Measurement of left ventricular ejection fraction and volumes with three-dimensional reconstructed transesophageal ultrasound scans: comparison to radionuclide and thermal dilution measurements

Echocardiographic Prediction of Left Ventricular Dysfunction After Transcatheter Patent Ductus Arteriosus Closure in Children

Objectives: To evaluate the change of left ventricular (LV) systolic function after transcatheter patent ductus arteriosus (PDA) closure in children, and to identify whether echocardiography parameters could be the predictors of LV dysfunction post-PDA closure if present. Methods: This study enrolled 191 pediatric PDA patients, and all of them underwent successful transcatheter PDA closure between January 2016 and December 2018. The patent ductus arteriosus diameter (PDAd), aortic root diameter (AOd), left atrial diameter (LAd), right ventricular outflow tract dimension (RVOT), LV end-diastolic dimension (LVEDD), and LV end-systolic dimension (LVESD) were all measured by echocardiography at pre-closure, post-closure (within 24 h after the procedure), and follow-up (3 months after the procedure). The ratio of PDAd to AOd (PDAd/AOd), the ratio of LAd to AOd (LAd/AOd), the left ventricular ejection fraction (LVEF), and the fractional shortening (FS) were calculated. Results: The LAd, LVESD, LVEDD, FS, and LVEF decreased significantly in the 24 h after closure, compared to pre-closure levels. However, all echocardiography parameters recovered to pre-closure levels at 3 months after PDA closure in all patients. Moreover, the pre-closure LAd, LVEF, PDAd/AOd, and LAd/AOd were higher in the patients with post-closure LV systolic dysfunction than in those without post-closure LV systolic dysfunction. Furthermore, the pre-closure LVEF, PDAd/AOd, and LAd/AOd were correlated with the post-closure LVEF, and pre-closure LVEF ≤ 66.5%, PDAd/AOd ≥ 0.28, and LAd/AOd ≥ 1.54 predict the post-closure LV systolic dysfunction. Conclusion: Transcatheter closure of PDA causes a significant deterioration in LV systolic function early after PDA closure, which recovered completely within 3 months of post-closure in children. Pre-closure LVEF, PDAd/AOd, and LAd/AOd can be the predictors of post-closure left ventricular systolic dysfunction.

Emerging Concepts in Transesophageal Echocardiography

Introduced in 1977, transesophageal echocardiography (TEE) offered imaging through a new acoustic window sitting directly behind the heart, allowing improved evaluation of many cardiac conditions. Shortly thereafter, TEE was applied to the intraoperative environment, as investigators quickly recognized that continuous cardiac evaluation and monitoring during surgery, particularly cardiac operations, were now possible. Among the many applications for perioperative TEE, this review will focus on four recent advances: three-dimensional TEE imaging, continuous TEE monitoring in the intensive care unit, strain imaging, and assessment of diastolic ventricular function.

The Influence of Percutaneous Closure of Patent Ductus Arteriosus on Left Ventricular Size and Function

OBJECTIVES

We aimed to evaluate the effect of percutaneous closure of patent ductus arteriosus (PDA) on left ventricular (LV) hemodynamics.

BACKGROUND

Today, most PDAs are closed percutaneously. Little is known, however, about hemodynamic changes after the procedure.

METHODS

Of 37 children (ages 0.6 to 10.6 years) taken to the catheterization laboratory for percutaneous PDA closure, the PDA was closed in 33. Left ventricular diastolic and systolic dimensions, volumes, and function were examined by two-dimensional (2D) and three-dimensional (3D) echocardiography and serum concentrations of natriuretic peptides measured before PDA closure, on the following day, and 6 months thereafter. Control subjects comprised 36 healthy children of comparable ages.

RESULTS

At baseline, LV diastolic diameter measured >+2 SD in 5 of 33 patients. In 3D echocardiography, a median LV diastolic volume measured 54.0 ml/m2 in the control subjects and 58.4 ml/m2 (p < 0.05) in the PDA group before closure and 57.2 ml/m2 (p = NS) 6 months after closure. A median N-terminal brain natriuretic peptide (pro-BNP) concentration measured 72 ng/l in the control group and 141 ng/l in the PDA group before closure (p = 0.001) and 78.5 ng/l (p = NS) 6 months after closure. Patients differed from control subjects in indices of LV systolic and diastolic function at baseline. By the end of follow-up, all these differences had disappeared. Even in the subgroup of patients with normal-sized LV at baseline, the LV diastolic volume decreased significantly during follow-up.

CONCLUSIONS

Changes in LV volume and function caused by PDA disappear by 6 months after percutaneous closure. Even the children with normal-sized LV benefit from the procedure.

Effect of three-dimensional valve shape on the hemodynamics of aortic stenosis: three-dimensional echocardiographic stereolithography and patient studies

OBJECTIVES

This study tested the hypothesis that the impact of a stenotic aortic valve depends not only on the cross-sectional area of its limiting orifice but also on three-dimensional (3D) valve geometry.

BACKGROUND

Valve shape can potentially affect the hemodynamic impact of aortic stenosis by altering the ratio of effective to anatomic orifice area (the coefficient of orifice contraction [Cc]). For a given flow rate and anatomic area, a lower Cc increases velocity and pressure gradient. This effect has been recognized in mitral stenosis but assumed to be absent in aortic stenosis (constant Cc of 1 in the Gorlin equation).

METHODS

In order to study this effect with actual valve shapes in patients, 3D echocardiography was used to reconstruct a typical spectrum of stenotic aortic valve geometrics from doming to flat. Three different shapes were reproduced as actual models by stereolithography (computerized laser polymerization) with orifice areas of 0.5, 0.75, and 1.0 cm(2) (total of nine valves) and studied with physiologic flows. To determine whether valve shape actually influences hemodynamics in the clinical setting, we also related Cc (= continuity/planimeter areas) to stenotic aortic valve shape in 35 patients with high-quality echocardiograms.

