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Ann Thorac Surg 2009;87:1751-1756. doi:10.1016/j.athoracsur.2009.03.058
© 2009 The Society of Thoracic Surgeons
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Original Articles: Adult Cardiac

The Toronto Root Bioprosthesis: Midterm Results in 186 Patients

Sven Lehmann, MD*, Thomas Walther, MD, PhD, Sergey Leontyev, MD, Jörg Kempfert, MD, Jens Garbade, MD, Michael A. Borger, MD, PhD, Friedrich W. Mohr, MD, PhD

Department of Cardiac Surgery, University of Leipzig, Heartcenter, Leipzig, Germany

Accepted for publication March 23, 2009.

* Address correspondence to Dr Lehmann, Universität Leipzig, Herzzentrum, Klinik für Herzchirurgie, Strümpellstr 39, Leipzig, 04289, Germany (Email: sven.lehmann{at}med.uni-leipzig.de).


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 References
 
Background: The Toronto Root bioprosthesis with BiLinx anticalcification treatment (St. Jude Medical, St. Paul, MN) was introduced into clinical practice in 2001, mainly for patients with aortic valve disease and additional pathology of the aorta. Patients included in the initial clinical study with core laboratory data evaluation were reviewed.

Methods: A total of 186 patients (62 ± 11 years, 38 female) received full root replacement at our institution with the Toronto Root bioprosthesis from June 2001 until November 2007. The predominant aortic valve lesion was stenosis in 34, incompetence in 80, and mixed lesions in 72 patients. Additional procedures included replacement of the ascending aorta in 139, replacement of the ascending aorta plus aortic arch in 38, coronary artery bypass graft surgery in 31, mitral valve repair in 26, atrial fibrillation ablation in 14, and atrial septal defect closure in 8 patients. Previous cardiac surgery had been performed in 10 patients. Mean follow-up was 50 ± 26 months (770 patient-years).

Results: The mean implanted valve size was 26.8 ± 1.8 mm (14 x 23 mm, 36 x 25 mm, 87 x 27 mm, and 48 x 29 mm). Aortic cross-clamp time was 99.8 ± 29 minutes, and cardiopulmonary bypass time was 140.9 ± 52 minutes. All patients showed a clinical improvement of at least one New York Heart Association class during follow-up. Most recent echocardiographic examination revealed a maximum transvalvular blood flow velocity of 2.1 ± 0.5 m/s and a mean pressure gradient of 9.6 ± 8.5 mm Hg. Left ventricular ejection fraction was 61% ± 11%. Early mortality was 5.9% ± 1.7%, and 5-year survival was 83.3% ± 3.0%. Patients who underwent isolated aortic root surgery had a 5-year survival of 90.3% ± 4.2%.

Conclusions: The Toronto Root bioprosthesis is safe and provides good clinical and hemodynamic function after full root replacement with or without additional aortic surgery. Owing to the specific anticalcification treatment, long-term durability may be promising.


   Introduction
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 Abstract
 Introduction
Material and Methods
 Results
 Comment
 References
 
Aortic stenosis is the most common acquired heart valve lesion in the Western world. It is usually caused by degenerative changes with complex calcification of the native leaflets and the aortic annulus. In symptomatic patients or in the presence of severe stenosis with significant additional left ventricular hypertrophy or reduced left ventricular function, aortic valve replacement (AVR) is indicated [1]. Biological xenografts are the standard therapeutic option for patients more than 65 years of age requiring AVR [1]. Of 10,000 patients receiving AVR in Germany in 2007, in-hospital mortality for isolated biological AVR was 2.9%. However, in patients that required aortic valve and additional ascending aortic surgery, in-hospital mortality was approximately 6.9% [2].

Similar outcomes regarding long-term survival were recently reported 20 years after mechanical and biological AVR [3]. Despite comparable survival, important differences were observed between groups, with mechanical AVR patients having an increased incidence of bleeding and biological AVR patients having an increased incidence of reoperation [3]. Such limitations have led to an ongoing search for the optimal artificial heart valve.

