Author + information
- Carlos E. Ruiz, MD, PhD⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Carlos E. Ruiz, Lenox Hill Heart and Vascular Institute of New York, Interventional Cardiology, 130 East 77th Street, 9th Floor, Black Hall, New York, New York 10021
Percutaneous aortic valve replacement (PAVR) is an exceptionally innovative procedure that will undoubtedly alter the way we treat patients with severe aortic stenosis. A procedure once reliant on the operative visual information and feedback afforded to the cardiovascular surgeon is now supplanted by a multitude of imaging technologies available to the interventional cardiologist. Already since the advent of this technology, interventionists have become more cognizant of the intricate anatomopathological relationships of the aortic valve complex. Unfortunately to date, no single imaging modality provides all of the necessary anatomical and functional information needed for safe and effective transcatheter valve implantation. It is now more imperative for us to be aware of the many different imaging modalities available and to be able to integrate their varied information in order to more accurately plan and deliver transcatheter prosthetic valves.
Currently, there are 2 transcatheter prosthetic valves that are commercially available outside the United States. Both valves have different profiles and mechanical properties. One valve is designed on a balloon-expandable frame with the coaptation line of the leaflets at the native annular level; the other valve is designed on a self-expandable frame with the coaptation line of the leaflets in a supra-annular level. Optimizing prosthesis selection should be based on matching the physiomechanical properties of the device intended with the anatomical and mechanical characteristics of the patient's cardiovascular structures. Regardless of the type of prosthesis, patient selection is paramount for improved safety and efficacy of these new procedures. Accurately defining the anatomic and mechanical properties of the cardiovascular structures is a necessity. This process begins by choosing the safest access site to minimize vascular complications and to effectively deliver the valve. Monoplanar measurements of the inner luminal diameters of the access vessels alone is clearly inadequate. The degree of tortuosity, angulation, and the location and quantification of vessel calcification must all be taken into consideration. Nonetheless, this information may not be sufficient to ensure safe passage of the delivery systems. We lack information on vessel compliance and are unable to estimate how the vascular structure will reconfigure during the passage of stiff devices.
In this issue of the Journal, Toggweiler et al. (1) report the improvement on vascular complications during PAVR in 137 consecutive patients during a 2-year period in a single institution. Vascular complications occurred in 18% of the patients, mostly in patients with identifiable vascular disease (37%). The use of screening multidetector computed tomographic (MDCT) angiography was progressively incorporated over the study period and was available in 60% of all patients. In this group of patients screened with MDCT, the vessel minimal luminal diameter being smaller than the sheath external diameter (23% vs. 5%) and the presence of calcified vessels (29% vs. 9%) were strong predictors for vascular complications. Major vascular complications decreased from 8% to 1% and minor vascular complications from 24% to 8% over the 2-year study period. The larger single-center experience of these investigators compared favorably with the recent PARTNER (Placement of Aortic Transcatheter Valve) trial, in which major vascular complications occurred in 16.2% of cohort B (2) and 11% of cohort A patients (3).
The decrease in vascular complications is multifactorial, owing to operator experience, device refinement, and foremost patient selection, by assessing the vasculature from the access site to the valve annulus. Although not reported in their study, the direct contribution of better image information, such as MDCT, may have played a significant role in decreasing vascular complications during PAVR. Currently, most interventionists rely on plain angiography and/or CT technologies to assess inner lumen diameters, tortuosity, and calcification of the vasculature. These methodologies trust single-diameter measurements of a 2-dimensional (2D) planar image, unless curve multiplanar reconstruction and 3-dimensional (3D) vessel analysis is performed. Perhaps routine 3D imaging interpretation could enhance the accuracy of vessel assessment. Yet imaging alone may not provide all the necessary information to significantly improve patient selection. Mechanical analysis of the vessels may be necessary. There is no substitute for experience on any type of procedure to minimize complications. Nonetheless, quantifiable imaging parameters that can be universally applied will be a major advance toward improving success and decreasing PAVR complications.
The major challenges to a functionally successful valve implantation remain the proper sizing of the prosthesis for the intended landing zone and establishing the appropriate angulation of the delivery system in relation to the annular plane. Ideally the valve should abolish any degree of obstruction between the left ventricle and the aorta, without resultant valvular or paravalvular regurgitation and without impact on the left ventricular outflow tract mechanics. The precise assessment required is impossible based solely on 2D image information; therefore, accurate measurement of this complex dynamic structure should rely on true 3D image measurements throughout the cardiac cycle (4-dimensional with the time factor), combined with hemodynamics. This would enable us to provide accurate quantifiable information on the annular dimensions and angulation while allowing a simultaneous estimation of the inherent mechanical properties of the aortic valve complex.
Also in this issue of the Journal, Hamdan et al. (4) assessed the deformation dynamics of the aortic annulus throughout the cardiac cycle using multiphase reconstruction of electrocardiogram-gated CT angiograms in 35 patients with severe aortic stenosis undergoing PAVR and in 11 normal control subjects. Their calculation of the Young's elastic modulus, a measure of aortic annular stiffness, relied on pressure data obtained at a different time interval than the CT image acquisition. They assumed many other important factors that make their data a vague quantitative expression of the annular mechanical properties. They describe the dynamic conformational changes that occur throughout the cardiac cycle of the aortic annulus, reshaping its elliptical shape in diastole to a more rounded shape in systole, to increase the cross-sectional flow area. This change occurs without a significant variation in the perimeter size, especially in patients with calcific aortic stenosis. The authors conclude that accurate measurement of the perimeter is therefore ideally suited for determining appropriate prosthesis size. This proposed methodology for sizing valve prosthesis obviates the need to depend on multiple size diameter measurements of a predominately elliptical-shape plane. Accommodation of a round prosthesis into a calcified elliptical annulus increases the risk of valve under-sizing or over-sizing depending on which diameter measurement is used. Inappropriate prosthesis size not only may result in embolization/migration of the prosthesis (5,6), but can also cause annular rupture (7,8), aortic dissection (9,10), and paravalvular leaks (11,12). Nevertheless, even when the perimeter of the annular plane is closely matched to the intended valve prosthesis, the mechanical response of the native tissue to the stress of the valve deployment cannot be predicted on the basis of imaging alone. The incorporation of hemodynamic data to the volumetric image acquisition during the cardiac cycle may add further understanding into the mechanical properties of the cardiovascular structures and assist in the valve selection process.
These 2 studies provide support for a rational integrated imaging strategy when assessing PAVR candidates. Guessing is defined as a prediction without sufficient information or knowledge. If we are to achieve improved safety and accuracy in PAVR, we must demand more relevant multi-imaging information to minimize the need for guessing. Eventually, all of this needed information will be accurately quantifiable and displayed in real-time 3D to provide similar, if not better, feedback compared with the surgeons' experience in the operating room.
Dr. Ruiz has reported that he has no relationships relevant to the contents of this paper to disclose.
↵⁎ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
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