Incidence and quantitative level of calcification of aortic valve and different segments of the vascular system according to the subtype of aortic stenosis

Background: We studied the differences between subtypes of aortic stenosis (AS) based on gradient and flow, focusing on the burden of aortic valve calcium (AVCS) and the distribution and severity of calcification in the vascular system.

Patients and Methods: This retrospective registry study was conducted at the Cardiovascular Centre Rotenburg and included 316 patients who underwent transfemoral transcatheter aortic valve implantation (TAVI) between January 2020 and December 2022 (Aortenklappenregister Rotenburg, AKRRO). Four AS subtype groups were compared in this analysis: high gradient (HGAS), low flow low gradient (LFLGAS), paradoxical low flow low gradient (PLFLGAS), and normal flow low gradient (NFLGAS). Aortic valve calcium scores (AVCS) were quantified using non-contrast computed tomography (ncCT) imaging with a threshold of 130 Hounsfield units (HU). Calcification volume (CV) was assessed in total and for each aortic valve cusp (NCC, RCC and LCC) using contrast-enhanced CT (ceCT) with a modifiable threshold. Vascular tree calcification was classified both, qualitatively (present=0, not present=1) and semi-quantitatively (none=0, mild=1, moderate=2, severe=3) in seven localizations (coronaries, carotid arteries, ascending aorta, aortic arch, thoracic descending aorta, abdominal descending aorta, and iliac/femoral arteries).

Results: For 315 out of 316 patients, AS subtype could be classified retrospectively as follows: 223 (70.8%) HGAS, 46 (14.6%) LFLGAS, 24 (7.6%) PLFLGAS and 22 (7.0%) NFLGAS. There was a significant difference between these subtype groups regarding the five calcium quantification parameters AVCS (p=0.008), CV (p<0.001), CVNCC (p=0.001), CVRCC (p=0.002) and CVLCC (p=0.001) with highest values in patients with HGAS. In detail, the median AVCS  was 3040 for HGAS, 2399 for LFLGAS, 1564 for PLFLGAS and 1873 for NFLGAS. The median CV (total) was 796 in HGAS, 644 in LFLGAS, 448 in PLFLGAS and 575 in NFLGAS. The median CV values for the separate cusps were as follows: NCC - 329 for HGAS, 257 for LFLGAS, 159 for PLFLGAS and 264 for NFLGAS;  RCC - 235 for HGAS, 200 for LFLGAS, 133 for PLFLGAS and 183 for NFLGAS; LCC - 233 for HGAS, 191 for LFLGAS, 144 for PLFLGAS, and 218 for NFLGAS. With respect to calcification in the different vascular segments described above, there were no differences between the subtypes, neither regarding the presence nor the severity (p=n.s.).

Conclusions: In elderly patients with severe, symptomatic AS treated by TAVI, calcification of the aortic valve is much higher in HAGS compared to other subtypes of AS. This finding might suggest differences in primary pathogenesis of AS subtypes and raises doubts that, e.g., LFLGAS should simply be considered as former HGAS with deteriorated systolic left ventricular function over time. Moreover, no relation between AS subtypes and distribution of vascular calcification could be evidenced in this single-center analysis.