Comprehensive assessment of aortic flow before and after aortic valve replacement in an ex vivo porcine model with four-dimensional flow magnetic resonance imaging.

Objectives: Aortic valve replacement (AVR) has shown to induce secondary flow patterns deviating from main flow. It is impossible to analyse the impact of surgical access and different AVR techniques under standardized conditions in patients or silicone models. Therefore, we developed an ex vivo swine model to analyse the impact of surgical access and to compare flow patterns after different AVR techniques within the ascending aorta.

Methods: Porcine aortas (n = 6) were anastomosed to a custom-made piston pump. The pulse duplicator perfused the aortas with a blood-mimicking fluid at 2.5 l/min and 64 bpm. 4D flow magnetic resonance imaging of each aorta was acquired prior to surgery (NAV, n = 6), after sham surgery (aortotomy and closure thereof without valve replacement, NAV-A, n = 6) and after Ozaki procedure (AVneo, n = 2), biological valve (BV, n = 2) or mechanical valve (MV, n = 2). Secondary flow patterns and peak velocity were analysed with GTFlow (GyroTools, Switzerland).

Results: Sham surgery alone induced secondary flow patterns in the ascending aorta in all specimens. After AVR, more secondary flow patterns were observed distal to BV compared to AVneo or MV. Three flow patterns developed after BV, two after AVneo and one after MV. In addition, peak velocity within the aortic sinuses of Valsalva increased after all AVR procedures, most strikingly after BV (NAV = 75 ± 22 cm/s, NAV-A = 79 ± 29 cm/s, AVneo = 115 ± 36 cm/s, BV = 142 ± 21 cm/s, MV = 107 ± 4 cm/s; mean±standard deviation).

Conclusions: We successfully established an ex vivo model suggesting that flow alterations not only depend on the type of AVR but are associated with surgical access. The strongest secondary flow patterns developed after BV followed by AVneo and MV.