Original Article
Left Ventricular Outflow Tract Area Measurements by Planimetry Using Two-Dimensional Simultaneous Orthogonal Plane Imaging During Transesophageal Echocardiography

https://doi.org/10.1053/j.jvca.2016.02.027Get rights and content

Objective

Calculations of the left ventricular outflow tract (LVOT) area are typically based on the assumption that the LVOT is circular. This study was conducted to determine whether simultaneous orthogonal plane imaging with tilt during two-dimensional (2D) transesophageal echocardiography provided more accurate measurements of the LVOT area than the standard method.

Design

The authors prospectively measured the LVOT area in 2D by (1) the standard calculation based on the diameter as viewed on the long axis, and (2) a direct measurement using planimetry of the short axis, in consecutive patients presenting for elective surgery. The authors validated the planimetric technique by obtaining three-dimensional (3D) measurements in a subset of the subjects.

Setting

An academic medical center.

Participants

Adult surgical patients with no evidence of aortic stenosis.

Interventions

Transesophageal images were acquired by anesthesiologists certified by the National Board of Echocardiography.

Measurements and Main Results

Image acquisition and assessment were performed in the operating room and found to be adequate for analysis in 52 of 55 subjects. Simultaneous orthogonal plane imaging with tilt enabled long- and short-axis visualization of the LVOT. The authors found that the standard method underestimated the area by 0.78 cm2 compared to the direct method (2D planimetry) when measured at the same beat at a similar point in the cardiac cycle. Moreover, 2D planimetry measurements were comparable to 3D planimetry measurements in the last 20 study subjects (R2 = 0.88, p<0.0001).

Conclusions

This study suggested that 2D planimetry may be more accurate than 2D diameter-based calculations.

Introduction

LEFT VENTRICULAR OUTFLOW TRACT (LVOT) measurements have important clinical applications, including the accurate calculation of aortic valve area and stroke volume. Errors could therefore impact patient care and treatment decisions. The LVOT long has been assumed to be circular in its cross-section1 and echocardiography typically is used to determine its diameter. Computed tomography (CT), magnetic resonance imaging (MRI), and three-dimensional (3D) echocardiographic imaging have demonstrated an elliptically shaped LVOT in a majority of the population2, 3, 4 and in only a minority of patients. During two-dimensional transesophageal echocardiography (2D TEE), the LVOT is visualized frequently in its long axis and its area is calculated using the diameter (0.785×diameter squared). This diameter corresponds to the minor diameter of an ellipse and hence tends to underestimate the true cross-sectional area of an elliptical LVOT. The authors hypothesized that planimetric measurements of the LVOT in the short-axis view by 2D TEE was plausible and closely approximated 3D planimetric measurements. The goal of this study was to demonstrate the feasibility of obtaining a short-axis view of the LVOT and to directly measure the area using planimetry during 2D TEE.

Section snippets

Methods

With IRB approval, 55 adult patients with no evidence of aortic stenosis who were undergoing intraoperative TEE for surgery were enrolled in the study. TEE images were acquired by physician anesthesiologists with advanced certification from the National Board of Echocardiography. LVOT image acquisition and assessment were performed in real time in the operating room using a standard surgical protocol. A 3D-matrix array TEE probe (iE33 or Epic 7; X7-2t; Philips Healthcare Inc., Andover, MA) was

Results

Of the 55 enrolled subjects, the LVOT area using 2D planimetry could be assessed in 94.5%. Three could not be assessed because of poor image quality and alignment of the LVOT and were excluded from the analysis. The assessable subjects were 48% male, with a median age of 61.5 years (range, 42-85 years). The median body surface area was 1.96 cm2 (range, 1.42-2.33 cm2) (Tables 1 and 2). Of the subjects undergoing cardiac surgery involving cardiopulmonary bypass, there were 33 coronary artery

Discussion

With advances in imaging technology, there are now multiple modalities well suited to imaging the LVOT, including CT angiography, magnetic resonance angiography, and echocardiography. No single modality is preferred for all patients or all clinical situations. The choice of imaging modality should be individualized to the patient’s clinical situation, diagnostic questions to be answered, and other factors, such as performer expertise and availability. Accurate LVOT area measurements are

Conclusion

The technique tested in this study appeared to provide a rapid and more accurate measurement of the LVOT area than when indirectly estimating the LVOT area under the assumption that the LVOT is circular, as is done customarily. Simultaneous orthogonal plane imaging enables visualization of the LVOT in the short axis, and planimetry of this live 2D image allows for a direct measurement of the area. In this study, the area measured using planimetry was greater in all subjects, thus providing

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