During the past decades, AVR using mechanical valves or conventional stented bioprotheses has become a routine procedure with low perioperative risk [3-8]. Stentless aortic valves have been used increasingly with good functional and hemodynamic results [4, 7-9]. Early regression of left ventricular hypertrophy after stentless valve implantation has been demonstrated in longitudinal studies [4, 9–11].

In elderly patients with combined aortic valve and aortic root pathology, aortic root replacement using a porcine xenograft has become a standard procedure. We started implanting the Toronto Root bioprosthesis in 2001. The aim of this study was to analyze our midterm clinical results after aortic root replacement using the Toronto Root xenograft.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 References
 
From June 2001 through November 2007, 186 patients with combined aortic valve and aortic root disease were prospectively evaluated as part of the post–market approval study for the Toronto Root bioprosthesis. The study was approved by the local Ethics Committee, and all patients gave informed consent. The inclusion and exclusion criteria are given in Table 1. Demographic data from the patients are displayed in Table 2.


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  		Table 1 Inclusion and Exclusion Criteria
 

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  		Table 2 Preoperative Patient Characteristics
 
All operations were performed with the use of complete (n = 39) or partial (n = 147) median sternotomy. Standard cardiopulmonary bypass was used with hypothermic cardioplegic arrest in 123 patients (Bretschneider HTK solution; Köhler Chemie, Alsbach-Hähnlein, Germany) or blood cardioplegia in 63 patients, applied in an antegrade or retrograde fashion. Because of known variability in actual diameters of similarly labeled bioprostheses, aortic annulus diameter was measured intraoperatively by use of a standard set of sizers before the new valve was implanted. Aortic annulus sizing was performed after excision of the diseased aortic valve and after complete decalcification [26]. Annulus diameter was divided by body surface area to obtain the annulus index as a baseline measure.

The Toronto Root xenograft is a stentless prosthetic heart valve with the porcine aortic root, valve cups, ostium of the coronary artery, and proximal ascending aorta. Valve fixation is performed with glutaraldehyde under low pressure conditions. An anticalcification treatment (Bilinx; St. Jude Medical, St. Paul, MN) is subsequently applied, consisting of exposure of the valve cusps to 95% ethanol for 24 hours and treatment of the aortic wall with aluminium chloride.

All patients received standard perioperative antibiotic therapy using cephalosporin. Patients with endocarditis received a broader antibiotic therapy.

Aortic valve implantation was performed according to standard techniques as described previously. All valves were implanted as full roots using Teflon (Impra, subsidiary of L. R. Bard, Tempe, AZ) reinforced everting mattress sutures at the annulus and a single polypropylene 4-0 suture for the anastomosis with the ascending aorta. Coronary buttons were reimplanted using continuous 5-0 Prolene suture.

All patients received postoperative systemic anticoagulation therapy using warfarin for 3 months. Warfarin was stopped thereafter, and aspirin 100 mg was given only if there was no other indication for continuation.

Follow-up consisted of annual examinations in our outpatient clinic and was complete in 99.9% of patients. Mean follow-up was 50 ± 26 months (range, 0 to 76.4). Total follow-up consisted of 770 patient-years. Patients living more than 150 km from the hospital (n = 2) were followed up by telephone interview, and physical and echocardiographic examination results were obtained from their family physicians. All patients were instructed to contact the hospital in the event of any unexpected deterioration of health conditions immediately.

Transthoracic echocardiographic examinations were performed preoperatively, before discharge, and at every follow-up visit. Multiplane transesophageal echocardiography was used intraoperatively or whenever additional information was required. Cardiac morphology and function as well as valve hemodynamics were assessed using standard measurements.

Valve-related morbidity and mortality were evaluated according to standard guidelines [12]. Categorical variables are displayed as absolute and relative frequencies. Continuous variables are displayed as means ± SD. For measurements within groups over time one-way analysis of variance with Bonferroni correction was used. In addition, univariate ({chi}2) and survival analysis (log rank) were performed. Multivariate analysis of survival was performed using the Cox model (SPSS, Chicago, IL). A p value of less than 0.05 was considered to indicate statistical significance.


