Glossary of abbreviations : AVR = aortic valve replacement

Objective: In patients with a small aortic root undergoing aortic valve replacement, the Freedom SOLO bioprosthesis may be the ideal prosthesis due to its stentless design and supraannular implantation. This study investigated if the stentless Freedom SOLO has an advantage when compared with a stented bioprosthesis in patients with a small aortic root. Methods: From April 2005 to July 2014, 269 consecutive patients underwent aortic valve replacement with either a Freedom SOLO (n=76) or Mitroflow (n=193) bioprosthesis size 19mm or 21mm. This retrospective comparison study presents clinical and echocardiographic followup data. Results: Operative outcome and survival were similar. At 7 years, cumulative incidence of aortic valve reoperation and structural valve deterioration favor the Freedom SOLO (0% vs 7.1%, P=0.03 and 0% vs 4.5%, P=0.08, respectively). Additionally, the postoperative peak and mean valvular gradients favor the Freedom SOLO (21±9mmHg vs 32±12mmHg and 12±5mmHg vs 19±8mmHg, both P=<0.001, respectively). During mid-term follow-up this hemodynamic advantage continued in favor of the Freedom SOLO. Also prosthesis-patient mismatch occurred less frequently in the Freedom SOLO (28% vs 52%, P=0.001). There were no differences in prosthetic valve endocarditis, thromboembolic or bleeding events. Conclusions: The stentless Freedom SOLO has several significant advantages for aortic valve replacement in patients with a small aortic root in comparison with a stented Mitroflow bioprosthesis. The Freedom SOLO shows superior hemodynamic performance with significantly lower valvular gradients that remained stable during mid-term follow-up. Additionally significantly fewer prosthesis-patient mismatch occurred and the Freedom SOLO showed superior durability. ULTRAMINI ABSTRACT This single-center retrospective study investigated if the stentless Freedom SOLO bioprosthesis has an advantage when compared with a stented Mitroflow bioprosthesis in 269 patients with a small aortic root. The Freedom SOLO shows superior hemodynamic performance, fewer prosthesis-patient mismatch and superior durability during mid-term follow-up. INTRODUCTION In patients with a small aortic root undergoing aortic valve replacement (AVR), operative mortality is increased [1]. Additionally, there is an increased risk for prosthesis-patient mismatch which is undesirable as it is associated with decreased hemodynamic function, less regression of left ventricular mass, more cardiac events and worse survival [2]. Surgical aortic annulus dilatation is an option, but this extends operation time and requires an experienced surgeon [3,4]. Patients with a small aortic root may profit from the implantation of a stentless bioprostheses since its design provides a larger effective orifice area. This leads to less prosthesis-patient mismatch, lower valvular gradients and better postoperative outcomes [5]. The Freedom SOLO (Sorin, Saluggia, Italy) is a stentless bioprosthesis with an excellent hemodynamic profile and crossclamp times that are equal to stented bioprostheses [6]. Its stentless design and supra-annular implantation technique offers the largest possible effective orifice area. This study investigates if the stentless Freedom SOLO has advantages over a stented bioprosthesis in patients with a small aortic root. We hypothesize that in patients with a small aortic root the hemodynamic performance of the Freedom SOLO is better than that of a stented bioprosthesis. MATERIAL AND METHODS Study population Between June 2005 and July 2014, 269 consecutive patients underwent AVR with either a stentless Freedom SOLO or a stented Mitroflow (Sorin, Saluggia, Italy) with a size 19mm or 21mm prosthesis. Both manufacturers’ 19mm and 21mm sizers are comparable in diameter. The Mitroflow prostheses were implanted supra-annular. All operations were performed at the Academic Medical Center in Amsterdam, The Netherlands. The choice of prosthesis was based on surgeon’s preference and made in consultation with the patient. Baseline patient characteristics, operative details and in-hospital complications were collected from the Academic Medical Center database. On January 6, 2015, information on vital status was obtained from the Dutch national population registry (Statistics Netherlands, Voorburg, The Netherlands). Follow-up data and echocardiographic results were collected retrospectively, during visits to the referring cardiology centers. Patients were censored at time of last contact. The Society of Thoracic Surgeons Adult Cardiac Surgery Database Data Specifications, version 2.81, was used for definitions of baseline characteristics and postoperative outcome [7]. Mortality was defined as 30-day and in-hospital mortality combined. Preoperative renal failure was defined as a calculated creatinine clearance <50ml/min using the Cockcroft-Gault formula [8]. For definitions of structural valve deterioration, nonstructural dysfunction, embolism, bleeding event, endocarditis and aortic valve reoperation, the guidelines for reporting mortality and morbidity after cardiac valve interventions were used [9]. Prosthesis-patient mismatch was defined as an indexed effective orifice area <0.85cm/m[2], measured with transthoracic echocardiography within 2 years postoperatively. Up to 2010, all patients received oral anticoagulation therapy for 3 months postoperatively followed by lifelong acetylsalicylate 100 mg daily. From 2010, all patients received only lifelong antiplatelet therapy with acetylsalicylate 100 mg daily unless otherwise indicated by concomitant morbidities. Statistical analysis Data are expressed as means ± standard deviations, medians with interquartiles or as numbers and percentiles as appropriate. Differences in baseline characteristics, operative details and outcomes were tested for significance by unpaired t-test, Mann-Whitney U test, Fisher’s exact test and χ (for trends) as appropriate. Survival, prosthetic valve endocarditis, thromboembolism and bleeding events were analyzed using the Kaplan-Meier method. The log-rank test was used to test for differences. Aortic valve reoperation and structural valve deterioration were analyzed using cumulative incidence function using a competing risk analysis [10]. For aortic valve reoperation ‘death’ was considered a competing risk. For structural valve deterioration both ‘death’ and ‘aortic valve reoperation’ were considered a competing risk. Gray’s log-rank test was used to test for differences between the groups in the competing risk analysis. Logistic regression analysis was used to identify if choice of prosthesis was a risk factor for prosthesispatient mismatch, considering age, gender and body mass index as variables. The longitudinal follow-up of echocardiographic results were analyzed using a mixed effects model. Statistical analyses were performed using SPSS, version 21 (IBM Corp., Armonk, NY, USA). The cumulative incidence function analysis and the mixed effects model were performed using R (R Foundation for Statistical Computing, Vienna, Austria). A P-value of <0.05 was considered statistically significant.