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Ann Thorac Surg 2005;80:2194-2198
© 2005 The Society of Thoracic Surgeons
Department of Thoracic and Cardiovascular Surgery, J. W. Goethe University, Frankfurt am Main, Germany
Accepted for publication June 3, 2005.
* Address correspondence to Dr Doss, Department of Thoracic and Cardiovascular Surgery, J. W. Goethe University Frankfurt am Main, Theodor Stern Kai 7, 60599 Frankfurt am Main, Germany (Email: mirkodoss{at}aol.com).
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Abstract |
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METHODS: Forty patients with aortic valve stenoses, and below the age of 55 years, were randomly assigned to receive either pulmonary autografts (n = 20) or mechanical valve (Edwards MIRA; Edwards Lifesciences, Irvine, CA) prostheses (n = 20). Clinical outcomes, left ventricular mass regression, effective orifice area, ejection fraction, and mean gradients were evaluated at discharge, 6 months, and one year after surgery. Follow-up was complete for all patients.
RESULTS: Hemodynamic performance was significantly better in the Ross group (mean gradient 2.6 mm Hg vs 10.9 mm Hg, p = 0.0005). Overall, a significant decrease in left ventricular mass was found one year postoperatively. However, there was no significant difference in the rate and extent of regression between the groups. There was one stroke in the Ross group and one major bleeding complication in the mechanical valve group. Both patients recovered fully.
CONCLUSIONS: In our randomized cohort of young patients with aortic valve stenoses, the Ross procedure was superior to the mechanical prostheses with regard to hemodynamic performance. However, this did not result in an accelerated left ventricular mass regression. Clinical advantages like reduced valve-related complications and lesser myocardial strain will have to be proven in the long term.
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Introduction |
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Advantages of pulmonary autograft performance have been extensively described and published. However, all of these findings were obtained in nonrandomized trials. Therefore, surgeon bias and a positive selection of patients may have played a role.
Any evaluation of optimal prostheses cannot be based on durability data alone, and must include assessment of hemodynamic and clinical performance [2]. Regression of left ventricular (LV) hypertrophy after AVR, being one of the key determinants of postoperative morbidity and mortality, serves as an ideal predictor for poor long-term outcome. The aim of the current study was to provide some rationale to select the optimal valve substitute, based on valve performance and its effects on regression of LV hypertrophy in a prospective randomized setting.
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Patients and Methods |
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Randomization
The study protocol was approved by our Institutional Review Board. All patients provided written informed consent before entering the study. Randomization was computer-generated and incorporated into sealed envelopes to allow for preoperative valve allocation. Patients were informed of the allocated valve on the morning of surgery, to allow for sufficient time for the logistics involved in pulmonary autograft procedures (ie, cryopreserved homograft availability). A study coordinator was primarily responsible for the randomization procedure and for ensuring that the protocol was strictly adhered to.
Inclusion and Exclusion Criteria
Eligible patients (age 18 to 55 years) included those with predominant aortic stenosis (maximum transvalvular gradient > 50 mm Hg or aortic valve area < 0.8 cm2) in whom preoperative evaluation indicated the need for an aortic valve replacement procedure. Patients with isolated or predominant aortic regurgitation were excluded from the study. Patients who specifically chose to have a certain valve substitute were excluded from enrollment. Patients that required repair or replacement of an additional heart valve and those that had prior implantation of a valve substitute were excluded from the study. In addition, patients with active endocarditis, emergency procedures, and a history of myocardial infarction were also not eligible for the study. Severe calcification of the aortic root, especially at the insertion of the coronary ostia, and atypical origin of the coronary ostia, diagnosed intraoperatively, excluded patients from receiving pulmonary autografts.
Operative Technique
Access to the heart was gained by median sternotomy. Standard extracorporeal circulation with moderate hypothermia was used. All patients had antegrade and retrograde cold blood cardioplegia.
All pulmonary autograft procedures were performed as root replacements with implantation of the coronary arteries into the graft. Reconstruction of the right ventricular outflow tract was performed with cryopreserved pulmonary valve homografts in all patients.
For the Edwards Mira mechanical aortic valves, access to the aortic valve was gained through a hockey-stick aortotomy. The valves were implanted in the supraannular position. Interrupted mattressed pledgeted 2-0 Ethibond (Ethicon, Inc, Somerville, NJ) sutures were placed circumferentially from below the annulus. Mechanical valves were oriented in the antianatomic position.
