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Localization of Aortic Annulus with Transesophageal Echocardiography for Transcatheter Aortic Valve Implantation
Maria E. Currie, MD1, A. Jonathan McLeod2, Rajni Patel, PhD3, Terry M. Peters, PhD4, Bob Kiaii, MD1.
1London Heath Sciences Centre, London, ON, Canada, 2Western University, London, ON, Canada, 3Canadian Surgical Technologies & Advanced Robotics, London, ON, Canada, 4Robarts Research Institute, London, ON, Canada.
OBJECTIVE: Transcatheter aortic valve implantation (TAVI) has emerged as a safe and effective treatment for aortic stenosis. However, valve deployment still relies on fluoroscopy that requires nephrotoxic contrast. We have developed a guidance system for TAVI that magnetically tracks the TAVI catheter in an augmented reality environment (Figure 1). This method uses only transesophageal echocardiography (TEE) to define the aortic valve annulus and eliminates the need for nephrotoxic contrast.
Accurate identification of the aortic annulus is essential for TAVI deployment using this system. Since the commissures of the aortic valve are stationary hinge points visible in echocardiography, these points can be used to define the aortic valve annulus. Other image guidance systems have employed the lowest point of the aortic valve leaflets,the nadirs, to guide TAVI deployment.
This study was conducted to determine how consistently the aortic valve annulus could be defined using either aortic valve commissures or nadirs from full volume TEE images.
METHODS: Inter-operator variability in identifying aortic valve commissures and nadirs was assessed between five subjects. Each subject identified the three commissures and leaflet nadirs in full volume TEE images of the aortic root in diastole acquired from eight patients. The nadir and commissure points were used to define a valve plane. The inter-operator variability in defining this plane was obtained by calculating the standard deviation of the valve centroid and orientation.
RESULTS: Using the commissural points, mean interoperator variability of 1.8mm and 9.1° were obtained over all 8 images. Similarly, using the nadir points resulted in an interoperator variability of 2.5mm and 7.8°.
CONCLUSIONS: Our results indicate that while both aortic valve commissures and aortic leaflet nadirs can be localized reliably, there is lower interoperator variability in the localization of aortic valve commissures. The increased variability in identifying valve orientation is unlikely to contribute to a significant error in valve deployment. This suggests that an accurate TEE guidance system is realizable using the commissures to define the valve plane.
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