MDCT is the gold stand for pre TAVR assessment of the aortic valve complex and assessing the iliofemoral vasculature for access consideration [3]. As compared to Two dimensional (2D) TEE, MDCT provides a more accurate assessment of the aortic annulus measurements and does not require sedation [4, 8]. The reliance on intraprocedural 2D TEE in TAVR has steadily declined over the past 5 years as conscious sedation became the standard approach. It has been associated with shorter hospital stay and a trend for lower mortality compared to general anesthesia [9]. Nevertheless, the quality of MDCT may occasionally be limited due to partial volume-averaging effects (blooming), heart/lung motion, arrhythmias, and patient motion [3], as was the case with the first patient presented. On the other hand, among patients with advanced CKD, the use of IV contrast for assessment of the iliofemoral arteries may be relatively contraindicated due to the increased risk of renal failure.
Far-field IVUS is a novel tool in the armamentarium of structural interventional cardiologists. Far-field IVUS has a maximum imaging diameter of 50 mm compared to a 20 mm diameter in traditional coronary IVUS catheters, which allows for adequate evaluation of the aortic valve complex. The use of IVUS in TAVR was first reported by Roy et al. in 2013 [10]. A case series in 2016 demonstrated an excellent correlation between aortic valve measurements obtained by MDCT and IVUS [11]. More recently, in 2017, Hakim et al. investigated the role of large-field IVUS vs. MDCT and 2D TEE for annular sizing and predicting PVR in 50 consecutive patients undergoing TAVR [12]. In their study, far-field IVUS demonstrated similar aortic annular diameters and area measurements compared to MDCT and performed as well in predicting PVR. There were strong correlations between IVUS and MDCT annular areas (r = 0.87, P < 0001) and mean diameters (r = 0.73, P < 0.0001). 2D TEE underestimated aortic annular diameter and did not correlate well with MDCT or IVUS. More recently, far-field IVUS use in TAVR has also been reported for the intraprocedural assessment of implanted valve frame geometry and leaflets mobility when under expansion is suspected [13].
Far-field IVUS has a strong correlation with MDCT and invasive angiography in the assessment of the iliofemoral arteries [14]. It carries the advantage of minimal contrast use and lower radiation exposure when performed at the- time of the routine pre-TAVR hemodynamic and coronary assessment as demonstrated in case number 2. Moreover, the data can be interpreted in real time, and are also a valuable adjunct to CTA in patients with borderline femoral access diameters or considerable CTA artifacts.
Far-field IVUS has a few limitations that should be acknowledged. If the IVUS catheter is not centralized, the images can be biased to one side, leading to oblique sections, and oversizing the aortic annulus. To avoid eccentric catheter position and motion artifacts, the IVUS catheter should be advanced over a stiff guidewire and measure the eccentricity index. If motion artifact is present the IVUS run can be repeated.
The IVUS catheter that was used during the cases was not primarily manufactured to visualize the aortic valve complex, so an IVUS catheter with better resolution can help in the assessment of the valve cusps, annulus, and PVR. The additional cost of utilizing the far-field IVUS catheter should also be considered.