Evaluation of transcatheter aortic valve frame expansion and geometry using intravascular ultrasound

Transcatheter aortic valve (TAV) frame under-expansion is associated with adverse haemodynamic valve performance and clinical outcomes. Current techniques to evaluate TAV frame expansion are limited to fluoroscopic assessment, which can be unreliable or transoesophageal echocardiography, which requires deep sedation or general anaesthesia.

We describe how intravascular ultrasound (IVUS) can be used to rapidly evaluate TAV frame expansion and geometry intra-procedurally and assess the impact of post-dilatation.

All severe aortic stenosis patients who underwent IVUS evaluation of TAV frame expansion and geometry were included. For all cases, a dedicated 10 Hz vascular IVUS catheter, compatible with a 0.035" guidewire was utilised. Following valve implantation, the IVUS catheter was advanced on the left ventricular guidewire and positioned at the stent frame inflow, and TAV frame geometry was assessed. If post-dilatation was deemed necessary, a repeat IVUS evaluation was performed after post-dilatation. For each case the minimum and maximum diameter and stent frame area were measured and used to calculate the percentage stent frame expansion (defined as [TAV inflow area / native annulus area] x 100) and the ellipticity index (defined as maximum diameter / minimum diameter). Results are expressed as mean ± standard deviation.

A total of 38 patients underwent IVUS evaluation during TAVI. 33/38 (87%) patients underwent TAVI using a self-expanding valve (SEV), whilst 5/38 (13%) had a balloon-expandable valve (BEV). 4/38 (10%) had a type 1 bicuspid valve (all treated by SEV), and 1/38 (3%) had a type 0 bicuspid valve (treated by BEV). Post-dilatation was performed in 22/38 (58%) patients.

Overall, mean TAV frame expansion following valve deployment alone was 83% ± 13% and ellipticity index was 1.31 ± 0,21. BEV compared to SEV were associated with better expansion (98% ± 5% vs. 81% ± 12%) and less ellipticity (1.14 ± 0.10 vs. 1.34 ± 0.22). Post-dilatation resulted in an increase in TAV frame expansion from 79% ± 14% to 87% ± 14% and improved ellipticity index from 1.36 ± 0.25 to 1.31 ± 0.19. The benefit of post-dilatation was most evident in BEVs, where frame expansion improved from 77% ± 13% to 86% ± 14% and ellipticity index decreased from 1.39 ± 0.24 to 1.32 ± 0.19. In tricuspid valves, final mean TAV frame expansion was 89% ± 13% in patients who underwent post-dilatation and similar to the final mean TAV frame expansion of 89% ± 7% in patients who did not undergo post-dilatation. In type 1 bicuspid valves, final mean TAV expansion was 74% ± 7% with greater ellipticity index of 1.48 ± 0.17, despite post-dilatation in all these patients.

Intra-procedural IVUS provides a rapid assessment of TAV stent frame expansion and geometry, which can be used to guide procedural strategy including the need for and effect of post-dilatation.