RESULTS

In the patient-derived 3D models, Cc varied prominently with valve shape, and was largest for long, tapered domes that allow more gradual flow convergence compared with more steeply converging flat valves (0.85 to 0.90 vs. 0.71 to 0.76). These variations translated into differences of up to 40% in pressure drop for the same anatomic area and flow rate, with corresponding variations in Gorlin (effective) area relative to anatomic values. In patients, Cc was significantly lower for flat versus doming bicuspid valves (0.73 +/- 0.14 vs. 0.94 +/- 0.14, p < 0.0001) with 40 +/- 5% higher gradients (p < 0.0001).

CONCLUSIONS

Three-dimensional valve shape is an important determinant of pressure loss in patients with aortic stenosis, with smaller effective areas and higher pressure gradients for flatter valves. This effect can translate into clinically important differences between planimeter and effective valve areas (continuity or Gorlin). Therefore, valve shape provides additional information beyond the planimeter orifice area in determining the impact of valvular aortic stenosis on patient hemodynamics.

Ultrasound processing and computing: review and future directions

Since the introduction of medical ultrasound in the 1950s, modern diagnostic ultrasound has progressed to see many major diagnostic tools come into widespread clinical use, such as B-mode imaging, color-flow imaging, and spectral Doppler. New applications, such as panoramic imaging, three-dimensional imaging, and quantitative imaging, are now beginning to be offered on some commercial ultrasound machines and are expected to grow in popularity. In this review, we focus on the various algorithms, their processing requirements, and the challenges of these ultrasound modes. Whereas the older, mature B and color-flow modes could be systolically implemented using hardwired components and boards, new applications, such as three-dimensional imaging and image feature extraction, are being implemented more by using programmable processors. This trend toward programmable ultrasound machines will continue, because the programmable approach offers the advantages of quick implementation of new applications without any additional hardware and the flexibility to adapt to the changing requirements of these dynamic new applications.

Three-dimensional echocardiographic determination of left ventricular volumes and function by multiplane transesophageal transducer: dynamic in vitro validation and in vivo comparison with angiography and thermodilution

The goal of this study was to validate 3-dimensional echocardiography by multiplane transesophageal transducer for the determination of left ventricular volumes and ejection fraction in an in vitro experiment and to compare the method in vivo with biplane angiography and the continuous thermodilution method. In the dynamic in vitro experiment, we scanned rubber balloons in a water tank by using a pulsatile flow model. Twenty-nine measurements of volumes and ejection fractions were performed at increasing heart rates. Three-dimensional echocardiography showed a very high accuracy for volume measurements and ejection fraction calculation (correlation coefficient, standard error of estimate, and mean difference for end-diastolic volume 0.998, 2.3 mL, and 0.1 mL; for end-systolic volume 0.996, 2.7 mL, and 0.5 mL; and for ejection fraction 0.995, 1.0%, and -0.4%, respectively). However, with increasing heart rate there was progressive underestimation of ejection fraction calculation (percent error for heart rate below and above 100 bpm 0.59% and -8.6%, P < .001). In the in vivo study, left ventricular volumes and ejection fraction of 24 patients with symmetric and distorted left ventricular shape were compared with angiography results. There was good agreement for the subgroup of patients with normal left ventricular shape (mean difference +/-95% confidence interval for end-diastolic volume 5.2+/-6.7 mL, P < .05; for end-systolic volume -0.5+/-8.4 mL, P = not significant; for ejection fraction 2.4%+/-7.2%, P = not significant) and significantly more variability in the patients with left ventricular aneurysms (end-diastolic volume 23.1+/-56.4 mL, P < .01; end-systolic volume 5.6+/-41.0 mL, P = not significant; ejection fraction 4.9%+/-16.0%, P < .05). Additionally, in 20 critically ill, ventilated patients, stroke volume and cardiac output measurements were compared with measurement from continuous thermodilution. Stroke volume as well as cardiac output correlated well to thermodilution (r = 0.89 and 0.84, respectively, P < .001), although both parameters were significantly underestimated by 3-dimensional echocardiography (mean difference +/-95% confidence interval = -6.4+/-16.0 mL and -0.6+/-1.6 L/min, respectively, P < .005).

A simplified, practical echocardiographic approach for 3-dimensional surfacing and quantitation of the left ventricle: clinical application in patients with abnormally shaped hearts

The goal of this study was to validate the quantitative accuracy of a system for 3-dimensional (3D) echocardiographic reconstruction of the left ventricle to assess its volume and function in human beings by using 3 apical views as a simplified technique to promote practical clinical application. End-diastolic and end-systolic volumes (EDV, ESV) and ejection fraction (EF) were obtained by 3D echocardiography in 50 patients with dilated or geometrically distorted left ventricles and compared with values from magnetic resonance imaging (20 consecutive patients), angiography (22 consecutive patients), and radionuclide imaging (8 consecutive patients). Three-dimensional results were also compared with 2-dimensional (2D) echocardiographic estimates. Three-dimensional left ventricular reconstruction provided values that correlated and agreed well with pooled data from the other techniques for EDV (y = 0.93x + 9.1, r = 0.95, standard error of the estimate [SEE] = 15.2 mL, mean difference = -0.5 +/- 15.4 mL), ESV (y = 0.94x + 4.3, r = 0. 96, SEE = 11.4 mL, mean difference = 0.4 +/- 11.5 mL), and EF (y = 0. 90x + 4.1, r = 0.92, SEE = 6.2%, mean difference = -0.9 +/- 6.4%) (all mean differences not significant versus 0), with greater errors by 2D echocardiography. Intraobserver and interobserver variabilities of 3D echocardiography were less than 6% for EDV, ESV, and EF. The overall time for image acquisition and 3D reconstruction was 5 to 8 minutes. Although this 3D method uses only a small number of apical views, it accurately calculates EDV, ESV, and EF in patients with dilated and asymmetric left ventricles and is more accurate than 2D echocardiography. The flexible surface fit used to combine the 3 views provides a convenient visual output as well as quantitation. This simple and rapid 3D method has the potential to facilitate routine clinical applications that assess left ventricular function and changes that occur with remodeling.