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 References
 
Mean age of the patients was 62 ± 11.1 years, and 20.4% were female. Preoperative patient characteristcs and hemodynamic function are given in Table 2. The predicted risk of perioperative mortality according to the logistic European System for Cardiac Operative Risk Evaluation (EuroSCORE) was 16.37% ± 14.8%. Aneurysm of the ascending aorta with aortic valve disease was the indication for Toronto Root valve implantation in the vast majority of patients.

Mean implanted xenograft size was 26.8 ± 1.8 mm (14 x 23 mm, 36 x 25 mm, 87 x 27 mm, and 49 x 29 mm). Additional intraoperative procedures are displayed in Table 3. Mean aortic cross-clamp time was 99.8 ± 28 minutes, and duration of cardiopulmonary bypass was 140.9 ± 52 minutes. Intra-aortic balloon pump was required in 8 patients (4.3%) who received moderate inotropic support for 67.1 ± 85.9 hours postoperatively.


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  		Table 3 Additional Cardiac Procedures
 
Arrhythmias that required intravenous antiarrhythmic therapy or cardioversion occurred in 45 patients (24.2%). Sinus rhythm was present in 83.2% of the patients preoperatively and in 87.6% at discharge. Fourteen patients (7.5%) had postoperative renal dysfunction requiring temporary venovenous ultrafiltration. Six patients (3.2%) had delirium, all with full recovery, and 4 patients (2.2%) had a perioperative stroke. Two stroke patients died in the intensive care unit.

Mean stay in the intensive care unit was 64 ± 135.5 hours (range, 4 to 912), and the mean ventilation time was 48.8 ± 112.5 hours (range, 8 to 899).

Echocardiography at discharge revealed a maximum transvalvular blood flow velocity of 2.3 ± 0.5 m/s and the maximum pressure gradient was 22.3 ± 9.2 mm Hg. The mean ejection fraction was 63.5% ± 8.6%. Detailed follow-up echocardiographic results are displayed in Table 4. There was no patient with moderate or more aortic insufficiency in their last follow-up examination.


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  		Table 4 Echocardiographic Hemodynamic Results During Follow-Up
 
There was significant regression of left ventricular mass (LVM) and LVM index within the first year postoperatively (Table 5). During later follow-up, LVM remained within normal ranges.


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  		Table 5 Preoperative and Follow-Up Left Ventricle Mass and Left Ventricle Mass Index
 
Early mortality was defined as all-cause mortality before hospital discharge or within 30 days of surgery. In patients undergoing isolated aortic valve and aortic root surgery for indications other than endocarditis, early mortality was 5.5% ± 3.1%. At 5-year follow-up, survival for this group of patients was 90.3% ± 4.2% (Fig 1). Early mortality for all patients was 5.9% ± 1.7%. The cause of early death was low cardiac output syndrome in 5 patients. Other causes of early death consisted of neurologic dysfunction (severe stroke) in 2 patients, sepsis in 1 patient, and respiratory failure in 1 patient.


Figure 1
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  		Fig 1. Kaplan-Meier survival function after isolated Toronto Root xenograft implantation, excluding patients with endocarditis.

 
During the follow-up interval, 14 additional patients died. The causes of death during follow-up were cardiac failure (3), cancer (3), multiorgan failure (2), accident (3), suicide (1), abdominal ischemia (1), and pneumonia (1). Causes of death during follow-up were noncardiac in 11 of 14 patients. Survival rate after 5 years in the total patient group was 83.3% ± 3.0%. After hospital discharge, there was no significant difference in mortality in comparison to an age- and sex-matched German control population (Fig 2).


Figure 2
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  		Fig 2. Kaplan-Meier survival function for all patients after Toronto Root xenograft implantation (solid line) and age- and sex-matched German normal population (dashed line).

