Asian Cardiovasc Thorac Ann 2005;13:143-148
© 2005 Asia Publishing EXchange Ltd
Aortic Valve Replacement with Toronto SPV in Elderly Patients: 10-Year Results
Muhammed Tamim, FETCS,
Thierry Bové, MD,
Yves Van Belleghem, MD,
Frank Caes, MD,
Katrien François, MD,
Guido J Van Nooten, PhD
Heart Center, University Hospital of Ghent, Ghent, Belgium
For reprint information contact: Thierry Bové, MD Tel: 32 9 240 4700 Fax: 32 9 240 3882 Email: thierry.bove{at}ugent.be, Cardiac Surgery Department, University Hospital of Ghent, 185 De Pintelaan, 5K12 9000, Ghent, Belgium.
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ABSTRACT
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A retrospective assessment of clinical and echocardiographic variables was performed in 145 patients who received a Toronto SPV aortic valve replacement. The majority (90%) of these elderly patients (mean age, 75.5 ± 7.4 years) were preoperatively in New York Heart Association class III–IV. Operative mortality was 4.8%. Follow-up was complete up to 10 years and revealed few valve-related complications: thromboembolism (7), bleeding (4), and prosthesis dysfunction necessitating reoperation (3). Late mortality was cardiac-related in 11.7% and noncardiac-related in 17.2%. Actuarial survival was 83% at 5 years and 63% at 8 years. Echocardiography showed low transvalvular gradients (peak, 17.5 ± 7.5 mm Hg; mean, 9.2 ± 4.2 mm Hg) resulting in a significant reduction in left ventricular mass index during the first 3 years. Independent of the transprosthetic gradient, left ventricular mass index tended to increase again beyond the 5th year, which correlated positively with the presence of arterial hypertension in this older population. The Toronto SPV bioprosthesis offers an aortic valve substitute with excellent long-term hemodynamics, resulting in significant early left ventricular mass regression. Considering the limitations of this selected elderly population, the clinical outcome and survival up to 10 years are encouraging, with few observed valve-related events.
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INTRODUCTION
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In the knowledge that the native dynamic aortic root itself represents the best stent for any valve substitute, the Toronto SPV bioprosthesis (St Jude Medical, Inc., St Paul, MN, USA) was developed to improve the hemodynamic performance of porcine aortic valves, and so to enhance their durability compared to stented prostheses.1 The stentless design and consequent possibility of implanting larger-sized valves has led to a significant reduction of left ventricular (LV) hypertrophy. This hemodynamic superiority has resulted in improved survival of patients who were eligible for this technically more demanding procedure. However, only a few reports of long-term outcomes with this bioprosthesis have been published.2,3 The purpose of this study was to review our 10-year experience of the Toronto SPV valve, and to describe the clinical and the hemodynamic performance in a selected group of mainly elderly patients.
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PATIENTS AND METHODS
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From July 1992 to December 2002, 145 patients (53 male and 92 female) underwent aortic valve replacement (AVR) using a Toronto stentless porcine valve in our department. Fifteen patients (10%) were in New York Heart Association (NYHA) class II, 129 were in class III (59%) and IV (31%). Other preoperative data are listed in Table 1
. The operative technique, including cardiopulmonary bypass management, has been described previously.4 Contraindications for Toronto SPV implantation were the presence of a heavily calcified aortic root and ascending aorta, dilatation of the sinotubular junction, and unfavorable coronary artery anatomy with facing coronary ostia, as in the occurrence of bicuspid aortic valve. All patients were given oral coumadin, with a target international normalized ratio of 2.0 to 3.0 during the first 3 months after valve implantation, except in the presence of bleeding diathesis or actual gastric disease. The patients were followed up clinically at 1 and 6 months and then yearly intervals. The follow-up was 100% complete, the mean duration was 56 months (range, 24 to 131 months). Total follow-up analysis comprised 1,519 patient-years. Follow-up data were recorded in a computerized database. Additional information was obtained by reviewing the medical records and by contacting the patients’ general practitioners or families, as required.
Transthoracic echocardiographic imaging (VIVID 7; General Electric Ltd., Vingmed, Norway) was performed in all patients at every clinical visit, and included two-dimensional and M-mode evaluation as well as continuous and pulsed-wave spectral Doppler imaging. The LV end-diastolic and end-systolic diameters were measured in the apical 4-chamber view. Intraventricular septum diameter and LV posterior wall diameter were measured using the parasternal short-axis view. Left ventricular mass index (LVMI) to body surface area was calculated by the modified ASE cube formula. Mean and peak transvalvular gradients were calculated by the simplified Bernoulli equation.