Clinical Determinations of Volumes of Normal and Aneurysmatic Left Ventricles by Three-Dimensional Transesophageal Echocardiography

Biplane methods of determining left ventricular volumes are inaccurate in the presence of aneurysmal distortions. Multiplane transesophageal echocardiography, which provides multiple, unobstructed cross-sectional views of the heart from a single, stable position, has the potential for more accurate determinations of volumes of irregular cavity forms than the biplane methods. The aim of the study was to determine the feasibility of three-dimensional measurements of ventricular volumes in patients with normal and aneurysmatic left ventricles by using multiplane transesophageal echocardiography. With the echotransducer in the mid-esophageal (transesophageal) position, nine echo cross-sectional images of the left ventricle in approximately 20 degrees angular increments were obtained from each of 29 patients with coronary artery disease who had undergone biplane ventriculography during diagnostic cardiac catheterization. In 17 of these 29 patients, echo cross-sectional images of the left ventricle with the echotransducer in transgastric position were also obtained. End-diastolic volume, end-systolic volume, and ejection fraction were determined from multiplane transesophageal echocardiographic images and biplane ventriculographic images by the disc-summation method and compared with each other. In another ten patients with indwelling pulmonary artery catheters, stroke volumes calculated from multiplane transesophageal echocardiographic images were compared with those derived from thermodilution cardiac output measurements. Correlations between biplane ventriculographic and multiplane transesophageal echocardiographic measurements were higher in the ten patients with normal ventricular shape [for end-diastolic volumes, r = 0.91, SEE = 19 ml; for end-systolic volumes, r = 0.98, SEE = 9.3 ml; for ejection fractions (EFs), r = 0.91, SEE = 5.4%] than in the 19 patients with ventricular aneurysms (for end-diastolic volumes, r = 0.61, SEE = 31.5 ml; for end-systolic volumes, r = 0.66, SEE = 32.5 ml; for EFs, r = 0.79, SEE = 8%). Correlations between echocardiographic volumes from the transesophageal and transgastric transducer positions were high independent of left ventricular geometry (for end-diastolic volumes, r = 0.84, SEE = 13.1 ml; for end-systolic volumes, r = 0.98, SEE = 9.6 ml; for EFs, r = 0.97, SEE = 3.4%). In 12 observations (4 normal and 8 aneurysmal) from the ten patients with indwelling pulmonary artery catheters, correlation between stroke volumes determined from thermodilution cardiac output measurements and those derived from multiplane transesophageal echocardiographic images was high (r = 0.91, SEE = 6 ml). The results indicate that three-dimensional measurements of volumes of irregular and distorted left ventricles are feasible with multiplane transesophageal echocardiography. This method may be more accurate than biplane methods, especially in the presence of left ventricular aneurysms.

Three-dimensional echocardiographic reconstruction: description and applications of a simplified technique for quantitative assessment of left ventricular size and function

A simplified system for three-dimensional (3D) reconstruction of the left ventricle and quantitation of its size and function is described. This system requires the acquisition of a minimum number of two-dimensional (2D) echocardiographic apical views, which are obtained by rotation of the probe about the initial imaging point. Traced endocardial borders are spatially reconstructed according to the common apex and longitudinal axis of the views and to the measured or assumed angular relation between scanned planes. This technique has been applied in vitro to regular and irregular ventricular phantoms, yielding excellent accuracy for volume calculation. Also, it has been applied clinically for left ventricular volume, stroke volume, and ejection fraction calculation in both normal subjects and patients with various cardiac diseases, providing good results compared with other independent imaging techniques and showing increased accuracy with respect to 2D echocardiographic methods. Because this is obtained without substantial increase in time, effort, or cost, this simplified technique for 3D reconstruction should therefore be of value in daily clinical echocardiographic practice.

Insights from three-dimensional echocardiography into the mechanism of functional mitral regurgitation: direct in vivo demonstration of altered leaflet tethering geometry

BACKGROUND

Recent advances in three-dimensional (3D) echocardiography allow us to address uniquely 3D scientific questions, such as the mechanism of functional mitral regurgitation (MR) in patients with left ventricular (LV) dysfunction and its relation to the 3D geometry of mitral leaflet attachments. Competing hypotheses include global LV dysfunction with inadequate leaflet closing force versus geometric distortion of the mitral apparatus by LV dilatation, which increases leaflet tethering and restricts closure. Because geometric changes generally accompany dysfunction, these possibilities have been difficult to separate.

METHODS AND RESULTS

We created a model of global LV dysfunction by esmolol and phenylephrine infusion in six dogs. initially with LV expansion limited by increasing pericardial restraint and then with the pericardium opened. The mid-systolic 3D relations of the papillary muscle (PM) tips and mitral valve were reconstructed. Despite severe LV dysfunction (ejection fraction, 18+/-6%), only trace MR developed when pericardial restraint limited LV dilatation; with the pericardium opened, moderate MR accompanied LV dilatation (end-systolic volume, 44+/-5 mL versus 12+/-5 mL control, P<.001). Mitral regurgitant volume and orifice area did not correlate with LV ejection fraction and dP/dt (global function) but did correlate with changes in the tethering distance from the PMs to the anterior annulus derived from the 3D reconstructions, especially PM shifts in the posterior and mediolateral directions, as well as with annular area (P<.0005). By multiple regression, only changes in the PM-to-annulus distance independently predicted MR volume and orifice area (R2=.82 to .85, P=2x10(-7) to 6x10(-8)).