 
During follow-up, 2 patients had a stroke and 1 patient with a thrombus in the vena cava inferior had a pulmonary embolus. Freedom from systemic thrombembolic events after 5 years was 98.3% ± 0.1% (Fig 3). During follow-up, there was 1 bleeding event in a patient who had arterial bleeding from the left circumflex artery 2 months postoperatively. He was receiving coumadin therapy at the time of the complication. Freedom from bleeding events after 5 years was 99.5% ± 0.05%. A total of 4 patients had prosthetic valve endocarditis during follow-up. The actuarial freedom from reoperation due to prosthetic valve endocarditis was 97.7% ± 1.1% (Fig 4).


Figure 3
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  		Fig 3. Freedom from thromboembolic events for all patients after Toronto Root implantation.

 

Figure 4
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  		Fig 4. Freedom from endocarditis for all patients after Toronto Root xenograft implantation.

 
We examined predictors of in-hospital and long-term mortality. Several factors were univariate predictors of an adverse outcome: patient age more than 70 years (p = 0.02, odds ratio [OR] 2.76, 95% confidence interval [CI]: 1.17 to 6.5), pulmonary hypertension (p = 0.016, OR 5.26, 95% CI: 1.35 to 20.43), logistic EuroSCORE more than 39% (p = 0.003, OR 5.88, 95% CI: 1.81 to 19.12), New York Heart Assocation functional class III or IV (p = 0.001, OR 4.55, 95% CI: 1.88 to 11.0), hyperlipoproteinemia (p = 0.014, OR 3.98, 95% CI: 1.32 to 12.02), and preoperative endocarditis (p = 0.018, OR 3.21, 95% CI: 1.22 to 8.42). Factors that were not associated with adverse outcomes consisted of additional surgical procedures, ejection fraction below 40%, sex, body surface area, atrial fibrillation, myocardial infarction, preoperative syncope, embolism, preoperative cardiac shock, preoperative resuscitation, arterial hypertension, diabetes mellitus, history of smoking, preoperative anticoagulation therapy, percutaneous transluminal coronary angioplasty, peripheral arterial occlusive disease, aortic aneurysm, type A aortic dissection, bypass time longer than 180 minutes, aortic cross-clamp time more than 110 minutes, need for perioperative circulatory arrest, and chronic obstructive pulmonary disease.

At multivariate logistic regression analysis, only New York Heart Association functional class III or IV was found to be a predictor for adverse outcome during follow-up (p = 0.027, OR 3.7, 95% CI: 1.16 to 11.74).


   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
References
 
The ideal aortic valve substitute would be simple to implant, provide a hemodynamic profile identical to a physiologic native valve, have unlimited durability, and have a low thrombogenic potential so that anticoagulants are unnecessary. No such device is available at present. The average age of patients requiring aortic valve surgery is steadily increasing with time, a trend that parallels a more frequent use of xenografts over time.

Stentless bioprosthetics have demonstrated superior hemodynamic parameters in comparison with stented xenografts [1, 8, 10, 11, 13]. They are associated with low transvalvular gradients, rapid regression of left ventricular hypertrophy, and increased effective orifice area as a result of elimination of the rigid sewing ring in the left ventricular outflow tract [4, 8, 11, 14]. The most commonly used stentless bioprosthesis for full aortic root replacement surgery is the Freestyle valve (Medtronic, Minneapolis, MN). A multicenter study investigated the impact of three different methods of Freestyle valve implantation. They noted superior hemodynamic profile, better functional class, and freedom from aortic regurgitation after implanting the bioprosthetis with a full root replacement technique, when compared with a root inclusion or subcoronary technique [13]. However, these investigators have also observed a higher operative mortality, with prolonged ischemic times and increased bleeding complications, for the full root replacement technique, leading some surgeons to avoid this technique whenever possible. However, perioperative risk of the full root replacement has been noted to decrease with increasing surgical experience [13].

