Marlene Busko

July 15, 2013

MONTREAL, QC — Emerging convincing data suggest that "[computed-tomography] CT angiography needs to be integrated in transcatheter aortic-valve replacement [TAVR], not just to produce 'pretty images' but to improve clinical outcomes," DrJonathon Leipsic (University of British Columbia, Vancouver)said in a presentation here at the Society of Cardiovascular Computed Tomography (SCCT) 2013 Scientific Meeting [1].

As reported by heartwire , in a consensus statement issued in November 2012, the SCCT recommended the use of CT imaging as part of the evaluation process for all patients being considered for TAVR, except those for whom CT is contraindicated.

As the use of TAVR is expanding, the role of CT is growing rapidly, and a few soon-to-be-published studies will shine even more light on how CT angiography can reduce complications in TAVR, Leipsic told heartwire .

When TAVR is "integrated in the screening process, [it] can help reduce paravalvular regurgitation, risk of annular injury, and coronary occlusion," he summarized.

Paravalvular Leak, a Major Complication

"While results from PARTNER A and PARTNER B have been remarkable and impressive and it's really changed the way we manage aortic stenosis, the procedure is not yet perfect, "Leipsic told the audience.

Paravalvular aortic regurgitation (PAR) is a major complication of TAVR, caused by implanting a transcatheter heart valve that is smaller than aortic-valve annulus (undersizing) or positioning the device too high or too low, he explained.

Even mild PAR is linked with a worse prognosis. A meta-analysis of nine studies by Athappan and colleagues, published in the April 16, 2013 issue of the Journal of the American College of Cardiology, showed that compared with patients without paravalvular regurgitation, those with this complication had a twofold higher risk of mortality (HR 2.2; 95% CI 1.8–2.8)[2]. Treating severe paravalvular regurgitation due to valve undersizing is "challenging and typically unsuccessful," he added. "So we need to do better."

CT Can Guide Valve-Size Selection

To select an optimal valve prosthesis size, it is important to realize that the aortic-valve ventricular ring (annulus) is elliptical, not circular. While clinicians may be comfortable using echocardiography to size valves, these "sizing guidelines . . . while intoxicatingly simple . . . [are] probably insufficient, given the complex nature of the aortic annulus," according to Leipsic.

Simply measuring a two-dimensional diameter cannot adequately characterize the "size" of the aortic annulus. CT imaging, on the other hand, provides reproducible area and perimeter measurements of aortic-valve geometry, which can be used to help optimize balloon-expandable transcatheter heart-valve size selection and reduce paravalvular leak.

In a multicenter study that Leipsic says will be forthcoming in the Journal of the American College of Cardiology, he and colleagues found that patients who underwent TAVR sizing with the integration of CT-based area sizing had a significant reduction in greater-than-mild PAR (5.8%) as compared with those who underwent exclusively two-dimensional echo-based sizing (12.3%)[3].

Annular Rupture May Not Be Random

A related concern for which cardiac CT may offer an improvement on current practice is aortic-root rupture during balloon-expandable TAVR, something Leipsic says "is so feared because of its seemingly random nature and high [associated] mortality." In a study using registry data, which he said will be published in the coming months in Circulation, Leipsic and colleagues found that among 20 patients with uncontained rupture following TAVR, 75% died, and among 11 with contained rupture, 18% had a disabling stroke[4].

The study also revealed that "annular rupture may not be as random as we once thought." Having moderate or severe left ventricular outflow tract (LVOT) calcifications predicted an 11-fold increased risk of annular rupture, and implanting a prosthesis that was at least 20% larger by area than the native annulus (oversized) was linked with an eightfold increased risk of this complication.

However, an "oversized" prosthesis that is implanted in the "right" patient with no LVOT calcification can result in an uneventful TAVR, with no annular rupture, Leipsic reported.

Controlling the degree of annular stretch with balloon underfilling is one way to help mitigate the potential risk of annular rupture. CT can also help predict an optimal angle of deployment of the prosthesis and help reduce the risk of coronary occlusion.

"I hope that I've convinced you . . . that while the randomized data to date are supported by echocardiographic-based sizing, over the past few years extensive research has created the burden of data that would suggest that CT needs to be integrated into TAVR," he concluded.

Leipsic is on the speaker's bureau for GE Healthcare and Edwards LifeSciences and on the advisory board for GE Healthcare, Edwards LifeSciences, Vital Images, and Circle CVI. He has received grant support from Canadian Institutes of Health Research, National Institutes of Health, GE Healthcare, and Heartflow and is an equity stakeholder in TC3.

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