CONCLUSIONS

LV dysfunction without dilatation fails to produce important MR. Functional MR relates strongly to changes in the 3D geometry of the mitral valve attachments at the PM and annular levels, with practical implications for approaches that would restore a more favorable configuration.

Comparison of transthoracic three dimensional echocardiography with magnetic resonance imaging in the assessment of right ventricular volume and mass

OBJECTIVE

Assessment of right ventricular volume and mass with three dimensional echocardiography and comparison with magnetic resonance imaging.

METHODS

Measurements of right ventricular volumes performed on three dimensional datasets acquired by transthoracic echocardiography were compared to those obtained from magnetic resonance imaging performed on the same day. Volumes were measured in end systole and end diastole and ejection fraction calculated. Right ventricular mass was assessed in end systole. With both methods, the areas of a 2 mm thick slice of the ventricle were manually outlined and multiplied by the slice thickness to obtain slice volume. Slice volumes were multiplied by the number of measured slices to obtain the ventricular volume.

PATIENTS

16 patients were studied: three with normal hearts, three after surgical repair of coarctation of the aorta, nine following repair of tetralogy of Fallot, and one with Mustard atrial repair of complete transposition of the great arteries.

RESULTS

Correlation between end diastolic volumes measured by both methods was r = 0.95 with limits of agreement ranging from -3.5 to 12.5 ml; correlation for end systolic volumes was r = 0.87 with limits of agreement between -4.0 and 16.4 ml; correlation for end systolic right ventricular mass was r = 0.81 with limits of agreement between -7.0 and 20.6 g. Interobserver variability ranged from 4.3% (range 0.2% to 9.3%) for end diastolic volume to 7.6% (1.8% to 15.4%) for mass measurements.

CONCLUSIONS

With transthoracic three dimensional echocardiography, end diastolic right ventricular volumes can be assessed with acceptable accuracy in normal hearts and those with enlarged right ventricles, whereas the current method of three dimensional echocardiography is less good for end systolic volumes and not satisfactory for right ventricular mass measurements.

Transesophageal echocardiography

This article presents an overview of the benefits and efficacy of transesophageal echocardiography (TEE) in the critically ill patient. The echocardiographic evaluation of ventricular function both regional and global, is discussed with special emphasis on ischemic heart disease; assessment of preload, interrogation of valvular heart disease (prosthetic and native) and its complications; endocarditis and its complications; intracardiac and extracardiac masses, including pulmonary embolism; aortic diseases (e.g., aneurysan, dissection, and traumatic tears); evaluation of patent foramen ovale and its association with central and peripheral embolic events; advancements in computer technology; and finally, the effect of TEE on critical care.

Insights from three-dimensional echocardiographic laser stereolithography. Effect of leaflet funnel geometry on the coefficient of orifice contraction, pressure loss, and the Gorlin formula in mitral stenosis

BACKGROUND

Three-dimensional echocardiography can allow us to address uniquely three-dimensional scientific questions, for example, the hypothesis that the impact of a stenotic valve depends not only on its limiting orifice area but also on its three-dimensional geometry proximal to the orifice. This can affect the coefficient of orifice contraction (Cc = effective/anatomic area), which is important because for a given flow rate and anatomic area, a lower Cc gives a higher velocity and pressure gradient, and Cc, routinely assumed constant in the Gorlin equation, may vary with valve shape (60% for a flat plate, 100% for a tube). To date, it has not been possible to study this with actual valve shapes in patients.

METHODS AND RESULTS

Three-dimensional echocardiography reconstructed valve geometries typical of the spectrum in patients with mitral stenosis: mobile doming, intermediate conical, and relatively flat immobile valves. Each geometry was constructed with orifice areas of 0.5, 1.0 and 1.5 cm2 by stereolithography (computerized laser polymerization) (total, nine valves) and studied at physiological flow rates. Cc varied prominently with shape and was larger for the longer, tapered dome (more gradual flow convergence proximal and distal to the limiting orifice): for an anatomic orifice of 1.5 cm2, Cc increased from 0.73 (flat) to 0.87 (dome), and for an area of 0.5 cm2, from 0.62 to 0.75. For each shape, Cc increased with increasing orifice size relative to the proximal funnel (more tubelike). These variations translated into important differences of up to 40% in pressure gradient for the same anatomic area and flow rate (greatest for the flattest valves), with a corresponding variation in calculated Gorlin area (an effective area) relative to anatomic values.

CONCLUSIONS

The coefficient of contraction and the related net pressure loss are importantly affected by the variations in leaflet geometry seen in patients with mitral stenosis. Three-dimensional echocardiography and stereolithography, with the use of actual information from patients, can address such uniquely three-dimensional questions to provide insight into the relations between cardiac structure, pressure, and flows.

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.

Three-dimensional echocardiography: the influence of number of component images on accuracy of left ventricular volume quantitation

One approach to three-dimensional echocardiography is to reconstruct the surface of cardiac structures from two-dimensional images positioned in three-dimensional space. This approach has yielded accurate measures; however, the relationship between the number of nonparallel images used in three-dimensional echocardiographic reconstruction to the accuracy of the volume calculated has not been determined. With a canine model in which instantaneous left ventricular volume could be measured in vivo, images were obtained from intersecting long- and short-axis scans and stored with their spatial coordinates. The left ventricle was reconstructed and its volume calculated. The difference between three-dimensional echocardiographic and true volume was determined in 84 different cavitary volumes (4 to 85 ml). In each case, long- and short-axis images were deleted serially from the original data set (maximum of 27) until there were only three images left in the reconstruction. After each set of deletions, left ventricular volume was recalculated with the remaining images. Three-dimensional echocardiography accurately quantified ventricular volume with eight to 12 intersecting images, with a mean error of less than 1 ml and an SD of 5 ml. With a reduction of component images below eight, there were progressive increases in both absolute and mean percentage error. Accurate assessment of stroke volume and ejection fraction in this beating heart model also required eight to 12 images. Left ventricular volume and systolic function can be quantitated by three-dimensional echocardiography with as few as eight to 12 intersecting or nonparallel images.

