Freehand three-dimensional echocardiography for measurement of left ventricular mass: in vivo anatomic validation using explanted human hearts

Necropsy Validation of a Novel Method for Left Ventricular Mass Quantification in Porcine Transthoracic and Transdiaphragmal Echocardiography

Introduction

Increased left ventricular mass (LVM) is one of the most powerful predictors of adverse cardiovascular events. Clinical evaluation requires reliable, accurate and reproducible echocardiographic LVM-quantification to manage patients. For this purpose, we have developed a novel two-dimensional (2D) method based on adding the mean wall thickness to the left ventricular volume acquired by the biplane method of disks, which has recently been validated in humans using cardiac magnetic resonance as reference value. We assessed the hypothesis that the novel method has better accuracy than conventional one-dimensional (1D) methods, when compared to necropsy LVM in pigs.

Materials and Methods

Echocardiography was performed during anesthesia in 34 Danish Landrace pigs, weight 47–59 kg. All pigs were euthanized, cardiac necropsy was performed and the left ventricle was trimmed and weighed for necropsy LVM. Trans-thoracic echocardiography was applied for parasternal images. Transdiaphragmal echocardiography was applied for the apical images, which are otherwise difficult to obtain in pigs. We compared the conventional 1D- and 2D-methods and the novel 2D-method to the LVM from cardiac necropsy.

Results

Necropsy LVM was 132 ± 11 g (mean ± SD). The novel method had better accuracy than other methods (mean difference ± 95% limits of agreement; coefficients of variation; standard error of the estimate, Pearson's correlation). Novel (−1 ± 20 g; 8%; 11 g; r = 0.70), Devereux (+26 ± 37 g; 15%; 33 g; r = 0.52), Area-Length (+27 ± 34 g; 13 %; 33 g; r = 0.63), Truncated Ellipsoid (+10 ± 30 g; 12%; 19 g; r = 0.63), biplane endo-/epicardial tracing (−3 ± 2 g; 10%; 14 g; r = 0.57). No proportional bias in linear regression was detected for any method, when compared to necropsy LVM.

Conclusion

We confirm high accuracy of the novel 2D-based method compared to conventional 1D/2D-methods.

Echocardiographic Left Ventricular Mass Estimation: Two-Dimensional Area-Length Method is Superior to M-Mode Linear Method in Swine Models of Cardiac Diseases

Echocardiography offers rapid and cost-effective estimations of left ventricular (LV) mass, but its accuracy in patients with cardiac disease remains unclear. LV mass was measured by M-mode-based linear method and two-dimensional echocardiography (2DE)-based area-length method in pig models and correlation with actual LV weight was assessed. Twenty-six normal, 195 ischemic heart disease (IHD), and 33 non-IHD HF pigs were included. A strong positive linear relationship to the actual LV weight was found with 2DE-based area-length method (r = 0.82, p < 0.001), whereas a moderate relationship was found with M-mode method in the overall population (r = 0.68, p < 0.001). Two correlation coefficients were significantly different (p < 0.001), and were driven mainly by incremental overestimation of LV mass in heavier hearts using the M-mode method. IHD and LV dilation were the factors contributing to overestimation using M-mode method. 2DE-based area-length method provides a better estimation of LV weight in swine models of HF, particularly in those with IHD.

Usefulness of Epicardial Area in the Short Axis to Identify Elevated Left Ventricular Mass in Men

Left ventricular (LV) hypertrophy is strongly associated with increased cardiovascular morbidity and mortality. The 2-dimensional LV mass algorithms suffer from measurement variability that can lead to misclassification of patients with LV hypertrophy as normal, or vice versa. Among the 4 echocardiographic measurements required by the 2-dimensional LV mass algorithms, epicardial and endocardial area have the lowest interobserver variation and could be used to corroborate LV mass calculations. We sought cut-off values that are able to discriminate between elevated and normal LV mass based on endocardial or epicardial area alone. Using data from 664 men enrolled in the Mind Your Heart Study, we calculated the correlation of LV mass index with epicardial area and endocardial area. We then used receiver operator characteristic curves to identify epicardial and endocardial area cut-points that could discriminate subjects with normal LV mass and LV hypertrophy. LV mass index was more strongly correlated with epicardial area compared with endocardial area, r = 0.70 versus r = 0.27, respectively. Epicardial area had a significantly higher area under the receiver operator characteristic curve (p <0.001) compared with endocardial area, 0.90 (95% confidence interval 0.86 to 0.93) versus 0.63 (95% confidence interval 0.57 to 0.71). An epicardial area cut-point of ≥38.0 cm² corresponded to a sensitivity of 95.0% and specificity of 54.4% for detecting LV hypertrophy. In conclusion, epicardial area showed promise as a method of rapid screening for LV hypertrophy and could be used to validate formal LV mass calculations.

3D and 4D Ultrasound: Current Progress and Future Perspectives

PURPOSE OF REVIEW

Three-dimensional (3D) echocardiography (3DE) and 4-dimensional echocardiography (4DE), also known as real-time (RT) 3DE (RT3DE), are rapidly emerging technologies which have made significant impact in the clinical arena over the years. This review will discuss the recent applications of 3DE in diagnosing and treating different types of cardiovascular disease.

RECENT FINDINGS

Recent studies using 3DE expanded on prior findings and introduced additional applications to different cardiac conditions. Some studies have used 3D parameters to prognosticate long-term outcomes. Numerous innovative software designs including fully automated algorithms have been introduced to better evaluate valvular heart disease and cardiac function.

SUMMARY

With further evolution of 3DE technologies, this imaging modality will emerge as a powerful tool and likely become the imaging modality of choice in the diagnosis and management of various cardiac disorders.

Review: New approaches to the assessment of left ventricular hypertrophy

In hypertension, Left ventricular hypertrophy is initially a useful compensatory process that represents an adaptation to increased ventricular wall stress; however, it is also the first step toward the development of overt clinical disease. For this reason most international guidelines recommend the assessment of cardiac target organ damage in hypertensive patients for cardiovascular risk stratification. It is therefore of great importance to keep in mind the strengths and weakness of the different available methods for LVH assessment.

Several methods are currently available for the assessment of LVH; however the various techniques differ in cost, availability, sensitivity and specificity. Due to its wide availability and its low cost, eLectrocardiography should be part of all routine assessment of subjects with high blood pressure; however, despite its good specificity, the sensitivity for LVH detection is low. Several other methods have been proposed for LVH detection. Cardiac magnetic resonance imaging allows 3D reconstruction of the heart with high spatial resolution; however its main limitation is represented by the relatively low availability and by its costs. Echocardiography certainly represents a valuable method for the detection of LVH in hypertensive patients, due to its wide availability and its relatively low cost. The main limitations of the technique are represented by the lower spatial resolution and reproducibility in comparison with magnetic resonance. The development of new matrix-array transducers and new software for 3D reconstruction with echocardiography make this approach particularly promising for the future; in the meantime, standard echocardiography, widely available and with low cost, will probably remain the most used tool for the evaluation of left ventricular structure and function in hypertension.

