In the early days of transcatheter aortic valve replacement (TAVR), there was a reliance on two-dimensional echocardiographic imaging for annular assessment with an under-appreciation of the non-circular configuration of the aortic annulus. While initial experiences of TAVR yielded strong results, there were numerous complications that were both frequent and associated with poor outcomes.^1,2 Through retrospective analyses, it has become increasingly clear that inappropriate device sizing owing to the limitations of two-dimensional imaging results  in both under-sizing yielding paravalvular aortic regurgitation (PAR) and extreme oversizing resulting in increased risk of annular rupture and possibly coronary occlusion. 

Multiple detector computed tomography (MDCT), with its multiplanar imaging capabilities and isotropic voxels, allows the reconstruction of the annulus in its true axis using standard double oblique transverse reconstruction that has now been well described and can be performed in a reproducible fashion.^3,4 Measurements thus obtained have been shown to be strongly discriminatory for those patients who have historically experienced greater than mild PAR.⁵ As a result, several groups have begun to integrate MDCT area measures to optimize the degree of annular oversizing while controlling the degree of annular stretch to reduce the risk of PAR and mitigate the risk of annular injury. CT allows reproducible multiplanar reformations that permit a thorough understanding of the patient-specific geometry. The integration of MDCT into device selection has moved from theoretical to reality over the past couple of years. Our group recently presented data from a prospective multicenter sizing trial, showing that greater than mild PAR can be reduced with the integration of MDCT into the transcatheter heart valve (THV) selection process (5.3% versus 12.8%; P=0.03).⁶ In addition, the recently presented data from the high-risk Medtronic self-expanding TAVR  trial showed excellent clinical results with the devices almost exclusively selected on the basis of MDCT.⁷ As valve technology has evolved, we have also realized the importance of defining valve-specific sizing algorithms that ensure optimal clinical outcomes without more oversizing than necessary.

MDCT provides additional important information that helps with both valve size and perhaps the type of device selected. Careful evaluation of the aortic root and left ventricular outflow tract (LVOT) allows for a deeper understanding of the potential risk of annular rupture with balloon expandable prostheses and PAR with both devices, although more commonly with the self-expanding platforms. Through a multi-center registry of patients who experienced annular rupture during TAVR, Barbanti et al. showed that moderate/severe subannular/LVOT calcium identified on MDCT, particularly when combined with area oversizing greater than 20%, resulted in a significantly increased risk of annular rupture.⁸ This knowledge in advance of the procedure allows for thoughtful device selection not only regarding size but perhaps also operator determinations of the potential need for balloon underfilling⁹ or the selection of a self-expanding rather than a balloon-expandable prosthesis. These strategies can help reduce the risk of annular injury. Protruding nodules of annular/sub-annular calcium uniquely identified on MDCT have also been shown to  be predictive of PAR, particularly with self-expanding prostheses.¹⁰ The pre-procedural awareness of these nodules is especially valuable so that the proceduralist is aware that PAR may be expected and is neither likely due to undersizing nor correctable by post-dilatation.

CT measurements of the annulus and root are also invaluable for the identification of patients at increased risk of coronary occlusion during TAVR. This complication was once thought to be random and risk assessment was left to anecdote and conjecture until the compilation of a large multi-center registry that systematically reviewed the drivers of coronary occlusion.¹¹ Through propensity matching, we have learned that patients with low coronary ostial heights as determined by computed tomography (<12mm for a male and <11mm for a female) are at increased risk of coronary occlusion. In addition, shallow sinuses of Valsalva (SOV) <30 mm (as defined by the mean of the 3 transverse measurements) , and, more significantly, a ratio of SOV /annulus diameter  <1.25 were associated with the highest risk of coronary occlusion, the latter having a hazard ratio of 10.9. Thus, information derived from CT has become incredibly powerful to improve the safety profile of TAVR and reduce the risk of coronary occlusion.

Over the last five years, MDCT has gone from being relegated to iliofemoral access assessment to an essential component of annular sizing and device selection. Through the integration of three-dimensional measures and the development of a deeper understanding of other essential root and LVOT findings on CT, the pre-procedural planning of TAVR has been transformed through the routine integration of MDCT. Importantly, the authors of this commentary feel strongly that device selection and annular sizing remains a multifactorial process particularly with a rapid evolution in three-dimensional echocardiography.

References:

1. Leon MB, Smith CR, Mack M, et al. Transcatheter aortic-valve implantation for aortic stenosis in patients who cannot undergo surgery. N Engl J Med 2010;363:1597-607.
2. Smith CR, Leon MB, Mack MJ, et al. Transcatheter versus surgical aortic-valve replacement in high-risk patients. N Engl J Med 2011;364:2187-98.
3. Kasel AM, Cassese S, Bleiziffer S, et al. Standardized imaging for aortic annular sizing: implications for transcatheter valve selection. JACC Cardiovasc Imaging 2013;6:249-62.
4. Achenbach S, Delgado V, Hausleiter J, Schoenhagen P, Min JK, Leipsic JA. SCCT expert consensus document on computed tomography imaging before transcatheter aortic valve implantation (TAVI)/transcatheter aortic valve replacement (TAVR). J Cardiovasc Comput Tomogr 2012;6:366-80.
5. Willson AB, Webb JG, Labounty TM, et al. 3-dimensional aortic annular assessment by multidetector computed tomography predicts moderate or severe paravalvular regurgitation after transcatheter aortic valve replacement: a multicenter retrospective analysis. J Am Coll Cardiol 2012;59:1287-94.
6. Binder RK, Webb JG, Willson AB, et al. The impact of integration of a multidetector computed tomography annulus area sizing algorithm on outcomes of transcatheter aortic valve replacement: a prospective, multicenter, controlled trial. J Am Coll Cardiol 2013;62:431-8.
7. Adams D, Popma J, Reardon MJ, et al. Transcatheter aortic-valve replacement with a self-expanding prosthesis. N Engl J Med 2014;370:1790-8.
8. Barbanti M, Yang TH, Rodes Cabau J, et al. Anatomical and procedural features associated with aortic root rupture during balloon-expandable transcatheter aortic valve replacement. Circulation 2013;128:244-53.
9. Barbanti M, Leipsic J, Binder R et al. Underexpansion and ad hoc post-dilation in selected patients undergoing balloon-expandable transcatheter aortic valve replacement. J Am Coll Cardiol 2014;63976-81.
10. Feuchtner G, Plank F, Bartel T, et al. Prediction of paravalvular regurgitation after transcatheter aortic valve implantation by computed tomography: value of aortic valve and annular calcification. Ann Thorac Surg 2013;96:1574-80.
11. Ribeiro HB, Webb JG, Makkar RR, et al. Predictive factors, management, and clinical outcomes of coronary obstruction following transcatheter aortic valve implantation: insights from a large multicenter registry. J Am Coll Cardiol 2013;62:1552-62.

Keywords: Aortic Valve Insufficiency, Coronary Occlusion, Echocardiography, Three-Dimensional, Prostheses and Implants, Registries, Risk Assessment, Sinus of Valsalva, Tomography, X-Ray Computed, Transcatheter Aortic Valve Replacement

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