Quantitative three-dimensional reconstruction of left ventricular volume with complete borders detected by acoustic quantification underestimates volume

Recently a new acoustic-quantification (AQ) technique has been developed to provide on-line automated border detection with an integrated backscatter analysis. Prior studies have largely correlated AQ areas with volumes without direct comparison of volumes for agreement. By using complete AQ-detected borders as the input to a validated method for three-dimensional echocardiographic (3DE) reconstruction, we can compare an entire cavity volume measured with the aid of AQ against a directly measured volume. This would also explore the possibility of applying AQ to 3DE reconstruction to reduce tracing time and enhance routine applicability. To compare reconstructed volumes with actual values in a stable standard allowing direct volume measurement, the left ventricles of 13 excised animal hearts were studied with a 3DE system that automatically combines two-dimensional (2D) images and their locations. Intersecting 2D views were obtained with conventional scanning and AQ imaging, with gains optimized to permit 3D reconstruction by detecting the most continuous AQ borders for each view, with maximal cavity size. Reconstruction was performed with manually traced central endocardial reflections and AQ-detected borders visually reproduced the left ventricular shapes; the AQ reconstructions, however, were consistently smaller. The reconstructed left ventricular (LV) volumes correlated well with actual values by both manual and AQ techniques (r = 0.93 and 0.88, with standard errors of 2.3 cc and 2.0 cc, p = not significant [NS]). Agreement with actual values was relatively close for the manually traced borders (y = 0.93x + 0.68, mean difference = -0.8 +/-2.2 cc). AQ-derived reconstructions consistently underestimated LV volume by 39 +/- 10% (y = 0.62x-0.09, mean difference = -7.8 +/- 3.0 cc, different from manually traced and actual volumes by analysis of variance [ANOVA], F = 69, p<0.00001). The AQ-detected threshold signal was displaced into the cavity, and volume between walls and false tendons was excluded, leading to underestimation, which increased with increasing cavity volume (r = 0.76). The AQ technique can therefore be applied to 3DE reconstruction, providing volumes that correlate well with directly measured values in a stable in vitro standard, minimizing observer decisions regarding manual border placement after image acquisition. However, when the complete borders needed for 3D reconstruction are used, absolute volumes are underestimated with current algorithms that integrate backscatter and displace the detected threshold into the ventricular cavity.

Elevation direction deconvolution in three-dimensional ultrasound imaging

One-dimensional (1-D) linear transducer arrays can be used for three-dimensional (3-D) ultrasound image acquisition. However, the relatively low spatial resolution of these arrays in the elevation direction results in blurry 3-D images. Here, the authors introduce an elevation direction deconvolution (EDD) method that increases the spatial resolution of 3-D ultrasound images in the elevation direction. EDD is based on a deconvolution technique called power spectrum equalization. To evaluate the authors' method, Cartesian volumes were reconstructed with and without EDD from a series of two-dimensional (2-D) images of phantoms. Using these reconstructed volumes, the authors first evaluated the effect of EDD on elevation resolution by computing the full-width-at-quarter-maximum (FWQM) of peaks along lines of constant depth. They then evaluated the effect of EDD on the accuracy of volume calculation by computing the phantom's volumes. EDD decreased the FWQM of the peaks on elevation lines by an average of 17%; however, EDD did not significantly alter the accuracy of volume calculation. It is concluded that EDD can increase the spatial resolution in the elevation direction in 3-D ultrasound images and that EDD may improve the accuracy of volume calculation if a more consistent edge detection method is used.

In vitro validation of right ventricular volume measurement by three dimensional echocardiography

OBJECTIVE

Evaluation of ability of three dimensional echocardiography to accurately assess right ventricular volumes in vitro.

METHODS

Silicone casts of normal human right ventricles were examined. Each was filled with three different volumes of water to yield 15 different measurements. The casts were examined in a waterbath with three dimensional echocardiography using a 7.5 MHz ultrasound probe mounted in a scan frame. It was steered by a stepper motor, which moved the probe in steps of 0.25 mm over a distance of 5.9 cm inside the frame, acquiring an image at each step. 236 parallel slices of the cast were thus obtained, forming the three dimensional dataset. The longest axis of the right ventricular volume was defined and the area of perpendicular 1 mm thick slices was outlined manually to calculate the area of each slice. This was multiplied by the slice thickness to obtain the volume of each slice; the respective volumes were added to obtain the volume of the whole cast.

RESULTS

The casts had a median volume of 31.1 (23) ml (range 15-100); three dimensional echocardiography gave a median volume of 29.0 (21.7) ml (15.7-91.7). Interobserver variability was 4.5% (0.4%-13.6%) and intraobserver variability 4.3% (0.2%-9.3%). Correlation between real cast volumes and volumes measured by three dimensional echocardiography was 0.99 (y = 1.08 x -0.16) with an SEE of 2.7 ml. Limits for agreement between methods ranged from -3.1 ml to 8.3 ml. In 14 of the 15 measurements, volume by three dimensional echocardiography was smaller than real volume, with the mean difference being 7.4% (2.8%-19.5%). This may be due to the thickening of surfaces of structures when imaged by ultrasonography.

