The Use of 3D Echocardiography in Surgical Planning of the Mitral Valve in Pediatric Cardiology

Summary

3D echocardiography of the mitral valve in pediatric cardiology produces full anatomic reconstructions that contribute to improved surgical management. Here, we outline a protocol for 3D acquisition and post-processing of the mitral valve in pediatric cardiology.

Abstract

Mitral valve disease in pediatric cardiology is complex and can involve a combination of annular, leaflet, chordae tendineae and papillary muscle abnormalities. Transthoracic two-dimensional echocardiography (2DE) remains the primary diagnostic imaging technique utilized in pediatric surgical planning. However, given that the mitral valve is a three-dimensional (3D) structure, the addition of 3D echocardiography (3DE) to better define the mechanisms of stenosis and/or regurgitation is advantageous. Transthoracic 3DE technology has improved with advances in probe technology and ultrasound scanners, producing images with good spatial resolution and adequate temporal resolution. Specifically, the addition of pediatric 3D transducers with higher frequencies and a smaller footprint provides better 3DE imaging in children. Improved efficiency of 3DE acquisition and analysis allow 3D assessment of the mitral valve to be more easily integrated by the sonographer, the cardiologist and the surgeon in mitral valve assessment. This improvement was also made possible by the postprocessing software optimization.

In this method paper, we aim to describe the transthoracic 3DE assessment of the mitral valve in children and its use in the surgical planning of pediatric mitral valve disease. Firstly, the 3DE assessment begins by selecting the correct probe and by obtaining a view of the mitral valve. Then, the appropriate data acquisition method should be selected based on the individual patient. Next, optimization of the data set is critical in order to properly balance spatial and temporal resolution. During live scanning or following acquisition, the data set can be cropped using innovative tools that allow the user to quickly obtain an infinite number of cut planes or volumetric reconstructions. The cardiologist and surgeon can view the mitral valve en face; thus, accurately reconstructing its morphology in order to support medical or surgical planning. Finally, a review of some clinical applications is proposed, showing examples in pediatric mitral valve managements.

Introduction

The mitral valve apparatus is a complex structure consisting of the mitral valve annulus, leaflets, chordae tendineae and left ventricular papillary muscles^1,2. Pediatric mitral valve disease consists of an extensive range of morphologic abnormalities associated with congenital and acquired heart anomalies³. The description of the morphology of mitral valve disease and its underlying mechanisms are key parameters for the surgical planning⁴. This requires the use of accurate diagnostic imaging modalities. Echocardiography is established as one of the primary diagnostic techniques used in pediatric mitral valve disease⁵. Specifically, two-dimensional (2D) echocardiography in pediatric mitral valve disease remains the most widely used diagnostic method. However, due to the nature of 2D imaging, the sonographer, the cardiologist and the surgeon must mentally reconstruct this complex 3D structure to determine the pathological mechanisms.

With the ability to produce anatomically correct views and an infinite number of cut planes, three-dimensional (3D) echocardiography has the ability to enhance mitral valve imaging. The value of 3D echocardiography is shown in its ability to provide specific information about annular shape and dynamics, leaflet scallop prolapse and the zone of leaflet coaptation^6,7. While 3D transesophageal echocardiography (TEE) has been shown to be the most accurate ultrasound modality in identifying adult mitral valve pathology⁸, 3D transthoracic echocardiography (TTE) is more feasible in children due to a better acoustic window. 3D TTE has been proven to be highly accurate in discerning simple vs. complex mitral valve lesions and the need for surgical intervention⁹. Additionally, acquiring a 3D volumetric dataset allows surgeons and cardiologists to collaborate in post-processing, further enhancing surgical planning.

3D TTE technology has continued to improve with advancement in probe technology, ultrasound processing power, and post-processing efficiencies. The current 3D matrix probes can now acquire a full volume single-beat data set at a volume rate of approximately 25 volumes per second¹⁰. It is possible to further increase the volume rate of a single-beat data set above 25 volumes per second depending on the ultrasound vendor, probe technology and volume optimization. However, if the ECG gated (sub volumes) full volume method is used, this number can more than double, providing volumes rates that are needed in children. The higher heart rates in children compared to adults require higher temporal 3D resolution for diagnostic accuracy. Additionally, the development of specific pediatric 3D probe technology allowed for a higher scanning frequency, providing better spatial resolution that is crucial regarding the small size of the mitral valve and its apparatus¹¹. Despite all these technological improvements, the vendors have managed to produce probes with footprints adapted to the anatomy of small children to maintain an optimal acoustic window. Lastly, new post-processing features, such as a quick cropping tools, allow for efficient post-processing.

In this paper, we describe the technique for 3D TTE assessment of the mitral valve in children, which can be applied to any ultrasound system with 3D TTE application. Additionally, post-processing of the 3D data will be reviewed and its benefit in the surgical planning. Finally, we will discuss some clinical applications of 3D imaging in children and include some examples.

Protocol

This protocol follows the guidelines of our institution's human research ethics committee. NOTE: For the implementation of this protocol, a General Electric (GE) Vivid E95 or Philips Epiq 7C ultrasound system is used. On the GE Vivid E95 system, the user has a choice between the 4Vc-D (adult probe) or 6Vc-D (pediatric probe). On the Philips Epiq 7C, the user has a choice between the X5-1 (adult probe) or X7-2 (pediatric probe). See Figure 1. <p class="jove…

Representative Results

A good quality 3D data set of the mitral valve in pediatric echocardiography will have an optimal volume rate that is appropriate for assessing leaflet motion and excellent spatial resolution that utilizes superior axial resolution. To assess the success of the protocols 3D ECG gated acquisition, first determine whether any significant "stitch" artifact is present. In the presence of no artifact and if the acquisition was made using an excellent quality 2D low parasternal long-axis view, this 3D data set will pro…

Discussion

For the operator/sonographer, 3D echocardiography is often met with several challenges. First, by nature there is significant variation in patient size, heart rate and cooperation during a pediatric echocardiography exam. These parameters make it difficult to have 3D specific protocols and therefore make the 3D acquisition operator dependent. Often training for sonographers is focused primarily on 2D imaging, leaving a gap in knowledge with regards to 3D image acquisition and interpretation. In addition, 3D temporal reso…

Materials

4Vc-D probe	General Electric		Ultraspound probe (GE)
6Vc-D probe	General Electric		Ultraspound probe (GE)
Epiq 7C	Philips		Ultrasound system
Vivid E95	General Electric		Ultrasound system
X5-1	Philips		Ultraspound probe (Philips)
X7-2	Philips		Ultraspound probe (Philips)