Longitudinal strain predicts left ventricular mass regression after aortic valve replacement for severe aortic stenosis and preserved left ventricular function

We explored the influence of global longitudinal strain (GLS) measured with two-dimensional speckle-tracking echocardiography on left ventricular mass regression (LVMR) in patients with pure aortic stenosis (AS) and normal left ventricular function undergoing aortic valve replacement (AVR). The study population included 83 patients with severe AS (aortic valve area <1 cm(2)) treated with AVR. Bioprostheses were implanted in 58 patients (69.8 %), and the 25 remaining patients (30.2 %) received mechanical prostheses. Peak systolic longitudinal strain was measured in four-chamber (PLS4ch), two-chamber (PLS2ch), and three-chamber (PLS3ch) views, and global longitudinal strain was obtained by averaging the peak systolic values of the 18 segments. Median follow-up was 66.6 months (interquartile range 49.7-86.3 months). At follow-up, values of PLS4ch, PLS2ch, PLS3ch, and GLS were significantly lower (less negative) in patients who did not show left ventricular (LV) mass regression (all P < 0.001). Baseline global strain was the strongest predictor of lack of LVMR (odds ratio 3.5 (95 % confidence interval 3.0-4.9), P < 0.001), and GLS value ≥-9.9 % predicted lack of LVMR with 95 % sensitivity and 87 % specificity (P < 0.001). Other multivariable predictors were the preoperative LV mass value (cutoff value ≥147 g/m(2), P < 0.001), baseline effective orifice area index (cutoff ≤0.35 cm(2)/m(2), P = 0.01), and baseline mean gradient (cutoff ≥58 mmHg, P = 0.01). Finally, we failed to find interactions between GLS and other significant parameters (all P < 0.05). Global longitudinal strain accurately predicts LV mass regression in patients with pure AS undergoing AVR. Our findings must be confirmed by further larger studies.

Cardiac toxicity screening by echocardiography in healthy volunteers: a study of the effects of diurnal variation and use of a core laboratory on the reproducibility of left ventricular function measurement

BACKGROUND

In investigational medicinal products testing centers (IMP), reliable methods for monitoring early signs of cardiotoxicity of a potential new drug in healthy volunteers are essential. This study examines what levels of left ventricular ejection fraction (LVEF) variance can be achieved with two-dimensional echocardiography (2DE) in a core laboratory versus a site laboratory. Diurnal variability of LVEF and diastolic parameters were also reviewed.

METHODS AND RESULTS

64 healthy males, (age range 18-40 years), with optimal echo windows were recruited. Two-dimensional and tissue Doppler (TDI) echocardiography was performed by one dedicated sonographer using an Acuson Sequoia C256 machine. Heart rate and blood pressure were recorded simultaneously. Echocardiograms were performed at set time points (0, 1, 4, and 20 hours) on all subjects. The images were analyzed independently by one on-site, unblinded, sonographer reader (site lab) and one experienced off-site blinded physician over reader (core lab). The core lab showed significantly less variance in LVEF measurements than the site lab (5.5% vs. 19.9%). There was no significant diurnal variation in mean blood pressure, LVEF or E:A ratio measurements over 20 hours.

CONCLUSIONS

The core lab had better reproducibility and significantly less variance in LVEF measurements by 2DE than the site lab. There was no diurnal variation in LV function measurement.

Mechanisms Underlying Improvements in Ejection Fraction With Carvedilol in Heart Failure

Background— Reductions in heart rate (HR) with β-blocker therapy have been associated with improvements in ejection fraction (EF). However, the relative contributions of HR reduction, positive inotropism, afterload reduction, and reverse remodeling to improvements in EF are unknown.

Methods and Results— Twenty-nine patients (63�12 years old) with New York Heart Association class II-III heart failure underwent serial measurements of left ventricular volumes using 3-dimensional echocardiography and blood pressures by sphygmomanometry at baseline, 2 weeks, 2, 6, and 12 months after initiation of carvedilol. From these parameters, left ventricular contractility (indexed by the end-systolic pressure-volume ratio), total peripheral resistance, and effective arterial elastance (E a ) were derived. Overall, EF increased by 7-percentage points after 6 months of therapy (from 25�9 to 32�9, P <0.0001). This change was due to an increase in stroke volume ( P <0.001) with no significant change in end-diastolic volume ( P =0.15). The EF change correlated with increased contractility, decreased HR and decreased total peripheral resistance ( P <0.003 in each case). In those patients whose EF increased at least 5 points, ≈60% of the increase was due to HR reduction, ≈30% was due to increased contractility, and <20% was due to the decrease in total peripheral resistance.

Conclusions— Decreased HR, improved chamber contractility and afterload reduction each contributed significantly to improved EF with carvedilol.

Overestimation of left ventricular mass and misclassification of ventricular geometry in heart failure patients by two-dimensional echocardiography in comparison with three-dimensional echocardiography

BACKGROUND

Accurate assessment of left ventricular hypertrophy (LVH) and ventricular geometry is important, especially in patients with heart failure (HF). The aim of this study was to compare the assessment of ventricular size and geometry by 2D and 3D echocardiography in normotensive controls and among HF patients with a normal and a reduced ejection fraction.

METHODS

One hundred eleven patients, including 42 normotensive patients without cardiac disease, 41 hypertensive patients with HF and a normal ejection fraction (HFNEF), and 28 patients with HF and a low ejection fraction (HFLEF), underwent 2DE and freehand 3DE. The differences between 2DE and 3DE derived LVM were evaluated by use of a Bland-Altman plot. Differences in classification of geometric types among the cohort between 2DE and 3DE were determined.

RESULTS

Two-dimensional echocardiography overestimated ventricular mass compared to 3D echocardiography (3DE) among normal (166 +/- 36 vs. 145 +/- 20 gm, P = 0.002), HFNEF (258 +/- 108 vs. 175 +/- 47gm, P < 0.001), and HFLEF (444 +/- 136 vs. 259 +/- 77 gm, P < 0.001) patients. The overestimation of mass by 2DE increased in patients with larger ventricular size. The use of 3DE to assess ventricular geometry resulted in reclassification of ventricular geometric patterns in 76% of patients with HFNEF and in 21% of patients with HFLEF.

CONCLUSION

2DE overestimates ventricular mass when compared to 3DE among patients with heart failure with both normal and low ejection fractions and leads to significant misclassification of ventricular geometry in many heart failure patients.

Effects of papillary muscles and trabeculae on left ventricular quantification: increased impact of methodological variability in patients with left ventricular hypertrophy

BACKGROUND

Accurate quantification of left ventricular mass and ejection fraction is important for patients with left ventricular hypertrophy. Although cardiac magnetic resonance imaging has been proposed as a standard for these indices, prior studies have variably included papillary muscles and trabeculae in myocardial volume. This study investigated the contribution of papillary muscles and trabeculae to left ventricular quantification in relation to the presence and pattern of hypertrophy.

METHODS

Cardiac magnetic resonance quantification was performed on patients with concentric or eccentric hypertrophy and normal controls (20 per group) using two established methods that included papillary muscles and trabeculae in myocardium (method 1) or intracavitary (method 2) volumes.