CONCLUSION

Right ventricular volumes can accurately be determined by three dimensional echocardiography.

Quantitative three-dimensional reconstruction of aneurysmal left ventricles. In vitro and in vivo validation

BACKGROUND

Current two-dimensional (2D) echocardiographic measures of left ventricular (LV) volume are most limited by aneurysmal distortion, which restricts application of simple geometric models that assume symmetrical shape. 2D methods also fail to provide separate volumes of the aneurysm and nonaneurysmal residual LV cavity, which could help assess the stroke volume wasted by dyskinesis and the potential residual LV body to guide surgical approaches and predict their outcome. Three-dimensional (3D) echocardiographic reconstruction has potential advantages for assessing aneurysmal left ventricles because it is not dependent on geometric assumptions, does not require standardized views that may exclude portions of the aneurysm, and can potentially measure separate aneurysm and nonaneurysm cavity volumes of any shape. The purpose of this study was first, to validate the accuracy of 3D echocardiographic reconstruction for quantifying total LV and separate LV body and aneurysm volumes in vitro so as to provide direct standards for the separate volumes; and second, to determine the feasibility and accuracy of 3D echocardiographic reconstruction for quantifying the total volume and function of aneurysmal left ventricles in an animal model, providing a reference standard for instantaneous LV volume.

METHODS AND RESULTS

A recently developed 3D system that automatically combines 2D images and their locations was applied (1) to reconstruct 10 aneurysmal ventricular phantoms and 12 gel-filled autopsied human hearts with aneurysms, comparing cavity volumes (total and aneurysm) to those measured by fluid displacement; and (2) to reconstruct the left ventricle during 19 hemodynamic stages in four dogs with surgically created LV aneurysms, comparing total volumes with actual instantaneous values measured by an intracavitary balloon attached to an external column for validation and also calculating the stroke volume wasted by aneurysmal dyskinesis. 3D reconstruction reproduced the distorted aneurysmal LV shapes. In vitro, calculated volumes (aneurysm, nonaneurysm, and total) agreed well with actual values, with correlation coefficients of .99 and SEEs of 3.2 to 6.1 cm3 for phantoms and 3.4 to 4.2 cm3 for autopsied hearts (mean error, < 4% for both). In vivo, LV end-diastolic, end-systolic, and stroke volumes as well as ejection fraction calculated by 3D echocardiography correlated well with actual values (r = .99, .99, .95, and .99, respectively) and agreed closely with them (SEE = 4.3 cm3, 3.5 cm3, 1.7 cm3, and 2%, respectively). The stroke volumes wasted by the aneurysm were -20.1 +/- 19.3% of LV body (nonaneurysm) stroke volume.

CONCLUSIONS

Despite distorted ventricular shapes, a recently developed 3D echocardiographic system and surfacing algorithm can accurately reconstruct aneurysmal left ventricles and quantify total LV volume (validated in vivo and in vitro) as well as the separate volumes of the aneurysm and residual LV body (validated in vitro). This should improve our ability to evaluate such ventricles and guide surgical approaches.

Diagnostic performance of two-dimensional versus three-dimensional transesophageal echocardiographic images of selected pathologies evaluated by receiver operating characteristic analysis

The sensitivity and specificity of 2-D and 3-D echocardiographic images for the detection of selected morphological abnormalities were compared using receiver operating characteristic (ROC) analysis. Five experienced clinical echocardiographers blinded to the patients' diagnoses evaluated the 20 original static 2-D image sets and 20 corresponding 3-D reconstructions using a five point categorical scale that ranged from definitely abnormal to definitely normal. The ROC curve for the 3-D images was significantly (P < 0.05) closer to the ideal discrimination function than was the ROC curve for the 2-D transesophageal images (i.e., the sensitivity of the 3-D images was higher than that of the 2-D sequential images at the same specificity).

IN CONCLUSION

3-D transesophageal images provided better visual clues for the identification of morphological abnormalities than did serial 2-D echocardiographic images despite the same input information in both image formats. The use of ROC analysis assisted in the comparison of these two imaging techniques.

Three-dimensional echocardiography: in vivo validation for right ventricular free wall mass as an index of hypertrophy

OBJECTIVES

This study tested the ability of three-dimensional echocardiography to reconstruct the right ventricular free wall and determine its mass in vivo using a system that automatically combines two-dimensional images with their spatial locations.

BACKGROUND

Right ventricular free wall thickness is limited as an index of right ventricular hypertrophy because right ventricular mass may increase by dilation without increased thickness and because trabeculations and oblique views can exaggerate thickness in individual M-mode and two-dimensional scans. Three-dimensional echocardiography may have potential advantages because it can integrate the entire free wall mass, uninfluenced by oblique views or geometric assumptions.

METHODS

The three-dimensional system was applied to 12 beating canine hearts to reconstruct the right ventricular free wall in intersecting views. The corresponding mass was compared with actual weights of the excised right ventricular free wall (15.5 to 78 g). For comparison, right ventricular sinus and outflow tract thickness were also measured by two-dimensional echocardiography, and the ability to predict mass from these values was determined.

RESULTS

The three-dimensional algorithm successfully reproduced right ventricular free wall mass, which agreed well with actual values: y = 1.04x + 0.02, r = 0.985, SEE = 2.7 g (5.7% of the mean value). The two-dimensional predictions showed increased scatter: The variance of mass estimation, based on thickness, was 9.5 to 12.5 (average 11) times higher than the three-dimensional method (p < 0.02).

CONCLUSIONS

Despite the irregular crescentic shape of the right ventricle, its free wall mass can be accurately measured by three-dimensional echocardiography in vivo, providing closer agreement with actual mass than predictions based on wall thickness. This method, with the increased efficiency of the three-dimensional system, can potentially improve our ability to evaluate the presence and progression of right ventricular hypertrophy.

