Three-dimensional echocardiographic assessment of annular shape changes in the normal and regurgitant mitral valve.

OBJECTIVES: To compare mitral annular shape and motion throughout the cardiac cycle in patients with normal hearts versus those with functional mitral regurgitation (FMR). BACKGROUND: The causes of mitral regurgitation without valvular disease are unclear, but the condition is associated with changes in annular shape and dynamics. Three-dimensional (3D) imaging provides a more comprehensive view of annular structure and allows accurate reconstructions at high spatial and temporal resolution. METHODS: Nine normal subjects and 8 patients with FMR undergoing surgery underwent rotationally scanned transesophageal echocardiography. At every video frame of 1 sinus beat, the mitral annulus was manually traced and reconstructed in 3D by Fourier series. Annular projected area, nonplanarity, eccentricity, perimeter length, and interpeak and intervalley spans were determined at 10 time points in systole and 10 points in diastole. RESULTS: The mitral annulus in patients with FMR had a larger area, perimeter, and interpeak span than in normal subjects (P <.001 for all). At mid-systole in normal annuli, area and perimeter reach a minimum, nonplanarity is greatest, and projected shape is least circular. These cyclic variations were not significant in patients with FMR. Annular area change closely paralleled perimeter change in all patients (mean r = 0.96 +/- 0.07). CONCLUSIONS: FMR is associated with annular dilation and reduced cyclic variation in annular shape and area. Normal mitral valve function may depend on normal annular 3D shape and dimensions as well as annular plasticity. These observations may have implications for design and selection of mitral annular prostheses.

Performance of a Fourier-based program for three-dimensional reconstruction of the mitral annulus on application to sparse, noisy data.

OBJECTIVES: We investigated the accuracy of mitral annular reconstruction from noisy, sparse data typical of three-dimensional (3D) transthoracic echocardiograms. BACKGROUND: Our Fourier-based method for reconstructing the annulus from dense, accurate 3D transesophageal echo (TEE) data has been validated in vitro with four harmonics in the x, y, and z coordinates (4,4,4). METHODS: Thirteen mitral annuli were reconstructed from 'complete' 3D TEE data using four harmonics (4,4,4) and used to measure area, eccentricity. height, perimeter, and interpeak and intervalley distances; these were the 'true values'. To simulate transthoracic echo data, the TEE data sets were reduced evenly and unevenly (randomly). The complete and reduced data sets were used to reconstruct the annuli using three sets of fitting parameters: (4,4,4), (1,1,3), and (1,1,4). The resulting size and shape measurements were compared with true values. RESULTS: Regardless of the fitting parameters used, area, 2D perimeter, and 3D perimeter measurements were more accurate using reconstructions from evenly-reduced than randomly-reduced data sets (p < 0.006), and depended significantly on both data density (p < 0.015 for all) and data distribution (p < 0.02 for all). Perimeter, height, and eccentricity of the reconstructed annuli were more accurately measured using four harmonics (4,4,4). CONCLUSIONS: Mitral annuli can be reconstructed from sparse, noisy data using the (4,4,4) fit if at least 25 points are obtained from evenly distributed imaging planes. These results suggest that detailed analysis of mitral annular size and shape can be made accurately from 3D transthoracic echocardiograms.

Three-dimensional measurement of the mitral annulus by multiplane transesophageal echocardiography: in vitro validation and in vivo demonstration.

Ten phantoms were scanned with a multiplane transesophageal echocardiographic probe in a water bath to assess a new method for three-dimensional modeling of the mitral annulus. The annulus was reconstructed from manually outlined borders with Fourier series in each of the three spatial coordinates. Comparisons with direct measurements by least-squares linear regression gave coefficients of determination of 0.99 for annular height, area, and circumference. Expressed as a percentage of their true values, the mean +/- SD of the errors were -0.1% +/- 3.0% for annular height, -2.8% +/- 3.1% for area, and -0.2% +/- 1.7% for circumference. The mean residual error length for phantoms was 0.64 mm compared with 1.21 mm in nine patients studied during general anesthesia. This method gives accurate and precise measurements of the mitral annulus in vitro and should be valuable for studying its morphology and dynamics in vivo.

Surgical suite utilization and capacity planning: a minimal cost analysis model.

In this paper, we are concerned with cost reduction, operating suite utilization, and capacity planning in surgical services. We studied 58,251 computerized surgical records from a teaching hospital to determine a model for measuring operating suite utilization, analyzing the quality of surgical schedules, and allocating surgical suite budgets (capacity planning). The classical definition of operating suite (OR) utilization, encountered in the literature is the ratio of the total OR time used to the total OR time allocated or budgeted. To create a better measure of utilization, we measured underutilization and overutilization providing a more complete description of the overall use of resources. Because the costs of under and overutilization of operating suites are high, they are attractive potential targets for cost minimization and the magnitude of the potential savings are such that attempts to measure and eliminate this inefficiency could be financially rewarding.

Statistical modeling to predict elective surgery time. Comparison with a computer scheduling system and surgeon-provided estimates.

