The assessment of MPV function is based on echocardiography, but adequate assessment of leaflet motion is limited by acoustic shadowing. Cinefluoroscopy has been considered the standard method to assess leaflet motion, while CT is considered as an alternative option. In the present study we compared fluoroscopy and CT for MPV leaflet motion assessment and found that: 1) achieving an “in profile” view of the prosthesis was feasible in 74% of cases by fluoroscopy and 100% by CT, 2) feasibility of fluoroscopic assessment was higher in aortic than in mitral position, 3) in prosthesis with feasible assessment by both techniques, fluoroscopy and CT yielded similar measurements, but CT scans required shorter time and lower irradiation for acquisition (Fig. 2).
Cinefluoroscopy and CT in MPV leaflet motion assessment; what we know and what this study adds:
Fluoroscopy is an easy and readily available non-invasive technique for evaluating MPV, providing a more reliable evaluation of leaflet mobility -especially in the aortic position- than echocardiography(3, 8). Leaflet motion should be viewed in the ‘in profile’ projection, allowing calculation of opening and closing angles(1). Due to variability in surgical prosthesis orientation, deliberate use of lateral and cranio-caudal angulation is often required to achieve such a projection. Montorsi et al.(4) evaluated the influence of different intraoperative valve orientation on feasibility of fluoroscopic evaluation of bileaflet MPVs (in mitral, aortic, and tricuspid positions). In prostheses oriented perpendicular to the ventricular septum, the prosthesis' "in profile" projection was rapidly (15 +/- 5 seconds) achieved in all patients. In prostheses oriented parallel to the ventricular septum, a proper fluoroscopic evaluation was impossible to obtain in 40%-95% of patients. In the remaining prostheses (with intermediate orientations), extremely angulated, uneasy projection was often required to achieve an appropriate fluoroscopic image.
Acknowledging these challenges of fluoroscopy, cardiac CT emerged as a tool that can provide incremental information on valvular mobility with very good image quality for most bileaflet MPVs(5). In an in vitro pulsatile model, CT yielded similar closing angle measurements as fluoroscopy(6). In pilot clinical studies, it was suggested that CT may have an even higher sensitivity than fluoroscopy in detecting leaflet motion restriction(7). Unlike on fluoroscopy (where the imaging plane is dependent on the in-situ orientation of the prosthesis), CT images can be reconstructed in any imaginary cross-sectional plane, making the desired “in profile” view achievable in virtually all scenarios.
In the present study, we found that achieving an ideal “in profile” view on fluoroscopy is challenging, especially in mitral prostheses. Although most mitral prostheses were optimally visualized in an RAO/CRA projection, the exact angulation was variable, and several mitral prostheses were better visualized in other C-arm quadrants (than RAO/CRA). This leads to a relatively prolonged session, with “trial-and-error” strategy until the desired view is reached, and eventually a significant incremental irradiation exposure. Moreover, an “in profile” view was impossible to achieve in one third of mitral prostheses. Feasibility of fluoroscopic assessment of aortic prostheses was much better, requiring less acquisition trials and -eventually- less irradiation. However, the overall feasibility of achieving an “in profile” view on fluoroscopy was 74% and CT prediction of the fluoroscopic projection confirmed that achieving such a projection would require an extreme C-arm angulation.
Like fluoroscopy, CT scan required no contrast, and -superior to fluoroscopy- the scan was consistently short with predictable relatively small irradiation exposure, yielding a reliable measurement in 100% of cases (as opposed to the above mentioned 74%).
These findings collectively suggest that CT scan is a more robust tool to assess MPV leaflet motion, and that it can serve as a first line tool after echocardiographic assessment. The advantages of CT over fluoroscopy are more relevant when a quicker scan is required, a lower irradiation is imperative (such as during pregnancy), and in mitral position. CT also seems to be a more suitable tool -than fluoroscopy- for serial and follow up assessments.
Notwithstanding, CT is not without limitations. Availability -although much improved- remains an issue, and heart rate control and respiratory training remain prerequisites to improve image quality.
The relatively small sample size is a limitation of the present study. Additionally, definition of the corresponding leaflets on fluoroscopy vs. on CT is limited as the anatomical landmarks that can define the leaflet on CT images are lacking on fluoroscopy. We considered C-arm angulations out of practical range if lateral (RAO/LAO) angle was > 120° or craniocaudal angle was > 45°. This range is rather theoretical as extreme angulations leads to excessive irradiation exposure and possible CRA/CAU angulation is decremental as the lateral (LAO/RAO) angulation increases (i.e. only shallow CRA/CAU angulation is feasible with extreme lateral angulations).