Three-dimensional echocardiography. In vivo validation for right ventricular volume and function

BACKGROUND

Current two-dimensional echocardiographic measures of right ventricular volume are limited by the asymmetrical and crescentic shape of the ventricle and by difficulty in obtaining standardized views. Three-dimensional echocardiographic reconstruction, which does not require geometric assumptions or standardized views, may therefore have potential advantages for determining right ventricular volume. Three-dimensional techniques, however, have not been applied to the right ventricle in vivo, where cardiac motion and contraction could affect accuracy. The purpose of this study was to determine the feasibility and accuracy of three-dimensional echocardiographic reconstruction for quantifying right ventricular volume and function in vivo. In particular, it was designed to test the accuracy of a newly developed system that provides rapid, efficient, and automated three-dimensional data collection (minimizing motion effects) and takes advantage of the full three-dimensional data set to obtain volume.

METHODS AND RESULTS

The three-dimensional system was applied to reconstruct the right ventricle and measure its volume and function during 20 hemodynamic stages created in five dogs. Actual instantaneous volumes were measured continuously by an intracavitary balloon connected to an external column. Hemodynamics were varied by volume loading and induction of ischemia. Three-dimensional reconstruction successfully reproduced right ventricular volume compared with actual values at end diastole (y = 1.0 chi-3.4, r = .99, SEE = 1.8 mL) and end systole (y = 1.0 chi+ 2.0, 4 = .98, SEE = 2.5 mL). The mean difference between calculated and actual volumes throughout the cycle was 2.1 mL, or 4.9% of the mean. Ejection fraction also correlated well with actual values (y = 0.96 chi-0.3, r = .98, SEE = 3.3%).

CONCLUSIONS

Despite the irregular crescentic shape of the right ventricle, this newly developed three-dimensional system and surfacing algorithm can accurately reconstruct its shape and quantitate its volume and function in vivo without geometric assumptions. The increased efficiency of the system should increase applicability to issues of clinical and research interest.

Three-dimensional echocardiographic reconstruction of right ventricular volume: in vitro comparison with two-dimensional methods

Two-dimensional echocardiographic measures of right ventricular volume are limited by the asymmetric and crescentic shape of that ventricle and the difficulty in obtaining standardized views. We have developed a three-dimensional echocardiographic system that automatically integrates images and positional data and calculates right ventricular volume without the need for geometric assumptions or standardized views and a surfacing algorithm that takes advantage of the full three-dimensional data set. The accuracy of this system was studied and compared with two-dimensional methods in 12 gel-filled excised human right ventricles (18 to 74 ml). Volumes calculated by three-dimensional echocardiography correlated well with actual values (r = 0.99) and agreed more closely with them than did those obtained by two-dimensional methods (p < 0.02).

The geometrical relationship between the human esophagus and left ventricle: implications for three-dimensional ultrasonic scanning

To establish design parameters for a transesophageal ultrasonic probe to image the left ventricle (LV) in three dimensions, the geometrical relationship between the esophagus and the heart was studied in computed tomographic sections of ten humans. Points describing the esophageal centerpoint and the left-ventricular endocardium were digitized. Algorithms were developed to determine from any esophageal viewpoint the ranges of motion required to cover the LV with four modes of scanning; transverse oblique, longitudinal oblique, rotary and linear. Longitudinal oblique scanning was the only single-degree-of-freedom method that allowed complete imaging of the LV in all patients. However, for both conventional and three-dimensional LV imaging, the most promising probe design appears to be a rotary scanning probe with an added degree of freedom to tilt the axis of rotation +/- 29 degrees away from an axis perpendicular to the local esophageal axis.

Three-dimensional echocardiography. In vivo validation for left ventricular volume and function

BACKGROUND

Current two-dimensional quantitative echocardiographic methods of volume assessment require image acquisition from standardized scanning planes. Left ventricular volume and ejection fraction are then calculated by assuming ventricular symmetry and geometry. These assumptions may not be valid in distorted ventricles. Three-dimensional echocardiography can quantify left ventricular volume without the limitations imposed by the assumptions of two-dimensional methods. We have developed a three-dimensional system that automatically integrates two-dimensional echocardiographic images and their positions in real time and calculates left ventricular volume directly from traced endocardial contours without geometric assumptions.

METHODS AND RESULTS

To study the accuracy of this method in quantifying left ventricular volume and performance in vivo, a canine model was developed in which instantaneous left ventricular volume can be measured directly with an intracavitary balloon connected to an external column. Ten dogs were studied at 84 different cavity volumes (4 to 85 cm3) and in conditions of altered left ventricular shape produced by either coronary occlusion or right ventricular volume overload. To demonstrate clinical feasibility, 19 adult human subjects were then studied by this method for quantification of stroke volume. Left ventricular volume, stroke volume, and ejection fraction calculated by three-dimensional echocardiography correlated well with directly measured values (r = .98, .96, .96 for volume, stroke volume, and ejection fraction, respectively) and agreed closely with them (mean difference, -0.78 cm3, -0.60 cm3, -0.32%). In humans, there was a good correlation (r = .94, SEE = 4.29 cm3) and agreement (mean difference, -0.98 +/- 4.2 cm3) between three-dimensional echocardiography and Doppler-derived stroke volumes.

CONCLUSIONS

Three-dimensional echocardiography allows accurate assessment of left ventricular volume and systolic function.

