Interaliasing distance of the flow convergence surface for determining mitral regurgitant volume: a validation study in a chronic animal model

Real-time 3-Dimensional Color Doppler Flow of Mitral and Tricuspid Regurgitation: Feasibility and Initial Quantitative Comparison with 2-Dimensional Methods

BACKGROUND

Visualization of valvular regurgitation using 3-dimensional (3D) echocardiography has been attempted but not routinely performed to date because of technical limitations. With the recent development of a fully sampled matrix-array probe, real-time color flow imaging allows display and analysis of regurgitant jets. Accordingly, the aim of this study was 2-fold. We: (1) investigated the feasibility of transthoracic, real-time visualization of 3D color flow jets; and (2) compared conventional 2-dimensional (2D) Doppler/color flow methods of quantitation (ie, 2D jet/left atrial [LA] area, flow convergence, and vena contracta [VC]) to 3D-derived measurements (3D jet/LA volume, flow convergence, and VC).

METHOD

In all, 56 patients with good acoustic windows and varying degrees of mitral regurgitation (MR) (n = 32) and tricuspid regurgitation (TR) (n = 24) scheduled for a routine echocardiogram were studied. Using a broadband transducer, 2D color Doppler imaging of TR and MR jets was performed to obtain jet/atrial area ratio, effective regurgitant orifice area, and VC measurements. Subsequently, real-time 3D echocardiography imaging of these jets was performed and analyzed offline using software, resulting in jet/atrial volume ratio, effective regurgitant orifice area, and VC (major and minor axes).

RESULTS

Of the 56 patients recruited into the study, 86% had sufficient data quality for analysis (87.5% in patients with MR and 83% in patients with TR). Both LA and right atrium were adequately visualized in all patients. Manually traced 3D MR and TR volumes had good agreement when compared with proximal isovelocity surface area-derived volumes (r = 0.7, y = 0.4x + 6.4; and r = 0.8, y = 1.1x + 5.1; respectively) with minimal underestimation and overestimation of volumes for MR and TR (8 and 7 mL, respectively), but with relatively wide limits of agreement for MR (28 mL) versus TR (12 mL). When comparing 3D MR jet/LA volume ratios and TR jet/right atrial volume ratios to 2D MR jet/LA area and 2D TR jet/right atrial area ratios, the former were significantly smaller. The 3D minimum and maximum VC diameter for MR were significantly different compared with those measured with 2D (minimum diameter = 0.7 +/- 0.1 cm, P < .01; maximum diameter = 1.1 +/- 0.5 cm, P < .02 vs 2D = 0.8 +/- 0.3 cm). Conversely, the TR VC minimum diameter was similar but maximum diameter measurements were larger in 3D compared with 2D (3D = 1.3 +/- 0.6 cm vs 2D = 0.7 +/- 0.2 cm, P < .001).

CONCLUSION

Three-dimensional echocardiography of color flow Doppler of MR and TR jets was feasible. Quantitative methods using 3D echocardiography such as MR and TR volumes correlated well with 2D flow convergence methods. TR VC has more of an elliptic shape, whereas MR is more circular or oval when visualized in 3D. Regurgitant/atrial volume ratios provide a new method of assessing the severity of regurgitant lesions; however, 3D volume-derived ratios were comparatively smaller than those measured with 2D echocardiography.

Three-Dimensional Echocardiography

Over the past 3 decades, echocardiography has become a major diagnostic tool in the arsenal of clinical cardiology for real-time imaging of cardiac dynamics. More and more, cardiologists' decisions are based on images created from ultrasound wave reflections. From the time ultrasound imaging technology provided the first insight into the human heart, our diagnostic capabilities have increased exponentially as a result of our growing knowledge and developing technology. One of the most significant developments of the last decades was the introduction of 3-dimensional (3D) imaging and its evolution from slow and labor-intense off-line reconstruction to real-time volumetric imaging. While continuing its meteoric rise instigated by constant technological refinements and continuing increase in computing power, this tool is guaranteed to be integrated in routine clinical practice. The major proven advantage of this technique is the improvement in the accuracy of the echocardiographic evaluation of cardiac chamber volumes, which is achieved by eliminating the need for geometric modeling and the errors caused by foreshortened views. Another benefit of 3D imaging is the realistic and unique comprehensive views of cardiac valves and congenital abnormalities. In addition, 3D imaging is extremely useful in the intraoperative and postoperative settings because it allows immediate feedback on the effectiveness of surgical interventions. In this article, we review the published reports that have provided the scientific basis for the clinical use of 3D ultrasound imaging of the heart and discuss its potential future applications.

Reproducibility of the proximal flow convergence method in mitral and tricuspid regurgitation

BACKGROUND

The follow-up of patients with mitral and tricuspid regurgitation is important for their clinical treatment. We aimed to evaluate the reproducibility of the flow convergence method in mitral and tricuspid regurgitation.

METHODS

The proximal flow convergence region was imaged with color Doppler ultrasound scanning echocardiography in 83 patients with mitral regurgitation, tricuspid regurgitation, or both. Proximal isovelocity surface area radii for aliasing velocities of 27 to 29 cm/s and 41 to 43 cm/s were repeatedly measured by the same experienced investigator on different days and by experienced and less experienced investigators at 1 day.

RESULTS

In mitral regurgitation, the intraobserver variability rate was 0.2% +/- 13.5% (2.8% +/- 13.3%) and the interobserver variability was 0.1% +/- 13.8% (1.7% +/- 18.0%) for an aliasing velocity of 27 to 29 cm/s (41-43 cm/s). For the aliasing velocity of 27 to 29 cm/s (41-43 cm/s), the 95% ranges for change of the proximal isovelocity surface area radii were +/- 2.7 mm (+/- 1.8 mm) for measurements repeated by the same investigator and +/- 2.7 mm ( +/- 2.4 mm) for different investigators. Interobserver variability was independent of the investigators' experience. Similar data were achieved in tricuspid regurgitation.

CONCLUSIONS

The proximal flow convergence method is acceptably reproducible in mitral and tricuspid regurgitation independent of the investigators experience. For the aliasing velocity of 27 to 29 cm/s (41-43 cm/s), the proximal isovelocity surface area radius has to change for >2.7 (2.4) mm before an altered severity of mitral or tricuspid regurgitation in a single patient can be assumed.