BACKGROUND: Accurate estimation of operating times is a prerequisite for the efficient scheduling of the operating suite. The authors, in this study, sought to compare surgeons' time estimates for elective cases with those of commercial scheduling software, and to ascertain whether improvements could be made by regression modeling. METHODS: The study was conducted at the University of Washington Medical Center in three phases. Phase 1 retrospectively reviewed surgeons' time estimates and the scheduling system's estimates throughout 1 yr. In phase 2, data were collected prospectively from participating surgeons by means of a data entry form completed at the time of scheduling elective cases. Data included the procedure code, estimated operating time, estimated case difficulty, and potential factors that might affect the duration. In phase 3, identical data were collected from five selected surgeons by personal interview. RESULTS: In phase 1, 26 of 43 surgeons provided significantly better estimates than did the scheduling system (P < 0.01), and no surgeon was significantly worse, although the absolute errors were large (34% of 157 min average case length). In phase 2, modeling improved the accuracy of the surgeons' estimates by 11.5%, compared with the scheduling system. In phase 3, applying the model from phase 2 improved the accuracy of the surgeons' estimates by 18.2%. CONCLUSIONS: Surgeons provide more accurate time estimates than does the scheduling software as it is used in our institution. Regression modeling effects modest improvements in accuracy. Further improvements would be likely if the hospital information system could provide timely historical data and feedback to the surgeons.

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 probe's 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.

3D ultrasonic image feature localization based on magnetic scanhead tracking: in vitro calibration and validation.

The basis of a three-dimensional (3D) ultrasound imaging system was constructed from a commercially available magnetometer-based position and orientation measurement (POM) device, a standard B-Mode ultrasound instrument and a personal computer. To evaluate the system's performance, a novel method was devised using an iterative, least-squares technique to simultaneously determine the system's calibration parameters and measure its precision in locating points in three-dimensional space. When tested separately, the POM system located single points with a root mean squared (RMS) uncertainty of from 1.4 mm to 3.2 mm over the 610 mm working radius of the system. When combined with the ultrasound instrument, the RMS uncertainty in locating point targets varied from 2.1 mm to 3.5 mm. These results establish the lower limits of variability to be expected from this system when locating fiducial anatomical landmarks for repeated examinations of the same region of the body, and when making numerical 3D reconstructions from multiple planar images.

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 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.

Electroencephalography during surgery with cardiopulmonary bypass and hypothermia.

After more than 30 yr of use, electroencephalographic (EEG) monitoring during cardiopulmonary bypass has not gained wide clinical acceptance. To assess its utility to predict central nervous system injury, two-channel recordings were made from 78 patients undergoing cardiopulmonary bypass and anesthetized with fentanyl/diazepam/enflurane. The perfusion regimen included the use of high pump flow, a bubble oxygenator, and no arterial tubing filter. Target values were 28-32 degrees C for the minimum rectal temperature, 60-80 mmHg for mean arterial pressure, and 20-25% for hematocrit. Eight descriptors of the Fourier power spectra of the EEG were calculated off-line, and outcome comparisons were made with the results from neuropsychological tests. Among 58 patients yielding complete data of acceptable quality, a statistically significant reduction in total power was observed from prebypass to postbypass, accompanied by an increase in the fractional power in the theta and beta frequency bands and in the spectral edge frequency. The shifts in total and theta power were weakly associated with short-term but not with long-term changes in neuropsychological scores. Nearly 40% of the patients' EEGs were corrupted with electrical noise at some time during bypass. In 15 patients selected for having high-quality recordings and no neuropsychological deficit, an extensive statistical analysis failed to reveal any consistent variation in the EEG descriptors with hypothermia. Under the conditions studied, it appears that for other than gross signal dropout, the strong background variability in the EEG makes it have little value for detecting harbingers of brain injury.

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)

Preoperative aspirin therapy and reoperation for bleeding after coronary artery bypass surgery.

We performed a case-control study to estimate the relative risk of reoperation for bleeding in coronary artery bypass graft patients who had taken aspirin within the 7 days preceding surgery. Comparison of 90 cases of reoperation with 180 matched control subjects gave an estimated odds ratio for reoperation of 1.82 (95% confidence interval, 1.23 to 3.32). Although their preoperative coagulation values were similar, cases used significantly more whole blood (cases, 9.5 +/- 5.2 units; control subjects, 3.0 +/- 2.0 units; median +/- interquartile range), packed red blood cells (cases, 2.1 +/- 4.0 units; control subjects, 0.9 +/- 2.0 units), and platelets (cases, 12.2 +/- 12.0 units; control subjects, 2.9 +/- 4.0 units) than control subjects. Cases had intensive care unit stays of 4.7 +/- 5.7 days (mean +/- SD) vs 2.1 +/- 1.9 days for control subjects and postoperative hospitalizations of 10.9 +/- 8.2 days vs 7.0 +/- 3.2 days for control subjects. We conclude that aspirin exposure within 7 days before coronary bypass surgery is associated with an increased rate of reoperation for bleeding and that reoperation is associated with large increases in transfusion requirements and intensive care unit and hospital stays.

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.