The full root technique was our method of choice when using the Toronto Root bioprosthesis, with no patients undergoing a subcoronary or root inclusion implantation. In addition, we used the Toronto Root valve only in patients with combined aortic valve and aortic root disease (most commonly aortic root aneurysm), which explains our rather high rate of additional procedures on the ascending aorta and arch. Our preferred use of the Toronto Root xenograft in patients requiring aortic valve, aortic root and ascending aortic replacement, with a risk that is known to be increased when compared with isolated aortic valve replacement surgery, may explain our slightly elevated observed perioperative mortality rate. When we excluded patients who were operated on for endocarditis, however, our observed mortality and morbidity rates were similar to those obtained from a recent report from the German Cardiac Surgery Society for patients undergoing isolated aortic valve and aortic root surgery [2].

In patients with a small aortic annulus, stentless root replacement surgery can be performed with upsizing of the bioprosthesis by one to two sizes to minimize the risk of patient-prosthesis mismatch [14, 15]. No patient in the current series, however, received a Toronto Root strictly on the grounds of a small aortic annulus. Optimal root geometry with preservation of functional leaflet, sinus, and root anatomy can be obtained by using the root replacement technique. We believe these characteristics may improve the durability of the implanted xenograft valve, as hemodynamic disturbances are known to be associated with decreased bioprosthetic durability [4].

Some studies on the long-term performance of stentless aortic valves implanted in a subcoronary position have shown increased aortic regurgitation from incompetent valve closure due to increased dilatation of the sinotubular junction over time [16], although other studies have not observed this phenomenon [4]. The decreased risk of subsequent aortic regurgitation is another advantage of the full root implantation technique [13]. Our findings confirm this hypothesis with no observed cases of moderate or more aortic insufficiency by dilatation of the sinotubular junction during medium-term follow-up.

As known from the literature, overall survival after aortic valve surgery is limited in the presence of endocarditis [17–19]. For example, David and coworkers [17] found an operative mortality of 12% plus an additional mortality of 23% at 5 years after surgery for endocarditis. Our results are consistent with these findings, with an increased risk of perioperative and medium-term mortality in endocarditis patients.

We observed very good hemodynamic function of the Toronto Root bioprosthesis during follow-up echocardiographic examinations. Trivial transvalvular reflux caused by the closing volume, as seen with most conventional heart valve prostheses, was frequently observed without any evidence of significant aortic insufficiency. Transvalvular flow velocities were comparable to those of other studies [4, 8–11, 13–15]. We did not observe any hemolysis or evidence of early structural valve deterioration after valve implantation.

The results from our univariate analysis suggested several possible risk factors for adverse outcomes during medium-term follow-up, but most factors failed to reach significance during multivariate analysis because of the relatively small number of adverse events. Of note, increased age was not identified as a significant risk factor during multivariate analysis, Similarly, Melby and associates [20] and Urso and colleagues [21] found no correlation between age and perioperative mortality. In addition, some multicenter studies have failed to find a correlation between patient age and postoperative mortality [22, 23]. Such findings underlines the clinical reality that numerical age alone is not an accurate predictor of an individual patient's risk for aortic valve surgery.

The durability of stentless aortic valves, particularly those implanted with a full root replacement technique, has been adequately demonstrated by freedom from reoperation and freedom from endocarditis in several studies. [4, 13, 25] The durability of the Toronto Root xenograft with its Bilinx anticalcification treatment will be a matter of interest in the coming years. In an experimental study using a rat model, we were able to show good efficacy of the BiLinx treatment with low levels of calcification in the aortic valve cusps and the aortic wall tissue [24]. That may well translate into good long-term durability. However, long-term clinical follow-up examinations still need to be performed.

In conclusion, excellent hemodynamics with low gradients and an acceptable operative risk can be achieved by full aortic root replacement with the Toronto Root bioprosthesis. Aortic root replacement with a biological xenograft is a particularly valuable option for elderly patients with aortic valve and aortic root pathology. Further long-term studies are necessary to verify good durability of this stentless root xenograft.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 References
 

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