Echocardiography
Two experienced operators performed all echocardiograms for the study. A simple echomachine (System Five, Sonotron Vingmed; Sonotron, Oslo, Norway) was used. Cardiac morphology and function, as well as hemodynamic parameters, were assessed. All hemodynamic measurements were performed with patients in stable conditions. Aortic valve flow velocities were assessed with continuous wave Doppler. End diastolic left ventricular posterior wall thickness greater than 12 mm was considered hypertrophied. Aortic valve incompetence was judged as transvalvular or paravalvular, and graded according to the regurgitant jet area in relation to left ventricle as mild, moderate, or severe. Apart from standard imaging views, preoperative echocardiography also included the measurement of the diameter of the native aortic annulus and the sinotubular junction, as well as the assessment of subvalvular gradients, in order to identify a possible mismatch between annulus and sinotubular junction or excessive subvalvular hypertrophy. Both conditions would render the patient unsuitable for the study.
Follow-Up
Follow-up examinations were scheduled for discharge from the hospital, at six months, and 12 months postoperatively. All patients were subject to detailed clinical and echocardiographic follow-up. This included the New York Heart Association (NYHA) functional class, blood data including signs of hemolysis, anticoagulation profile, assessment of cardiac rhythm and blood pressure, and documentation of occurrence of early and late complications.
In echocardiography follow-up, our special attention was focused on the regression of LV hypertrophy. Both completeness and rate of LV mass regression were assessed. In addition, changes in LV function and hemodynamics including effective orifice area, as well as changes in postoperative transvalvular gradients, were analyzed.
Anticoagulation Regime
Our anticoagulation regime was as follows: patients with pulmonary autografts did not receive oral anticoagulation; patients with mechanical valves had lifelong oral anticoagulation. Our protocol included subcutaneous low molecular heparin for the first day and parallel oral anticoagulation with vitamin K antagonists. As soon as the international normalized ration (INR) levels reached the therapeutic target range of 2.5 to 3.5 heparin was discontinued. Initially, oral anticoagulation was monitored by the patient's general practitioners. However, most patients who received mechanical valves soon attended a structured course on oral anticoagulation self management, and henceforth monitored their own INR levels, using the portable CoaguCheck (Roche Diagnostics, Mannheim, Germany) device.
Statistical Methods
All data were compiled and analyzed using Microsoft Access, Microsoft Excel (Microsoft, Redmond, WA), and StatView (SAS Institute, Cary, NC). The baseline characteristics and hospital outcomes for the two groups were compared using the 
2 or Fisher's exact test for categorical data and unpaired t tests for continuous variables. Results are reported as mean ± standard deviation in text and tables. Statistical significance was defined as a p value less than 0.05.
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Results |
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Another two patients in the pulmonary autograft group required reoperation for aortic root dilatation and subsequent severe aortic regurgitation. Both patients received mechanical heart valves 7 and 11 months after their initial procedure.
At follow-up, all patients were in NYHA functional class I and II. The mean systolic blood pressure was 129 ± 21 mm Hg in the pulmonary autograft group and 123 ± 19 mm Hg in the mechanical valve group. Two patients had atrial fibrillation in the mechanical valve group and none in the pulmonary autograft group.
There was one anticoagulation-related complication in the mechanical valve group. The patient had a gastrointestinal bleed and required hospitalization. One patient in the pulmonary autograft group suffered a stroke 6 months after surgery. At the time he was in sinus rhythm and underwent an intensive search for what might have caused this stroke. However, apart from his past aortic valve surgery, no other risk factors could be identified. There were no other valve-related complications in this group. Hemodynamic performance was significantly better in the pulmonary autograft group. The LV mass regression, however, did not differ significantly between the groups. All echocardiographic data regarding regression of LV mass, ejection fraction, transvalvular gradients, and effective orifice area are summarized in Table 3.
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Comment |
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However, all currently available models necessitate lifelong anticoagulation, with all the inherent risks of this therapy.
Still, anticoagulation-related complications only account for 0.7% and 1.8% of early and late mortality after AVR, respectively. In comparison, 33.1% of early and 34.6% of late mortality after AVR are cardiac in origin [3]. Despite excellent perioperative results of mechanical valve replacement for aortic stenosis, the 15-year survival rate is only 44% [4].