The definition of complications was in accordance with the published guidelines for reporting valve-related morbidity and mortality, as proposed by Edmunds and colleagues.5 Statistical analysis was performed with SPSS 10.1 software (SPSS, Inc., Chicago, IL, USA). The results are expressed as ranges and mean values with standard deviations. The 2-tailed Student t test was used for parametric data. The chi-squared test was used for nonparametric data. Survival or event-free survival was analyzed using the Kaplan-Meier product-limit estimation. Univariate analysis of survival curves was carried out by the log-rank test. Multivariate analysis of survival was carried out using Cox’s regression proportional hazards model. A p value less than 0.05 was considered statistically significant.
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RESULTS
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The mean size of the implanted stentless prostheses was 24.5 ± 2.1 mm (range, 20–29 mm), for a mean body surface area of 1.74 ± 0.18 m2 (range, 1.25–2.37 m2). Concomitant coronary artery bypass grafting was performed in 67 patients (46%). Other combined procedures were mitral valve replacement in 1, mitral valve repair in 3, septal myotomy in 1, and carotid endarterectomy in 3 patients. The mean cardiopulmonary bypass time was 124.5 ± 24.3 min (range, 68–205 min). The mean aortic crossclamp time was 69.5 ± 14.4 min (range, 45–134 min). In 2 patients, a Toronto valve was used in a reoperation because of thrombosis of a mechanical prosthesis, due to inadequate anticoagulation therapy.
There were 7 (4.8%) early deaths. Causes of early death were cardiac failure (4), respiratory insufficiency with pulmonary sepsis (2), and massive gastric ulcer bleeding (1). Major complications were heart failure requiring the use of an intraaortic balloon in 7 patients, pneumonia in 8, renal failure requiring hemodialysis in 5, and neurological insult with complete resolution in 2 patients. Postoperatively, 57 patients (39%) developed temporary atrial fibrillation, occurring more frequently in female patients (35 female vs. 22 male). In 26 cases, conversion was achieved with medical treatment, 10 patients underwent successful electrical cardioversion before discharge, and a definitive pacemaker was implanted for complete atrioventricular block in 3 patients. The hospital stay averaged 14.3 ± 9.5 days.
There were 42 (29%) late deaths after Toronto AVR, of which 13 were cardiac-related. Twenty-two patients died of a documented noncardiac cause, including 6 due to cancer. However, in 7 patients, the cause of death remained unknown and was classified as potentially valve-related. The Kaplan-Meier actuarial survival rate was 83.2% ± 3.2% at 5 years and 63.2% ± 4.9% at 8 years (Figure 1). Univariate independent risk factors for late death were the occurrence of postoperative atrial fibrillation (p = 0.0001), age over 80 years at operation (p = 0.0009), and preoperative NYHA functional class III or IV (p = 0.0008). Multivariate analysis using Cox’s regression model identified age over 80 years at the time of AVR (p < 0.001), preoperative NYHA functional class III or IV (p < 0.0001), and atrial fibrillation (p < 0.003) as significant risk factors for death.
All patients improved to NYHA functional class I or II at the last visit, resulting in a mean late functional class of 1.4. Of note, was the frequent manifestation of arterial hypertension despite most patients being treated with antihypertension drugs during the study period. In 80 patients (55%), a systolic blood pressure exceeding 160 mm Hg was measured repeatedly at subsequent out-of-hospital visits.
There were 7 (5%) thromboembolic events (4 strokes and 3 transient ischemic attacks). These mostly occurred early after valve surgery, within an average time of 14.5 ± 3.3 months (range, 7–25 months); 4 of these patients had severe hypertension. The linearized freedom from thromboembolic events at 1 and 5 years was 96% ± 1.5% and 94% ± 2 %, respectively (Figure 2). No independent risk factors for thromboembolism were identified. Three patients (2%) noticed a bleeding event, due to a duodenal ulcer in 2 and to an intrauterine fibroma in 1. Oral anticoagulation was promptly stopped. No episode of infective endocarditis was diagnosed during early or late follow-up. Three patients needed reoperation. One hypertensive patient had progressive enlargement of the ascending aorta, developing major aortic regurgitation 4 years after a 29-mm Toronto SPV implant. At explantation, neither calcification nor rupture of the valve was detected. Two patients with 25-mm and 27-mm Toronto valves had structural valve deterioration at 108 and 114 months after implantation. Both explanted valves revealed an isolated cusp rupture without leaflet calcification, as shown by the low calcium content of the investigated cusps (9 and 75 µg·mg–1). The actuarial freedom from structural valve deterioration at 5 and 9 years was 99% ± 0.6% and 97% ± 1.2%, respectively (Figure 3).