RESULTS

Among all patients, papillary muscles and trabeculae accounted for 10.5% of ventricular mass, with greater contribution with left ventricular hypertrophy than normals (12.6 vs. 6.2%, P < 0.001). Papillary muscles and trabeculae mass correlated with ventricular wall mass (r = 0.53) and end-diastolic volume (r = 0.52; P < 0.001). Papillary muscles and trabeculae inclusion in myocardium (method 1) yielded smaller differences with a standard of mass quantification from linear ventricular measurements than did method 2 (P < 0.001). Method 1 in comparison with method 2 yielded differences in left ventricular mass, ejection fraction and volume in all groups, especially in patients with hypertrophy: the difference in ventricular mass index was three-fold to six-fold greater in hypertrophy than normal groups (P < 0.001). Difference in ejection fraction, greatest in concentric hypertrophy (P < 0.001), was independently related to papillary muscles and trabeculae mass, ventricular wall mass, and smaller ventricular volume (R = 0.56, P < 0.001).

CONCLUSION

Established cardiac magnetic resonance methods yield differences in left ventricular quantification due to variable exclusion of papillary muscles and trabeculae from myocardium. The relative impact of papillary muscles and trabeculae exclusion on calculated mass and ejection fraction is increased among patients with hypertrophy-associated left ventricular remodeling.

Registration of multiview real-time 3-D echocardiographic sequences

Real-time 3-D echocardiography opens up the possibility of interactive, fast 3-D analysis of cardiac anatomy and function. However, at the present time its quantitative power cannot be fully exploited due to the limited quality of the images. In this paper, we present an algorithm to register apical and parasternal echocardiographic datasets that uses a new similarity measure, based on local orientation and phase differences. By using phase and orientation to guide registration, the effect of artifacts intrinsic to ultrasound images is minimized. The presented method is fully automatic except for initialization. The accuracy of the method was validated qualitatively, resulting in 85% of the cardiac segments estimated having a registration error smaller than 2 mm, and no segments with an error larger than 5 mm. Robustness with respect to landmark initialization was validated quantitatively, with average errors smaller than 0.2 mm and 0.5 degrees for initialization landmarks rotations of up to 15 degrees and translations of up to 10 mm.

Analysis of Cardiac Dimensions, Mass and Function in Heart Transplant Recipients Using 64-slice Multi-detector Computed Tomography

BACKGROUND

Heart transplant recipients present a challenge to cardiac multi-detector computed tomography (MDCT) imaging due to high resting heart rates and body mass indices. Previous studies demonstrated the feasibility of coronary allograft vasculopathy detection by MDCT in heart transplant recipients. However, its performance in assessing cardiac structure and function in these patients has not been evaluated. The aim of this study was to compare 64-slice MDCT analysis of cardiac structure and function to 2-dimensional echocardiography in heart transplant recipients.

METHODS

Two independent observers used both semi-automated and automated software to measure chamber dimensions and left ventricular ejection fraction and mass in 20 heart transplant recipients by 64-slice MDCT. Inter-observer variability was determined. The results were compared with echocardiographic measurements provided by another blinded observer.

RESULTS

There was moderate agreement between MDCT and echocardiography for chamber dimension measurements, except for left atrial diameter. Ejection fraction by MDCT was slightly lower (mean difference: -2 +/- 9%, p = 0.29) than that obtained by echocardiography and the correlation was moderate (R = 0.49 to 0.54). Left ventricular mass measurements were significantly lower by MDCT (mean difference: -87 +/- 44 g, p < 0.001). Inter-observer agreement for MDCT analysis of left ventricular function (R = 0.90) and mass (R = 0.83) were excellent.

CONCLUSIONS

These findings demonstrate moderate agreement between 64-slice MDCT and echocardiography in the assessment of chamber dimensions as well as left ventricular mass and function in heart transplant recipients with low inter-observer variability. Also, the addition of cardiac structural and functional analysis to MDCT coronary angiography requires no additional scan time, contrast administration or radiation exposure.

Left ventricular mass in 169 healthy children and young adults assessed by three-dimensional echocardiography

The aims of this study were to establish normal values of left ventricular (LV) mass in children and young adults using three-dimensional echocardiography (3-DE) and to compare 3-DE LV mass estimates with those obtained by conventional echocardiographic methods. We studied 169 healthy subjects aged 2-27 years by digitized 3-D, two-dimensional (2-D), and M-mode echocardiography. 3-D echocardiography was performed by using rotational acquisition of planes at 18 degrees intervals from apical view with ECG gating and without respiratory gating. 3-DE gave smaller LV mass estimates than 2-DE and M-mode echocardiography (p < 0.001). Agreement analysis resulted in a bias of -9.3 +/- 36.5 g between 3-DE and 2-DE, and -18.5 +/- 47.9 g between 3-DE and M-mode. For the analysis, the subjects were divided into five groups according to body surface area (BSA): 0.5-0.75, 0.75-1.0, 1.0-1.25, 1.25-1.5, and greater than 1.5 m(2). LV mass/BSA by 3-DE was 45.6 (5.1), 54.3 (7.7), 55.2 (7.9), 58.8 (8.1), and 65.0 (9.9) g/m(2). LV mass/end diastolic volume (EDV) by 3-DE was 0.9 (0.1) g/ml in the BSA group of 0.5-0.75 m(2) and 1.0 (0.2) g/ml in the other BSA groups. LV mass increased linearly in relation to BSA, height, and body mass (r = 0.93, 0.90, and 0.92, respectively; p < 0.001 for all). The results showed a linear increase in LV mass, whereas LV mass/EDV ratio remained unchanged. However, LV mass estimates by 3-DE were lower than those obtained by 2-DE and M-mode echocardiography. The data obtained by 3-DE from 169 healthy subjects will serve as a reference for further studies in patients with various cardiac abnormalities.

Relation between number of component views and accuracy of left ventricular mass determined by three-dimensional echocardiography

Three-dimensional echocardiography (3DE) allows the accurate determination of left ventricular (LV) mass, but the optimal number of component or extracted 2-dimensional (2D) image planes that should be used to calculate LV mass is not known. This study was performed to determine the relation between the number of 2D image planes used for 3DE and the accuracy of LV mass, using cardiovascular magnetic resonance (CMR) imaging as the reference standard. Three-dimensional echocardiography data sets were analyzed using 4, 6, 8, 10 and 20 component 2D planes as well as biplane 2D echocardiography and CMR in 25 subjects with a variety of LV pathologies. Repeated-measures analysis of variance and the Bland-Altman method were used to compare measures of LV mass. To further assess the potential clinical impact of reducing the number of component image planes used for 3DE, the number of discrepancies between CMR and each of the 3DE estimates of LV mass at prespecified levels (i.e., > or =5%, > or =10%, and > or =20% difference from CMR LV mass) was tabulated. The mean LV mass by magnetic resonance imaging was 177 +/- 56 g (range 91 to 316). Biplane 2-dimensional echocardiography significantly underestimated CMR LV mass (p <0.05), but LV mass by 3DE was not statistically different from that by CMR regardless of the number of planes used. However, error variability and Bland-Altman 95% confidence intervals decreased with the use of additional image planes. In conclusion, transthoracic 3DE measures LV mass more accurately than biplane 2-dimensional echocardiography when > or =6 component 2D image planes are used. The use of >6 planes further increases the accuracy of 3DE, but at the cost of greater analysis time and potentially increased scanning times.

