The Freestyle stentless aortic bioprosthesis has demonstrated excellent long-term clinical and hemodynamic results (9). The aim of this study was to evaluate the geometrical changes of the aorta following Freestyle prosthesis implantation in the context of clinical outcomes.
In our cohort, Freestyle prosthesis was deployed in high-risk patients with infective endocarditis, aortic root enlargement, or aortic dissection. In the vast majority of these patients (87.5%), a concomitant procedure was necessary. Moreover, four patients (12.5%) underwent an isolated root replacement, two of which were redo procedures. One patient suffered from infective endocarditis and the other presented with isolated root dilatation. The population of this particular study group could be explained through the inclusion criteria for performing preoperative CTAs. Furthermore, this study population accounts for an in-hospital mortality of 18.6%, which is elavated when compared to isolated AVR with Freestyle prosthesis. Indeed, in their systematic review Sherrah et al., reported an in-hospital mortality of 5.2% after Freestyle implantation (10). When our results are placed into perspective, and consideration is made of mortality rates in combined aortic root procedures, high-risk patients, reoperations, or freestyle prosthesis implantation in destructive endocarditis, the outcomes could be considered comparable (11–15).
Following AVR, a high residual transvalvular gradient constitutes a risk factor for worse outcomes, impaired left ventricular diastolic dysfunction, and incomplete regression of left ventricular hypertrophy (16, 17). The Freestyle aortic bioprosthesis was designed to provide superior hemodynamic performance, more physiological flow patterns, and lower transvalvular gradients (18, 19). Indeed, a reduction of the mean transvalvular gradient has been described by multiple studies (20). Yun and colleagues, reported a 41% decrease after AVR with Freestyle prosthesis within the first 6 months, with a corresponding increase in EOA. After 6 months, the gradients remained relatively stable (21). Accordingly, in our study median transvalvular gradients declined from 23.5 mmHg [IQR: 10.25–41] preoperatively to 5.0 mmHg [IQR: 3.5–13.5] during the postoperative course.
Echocardiographic diagnostics is the gold standard for AVR, evaluating not only the valve itself but also the dimensions of the aorta, which, currently remains the most influential parameter for assessing the risk for aortic dissection and deciding on surgery (22). As a matter of fact, precise evaluation of the aortic diameter is essential for an accurate diagnosis and further planning of the surgical procedure (23, 24). Due to the elliptical shape of the aortic annulus, with its maximum diameter lying in the coronary plane, its dimensions can be subject to significant underestimation when using echocardiography or only 2D CT measurements (25). CT allows for the assessment of the valve anatomy, differentiation between bicuspid and tricuspid valves, and the shape and diameter of the aortic annulus and the left ventricular outflow tract. In our study, the measurements of the aortic annulus strongly correlated with the implanted size of the Freestyle prosthesis. Despite the advantage of sizing under direct vision, accurate pre-operative assessment is important for valve selection and the decision of whether additional surgery is necessary. Especially in patients with asymmetrical aneurysms and bicuspid aortic valve, a significant difference between the minimum and maximum diameter of the aortic root has been described (7). In the present study, the comparison between the minimum and maximum measured diameter resulted in a more than 20% higher diagnosis rate of root aneurysms > 4.5 cm. On the other hand, 3D volume reconstructions allow the measurement of the entire volume of interest. Therefore, 3D volume measurements are more accurate in detecting small changes in the size of an aneurysm than diameter measurements (26). Geisbüsch et al. assessed the volume of the ascending aorta in patients with aneurysms compared to a control group (27) and reported a volume of 132.9 ± 39.4 ml in patients with ascending aortic aneurysm and 78.0 ± 24.5 ml in the control group. In our study, the pre-operative volume of the aortic root and ascending aorta were similar (137.27 ± 65.24 cm3). Subsequent to Freestyle prosthesis implantation, the length from the aortic root to the proximal aortic arch decreased by approximately 3 cm. Moreover, the diameters and areas decreased to normal values, resulting in a mean volume of 54.5 ± 21.1 cm3 (28). These volumetry results demonstrate an excellent restoration of the aortic root and ascending aortic geometry.
Study limitations
The main limitation of this study is the relatively small cohort size, caused by the inclusion criterion for the availability of preoperative CTAs. Furthermore, the study is limited by its retrospective, nonrandomized, single-center nature.