Peak and mean transvalvular gradients across the Toronto SPV decreased significantly during the first 6 months after AVR, and remained low over time (Figure 4). Illustrating the LV remodeling, both intraventricular septal and LV posterior wall thickness decreased rapidly after surgery. This was associated with a significant early regression of LVMI, continuing during the first 3 years (p = 0.001); however, the LVMI rose later (Table 2). The common trend of early LVMI reduction and late increase was observed equally in male and female patients (Figure 5). Simultaneously, the LV end-diastolic volume decreased significantly after AVR (p = 0.018); all hemodynamic data are listed in Table 2. Investigation of factors influencing the late evolution of LV mass (arterial hypertension, coronary artery disease, gender, age, and peripheral vascular disease) showed a positive correlation only with persistent arterial hypertension (correlation factor, 0.55). Eighty-eight patients (61%) had a competent valve at the last follow-up, while trivial to mild aortic valve regurgitation was noticed in 28 (19%) and 20 (14%) patients. In 2 patients, aortic valve insufficiency grade 2+ was seen (Figure 6). However, none of these observations worsened over the study period.
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DISCUSSION
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Stentless aortic xenografts were designed to resemble the native aortic root anatomy. The underlying assumption was that mechanical stress on the leaflets would be reduced and thereby result in superior hemodynamic behavior, and thus a longer durability.1 These properties were expected to overcome two of the major shortcomings of stented bioprostheses.6 Several reports focusing on the comparison of hemodynamics between stentless and stented aortic valve grafts have already shown a favorable impact of the stentless concept on geometry and LV performance. Subsequently, the enhanced regression of LV hypertrophy led to improved patient survival.7–9 However, few data are available on the clinical and hemodynamic outcomes of the Toronto SPV bioprosthesis in the longer term.2,3
Our patient population was characterized by a majority of female patients, often presenting with arterial hypertension, a high association of coronary artery disease, and advanced age. This demographic distribution compares favorably with the patient profile of the multicenter survey, conducted by Westaby and colleagues10 who reported an operative mortality of 7.5% in patients undergoing a selected stentless graft implantation. Despite significantly prolonged aortic crossclamp and cardiopulmonary bypass times due to the greater technical requisites, the early mortality in our series was 4.8%. As already shown by our group, the in-hospital outcome is comparable between stentless and stented valve procedures.8 This strengthens the conclusion that the risk related to the use of a stentless prosthesis weakens with growing experience and must be weighed against the hemodynamic and medium-term survival benefits.
A constant and progressive decrease in LVMI appeared during the first 3 years after stentless AVR. This phenomenon was directly related to low transvalvular gradients. However, most studies have been limited to early hemodynamic assessment in the first 3 to 5 years.11,12 In an 8-year hemodynamic follow-up of AVR with the Toronto SPV, Bach and colleagues13 found a linear regression of LV mass, reaching a minimum at 3 to 5 years after surgery, with a slight increase beyond the 6th year. We made a similar observation of a rapid decline of LV mass, having its nadir at the 3rd year, followed by a slow increase of LV wall thickness after 5 years. The expression of LV remodeling after stentless AVR seemed unaffected by gender, although the hypertrophic response of the ventricle to chronic systolic overload is known to be gender-related.14 With simultaneous stable transvalvular gradients, it appears that the late increase of LV mass could possibly be due to non-valve-related factors. Investigation of potential contributing factors revealed a high correlation only with arterial hypertension which severely affected our older population. Ongoing aging, less dependable medication intake, and age-related poorer drug response are potential explanations for extensive hypertensive periods. Gelsomino and colleagues15 demonstrated that LV mass regression is likely to be multifactorial and patient-related. This would suggest that LVMI might be a less reliable parameter for long-term evaluation of prosthetic valve hemodynamic performance.
The Toronto SPV was similar to other bioprostheses in terms of valve-related morbidity.16 The incidence of thromboembolism during follow-up was low, generally occurring within the first postoperative year, and often associated with arterial hypertension, advanced age, and vascular disease. Three patients in our series needed late reoperation for prosthetic valve dysfunction. Poorly treated hypertension and borderline indications for a stentless valve implantation because of a discordant aortic annulus to sinotubular junction relation, were probably responsible for these failures. In our series, 38% showed trivial to mild aortic valve incompetence, currently stable over time. Nevertheless, we became more reluctant to use a stentless valve in patients presenting mainly with aortic valve insufficiency, even if the ascending aorta was not dilated originally. These data correlate with the findings of Dellgren and colleagues3 who reported identical conclusions on structural degeneration and reoperation with the Toronto SPV. However, only 8% of their patients developed aortic insufficiency of more than grade 1, without aggravation over time.
Several studies have emphasized the obvious advantage of stentless bioprostheses on overall survival, freedom from cardiac death, and freedom from valve-related events. It is clear that this reflects the excellent hemodynamic performance of such valves, minimizing the potential for a patient-prosthesis mismatch.17 This study confirms the steady hemodynamic performance of the stentless Toronto SPV over a time span of up to 10 years, with a low valve-related complication rate. However, whether this stentless valve affords improved durability or a superior long-term survival in comparison with a stented prosthesis, remains to be proven, given the limitations of this selected elderly patient population.
Presented at the 12th Annual Meeting of The Asian Society of Cardiovascular Surgery, April 19–23, 2004, Istanbul, Turkey.
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REFERENCES
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ABSTRACT
INTRODUCTION
