Studies Suggest 3-D CT Prior to TAVR Should Be ‘Gold Standard’

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Use of 3-D computed tomography (CT) to assess aortic annulus size prior to transcatheter aortic valve replacement (TAVR) has distinct advantages over traditional 2-D echocardiographic imaging, according to 2 studies published online February 22, 2012, ahead of print in the Journal of the American College of Cardiology. Both papers suggest standard imaging procedures should be changed.

For the first study, Raj R. Makkar, MD, of Cedars-Sinai Medical Center (Los Angeles, CA), and colleagues looked at the discriminatory value of multiple CT annular measures for assessing post-TAVR aortic regurgitation. The researchers retrospectively analyzed 192 consecutive patients enrolled in the PARTNER trial at their center from January 2008 to March 2011. Patients either had CT (n = 40; Siemens Medical Solutions, Malvern, PA) or received ECG-gated contrast CT using a traditional transesophageal echocardiography (TEE) approach (n = 96).

In receiver-operating models, 2 different cross-sectional CT parameters had the highest discriminatory value for significant (defined as greater than mild) post-TAVR regurgitation (table 1).

Table 1. Characteristic Curve Analysis for Measures of the Aortic Annulus

Sensitivity and specificity measures were greater for both CT measurements (cross-sectional circumference: 82% and 80%; maximal cross-sectional diameter: 88% and 73%) than both echocardiographic measurements (transthoracic echocardiography: 47% and 60%; TEE: 53% and 87%).

Moderate or greater central aortic regurgitation was observed in only 1 patient (0.73%). Hemodynamic outcomes were achieved with CT with a significant reduction in the incidence of regurgitation (table 2). Only 2 cases of moderate regurgitation (5%) occurred after observing the annular sizing protocol dictated by CT.

Table 2. Hemodynamic Outcomes

In multivariate analysis, using the circumference measurement without the maximum diameter measurement yielded only the presence of left ventricular outflow tract calcium (OR 19.4; 95% CI 1.7-226; P = 0.018) and circumference measurement (OR per mm of circumference 1.71; 95% CI 1.2-2.4; P = 0.003) as independent predictors of significant regurgitation.

3-D Imaging Confirmed Effective

In the second paper, Jonathon Leipsic, MD, of St. Paul’s Hospital (Vancouver, Canada), and colleagues analyzed 109 consecutive patients who underwent 3-D CT before TAVR at 2 Canadian centers between January 2010 and June 2011. Device positioning was assessed by 2 blinded interventional cardiologists as correct, too high, or too low based on pre- and post-implant aortic root angiography. All patients underwent TEE predischarge; 3-D CT was repeated in 50 patients to assess valve eccentricity and expansion.

Moderate or severe paravalvular regurgitation (12.7%) was associated with device undersizing (device diameter – mean diameter = -0.7 ± 1.4 mm vs. 0.9 ± 1.8 mm for trivial to mild paravalvular regurgitation, P < 0.01). Also, the difference between valve size and annulus size as predicted by 3-D CT was predictive of regurgitation:

• Mean diameter: area under the curve 0.81; 95% CI 0.68-0.88
• Area: area under the curve 0.80; 95% CI 0.65-0.90
• Circumference: area under the curve 0.76; 95% CI 0.59-0.91

Devices were found to be undersized relative to the 3-D CT mean diameter (35.3%) and area (45.1%). Lastly, valve oversizing relative to the annular area was not associated with valve underexpansion (102.7 ± 5.3% vs. 106.1 ± 5.6%; P = 0.03) or eccentricity (1.7% vs. 1.7%; P = 0.28).

‘Apples to Oranges’ Comparison

In a telephone interview with TCTMD, Dr. Makkar and co-author Hasan Jilaihawi, BSc, MB, ChB, of Cedars-Sinai Heart Institute, said they were each surprised by how poorly predictive the TEE measurements were in their study.

“This essentially explains why we have this complication despite careful selection of patients,” Dr. Jilaihawi said. “The aortic annulus is not a circular structure, but elliptical. The larger dimension is not appreciated by 2-dimensional measurement.”

Dr. Makkar stressed that the take-home message is the importance of measurement analysis in a cross-sectional fashion because “that’s when you really appreciate the entire size of the annulus and that is what helps us size the devices.” His team currently is evaluating the same outcome correlation with 3-D echocardiography.

Philippe Pibarot, DVM, PhD, of Laval University (Quebec City, Canada), agreed. Comparing 2-D TEE to 3-D CT is like “comparing apples to oranges,” he told TCTMD in a telephone interview. “It’s not an issue of imaging modality, it’s more an issue of 3-D vs. 2-D.”

Image resolution is “comparable” between echocardiography and CT, Dr. Pibarot continued, and if 3-D echocardiography does prove predictive, certain patient groups may benefit.

“With CT you need to inject the patients with contrast agents . . . which might be an issue in patients with vulnerable kidney function,” he said. “We have a substantial proportion of patients where we don’t want to use too much contrast agents. . . . So there are two advantages of echo over CT—no exposure to radiation and no administration of contrast agents, so better protection of kidney function.”

A Few Caveats

Dr. Pibarot cautioned that in order to avoid aortic rupture, distribution and amount of calcification needs to be assessed.

“Let’s say that because of intense calcification . . . the short axis is relatively fixed,” he explained. “And then you select the prosthesis size based on the long axis or the circumference. Then the circularization [of the aorta post-implantation] that you expect to see will not occur in this case and you will force the short axis diameter, which is rigid, to eventually rupture. Then you have a dissection of the aortic annulus, which is a catastrophic complication.”

Dr. Pibarot warned against oversizing valves in all patients. “I would say yes, but be careful,” he said adding that so long as accurate measurements are obtained by 3-D imaging with good resolution, the oversizing should depend on the amount of calcification present.

Dr. Makkar added that “more and more people are beginning to realize the importance of the method and are incorporating this into their practice.” As to whether or not these findings will hold up with other TAVR devices, “there is no reason to believe that what is true for one device is not going to be true for other devices because the sizing has to be done properly irrespective of the device,” he said.

Note: One of Dr. Makkar’s co-authors, Martin B. Leon, MD, is a faculty member of the Cardiovascular Research Foundation, which owns and operates TCTMD.

 

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Sources:
1. Jilaihawi H, Kashif M, Fontana G, et al. Cross-sectional computed tomographic assessment improves accuracy of aortic annular sizing for transcatheter aortic valve replacement and reduces the incidence of paravalvular aortic regurgitation. J Am Coll Cardiol. 2012;Epub ahead of print.

2. 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;Epub ahead of print.

 

 

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