Page 14 - Journal of Structural Heart Disease Volume 5, Issue 3

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Original Scientific Article
the most common VHD requiring valve replacement in Europe and North America [1, 2]. Its clinical im- portance has increased health care expenditure and caused exponential growth in the application of tran- scatheter aortic valve replacement (TAVR) [3].
Echocardiography and computed tomography (CT) are complementary imaging techniques for TAVR. They are used to evaluate patient selection and optimal transcatheter valve size selection in pa- tients with symptomatic severe AS and degenerative tricuspid valve [4-6]. Appropriate patient selection based on clinical symptoms and the severity of AS is of maximal importance for successful TAVR proce- dure [7]. The aortic valve area (AVA) is an important and widely used parameter to determine AS hemo- dynamic severity. It is traditionally calculated at Dop- pler transthoracic echocardiography (TTE) by using the continuity equation (AVATTE). It is considered as the major independent predictor of outcome in AS [8, 9]. Cardiac CT (CCT) using multiphase reconstruc- tion of the cardiac cycle can provide imaging of aortic valve motion. Measurement of AVA can be obtained using direct planimetry on CCT images (AVACCT) [10]. However, there is no objective non-invasive reference standard to determine true AVA in patients with se- vere AS. The functional AVA or AVATTE can significantly underestimate AVA because the left ventricular out- flow tract (LVOT) area is underestimated by using a single-diameter measurement assuming circular ge- ometry [11]. Most frequently, the LVOT is ellipsoid. The anatomical AVA or AVACCT is larger than AVATTE. Several factors such as aortic valve calcification and LVOT morphology can affect AVA or AVACCT [12-15].
No studies have assessed factors affecting mea- surement differences of AVA between TTE and CCT. We hypothesize that the different size of LVOT mea- sured with CCT and TTE and shape (or eccentricity) of LVOT obtained by CCT are associated with differences of AVA measured with TTE and CCT. However, other variables might significantly affect this difference. This may have important clinical implication in calcu- lating AVA in patients with severe AS. Thus, the aim of this study was to identify factors affecting the differ- ence between AVA measured by planimetry on CCT and AVA obtained by continuity equation on TTE in patients with symptomatic severe AS.
Material and Methods
Study Population
Patients were drawn from a single-center study of patients who underwent balloon expandable TAVR (SAPEIN and SAPIEN XT, Edwards Lifescience, Irvine, CA, USA) from January 1st, 2013 to November 30th, 2014. The inclusion criteria were: patients who had severe AS (defined as AVA < 1 cm2, mean transvalvu- lar gradient > 40mmHg, or peak transvalvular veloc- ity > 4 m/s or any combination) [16], with New York Heart Association (NYHA) class II, III, or IV heart fail- ure symptoms, and with high surgical risk based on the Society for Thoracic Surgeons (STS) risk score. The exclusion criteria were: patients who needed valve- in-valve procedures and those who had previous mi- tral valve replacement. TTE and CCT were performed within 4 weeks without interval change in clinical sta- tus or cardiovascular event. This retrospective study was approved and performed in accordance with the regulations of the hospital Institutional Review Board. All patients gave written informed consent before participation.
Transthoracic echocardiography
A single highly experienced operator performed TTE in all patients using VIVID 7 ultrasound machine (General Electric, Milwaukee, WI, USA). Collected data were as follows: maximal blood flow velocities at aor- tic valve and LVOT, time velocity integrals at aortic valve and LVOT, LVOT diameter, and AVA obtained from the continuity equation [π × (LVOT diameter/2)2 × (velocity time integral of the LVOT/velocity time integral of the transaortic flow)]. Mean and maximal transvalvular aortic pressure gradients were recorded.
Cardiac Computed Tomography Examination
All ECG-gated contrast-enhanced CCT examina- tions were performed using a dual-source CT scan- ner (Somatom Definition, Siemens Medical Solu- tions, Forchheim, Germany). Data acquisition was performed in a craniocaudal direction with detector collimation of 2 × 32 × 0.6 mm, slice acquisition of 2 × 64 × 0.6 mm, gantry rotation time of 330ms, pitch of 0.20–0.43 adapted to HR, tube voltages of 120 kV for calcium scoring and CCT, tube current-time product of 100–140 mAs per rotation for calcium scoring, and
Ko S. M. et al.
Aortic Valve Area Measured with CT and TTE