Author + information
- Mohamad Alkhouli, MD∗ ( and )
- Partho P. Sengupta, MD
- ↵∗Address for correspondence:
Dr. Mohamad Alkhouli, West Virginia University Heart & Vascular Institute, 1 Medical Drive, Morgantown, West Virginia 26505.
“The future is like a corridor into which we can see only by the light coming from behind.”
—Edward Weyer Jr. (1)
Paravalvular leak (PVL) has been the Achilles’ heel of transcatheter aortic valve replacement (TAVR), especially with self-expandable valves. In the pivotal CoreValve and PARTNER (Placement of AoRtic TraNscathetER Valves) I trials, moderate to severe PVL occurred in 7.8% and 11.8% of patients, respectively, and was associated with excess short- and long-term mortality (2–4). In recent years, novel designs of the newer transcatheter heart valves (THVs), along with our enhanced understanding of the optimal sizing and implantation of these valves, led to a significant reduction in the rates of PVL. Moderate to severe PVL was only reported in 5.4% and 3.7% of patients in the recently published SURTAVI (SUrgical Replacement and Transcatheter Aortic Valve Implantation) and PARTNER II trials, respectively (5,6). However, these rates of significant PVL are higher than what is observed with surgical bioprosthetic valves, calling for further efforts to mitigate the risk of PVL following TAVR (7).
In this issue of iJACC, Qian et al. (8) aim to assess the utility of tissue-mimicking 3-dimensional (3D) printing in predicting PVL after TAVR with self-expandable valves. The authors used pre-procedural computed tomographic images in 18 patients who received CoreValve (self-expanding valve) and Evolut R (second generation self-expanding transcatheter aortic valve) (Medtronic, Minneapolis, Minnesota) THVs at their institution to print 3D phantoms of the aortic valve and aortic root. They then implanted the THV in vitro after attaching small radiopaque beads to the phantoms. These beads acted as sensors that were detected before and after in vivo TAVR by a novel bulge detector designed by the authors. The relative change in position of these beads before and after TAVR was used to calculate annular strain. A bulge detector was then used to detect areas of low-high-low strain patterns along the phantom annulus after the simulated in vitro implantation of the valve. These data were integrated to calculate the “bulge index,” a novel measure of post-TAVR annular unevenness. The authors then evaluated the predictive value of the bulge index in predicting post-TAVR PVL, and concluded that this index can effectively predict post-TAVR PVL with contemporary self-expandable valves.
This novel study highlights several findings that have important implications:
1. Computed tomography–based 3D tissue printing can produce a feasible platform to assess annular strain and its new derivative “the bulge index” in patients undergoing TAVR. The process currently takes ∼45 min and costs ∼$150 to $200.
2. The bulge index achieved high degree of accuracy in predicting not only the occurrence of post-TAVR PVL but also in predicting its severity and location.
3. The performance of the bulge index was compared with other established predictors of post-TAVR PVL (aortic, annular, and left ventricular outflow calcium volume; annular ellipticity; and prosthesis to annular diameter ratio) at 2 stages: 1) immediately after valve deployment; and 2) after post-balloon dilation.
Both the bulge index and the annular calcium volume predicted PVL after valve deployment. However, the bulge index was the only significant predictor of PVL after balloon dilation outperforming all other predictors. However, this finding deserves more scrutiny: although landing zone calcifications, circularity index of the annulus, and degree of oversizing were included in the comparative analysis between the different predictors of PVL, other important factors such as the valve implantation depth were not studied. It is, therefore, important to understand the value of this novel index within the context of the complex interconnected PVL pathophysiology (9,10). This finding also highlights the need for collaborative research to develop a comprehensive “holistic” PVL prediction score that sums all of the previously mentioned variables.
The current investigation serves to narrow the knowledge gap on the very important issue of PVL after TAVR. However, it does also raise several intriguing questions:
1. 3D tissue printing versus computer simulation. Although the utility of 3D tissue printing in structural heart disease interventions has been previously demonstrated, a unique feature of this study was the designation of metamaterials that can mimic the mechanical property of the human tissue. This allowed close, in vitro mimicking of the annular tissue response to TAVR and increased the fidelity of the simulation. However, the 3D printing process, albeit relatively inexpensive in this study, is laborious and will probably remain so in the foreseeable future. Yet, several practical and intuitive computer-based simulation models are being developed to serve the same purpose of predicting post-TAVR PVL. These models utilize advanced analyses, such as patient-specific finite element analysis, to predict stress distributions, geometrical changes, coaptation values, and risk of PVL (11–13). Although both computer-based simulation and 3D tissue printing models are in their infancy, a tight competition between these novel technologies can be expected in the near future.
2. Routine versus selective 3D tissue printing. Given the declining rates of PVL with contemporary THVs, and the expansion of TAVR to lower risk populations, defining the target population for the application of this technology becomes important. Will we be screening every patient for post-TAVR PVL with 3D tissue printing, or would the screening be reserved for patients who are at higher risk for PVL?
3. Patient-specific phantoms for different THVs. The majority of TAVRs are currently performed with the Sapien S3 (Edwards Lifesciences, Irvine, California) and second generation self-expanding transcatheter aortic valve. However, the landscape of THVs is rapidly changing, with a number of novel balloon- and self-expandable valves under investigation (14). Can a single 3D-printed phantom be used to predict PVL after TAVR with various THVs? Would these phantoms be able to predict the best suitable THV for a specific anatomy? Would the information collected from these phantoms help refine the design of future THVs?
4. Ultimate role of 3D printing. The current 3D models aim to serve a specific goal: minimize the risk of PVL. However, one can speculate a more central role for this technology in the future of transcatheter valve therapies (15). Perhaps the wealth of a patient’s specific anatomical details afforded by multimodality imaging can be integrated to develop a personalized tissue valve that can then be virtually implanted, assessed, and optimized with computer simulation models. This “custom-made” valve can then be 3D printed and implanted in vivo. Although this seems a far stretch of imagination at present, it may become the final roadmap in the future.
The advances in the TAVR field brought forth an unprecedented orchestration of collaborations in clinical medicine, advanced imaging, and bioengineering. The finding of this exploratory study, albeit “proof of concept,” are symbolic of the next wave of innovation in transcatheter valve therapies, toward seeking a personalized patient-centered TAVR.
↵∗ Editorials published in JACC: Cardiovascular Imaging reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Imaging or the American College of Cardiology.
Both authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- 2017 American College of Cardiology Foundation
- ↵GoodReads. Edward Weyer Jr. quotes. Available at: http://www.goodreads.com/quotes/476487-the-future-is-like-a-corridor-into-which-we-can. Accessed May 15, 2017.
- Kodali S.,
- Pibarot P.,
- Douglas P.S.,
- et al.
- Reardon M.J.,
- Van Mieghem N.M.,
- Popma J.J.,
- et al.
- Alkhouli M.,
- Sarraf M.,
- Maor E.,
- et al.
- Qian Z.,
- Wang K.,
- Liu S.,
- et al.
- Sherif M.A.,
- Abdel-Wahab M.,
- Stocker B.,
- et al.
- Wang Q.,
- Primiano C.,
- McKay R.,
- Kodali S.,
- Sun W.
- Vahl T.P.,
- Kodali S.K.,
- Leon M.B.
- Giannopoulos A.A.,
- Mitsouras D.,
- Yoo S.J.,
- Liu P.P.,
- Chatzizisis Y.S.,
- Rybicki F.J.