|ECR 2013 / C-0677|
|Aortic valve evaluation by 128-DSCT prior to TAVI: Optimal time interval for AVA sizing in comparison with echocardiography|
The phase with widest opening of the aortic valve was most likely to be found in early-to-mid systole at 20-25% of RR interval. This was also the interval of the cardiac cycle, where best image quality was achieved and is therefore the interval most suitable for AVA planimetry. That accords to data previously published for 16- and 64-slice CT, where 20-30% , 20-25% , 5-20%  and 12%  were suggested to be the phases of widest opening of aortic valve.
AVAmax showed a good correlation with AVATTE with a slight overestimation of AVA by CT. An overestimation of planimetry compared to TTE estimation was also described by several other studies and is result of a meta-analysis by Shah et al.  that included 437 patients from 9 studies.
The phase of best correlation between AVA measured by CT and AVA estimated by TTE was found most often at 35% of RR-interval (11/44 [25%]), which is later than the phase of maximal AVA. Thus an explanation for the systematic overestimation of AVAmax compared to AVATTE could be, that the flow-dependent AVATTE corresponds to a cardiac phase, later than the one used for CT-planimetry when the aortic valve is already partially closed.
Shah et al. supposed the systematic overestimation to be caused by two different aortic valve orifices, measured by CT and TTE respectively. Through the continuity equation, the ‘‘effective’’ orifice area is measured which is always smaller than the actual anatomic orifice because blood flow tends tostream centrally from the anatomic orifice. 
A limitation of this study is the fact, that AVA measurement by CT could not be compared to catheter based calculation, because not all patients included had received invasive coronary angiography. Moreover it would have been interesting, but not practicable to compare AVA measured by CT to cardiac MRI. Furthermore a lot of patients scheduled for TAVI had renal insufficiency so that they had to be excluded from CT-study.
128-slice DSCT allows direct measurement of the anatomic aortic valve area, independent from hemodynamics. Results correlate good with TTE calculations. However, cardiac CT causes a radiation exposure for the patients and requires administration of contrast medium. TTE should therefore remain diagnostic standard for AVA-quantification. However, as a cardiac CT scan is performed anyway if TAVI intervention is planned, AVA should be measured by CT in these patient additionally to TTE calculation.
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