Ventricular Pump Function in Heart Failure with Normal Ejection Fraction: Insights from Pressure-Volume Measurements

The syndrome of heart failure in the setting of normal ejection fraction (HFNEF) is manifest in a clinically heterogeneous group of patients with multiple and varied comorbid conditions. In this report, we review available data derived from pressure-volume (PV) analyses in patients with and in animal models of HFNEF. Pressure-volume analysis of ventricular function is challenging in the clinical setting but provides unique insights into the systolic, diastolic, and overall pumping characteristics of the heart. Results of such analyses have thus far been limited to small cohorts of patients but suggest that different cohorts of patients with HFNEF having PV relations that imply different pathophysiologic mechanisms exist. This emphasizes the need to take a view of this syndrome, which extends beyond diastolic dysfunction, particularly when it comes to proposing and investigating therapeutic targets. We therefore propose that progress can be made in advancing therapeutics for HFNEF if it is appreciated that different underlying pathophysiologic mechanisms may be important in different cohorts and if attention expands beyond diastolic dysfunction as the sole target. Similar to the success that was achieved in advancing therapeutics for systolic heart failure when attention shifted away from the heart to the neurohormonal and renal axes, our interpretation of data in human beings and in animal models suggests that addressing similar targets (perhaps not in exactly the same manner) may prove to be fruitful, at least for some patients with HFNEF as well.

Transesophageal Real-Time Three-Dimensional Echocardiography

OBJECTIVES

The purpose of this study was to develop a transesophageal probe that: 1) enables on-line representation of the spatial structures of the heart, and 2) enables navigation of medical instruments.

BACKGROUND

Whereas transthoracic real-time 3-dimensional (3D) echocardiography could recently be implemented, there is still no corresponding transesophageal system. Transesophageal real-time 3D echocardiography would have great potential for numerous clinical applications, such as navigation of catheters.

METHODS

The newly developed real-time 3D system is based on a transesophageal probe in which multiple transducers are arranged in an interlaced pattern on a rotating cylinder. This enables continuous recording of a large echo volume of 70 mm in length and a sector angle of 120 degrees . The presentation of the volume-reconstructed data is made with a time lag of <100 ms. The frame rate is up to 20 Hz. In addition to conventional imaging, the observer can obtain a stereoscopic image of the structures examined with red/blue goggles.

RESULTS

It was shown in vitro on ventricle- and aorta-form agar models and in vivo that the system enables excellent visualization of the 3D structures. Shape, spatial orientation, and the navigation of various catheters (e.g., EPS-catheter, Swan-Ganz-catheter), stents, or atrial septal defect occluders could be recorded on-line and stereoscopically depicted. The size of the echo sector enables a wide field of view without changing the position of the probe.

CONCLUSIONS

Transesophageal real-time 3D echocardiography can be technically realized with the system presented here. The in vitro and in vivo studies show particularly the potential for navigation in the heart and large vessels on the basis of stereoscopic images.

Evaluation of the Electrocardiographic Criteria for Left Ventricular Hypertrophy With Use of Three-Dimensional Echocardiography

BACKGROUND

Left ventricular hypertrophy (LVH) is a common condition that carries an increased risk of cardiovascular events. Use of ECG in detection of LVH is limited because of the reported low sensitivity. Conventional echocardiographic techniques used as the standard for estimating left ventricular (LV) mass have limitations related to the position of the image plane and shape of the ventricle. Three-dimensional echocardiography is free of these limitations and therefore is more accurate. We hypothesized that accuracy of ECG criteria for LVH would improve when LV mass was assessed by three-dimensional echocardiography.

RESULTS

For most of the criteria, sensitivity, specificity and accuracy improved when LV mass was assessed by three-dimensional echocardiography. Two-dimensional echocardiography significantly overestimated LV mass as compared with the three-dimensional method.

CONCLUSIONS

Sensitivity, specificity, and accuracy of the ECG criteria improved when LV mass was estimated by three-dimensional echocardiography. This improvement may be attributed at least in part to superior accuracy of three-dimensional measurements.

Improved quantification of left ventricular mass based on endocardial and epicardial surface detection with real time three dimensional echocardiography

OBJECTIVE

To develop a technique for volumetric analysis of real time three dimensional echocardiography (RT3DE) data aimed at quantifying left ventricular (LV) mass and to validate the technique against magnetic resonance (MR) assumed as the reference standard.

DESIGN

RT3DE, which has recently become widely available, provides dynamic pyramidal data structures that encompass the entire heart and allows four dimensional assessment of cardiac anatomy and function. However, analysis techniques for the quantification of LV mass from RT3DE data are fundamentally two dimensional, rely on geometric modelling, and do not fully exploit the volumetric information contained in RT3DE datasets. Twenty one patients underwent two dimensional echocardiography (2DE), RT3DE, and cardiac MR. LV mass was measured from 2DE and MR images by conventional techniques. RT3DE data were analysed to semiautomatically detect endocardial and epicardial LV surfaces by the level set approach. From the detected surfaces, LV mass was computed directly in the three dimensional space as voxel counts.

RESULTS

RT3DE measurement was feasible in 19 of 21 patients and resulted in higher correlation with MR (r = 0.96) than did 2DE (r = 0.79). RT3DE measurements also had a significantly smaller bias (-2.1 g) and tighter limits of agreement (2SD = +/-23 g) with MR than did the 2DE values (bias (2SD) -34.9 (50) g). Additionally, interobserver variability of RT3DE (12.5%) was significantly lower than that of 2DE (24.1%).

CONCLUSIONS

Direct three dimensional model independent LV mass measurement from RT3DE images is feasible in the clinical setting and provides fast and accurate assessment of LV mass, superior to the two dimensional analysis techniques.

Ventricular Volume and Length in Hypertensive Diastolic Heart Failure

BACKGROUND

Patients with diastolic heart failure are thought to have a normal or small ventricle with impaired ventricular filling that requires increased filling pressure to maintain normal stroke volume. In this study we test the hypothesis that patients with hypertensive diastolic heart failure have increased left ventricular volumes compared with age-, sex-, and body size-matched control subjects.

METHOD

Left ventricular chordal dimensions from 2-dimensional echocardiography and volumes from 3-dimensional echocardiography were obtained in control subjects (n = 96) and patients with hypertensive diastolic heart failure (n = 28) and compared before and after controlling for age, sex, and body size.

RESULTS

Volumes by 3-dimensional echocardiography were significantly larger in the heart failure group than in the control group (P < .05). After matching for age, sex, and body size, volumes remained significantly larger in the patients with heart failure (P < .05). Chordal dimensions were not significantly different between the two groups. Stroke volume and centerline length of the ventricle were significantly increased in the heart failure group compared with matched control subjects (P < .05).

CONCLUSIONS

Our group of patients with hypertensive diastolic heart failure had significantly increased left ventricular volumes and stroke volume compared with control subjects, compatible with volume overload heart failure. Two-dimensional echocardiographic measurement of the ventricular chordal dimension failed to detect this enlargement. Ventricular length appeared to be preferentially increased in the patients with hypertensive diastolic heart failure.

