Malcolm E. Legget

Prospective Study of Asymptomatic Valvular Aortic Stenosis Clinical, Echocardiographic, and Exercise Predictors of Outcome

BACKGROUNDnOnly limited data on the rate of hemodynamic progression and predictors of outcome in asymptomatic patients with valvular aortic stenosis (AS) are available.nnnMETHODS AND RESULTSnIn 123 adults (mean age, 63 +/- 16 years) with asymptomatic AS, annual clinical, echocardiographic, and exercise data were obtained prospectively (mean follow-up of 2.5 +/- 1.4 years). Aortic jet velocity increased by 0.32 +/- 0.34 m/s per year and mean gradient by 7 +/- 7 mm Hg per year; valve area decreased by 0.12 +/- 0.19 cm2 per year. Kaplan-Meier event-free survival, with end points defined as death (n = 8) or aortic valve surgery (n = 48), was 93 +/- 5% at 1 year, 62 +/- 8% at 3 years, and 26 +/- 10% at 5 years. Univariate predictors of outcome included baseline jet velocity, mean gradient, valve area, and the rate of increase in jet velocity (all P < or = .001) but not age, sex, or cause of AS. Those with an end point had a smaller exercise increase in valve area, blood pressure, and cardiac output and a greater exercise decrease in stroke volume. Multivariate predictors of outcome were jet velocity at baseline (P < .0001), the rate of change in jet velocity (P < .0001), and functional status score (P = .002). The likelihood of remaining alive without valve replacement at 2 years was only 21 +/- 18% for a jet velocity at entry > 4.0 m/s, compared with 66 +/- 13% for a velocity of 3.0 to 4.0 m/s and 84 +/- 16% for a jet velocity < 3.0 m/s (P < .0001).nnnCONCLUSIONSnIn adults with asymptomatic AS, the rate of hemodynamic progression and clinical outcome are predicted by jet velocity, the rate of change in jet velocity, and functional status.

System for quantitative three-dimensional echocardiography of the left ventricle based on a magnetic-field position and orientation sensing system

Accurate measurement of left-ventricular (LV) volume and function are important to monitor disease progression and assess prognosis in patients with heart disease. Existing methods of three-dimensional (3-D) imaging of the heart using ultrasound have shown the potential of this modality, but each suffers from inherent restrictions which limit its applicability to the full range of clinical situations. The authors have developed a technique for image acquisition using a magnetic-field system to track the 3-D echocardiographic imaging planes and 3-D image analysis software including the piecewise smooth subdivision method for surface reconstruction. The technique offers several advantages over existing methods of 3-D echocardiography. The results of validation using in vitro LVs show that the technique allows accurate measurement of LV volume and anatomically accurate 3-D reconstruction of LV shape and is, therefore, suitable for analysis of regional as well as global function.

Gender differences in left ventricular function at rest and with exercise in asymptomatic aortic stenosis

In 29 women and 53 men with asymptomatic aortic stenosis, two-dimensional (2-D) and Doppler echocardiography were performed at rest and immediately after treadmill exercise testing to examine gender differences in left ventricular geometry, systolic and diastolic function, functional status, and exercise capacity. Aortic stenosis severity was similar between men and women. Women reported more functional impairment than men (88% +/- 14% vs 95% +/- 7%; p = 0.02). When indexed to body surface area, women had a smaller end-diastolic volume (39 +/- 14 vs 50 +/- 15 ml/m2; p = 0.002), end-systolic volume (13 +/- 6 ml/m2 vs 18 +/- 9 ml/m2; p = 0.01) and left ventricular mass (73 +/- 26 gm/m2 vs 84 +/- 21 gm/m2; p = 0.05), but a higher relative wall thickness in systole (1.5 +/- 0.4 cm vs 1.3 +/- 0.4 cm; p = 0.05), and fractional shortening (43% +/- 7% vs 39% +/- 10%; p = 0.03). Women had higher early and late transmitral velocities than did men (early, 92 +/- 24 cm/sec vs 79 +/- 29 cm/sec; p = 0.05; late, 97 +/- 30 cm/sec vs 68 +/- 23 cm/sec; p < 0.0001), a higher time-velocity integral in early diastole (18.2 +/- 4.8 cm vs 15.1 +/- 4.3 cm; p = 0.006), a significantly shorter exercise duration (4.5 +/- 4.1 minutes vs 8.0 +/- 3.9 minutes; p < 0.0001), a greater degree of functional aerobic impairment (25% +/- 48% vs 2% +/- 33%; p = 0.02), and a smaller increase in cardiac output with exercise (5.4 +/- 3.5 L/min vs 8.0 +/- 4.3 L/min; p = 0.01), in spite of similar peak heart rate and blood pressure responses. In these asymptomatic subjects with aortic stenosis, women had smaller, relatively hypercontractile ventricles, a different diastolic filling profile, more exercise limitation, and poorer functional capacity. These findings demonstrate the importance of gender in the response of the left ventricle to chronic pressure overload.

