BACKGROUND:
Degenerative aortic valve stenosis is characterized by increased calcium burden of the aortic valve leaflets. Quantification of aortic valve calcium has been proposed by guidelines as a diagnostic adjunct to diagnose severe valvular stenosis especially in the work up of patients with low flow, low gradient hemodynamics with gender-based thresholds for likely versus unlikely severe aortic valve stenoses. We analyzed a cohort of aortic valve stenosis patients referred for CT assessment prior to transcatheter aortic valve replacement stratified according to the published cut-off thresholds for unlikely vs. likely severe aortic valve stenosis.

METHODS:
Consecutive patients referred for CT assessment of aortic root anatomy and peripheral access prior to transcatheter aortic valve implantation due to symptomatic aortic valve stenosis were screened for inclusion in this analysis. In all patients, a native data set for assessment aortic valve calcifications was acquired prior to acquisition of contrast-enhanced data sets of the aortic root and peripheral vasculature. Native acquisitions were performed using prospectively ECG-gated spiral data acquisition with a third generation CT system. Data sets were transferred to a workstation and calcium scoring was performed using commercially available software. The Agatston method was used for quantification of aortic valve calcification using a threshold of 130 Hounsfield units (HU) for calcium detection. A cut off of 1600 Agatston units for men and 800 Agatston units for women was used to stratify the cohort into a low and high calcium burden group.

RESULTS:
Between 2017 and 2019, 300 consecutive patients were screened for inclusion in this analysis. Out of these, 35 patients were excluded due to prior aortic valve replacement, severe artefacts rendering calcium quantification not possible or echocardiographic indexed aortic valve area (AVAi) > 0.6 cm²/m² or  AVAi > 1.0 cm². 242 patients were stratified in the high calcium burden group and 23 patients in the low calcium burden group. Mean age was 79±8 years, 55% males vs. 81±5 years, 60% males for the high vs. low group, respectively. (p=n. s.) The median Agatston score for the high vs. low group was 3199 vs. 987 Agatston units (p<0.0001).  Echocardiographic AVAi, ejection fraction and stroke volume index showed no significant differences in both groups (mean AVAi 0.45±0.1 cm²/m², EF 51±11% and SVi 36±17 ml/m² vs. 0.46±0.1 cm²/m², 50±15% and 36±17 ml/m², respectively). Patients with high calcium burden showed higher maximum and mean aortic valve gradients, larger sinus of valsalva measured in CT and thicker interventricular septum measured in echocardiography (63±22 mmHg, 38±14 mmHg, 33±4 mm and 13±2 mm vs. 43±20 mmHg, 25±13 mmHg, 31±2 mm and 12±1 mm, respectively, p<0.05 for all).The number of patients with concordant aortic valve area and mean gradient (AVA≤ 1.0 cm², mean gradient ≥ 40 mmHg) was not significantly different between both groups (39% vs. 22% for high/low calcium burden groups, respectively,p=0.09).

CONCLUSION:
In 9% of patients with severe aortic valve stenosis referred for TAVI, the amount of valvular calcification was below the published thresholds for likely aortic valve stenosis. Relevant aortic valve stenosis with low calcium burden is possible albeit less frequent with patients exhibiting lower gradients and smaller dimensions of the sinus of valsalva compared to patients with high calcium burden.