Left heart failure with a normal ejection fraction: identification of different pathophysiologic mechanisms

BACKGROUND

Although heart failure with a normal ejection fraction (HFNEF) is a clinically heterogeneous syndrome, a single pathophysiologic mechanism, diastolic dysfunction, is often ascribed to explain this condition. In view of the clinical heterogeneity of these patients, we hypothesized that subgroups of HFNEF patients may have different underlying pathophysiologic mechanisms.

METHODS AND RESULTS

Freehand 3-dimensional echocardiography was used to measure left ventricular end-systolic and end-diastolic volumes in 99 asymptomatic normal controls and 2 groups with chronic heart failure: 35 patients with normal ejection fraction with longstanding hypertension (hypertensive HFNEF) and 11 patients with hypertrophic cardiomyopathy without a history of hypertension (nonhypertensive HFNEF). These data, combined with cuff sphygmomanometry and Doppler estimates of LV end-diastolic pressure (EDP) yielded estimated pressure-volume loops and slope (E es,sb ) of the end-systolic pressure-volume relationship, a load independent index of chamber contractility. Nonhypertensive HFNEF patients required high EDPs (21 +/- 2 versus 15 +/- 3 mm Hg in normals, P < .0001) to achieve normal EDVs (98 +/- 25 versus 95 +/- 21 mL in normals, P = NS). Although systolic function (E es,sb ) did not differ from normal, systolic blood pressure was lower than normal in these patients (114 +/- 10 versus 124 +/- 14 mm Hg in normals, P < .05). Hypertensive HFNEF patients also had increased EDP (20 +/- 2 mm Hg), but this was observed at higher than normal EDVs (118 +/- 29 mL, P < .05). Among patients with hypertensive HFNEF, 2 subgroups emerged, 1 with a high E es,sb (4.23 +/- 0.54 versus 2.1 +/- 0.7 mm Hg/mL) and 1 with normal E es,sb (2.31 +/- 0.51 mm Hg/mL). The former group was composed of elderly women with small body size (body surface area 1.7 +/- 0.2 versus 1.9 +/- 0.2 m 2 , P = .02) who had concentrically remodeled ventricles and low stroke volumes. The latter group was more diverse in age, body size, and included patients of both genders with increases in ventricular volumes, stroke volume, and mass consistent with a volume overload state.

CONCLUSION

Although HFNEF is commonly thought of as being the result of a single hemodynamic mechanism, these data indicate that subgroups exist with distinctly different underlying pathophysiologies.

Fast Measurement of Left Ventricular Mass With Real-Time Three-Dimensional Echocardiography

BACKGROUND

Left ventricular (LV) mass is an important predictor of morbidity and mortality, especially in patients with systemic hypertension. However, the accuracy of 2D echocardiographic LV mass measurements is limited because acquiring anatomically correct apical views is often difficult. We tested the hypothesis that LV mass could be measured more accurately from real-time 3D (RT3D) data sets, which allow offline selection of nonforeshortened apical views, by comparing 2D and RT3D measurements against cardiac MR (CMR) measurements.

METHODS AND RESULTS

Echocardiographic imaging was performed (Philips 7500) in 21 patients referred for CMR imaging (1.5 T, GE). Apical 2- and 4-chamber views and RT3D data sets were acquired and analyzed by 2 independent observers. The RT3D data sets were used to select nonforeshortened apical 2- and 4-chamber views (3DQ-QLAB, Philips). In both 2D and RT3D images, LV long axis was measured; endocardial and epicardial boundaries were traced, and mass was calculated by use of the biplane method of disks. CMR LV mass values were obtained through standard techniques (MASS Analysis, GE). The RT3D data resulted in significantly larger LV long-axis dimensions and measurements of LV mass that correlated with CMR better (r=0.90) than 2D (r=0.79). The 2D technique underestimated LV mass (bias, 39%), whereas RT3D measurements showed only minimal bias (3%). The 95% limits of agreement were significantly wider for 2D (52%) than RT3D (28%). Additionally, the RT3D technique reduced the interobserver variability (37% to 7%) and intraobserver variability (19% to 8%).

CONCLUSIONS

RT3D imaging provides the basis for accurate and reliable measurement of LV mass.

Reproducibility and accuracy of echocardiographic measurements of left ventricular parameters using real-time three-dimensional echocardiography

OBJECTIVES

We sought to determine whether assessment of left ventricular (LV) function with real-time (RT) three-dimensional echocardiography (3DE) could reduce the variation of sequential LV measurements and provide greater accuracy than two-dimensional echocardiography (2DE).

BACKGROUND

Real-time 3DE has become feasible as a standard clinical tool, but its accuracy for LV assessment has not been validated.

METHODS

Unselected patients (n = 50; 41 men; age, 64 +/- 8 years) presenting for evaluation of LV function were studied with 2DE and RT-3DE. Test-retest variation was performed by a complete restudy by a separate sonographer within 1 h without alteration of hemodynamics or therapy. Magnetic resonance imaging (MRI) images were obtained during a breath-hold, and measurements were made off-line.

RESULTS

The test-retest variation showed similar measurements for volumes but wider scatter of LV mass measurements with M-mode and 2DE than 3DE. The average MRI end-diastolic volume was 172 +/- 53 ml; LV volumes were underestimated by 2DE (mean difference, -54 +/- 33; p < 0.01) but only slightly by RT-3DE (-4 +/- 29; p = 0.31). Similarly, end-systolic volume by MRI (91 +/- 53 ml) was underestimated by 2DE (mean difference, -28 +/- 28; p < 0.01) and by RT-3DE (mean difference, -3 +/- 18; p = 0.23). Ejection fraction by MRI was similar by 2DE (p = 0.76) and RT-3DE (p = 0.74). Left ventricular mass (183 +/- 50 g) was overestimated by M-mode (mean difference, 68 +/- 86 g; p < 0.01) and 2DE (16 +/- 57; p = 0.04) but not RT-3DE (0 +/- 38 g; p = 0.94). There was good inter- and intra-observer correlation between RT-3DE by two sonographers for volumes, ejection fraction, and mass.

CONCLUSIONS

Real-time 3DE is a feasible approach to reduce test-retest variation of LV volume, ejection fraction, and mass measurements in follow-up LV assessment in daily practice.

Comparison of LV mass and volume measurements derived from electron beam tomography using cine imaging and angiographic imaging

PURPOSE

To estimate the variation of left ventricular (LV) mass and volume measurement with cine and angiography by electron beam tomography (EBT).

METHOD AND MATERIALS

Sixty-three consecutive patients (41 men, 22 women; age range 46-91) referred for cardiac imaging for clinical indications underwent cine and coronary artery electron beam angiography (EBA) studies on the same day. The cine images consisted of 144 images (12 slices/level x 12 levels), taken 12 frames/s for a full cardiac cycle. The EBA images consisted of 50-70 slices triggered at end-systole, with an acquisition time of 100 ms/slice. Slice thickness was 8 mm for the cine images and 1.5 mm for the EBA images. A total volume of 120-180 ml of nonionic contrast was used for each subject. The LV mass (myocardial tissue volume), LV cavity volume and total LV volume (tissue + cavity) measurements were completed using the software from the EBT computer console (G.E., S. San Francisco, CA).

