RSNA 2017: CT imaging crucial to accurate annular valve measurements

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 - Aortic valve calcium on heart CT
Aortic valve calcium and coronary artery calcification.
Source: J. of Cardiovascular CT (doi:10.1016/j.jcct.2012.02.008)

Multidetector computed tomography (CT) could play a pivotal role in improving the outcomes of transcatheter aortic valve replacement (TAVR) procedures, research presented at the 103rd annual RSNA symposium suggests.

The field of TAVR continues to grow more than a decade after its conception, Vancouver-based doctor Jonathan A. Leipsic, MD, said at the Chicago meeting, and radiologists continue to work to develop safer, less invasive alternatives to open-heart surgery for high-risk patients.

“The case for TAVR is frankly overwhelming at present,” he said, citing the success of the PARTNER trials and Edwards SAPIEN 3 device. “We have to drive the field of imaging forward to better identify patients who are going to benefit and not benefit from TAVR.”

Imaging could be a crucial tool for ensuring accuracy during TAVR procedures, Leipisic said—especially when it comes to annular valve sizing. Physicians often run into roadblocks when measuring the annulus for accurate valve replacement, especially since annuli aren’t uniform structures. They vary from elliptical shapes to near-perfect circles, he said, and there isn’t a single formula for calculating their dimensions.

In his research, Leipsic and his colleagues attempt to imagine the annulus as it was when a patient was born for the best results. The goal, he said, is to “maintain normal, harmonious annuli.”

Sizing thresholds, though, also vary based on the type of device being implanted. These replacement valves differ by design profiles and radial measurements, but Leipsic’s team focused on one genre—balloon expandable devices.

The debate between systolic and diastolic sizing in annuli continues, he said, and both have their merits. Still, his stance on balloon expandable stents is clear: Clinicians should always be using the largest cardiac measurement in the annular cycle, and that’s typically systolic.

The conversation about using perimeter versus area measurements is more unclear, he said, since the paradigm has shifted over the years. Historically, doctors took area measurements of annuli, since perimeter isn’t a reproducible measurement.

“Accuracy is impossible without reproducibility,” Leipsic said, repeating his research mantra.

Mapping perimeters would be messier since valve shapes can waver, he said, but smoothing algorithms have changed that. Still, defaulting to perimeter measurements means you’ll always “go big.” Since some annuli are circular and others take on an elliptical shape, even valves with the same area would have different perimeters. Oversizing is dangerous, Leipsic said, since it can result in root rupture and, at times, patient death. For those reasons, he recommends area measurements in balloon stent cases.

CT has been able to change the likelihood of oversizing annuli, Leipsic said, and our understanding of 3D anatomy has improved patient outcomes, but CT sizing algorithms still need to evolve.

“Our work is not done,” he said. “We as imagers need to be integrated in the heart team and providing guidance.”