Two and three dimensional echocardiography for pre-operative assessment of mitral valve regurgitation

The mitral valve apparatus is a complex structure made of the annulus, the leaflets, the chordae, the papillary muscles, and the left ventricular wall [1]. Mitral regurgitation may develop when the leaflets or any other portion of the apparatus becomes abnormal. The mitral valve apparatus may also become dysfunctional when the left ventricle dilates and the papillary muscles are displaced. As the repair techniques for mitral valve disease evolved, so has the need for detailed and accurate imaging of the mitral valve prior to surgery in order to better define the mechanism of valve dysfunction and the severity of regurgitation.

In patients with significant mitral valve disease who require surgical intervention, multiplane transesophageal echocardiogram (TEE) is invaluable for surgical planning. TEE can identify the mechanism of valve pathology and the specific area on the valve causing the malfunction. However, a comprehensive TEE in a patient with complex mitral valve disease requires great experience and skill [2‐4], (Figure 1). Even in experienced hands, using multiplane 2D TEE alone can sometimes lead to misinterpretation of scallops. There is evidence to suggest that 3D echocardiography can overcome some of the limitations of 2D multiplane TEE and thus is crucial in evaluation of patients undergoing mitral valve surgery [5‐7]. In addition, 3D TEE unifies the language used by the echocardiographer to communicate mitral valve pathology to the surgeon by providing an en face (surgeon’s view) of the mitral valve [8].

Mitral valve leaflet anatomy has been described by Carpentier [9] as being divided into six scallops: three that form the anterior leaflet and three that form the posterior leaflet (Figure 2). In addition, Carpentier classified the etiology of mitral valve regurgitation into Type 1-normal leaflet motion, Type II: leaflet prolapse, Type III-restricted leaflet motion. The echocardiographic must be familiar with this nomenclature as part of the preoperative assessment of mitral valve.

The following sections highlight some crucial steps that must be undertaken by the echocardiographer to accurately image the mitral valve. This includes both 2D and 3D assessment of the valve. Of note, the iE33 xMATRIX Echocardiography System (Phillips Healthcare, MA) was utilized for image acquisitions in this paper. Multiple other ultrasound companies also manufacture 3D echo systems. Image acquisition in other systems may vary slightly but the anatomic concepts are similar.

The mitral valve is usually beautifully seen using 3D TEE. However, in order to obtain the best images, it is important to understand the basic concepts about image acquisition using this technology. There are three basic modes of image acquisition: Real-time 3D, 3D zoom and full volume acquisition. Each is a tradeoff between sector width, frame rate and spatial resolution.Real-time 3D imaging provides an easy view of the mitral valve with a high frame rate but at the expense of a very narrow sector width (Figure 3). This type of imaging is useful for a quick look at small structures in a limited viewing plane. The second type of image acquisition is called the 3D zoom mode. In this case, the entire mitral valve data set can be acquired in one beat (Figure 4). This mode is useful when there are arrhythmias or a noisy ECG. The disadvantage, however, is the low frame rate and lower spatial resolution. Finally, there is the full volume acquisition mode. In this modality, multiple 3D volumes are acquired over multiple beats. The volumes are then “stitched” together in order to form the complete image. Since multiple volumes are used to create the image, both temporal (frame rate) and spatial resolution is improved (Figure 5). The echocardiographer can choose the number of beats to acquire for each full volume acquisition (usually 1–7 beats). The more beats that are used to form the image, the higher are the frame rate and image quality (Figure 6). However, this type of acquisition requires a stable ECG with a regular rhythm and no movement on the part of the patient or the echocardiographer. If the volumes cannot be properly aligned, stitch artifacts are seen in the final image (Figure 7). Color Doppler images are most often acquired using a full volume acquisition. Recently, a new mode called a “high volume rate (HVR)” mode has been developed. In this modality, the acquisition can be made in one beat with a preserved frame rate. However, the trade-off is in the spatial resolution. Thus, this mode is useful for color Doppler acquisition where frame rate and the ease of a 1 beat acquisition are the priorities. In this case, image quality is less important.

Carpentier classification Type I mitral regurgitation (MR) is due to a perforated leaflet or incomplete mitral leaflet closure due to annular dilation. In the case of annular dilatation, the leaflets and the subvalvular apparatus are usually normal in morphology.The first step in evaluating for type I MR involves multiplane 2D TEE. One must recognize that one of the etiologies of the MR in this group is when the leaflets are usually normal but do not coapt as a result of annular dilatation (Figure 8). The malcoaption of the leaflets results in severe mitral regurgitation.

In addition to measuring the mitral annulus to establish that the MR is indeed due to annular dilation, the echocardiographer should also measure the tricuspid annulus (Figure 8). There have been several studies demonstrating that the pre-surgical tricuspid annulus measurement predicts residual functional tricuspid regurgitation post mitral valve surgery [10, 11]. The echocardiographer should determine the amount of tricuspid regurgitation to determine if a concomitant tricuspid annuloplasty ring is warranted at the time of mitral valve surgery. Lastly, one should also determine pulmonary artery systolic pressures since this may help in the assessment of the right ventricle post mitral valve surgery.

In addition to recognizing that there is type I MR present, the echocardiographer should also make an attempt to quantify the severity of MR according to established guidelines [12‐15]. Figure 9 demonstrates the parameters needed to quantify mitral regurgitation. The echocardiographic should be familiar with the valvular heart disease guidelines and be cognizant of the qualitative and quantitative signs of severe MR [12‐15].Lastly, 3D TEE is very helpful in the evaluation of type I MR. Some echocardiographers may choose to perform 3D TEE before even the 2D portion since this provides and enface view of the mitral valve and can be acquired relatively quickly. 3D TEE with color can be used to establish the origin of the MR jet (Figure 10). In addition, 3D TEE mitral valve quantification (MVQ) function can be used to assess the mitral annulus to confirm the size and shape of the annulus (Figure 11).

This group consists of patients with mitral valve prolapse or flail leaflet either due to Barlow’s disease or due to fibroelastic deficiency. It is important to differentiate between these two entities since this may affect surgical management. Once the pathology has been identified as mitral valve prolapse, the echocardiographer must then accurately determine the scallops involved 2D TEE can identify the diseased scallops by performing a detailed, multiplane assessment [16]. The echocardiographer should also measure the coaptation-septum distance as this is one of the determinants of postoperative systolic anterior motion of mitral valve [17]; (Figure 12). Also, the left ventricular (LV) dimensions and estimated ejection fraction should be determined. The LV chamber dimensions are measured from the midesophageal and gastric two chamber views [18]; (Figure 13).3D TEE can be acquired in a few simple steps (Figure 14). This can significantly help in the diagnosis by complementing the images obtained on 2D imaging. Once the 3D image has been acquired, a few simple post-processing steps as highlighted in Figure 14 can be performed so that the image can be oriented properly in the surgeon’s view. 3D Color Doppler imaging can then be performed to localize the origin of the regurgitant jet (Figure 15).

Mitral regurgitation is a complex yet common valvular disease, which requires careful assessment to elucidate the etiology. The echocardiographer should have the knowledge and expertise to assess mitral valve disease and convey the findings to the surgeon preoperatively. 3D echo is complimentary to 2D multiple TEE and should be utilized as part of mitral valve preoperative assessment. Lastly, every attempt should be made to quantitate the amount of MR regardless of the visual impression.