Applying the CenterSurface model to 3-D reconstructions of the left ventricle for regional function analysis

Reconstruction of heart chambers from tomographic images has traditionally been done from either parallel or fixed position rotational scans. We introduce a method of reconstruction from random slice orientations, using labeled landmark features to guide fitting to a labeled predesigned surface-generating mesh. This method is applied specifically to ultrasound sector scanning, but is applicable to any tomographic imaging technique. Given surface descriptions of the left ventricle (LV) endocardium and epicardium at end diastole (ED) and end systole (ES) (or other time points), LV wall motion can be computed by matching the ED and ES surface features. Wall thickness at ED and ES is computed using the CenterSurface method. A new method of computing the CenterSurface is described.

How positionally stable is a transesophageal echocardiographic probe? Implications for three-dimensional reconstruction.

Three-dimensional (3D) reconstruction from a single esophageal scanning position requires a stable relationship between the probe and the heart. The purpose of this study was to examine the movement of a transesophageal echocardiographic probe during 3D image acquisition. A new dual-axis multiplane probe was used that includes a miniature (6 x 6 x 9 mm) magnetic sensor in the tip. The sensor identifies the probes 3D position and 3D orientation in space with respect to the location of a magnetic field generator placed beneath the subject. In vivo 3D scanning was performed in five anesthetized, ventilated dogs, with positional determinations acquired every 66 msec. Probe movement was estimated by computing the deviations of each x, y, and z position and orientation determination, compared with the average values during each 3D scan or cardiac cycle. Ten 3D scans were analyzed, involving 263 cardiac cycles and 2328 determinations. The range and SD of the translational movement of the transducer were 2.3 and 0.8 mm, 1.7 and 0.5 mm, and 2.4 and 0.7 mm in x, y, and z directions, respectively, during 3D scanning. Translational movement was more dominant than was rotational movement. Misregistration of three-dimensional reconstructions may be due to subtle probe movement. The ability to monitor probe movement may be helpful in optimizing 3D data sets.

Automatic border detection and three-dimensional reconstruction with echocardiography

This article reviews two important innovations in echocardiography resulting from the recent advances in the capabilities of microprocessors. The first, automatic endocardial border detection, has been implemented on computers contained entirely within echocardiograph machines and is gaining wide clinical use. The second, three-dimensional imaging, is currently under intense investigation and shows great promise for clinical application. It requires, however, further development of the specialized transducer apparatus necessary for image acquisition and the sophisticated computer-processing capability necessary for image reconstruction and display.

Stereographic viewing of 3D ultrasound images: a novelty or a tool?

Three dimensional (3D) reconstruction of multiple two dimensional images, spatially and time registered, is increasingly being employed. These can be visualized on computer screens in full stereographic perspective using software and stereographic glasses now available. The authors have applied stereographic viewing to over 40 reconstructions of outlines of the endo and epicardiums of ultrasound imaged hearts. They found that standard viewing often mislead them into believing that misregistration existed. However, when viewed in stereographic mode, they found that these suspected lines did intersect, but at other places in the 3D reconstruction. The stereographic method has proven very useful in this and in distinguishing the separability of various 3D structural features in grid, surface, and voxel echocardiogram reconstructions.