RESULTS

The LV mass, cavity volume and total LV volumes at end-systole were 124.11 g, 45.66 and 163.86 ml when derived from the cine images and 130.74 g, 41.31 and 165.82 ml when derived from the EBA images. There were no significant differences between the cine and EBA-derived measurements, however the EBA-derived measurements showed slightly larger LV mass (mean 6.63 g), smaller cavity volume (mean -4.35 ml) and larger total LV volume (mean 1.96 ml, all p > 0.05) than did the cine-derived measurements. Based on case-by-case observations, these differences appear to be related to the higher spatial resolution of the thinner EBA images which allows better discrimination between papillary and trabecular muscle and LV. This leads to slightly smaller cavity size estimations and greater LV mass measurements. There was significant correlation between cine and EBA-derived measurements. Formulas were developed for relating the measurements made from the two modalities as follows: For LV mass: EBA value = 0.91 x cine value + 17.09, R = 0.95, p < 0.001; For LV cavity volume: EBA value = 1.06 x cine value - 6.91, R = 0.96, p < 0.001; For total LV volume: EBA value = 0.98 x cine value + 5.09 in ml, p < 0.001. The mean differences in measurements using the two modalities were 8.1, 18.2 and 6.5% for LV mass, LV cavity volume and total LV volume, respectively.

CONCLUSION

Both cine and EBA images were useful for measuring LV mass and volume with good intertest agreement. Cardiac volume and mass measurements derived from cine EBT studies probably slightly underestimate LV mass and overestimate LV volume.

Left Ventricular Mass: Manual and Automatic Segmentation of True FISP and FLASH Cine MR Images in Dogs and Pigs

PURPOSE

To evaluate the accuracy of manually and automatically segmented true fast imaging with steady-state precession (FISP) and fast low-angle shot (FLASH) cine magnetic resonance (MR) imaging in the determination of left ventricular (LV) mass.

MATERIALS AND METHODS

Nine dogs and five pigs underwent cine MR imaging of the entire LV from base to apex. Manual and automatic segmentation times were recorded, and LV masses determined with each were compared with each other and with the true LV mass at autopsy. Estimated mass and true mass at autopsy were compared by calculating the correlation coefficient and the mean difference between the two for each MR sequence and segmentation method.

RESULTS

True LV mass at autopsy correlated well with masses determined with manual and automatic contours on true FISP MR images. Mean differences between true LV mass and masses determined from manual contours on true FISP and FLASH images were -0.8 g +/- 2.6 and 3.7 g +/- 6.8, respectively. When manually drawn end-diastolic contours were automatically propagated to end systole, mean differences were 2.0 g +/- 3.6 (P =.05) and 9.1 g +/- 6.5 (P <.05) for true FISP and FLASH images, respectively. For automatic contours, mean differences were 10.6 g +/- 8.5 (P <.05) and 27.7 g +/- 13.4 (P <.05) for true FISP and FLASH images, respectively. Mean automatic segmentation time was six times less than mean manual segmentation time.

CONCLUSION

LV mass was determined most accurately by using manual contours on true FISP images. In these animal models, fully automatic segmentation of true FISP images was performed in one-sixth of the time of manual segmentation and yielded LV masses with a mean error of approximately 5% of true LV mass.

Real-Time Three-Dimensional Echocardiography Using a Novel Matrix Array Transducer

Three-dimensional echocardiography has multiple advantages over two-dimensional echocardiography, such as accurate left ventricular quantification and improved spatial relationships. However, clinical use of three-dimensional echocardiography has been impeded by tedious and time-consuming methods for data acquisition and post-processing. A newly developed matrix array probe, which allows real-time three-dimensional imaging with instantaneous on-line volume-rendered reconstruction, direct manipulation of thresholding, and cut planes on the ultrasound unit may overcome the aforementioned limitations. This report will review current methods of three-dimensional data acquisition, emphasizing the real-time methods and clinical applications of the new matrix array probe.

Left ventricular mass measured by myocardial perfusion gated SPECT. Relation to three-dimensional echocardiography

PURPOSE

The purpose of this investigation was to determine whether left ventricular mass (LVM) assessed from myocardial perfusion gated SPECT (GSPECT) data corresponds with echocardiographic estimates, and whether mass accuracy decreases as relative myocardial wall thickness increases.

MATERIALS AND METHODS

Myocardial perfusion tomograms were selected retrospectively for 37 patients, of whom 18 had Tl-201 and 19 had Tc-99m sestamibi GSPECT poststress data collections, which were subsequently processed using quantitative gated SPECT software (Cedars Sinai Medical Center, Los Angeles, CA). These patients also had clinically indicated echocardiograms for assessment of wall thickness and possible valvular involvement. In addition, LV internal diameter and posterior wall thickness were measured at end-diastole by two-dimensional guided M-mode echocardiography to assess relative myocardial wall thickness, and LVM was measured by three-dimensional echocardiography using an acoustic spatial locator device.

RESULTS

LVM values were not significantly different between GSPECT and three-dimensional echocardiography (153 +/- 39 g versus 146 +/- 35 g, respectively; P = NS). GSPECT correlated significantly (r = 0.63, P < 0.0001) with three-dimensional echocardiography, with a mean difference of 7 +/- 32 g but a substantial root mean squared error of 31 g. Results were similar for similar mass ranges when subgrouped by isotope and by the presence of significant myocardial perfusion defects. Results were independent of relative myocardial wall thickness determined by two-dimensional echocardiography. The two methods yielded similar results in the highest mass range of 400 to 500 g.

CONCLUSIONS

GSPECT and three-dimensional echo LVM correlated significantly, but given the large spread of statistical errors, these two techniques should not be considered interchangeable. Because gamma camera resolution is limited, GSPECT LVM should be viewed as an approximation.

Rapid and accurate left ventricular surface generation from three-dimensional echocardiography by a catalog based method. Rapid LV surface generation by three-dimensional echo

BACKGROUND

Quantitative analysis from three-dimensional (3D) echocardiography requires accurate reconstruction of left ventricular (LV) surfaces. This currently requires time-consuming manual image tracing. We describe and validate an alternative rapid method of generating LV surfaces.

METHODS

A 3D-image set is acquired using transthoracic scanning. Images from five standard echo views are displayed and border points selected where anatomic landmarks are well defined. A LV surface is reconstructed as a convex weighted sum of LVs from a catalog of 80 LVs. The intersections of the surface with the five views are presented on these images. The routine may be rerun until the LV surface matches the images. One LV surface is generated in 3 min +/- 27 s. In 41 studies (19 normal, 15 previous infarction, seven cardiomyopathy) the volumes of the catalog-fit endocardial and epicardial surfaces were compared with volumes from surfaces reconstructed from full manual tracing.

RESULTS

Over a wide range of LV volumes and ejection fraction (EF), the catalog-fit results correlated closely to those from manual tracing: end-diastolic volume (194 +/- 99 vs. 204 +/- 110 ml, y = 0.93x, R2 = 0.99, SEE = 19 ml, p < 0.001), end-systolic volume (122 +/- 95 vs. 131 +/- 106 ml, y = 0.92x, R2 = 0.99, SEE = 13 ml, p < 0.001), EF (42 +/- 16 vs. 42 +/- 15%, y = x, R2 = 0.99, SEE = 4%, p < 0.001) and mass (220 +/- 88 vs. 204 +/- 86 g, y = 1.1x, R2 = 0.99, SEE = 24 g, p < 0.001). The endocardial catalog surface was generated from an average of 20 points and three computational runs for both end-diastole and end-systole.

