greater (p = 0.05), and the dimensionless performance index higher in the stentless versus the stented group. There was important LV mass regression at 6 months after operation in both groups, but the reduction was greater in the stentless (p = 0.04).
Evidence has certainly accumulated that stentless valves enhance LV hypertrophic regression faster and more completely than do stented valves. Jin and associates [23] compared the hemodynamic data of homografts, stentless (Toronto SPV) and stented valves. Both types of stentless valves caused less resistance to LV ejection and produced greater early improvement in LV function and consequently more complete resolution of LV hypertrophy. These important findings were verified by Del Rizzo and coworkers [24] with the Toronto SPV valve.
The highly favorable echocardiographic features probably reinforce the opinion that good hemodynamics facilitate good recovery, and low mortality and morbidity. The subjective impressions that these elderly patients feel "so well", which is much better than their stented valved colleagues, suggest also that exercise-induced variations in cardiac output are more possible and better tolerated with a stentless valve. Although a comparative study during exercise has not been completed, the new techniques of three-dimensional and four-dimensional echocardiography, and especially MRI studies, are focusing our attention and that of Dagum and colleagues [25] to the restoration towards normality of the aortic annulus during the dynamic phases of the cardiac cycle. During isovolumic contraction both the annulus and sinotubular junction underwent rapid circumferential expansion. The MRI conclusions in all 10 patients examined so far were even more significant as the studies were carried out some years (mean 6 years) after valve implantation. These recent findings with the CryoLife-O'Brien supra-annular valve raise several questions. Will the restoration of annular extensibility be an important reason for the improved durability of this particular valve implanted supra-annularly? If so, how can it be proven? Of course the opposite view is — does stent mounting and annular fixation diminish durability? This was perhaps clearly answered years ago with our own experience and that of others with the stentless and stented homograft [26]. The latter valve had decreased durability. In addition, the former earlier version of this composite porcine valve in our hands in the late 1960s demonstrated that the actuarial 50% freedom from structural degeneration of the formaldehyde composite valve (if stented) was only 2.5 years, while that of the similar preserved but composite nonstented three noncoronary leaflet valve was 5 years. In summary, it may be difficult to prove that the presence of annular extensibility is important in improving durability. No further assistance in this debate can come from the homograft that, in its late phase, becomes fibrotic and even calcified in its intraannular implantation site. However the autograft may well show annular extensibility but other variables such as its ability to grow coupled with the presence of viable leaflet tissue capable of cellular replenishment, would confuse the issue and the debate.
The possible advantages of stentlessness are many. This stentless valve has some of the early attributes of the aortic homograft valve. In the small aortic root, its performance is excellent and where an additional LV myomectomy is indicated, all such elderly patients have had a very smooth postoperative course. In essence no stent should imply no obstruction.
The effective orifice within a given host aortic root is much greater compared with other stented mechanical or stented biological protheses. This applies particularly to the CryoLife-O'Brien valve where, for example, a 27-mm valve is inserted supra-annularly into a 25-mm host annulus. Although the xenograft leaflets are a little stiff, they still produce a low mean transvalvar gradient almost but not quite as good as that of the homograft valve.
Although most elderly patients are suitable candidates for this valve, there are three contraindications. First, excessive aortic root calcification may preclude suturing in the supra-annular and pericommissural aortic wall tissue. This probably applies as well to other models of stentless valves using subcoronary implantation. Such calcification is not common, but if present, an alternative stented bioprosthesis should be chosen. In this series, no stentless valve implantation has had to be abandoned in the middle of implantation because of aortic wall calcification. This decision has always been made on inspection of the aortic root, before selection of the particular valve. Secondly, the large aortic annulus (
30 mm) is a contraindication for this valve, the largest size of which is a 29-mm CryoLife-O'Brien valve. Third, for the subcoronary supra-annular implant of this type of stentless xenograft, gross asymmetry of the aortic root (bicuspid valve with a transverse orifice), although rare in the elderly, may produce a less desirable result than that obtainable with a stented xenograft valve. Fortunately, most elderly patients have a symmetrical trileaflet configuration to their calcific aortic valve stenosis.
Stentless valves are technically more difficult to implant compared with stented bioprostheses or mechanical valves. In addition, implantation techniques are more difficult to learn and more difficult to teach. Not every surgical center is interested in adopting a program of stentless valve usage, which requires the interested surgeon to focus more on aortic root symmetry, orientation of a trileaflet valve, measurement of annular and sinotubular diameters. Ultimately patient understanding, cooperation, and preference are essential for patient factors; pathological valve disease factors and surgeon factors dictate valve choice and the final short- and long-term outcome. Why should a surgeon choose a stentless valve over a stented valve such as the commonly used stented pericardial valves? Surgical techniques are simpler with the stented bioprostheses and probably the immediate outcomes with either valve used by the same surgical team are no different. The authors consider it is a good forward-looking research concept to gather data from patients having a variety of valves in order that 15 to 20 years comparative analyses can be forthcoming. The authors have a large patient cohort with stented pericardial valves.
Patient Age Selection
From the very onset of this patient study with a new bioprosthesis in 1992, the decision was made to restrict this stentless valve to elderly patients. This was because the durability record of glutaraldehyde preserved stented aortic porcine valves in younger patients was so unsatisfactory, requiring many reoperations in the 1980s, that their use was virtually discontinued. The stented xenograft was relegated to elderly patients where the subsequent record proved and has remained acceptable. So, a careful approach in the early 1990s with this stentless valve was adopted in using it only for elderly patients.
The time has come to use the stentless valve in the less than 60-year-old age group. Although the homograft gives an excellent record in this age group, the supply of such valves is becoming in many countries more and more of an insurmountable problem. In such situations a stentless porcine valve may fill the hiatus. This latter scenario of use in younger patients is indicated even more in countries where rheumatic valve disease predominates and in countries where anticoagulants are best avoided. If this stentless valve begins to be used in younger, nonrheumatic patients, the more frequent findings of an asymmetrical aortic root may constitute a contraindication to its use. Aortic root tailoring techniques may not reliably correct such asymmetry long-term. Therefore, for the younger patient, wise decisions in valve choice become more crucial for optimal long-term results.
Conclusion
The CryoLife-O'Brien stentless composite porcine aortic valve has proven itself to be a reliable device in the elderly patient cohort in this series in these two institutions by this surgical team. The low immediate operation mortality and good long-term survival is most acceptable especially considering that the patient cohort is elderly and destined to die of natural causes. The incidence of morbid events is considered low for this patient group. Of the total patient cohort of 402, the solitary single valve structural failure requiring reoperation over the maximum 10 years with a 100% patient follow-up may be the crucial objective observation. This valve has rewarded its recipients with a good device.
From the research and scientific arena, the MRI findings of restoring the postimplant aortic annular extensibility, in relation to the dynamics of the cardiac cycle, may be one of the most important findings of a valve that is truly stentless and mounted supra-annularly.
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Acknowledgments
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Acknowledgements are given to the ethics committee of the two institutions (The Prince Charles Hospital and St. Andrew's War Memorial Hospital) for allowing this study to commence in 1992; to Susan Smith who provided the artwork (Fig 1); and especially to the coauthor Julie Gordon, whose dedication as data manager in achieving the 100% patient follow-up and upon whom was given the arduous task of redoing data collection to improve the final accuracy of information for this analysis.
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References
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- Binet JP, Duran CG, Carpentier A, Langlois J. Heterologous aortic valve transplantation Lancet 1965;2:1275.[Medline]
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Abstract
Introduction