901-51 Three Dimensional Reconstruction Using a New Dual Axis Multiplane Transesophageal Echo Probe: Calculation of Left Ventricular Volume

The purpose of this study is to validate LV volume measurements using a newtransesophageal echo (TEE) probe for 3 dimensional (3D) imaging which allows multiple intersecting “fan-like” scans of the heart to be obtained from a single scanning position. The transducer can be tilted (±30°), and rotated (0°–104°), without moving the probes tip. A locator system, with a magnetic sensor in the probes tip, tracks movement in three x, y, and z axes. A customized computer system directly digitizes echo images, and endocardial borders are manually traced and applied to a surface reconstruction algorithm. Scans of 6 excised canine left ventricles have been initially performed. Volumes computed from the 3D reconstructions compared to true volumes are shown below. The regression equation was 3d volume = 0.82 true volume +0.6, r2= 0.95, p = 0.01. n n n n n n LV no. 1 2 3 4 5 6 nTrue vol (ml) 30.3 23.0 24.0 27.5 60.5 28.8 n3D vol (ml) 30.3 18.3 19.2 23.7 49.5 21.2 n nFull-size table n nTable options n n n nView in workspace n nDownload as CSV n n n n n n n n nThe underestimation of LV volumes with these preliminary results may be due to inaccuracies related to the probe, the reconstruction algorithm, and ultrasound beam width. An example of intersecting LV endocardial borders and a wireframe reconstruction are shown: n n n n n n nFigure options n n n nDownload full-size image nDownload high-quality image (103 K) nDownload as PowerPoint slide n n n n n n nConclusions nDual axis multiplane transesophageal scanning enables: acquisition of multiple intersecting scans from a single probe position, 3D reconstruction of the LV, and calculation of the volume.

Volumetric reconstruction and visualization in three dimensional echocardiography: in vitro investigation

An object spinning scan method was applied to acquire high resolution in vitro ultrasound images for the purpose of studying volume interpolation and rendering. Three dimensional (3D) reconstructions were accomplished for nineteen excised porcine and canine hearts. The resulting 3D images clearly revealed the 3D features with a user developed weighted opacity based interactive volume rendering approach. The 3D calculated left ventricular volumes correlated well to those measured from water displacement (r=0.9548). This study not only provides superior reference data sets investigation of volumetric reconstruction visualization methodologies, the employed methods of reconstruction and visualization can also be adapted to in vivo transesophageal 3D imaging.

922-60 How Positionally Stable is a Transesophageal Echo Probe During 3 Dimensional Imaging? Implications for 3 Dimensional Reconstruction

Three dimensional (3D) reconstruction from a single esophageal scanning position requires a stable relationship between the probe and the heart. The purpose of this study was to examine the movement of a transesophageal echo (TEE) probe during 3D image acquisition. A new dual axis multiplane probe was used which includes a miniature (6xa0×xa06xa0×xa09xa0mm) 6D sensor in the tip. The sensor identifies the probes 3D position and orientation in space with respect to the location of a magnetic field generator placed beneath the subject. In vivo 3D scans were performed in 5 anesthetized, ventilated dogs. Positional determinations were acquired every 66xa0ms. The sensor axes were: x-mediolateral. y-superoinferior, z-anteroposterior, and r-radial distancexa0=xa0√(x2xa0+xa0y2xa0+xa0z2). The movement was estimated by computing standard deviations of the x, y, and z positions during each 3D scan and each cardiac cycle. From 2337 determinations, the mean standard deviation for 10 3D scans and 264 cardiac cycles and histograms of the radial movement were calculated and are shown. x(mm) y(mm) z(mm) r(mm) Total 3D scans 0.63xa0±xa00.63 0.56xa0±xa00.64 0.65xa0±xa00.45 0.57xa0±xa00.43 Cardiac cycle 0.28xa0±xa00.36 0.21xa0±xa00.28 0.25xa0±xa00.35 0.24xa0±xa00.35 Conclusion Probe movement during 3D imaging is measurable and in these anesthetized subjects was within acceptable limits. This capability will be useful in awake patients where greater movement is expected, and will optimize the 3D data set by discarding scans where significant probe movement has occurred.