CONCLUSIONS

The catalog method of LV reconstruction from 3D-echo provides accurate measurement of volume, EF and mass. The speed of the method is a major advantage.

Noncompressibility of myocardium during systole with freehand three-dimensional echocardiography

BACKGROUND

Measures of ventricular performance, such as the ejection fraction, assume that myocardium is noncompressible and does not change volume significantly from end diastole to end systole. Although this principle is widely accepted as true, little data exist in the literature to support it. Freehand 3-dimensional (3D) echocardiography has previously been shown to be highly accurate for measurement of myocardial mass and volume. Therefore, we hypothesized that it has sufficient accuracy to test the validity of this assumption. We measured myocardial volume at end diastole and end systole in 2 groups of subjects with hypertrophy.

METHODS

Forty-one healthy young adult athletes and 17 adult patients with hypertension, hypertrophy, normal ejection fraction, and heart failure symptoms underwent examination with freehand 3D echocardiography. Endocardial and epicardial surfaces at end diastole and end systole were reconstructed, and their volumes were computed. From these surface volumes, myocardial volume at end diastole and end systole and epicardial stroke volume and endocardial stroke volume were calculated. These volumes were compared with the 2 sample paired t test.

RESULTS

Myocardial volume was constant from diastole to systole (174.7 +/- 45.3 mL versus 174.6 +/- 45.8 mL; P = not significant), and endocardial and epicardial stroke volumes were identical (76.0 +/- 17.4 mL versus 76.0 +/- 17.1 mL; P = not significant). The average absolute difference between the end-diastolic and end-systolic myocardial volumes was 1.9 mL, or less than 1.1% of end-diastolic volume.

CONCLUSION

Myocardial volume measured with freehand 3D echocardiography does not change significantly during systole. Myocardial volume may be considered noncompressible for purposes of measurement of ventricular function with freehand 3D echocardiography. Comparison of end-diastolic and end-systolic myocardial volumes may be used for quality assurance in performing 3D reconstructions.

Left ventricular mass: reliability of M-mode and 2-dimensional echocardiographic formulas

The study of left ventricular (LV) hypertrophy is hindered by problems with LV mass measurement by echocardiography. Both the M-mode and 2D area-length formulas for calculating LV mass assume a fixed geometric shape, which may be a source of error. We examined this hypothesis by using cardiovascular magnetic resonance images to eliminate the confounding effects of acoustic access and image quality. LV mass was measured directly in 212 healthy subjects by means of a standard 3D cardiovascular magnetic resonance technique. LV mass was also calculated by using the cube-function and area-length formulas with measurements from the magnetic resonance images. A comparison of serial measurements was made by examining the changes in LV mass by all 3 techniques in those completing an exercise program (n=140). The cube-function technique showed a consistent underestimation of LV mass of 14.3 g, and there were wide 95% limits of agreement (+/-57.6 g and +/-46.3 g for cube-function and area-length techniques, respectively) when compared with 3D measurement. There were similarly wide limits of agreement for the change in mass (+/-55.2 g and +/-44.8 g for cube-function and area-length, respectively). The assumption of geometric shape in the cube-function and area-length formulas resulted in significant variation in LV mass estimates from direct measurement by using a 3D technique. The technique cannot be recommended either at a single time point or for serial studies in small populations; 3D imaging techniques, such as cardiovascular magnetic resonance, are preferable.

Augmentation of myocardial blood flow in hypertensive heart disease by angiotensin antagonists: a comparison of lisinopril and losartan

OBJECTIVES

The goal of this study was to compare myocardial perfusion reserve (MPR) before and after long-term treatment with lisinopril and losartan in patients with hypertension and left ventricular hypertrophy (LVH).

BACKGROUND

Studies have suggested that treatment with angiotensin-converting enzyme inhibitors (ACEIs) improves MPR in patients with hypertension by potentiating endogenous bradykinins. Because angiotensin receptor blockers (ARBs) lack a direct effect on bradykinins, we hypothesized that they may not improve MPR.

METHODS

We measured pre- and post-treatment myocardial blood flow (MBF) by positron emission tomography in 17 patients (lisinopril: 9 patients, losartan: 8 patients) with hypertension and LVH at baseline and after coronary vasodilation with intravenous dipyridamole. In addition, we measured rest and hyperemic blood flow in eight normotensive controls.

RESULTS

Post-treatment maximal coronary blood flow and MPR in the lisinopril group increased significantly compared with pretreatment values (3.5 +/- 1.2 vs. 2.6 +/- 1.1 ml/min/g, p = 0.02; 3.7 +/- 1.1 vs. 2.4 +/- 1 ml/min/g, respectively, p = 0.002, respectively). Post-treatment hyperemic flow in the patients treated with lisinopril was not significantly different from corresponding measurements in controls (3.5 +/- 1.2 vs. 3.9 +/- 1 ml/min/g, respectively, p = NS). In the patients treated with losartan, there was no difference between pre- and post-treatment MBF values and MPR.

CONCLUSIONS

Myocardial perfusion reserve and maximal coronary flow improved in asymptomatic patients with hypertension-induced LVH after long-term treatment with lisinopril but not with losartan. Thus, ACEIs, but not ARBs, might be effective in repairing the coronary microangiopathy associated with hypertension-induced LVH.

Effect of annular shape on leaflet curvature in reducing mitral leaflet stress

BACKGROUND

Leaflet curvature is known to reduce mechanical stress. There are 2 major components that contribute to this curvature. Leaflet billowing introduces the most obvious form of leaflet curvature. The saddle shape of the mitral annulus imparts a more subtle form of leaflet curvature. This study explores the relative contributions of leaflet billowing and annular shape on leaflet curvature and stress distribution.

METHODS AND RESULTS

Both numerical simulation and experimental data were used. The simulation consisted of an array of numerically generated mitral annular phantoms encompassing flat to markedly saddle-shaped annular heights. Highest peak leaflet stresses occurred for the flat annulus. As saddle height increased, peak stresses decreased. The minimum peak leaflet stress occurred at an annular height to commissural width ratio of 15% to 25%. The second phase involved data acquisition for the annulus from 3 humans by 3D echocardiography, 3 sheep by sonomicrometry array localization, 2 sheep by 3D echocardiography, and 2 baboons by 3D echocardiography. All 3 species imaged had annuli of a similar shape, with an annular height to commissural width ratio of 10% to 15%.

CONCLUSION

The saddle shape of the mitral annulus confers a mechanical advantage to the leaflets by adding curvature. This may be valuable when leaflet curvature becomes reduced due to diminished leaflet billowing caused by annular dilatation. The fact that the saddle shape is conserved across mammalian species provides indirect evidence of the advantages it confers. This analysis of mitral annular contour may prove applicable in developing the next generation of mitral annular prostheses.