Compelling evidence suggests that such poor long-term results may be related to the incomplete regression of left ventricular hypertrophy caused by persistently elevated transvalvular gradients [5]. Mechanical aortic valves are prone to high transvalvular gradients due to the obstructive nature of their pyrolitic carbon housing and sewing rings, especially during exercise [3]. Reduction of transvalvular is an important predictor of regression of LV hypertrophy after AVR [6].
Therefore, one could argue that to achieve an optimal postoperative result a valve substitute has to be chosen that is the least obstructive with the best hemodynamic performance. We would expect a subsequent faster and more complete regression of LV hypertrophy with the use of such a prosthesis. The pulmonary autograft, being a viable biologic substitute with nearly perfect hemodynamic performance and a low valve-related complication rate, could be such an ideal prosthesis.
The beneficial effects of the less obstructive nature of a pulmonary autograft have often been demonstrated [6–9]. However, no randomized trials comparing its performance with more obstructive valves (mechanical valves) are reported in literature.
In our study, the pulmonary autografts had significantly lower transvalvular gradients than the mechanical valves. From our understanding of the pathophysiology of aortic valve stenosis, we would have expected a significant difference in the regression of LV hypertrophy between the two valve substitutes. However, in this randomized group of patients, LV mass regression was similar in both groups at 6 and 12 months, despite the superior hemodynamic performance of the pulmonary autografts. Significant regression of LV hypertrophy has been reported in literature after AV replacement with both substitutes [9–12]. The 12-month postoperative follow-up period also seems to be sufficient to assess the regression of LV hypertrophy. Several authors have demonstrated that no difference in LV mass regression is found between 1 year and 3 years of follow-up [6, 12, 13].
A nonrandomized study comparing AVR with pulmonary autografts with mechnical valves in children was reported by Lupinetti and colleagues [8]. Reoperation-free survival at two years was 96% in the autograft group and 67% in the mechanical valve group. This was largely caused by the tendency of children to outgrow their prosthetic valves. However, there was no significant difference in actuarial patient survival, including operative mortality, between the two groups. The latter results are consistent with our findings in young adults and confirm that good postoperative outcomes are achieved with both types of valve substitutes.
Similar results are reported by De Paulis and colleagues [9], who compared (less obstructive) stentless and (more obstructive) mechanical valves. Although stentless valves resulted in a significantly lower peak systolic gradient, there was no significant difference in the rate and completeness of LV mass regression after 12 months.
Thromboembolic episodes have been rare and endocarditis has occurred infrequently with the use of pulmonary autografts [14]. In our study, there were no cases of endocarditis in either group. However, one patient in the pulmonary autograft group developed a stroke 6 months after his surgery. This was a surprising finding to us as pulmonary autografts, being viable tissue, generally do not require anticoagulation.
Progressive aortic valve regurgitation has been observed with continued follow-up and is the most important complication of the pulmonary autografts. Progressive aortic root dilatation and technical problems are the major cause of reoperation [15]. Additionally, malfunctioning pulmonary allografts, in the right ventricular outflow tract, are also a cause of reoperation [16]. In our study, there were two patients in the autograft group who required reoperation within the first 12 months. Both had severe aortic regurgitation due to progressive aortic root dilatation. None of the patients in the mechanical valve group required reoperation.
In conclusion, we would expect an aortic valve substitute with optimized hemodynamic performance and minimal or no residual postoperative gradient, as in pulmonary autografts, to result in better left ventricular remodeling and function. At 12-month follow-up, however, looking at LV mass regression we could not distinguish between patients receiving less or more obstructive valve substitutes. Also, 12-month morbidity and mortality rates did not differ significantly between the groups.
Based on the findings of our prospective randomized trial, we can recommend the use of both valve substitutes in young patients. The personal preference and skill of the implanting surgeon will continue to play an important role in choosing a certain valve type. However, the overall complexity of pulmonary autograft implantation, with its prolonged cross-clamping times, might under these circumstances not be justifiable if, as we found, the same results can be achieved with standard mechanical valves.
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References |
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  P. M. Dohmen, A. Lembcke, S. Holinski, D. Kivelitz, J. P. Braun, A. Pruss, and W. Konertz Mid-Term Clinical Results Using a Tissue-Engineered Pulmonary Valve to Reconstruct the Right Ventricular Outflow Tract During the Ross Procedure Ann. Thorac. Surg., September 1, 2007; 84(3): 729 - 736. [Abstract] [Full Text] [PDF]
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