Three-dimensional transesophageal echocardiography for depiction of regional left-ventricular performance: initial results and future directions

To assess the potential of a prototype transesophageal echocardiography probe for evaluating left-ventricular wall motion in three dimensions, we acquired images under anesthesia in 15 patients who had akinesia or dyskinesia and 8 patients who had normal function demonstrated on preoperative ventriculography. Short-axis, oblique transgastric scans were obtained in 16 of the patients and four-chamber, long-axis oblique scans were obtained in 12 patients, with five patients (22%) yielding good-quality scans of both types. Off-line, we outlined the endocardial borders manually and used the outlines to make computer-generated three-dimensional models of the endocardial surfaces, color-tiled according to regional ejection fraction. Compared with contrast ventriculograms, the regional ejection fraction histograms derived from these models showed 86% concordance for detecting dyssynergy. However, the concordance between the ventriculograms and the color-tiled models in localizing the dyssynergy was only 67% overall. Uncertainty in rotational alignment between the reconstructions and the ventriculograms appeared to contribute to misreading the location of dyssynergy. In addition, the apical region appeared to have been missed in 8 (50%) of the short-axis scans, whereas it was visualized in all long-axis scans. We conclude that three-dimensional analysis of the location, extent, and degree of left-ventricular dyssynergy is feasible from transesophageal echocardiograms and could have wide application in the study of regional ventricular function. However, improvements are necessary to enable the transducer to scan the cardiac apex more reliably from the short-axis viewpoint and to have a means for spatially orienting the images with respect to an external frame of reference.

Methodology for three-dimensional reconstruction of the left ventricle from transesophageal echocardiograms

A technique is presented for three-dimensional (3-D) reconstruction of the left-ventricular endocardial surface from multiplanar transesophageal echocardiograms, using both commercial software and investigator written Fortran programs for Intel 80286 and 80386 microcomputers. The approach provides quantitative global and regional cardiac performance measures and allows viewing the endocardial surface, at end-diastole and end-systole, from chosen perspectives. Anatomical landmarks are incorporated to aid in orientation. For regional calculation, the surface is divided into equal angular elements with each conceptually connected to the left-ventricular end-diastole centroid, forming a pyramidal volume element. This angular division automatically normalizes for heart size. The fractional change of these elements over the cardiac cycle provides a regional ejection fraction measure which is color-coded on the reconstructed endocardial surface. Composite perspective views, regional ejection fraction histograms and calculations of global end-diastolic, end-systolic, and stroke volumes, are all performed by the method.

What's new in monitoring the coronary surgery patient?

Monitoring has been extensively reviewed in most textbooks of cardiothoracic surgery and anaesthesia, particularly in the recent textbooks on monitoring edited by Carol L Lake 1 and Casey D Blitt 2 and in the Journal of Clinical Monitoring. Although monitoring properly includes both pre- and postoperative periods, this review will concentrate exclusively on the operative period. I will also concentrate on new approaches or information which relate to more traditional approaches to monitoring. The emphasis in this review will not be on what we can monitor, but rather on what we should monitor. In this regard, I will analyse accuracy and identify sources of error and try to answer the following questions. Does the device or parameter measure (monitor) what we want to know? Does it improve patient outcome and safety? Is it cost-effective? Unfortunately, data are not always available to answer all these questions at present, but hopefully the discussions will make us aware of what we do and do not know, and what we should look for in the near future.

Left ventricular ejection fraction: single-plane and multiplanar transesophageal echocardiography versus equilibrium gated-pool scintigraphy

The relative accuracy and precision of estimating left ventricular ejection fraction (EF) in dogs were assessed by two-dimensional transesophageal echocardiography (2D-TEE) and by three-dimensional transesophageal echocardiographic (3D-TEE) imaging and reconstruction. This assessment was accomplished by comparing each echocardiographic method to a gated equilibrium blood pool radionuclide (RN) standard. By using both correlation and regression analysis, 2D-TEE performed reasonably well in estimating RNEF (correlation coefficient [r] = 0.80, slope = 1.01, intercept = 6.37, standard error of the estimate [SEE], 8.98), but not as well as 3D-TEE (r = 0.86, slope = 0.83, intercept = 3.38, SEE, 5.74). Using Altman and Bland's methods of comparison analysis, it was found that 2D-TEE overestimated RNEF by 7% (standard deviation [SD], 8.8). This degree of overestimation was not consistent across the range of measurement. In contrast, 3D-TEE slightly underestimated RNEF by less than 3% and showed less variability (SD, 6.0). The accuracy of the 3D-TEE determinations was not dependent on the magnitude of EF. Additionally, a significantly higher proportion of the 2D-TEE measurements (0.30) compared with the 3D-TEE measurements (0.10) differed from RN values by more than 10% (P = 0.009, McNemar's test). At the clinically important low end of the EF range (RNEF less than or equal to 35%), 2D-TEE may be expected (with 95% confidence) to be within -15% to +28% EF of reference values, whereas 3D-TEE can be expected to be within -8% to +5% EF relative to RN.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular volume measurement from a multiplanar transesophageal ultrasonic imaging system: an in vitro study

We have developed a system to assess the feasibility of using multiple transesophageal ultrasonic images to measure left-ventricular volume, an important variable in patient management. The system includes a special transesophageal probe with a micromanipulator for acquiring cardiac images in multiple planes with known interplanar spatial relationship and an off-line processing system to compute the volume. In vitro studies with the probe demonstrated that the distance between two targets in space can be identified within 2 mm (SD = 0.4 mm) for points in the imaging plane 3.4 mm (SD = 0.5 mm) for points not lying in the imaging plane. This gives an average accuracy of +/- 6.5% for distances greater than 4.5 cm. Comparison of ultrasonic measurements of the volume of water-filled balloons and excised hearts to the volume required to fill them, revealed a correlation coefficient of 0.992, a regression line having a slope of 1.0 and an ordinate intercept at 0.2 mL, and a standard error of the estimate of 8 mL.