Myocardial contraction fraction: a volumetric index of myocardial shortening by freehand three-dimensional echocardiography

OBJECTIVES

This study sought to evaluate myocardial contraction fraction (MCF) as an index of myocardial shortening by comparison to conventional shortening indices in patients with hypertensive hypertrophy, athletes with physiologic hypertrophy and sedentary normal adult subjects.

BACKGROUND

A significant percentage of patients with hypertensive hypertrophy have "normal" or "preserved" left ventricular (LV) systolic function by conventional echocardiographic measures whereas their systolic function is depressed when measured by the two-dimensional echocardiographic mid-wall shortening fraction (MWSF). A three-dimensional echocardiographic measure of myocardial shortening analogous to MWSF has been lacking. We describe a volumetric measure of myocardial shortening, the MCF, as the ratio of stroke volume (SV) to myocardial volume (MV), and hypothesize that it may be useful to compare myocardial performance in patients with different degrees and types of hypertrophy.

METHODS

We compared the MCF using freehand three-dimensional echocardiographic reconstruction of the LV to conventional measures of LV function (ejection fraction [EF], endocardial shortening fraction [SF] and MWSF) in subjects with pathologic hypertensive hypertrophy, heart failure symptoms and preserved EF (n = 17), athletes with physiologic hypertrophy (n = 41) and normal sedentary adults (n = 80).

RESULTS

The EF was in the normal range for all three groups. The MCF was lower in hypertensive hypertrophy compared with normal subjects (0.33 +/- 0.05 vs. 0.44 +/- 0.07, p < 0.01). It also successfully differentiated physiologic hypertrophy from normal subjects (0.50 +/- 0.05 vs. 0.44 +/- 0.07, p < 0.01). The endocardial SF did not distinguish athletes from normal subjects and the MWSF did not distinguish hypertensive from physiologic hypertrophy.

CONCLUSIONS

The MCF, a volumetric measure of myocardial shortening, demonstrates that myocardial shortening is decreased in hypertensive hypertrophy and increased in physiologic hypertrophy. The MCF may be useful in assessing differences in myocardial performance in patients with similar degrees of hypertrophy.

Errors as a result of metal in the near environment when using an electromagnetic locator with freehand three-dimensional echocardiography

BACKGROUND

Quantitative ventriculography by freehand 3-dimensional (3D) echocardiography with an acoustic spatial locator has been proven to provide highly accurate reproducible measurements of left ventricular volume, mass, and function. It has been shown to be 2 to 3 times better than conventional 2-dimensional echocardiographic techniques. Although accurate, the acoustic spatial locator uses a spark gap to generate hypersound for locating and is somewhat bulky. The Bird direct current electromagnetic locator (Ascension Technology Corp, Burlington, Vt) is a notable alternative locator for the freehand 3D system because it is small and easily portable. However, conductive metals in the near environment may adversely affect electromagnetic locator accuracy. To determine the feasibility of using the electromagnetic locator in a freehand 3D echocardiographic system in the conventional hospital environment, a series of experiments was carried out assessing the accuracy of such a system under various conditions of exposure to conductive metal.

METHODS

Using tissue equivalent ellipsoid phantoms of known volumes, we compared volume measurement accuracy of the freehand 3D echocardiographic system equipped with the standard Bird or miniBird electromagnetic locator systems with our freehand acoustic spatial locator 3D echocardiographic system in 3 experiments: (experiment 1) no metal within 30 in (76.2 cm) of the phantoms and electromagnetic locator; (experiment 2) phantoms placed on a standard metal hospital stretcher with conductive metal less than 10 in (25.4 cm) from the phantoms and electromagnetic locator and with the echocardiographic machine greater than 30 in (76.2 cm) from the electromagnetic locator; and (experiment 3) phantoms placed on the same stretcher with conductive metal less than 10 in (25.4 cm) from the phantoms and electromagnetic locator and with the echocardiographic machine in its usual position approximately 10 in (25.4 cm) from the electromagnetic locator.

RESULTS

For experiment 1 there was no significant volume error (<1%) by any system; no significant difference among the 3 locator systems (acoustic, Bird, or miniBird). For experiment 2 there was significant volume underestimation error by both electromagnetic locator systems (-10.9%, P <.05). For experiment 3 there was significant and greater volume underestimation error by both electromagnetic locator systems (-14.7%, P <.05) in close proximity to the echocardiographic machine. Interobserver variability was 5.1%.

CONCLUSION

For quantitative ventriculography by a freehand 3D echocardiographic system, electromagnetic locator systems should not be used if conductive metal is in the near environment (<30 in [76.2 cm] from the locator). Accurate quantitative ventriculography may be performed with an electromagnetic locator system if the near environment is free of conductive metals.

Determination of left ventricular mass by three-dimensional echocardiography: in vitro validation of a novel quantification method using multiple equi-angular rotational planes for rapid measurements

Measuring left ventricular mass by m-mode echocardiography or two-dimensional echocardiography is limited by the fact that calculations are based on assumptions, which describe left ventricular shape by simple geometric figures. The ability of three-dimensional echocardiography (3-DE) to accurately assess left ventricular mass has been shown previously, but 3-DE approaches to quantitative analysis of ventricular mass required multiple tomographic sectioning, manual tracing in various cut planes and were time consuming and laborious. We investigated the accuracy of a novel, rapid method of 3-DE mass quantification using multiple rotational planes in left ventricles in vitro.

METHODS

Three-dimensional data sets of 10 fixed pig hearts were obtained using a TomTec 3-DE system. For 3-DE mass calculations, a rotational axis in the center of the ventricle (apical-basal orientation) was defined and 3, 6 and 12 equi-angular rotational planes were created. The endocardial and epicardial contour of the left ventricle was traced in each cut plane and the volume of the corresponding myocardial wedge was automatically calculated. Mass was calculated by multiplying the resulting myocardial volume by the specific weight of myocardial tissue. The measurements were performed by two investigators blinded to the anatomic true mass and were analyzed for interobserver and intraobserver variability.

RESULTS

The anatomic left ventricular mass was measured 73-219 (168 +/- 50) g. 3-DE mass ranged from 88-247 (207 +/- 51) g (three planes), 84-250 (205 +/- 52) g (six planes) and 86-241 (202 +/- 50) g (12 planes) respectively. The correlation between 3-DE mass and anatomic LV mass measurements (r = 0.92) and between two observers (r = 0.97-0.98) was good. True mass was slightly overestimated by 3-DE measurement (SEE = 22-23 g). The intraobserver and interobserver variabilities were < or = 4 and < or = 7% respectively for all measurements.

CONCLUSION

This new 3-DE method of left ventricular mass quantification with rotational approach provides accurate and reproducible measurements. In normal shaped left ventricles even three planes were sufficient to provide accurate mass measurements in vitro.

Gender differences and normal left ventricular anatomy in an adult population free of hypertension. A cardiovascular magnetic resonance study of the Framingham Heart Study Offspring cohort

OBJECTIVES

We sought to derive gender-specific cardiovascular magnetic resonance (CMR) reference values for normative left ventricular (LV) anatomy and function in a healthy adult population of clinically relevant age.

BACKGROUND

Cardiovascular magnetic resonance imaging is increasingly applied in the clinical setting, but age-relevant, gender-specific normative values are currently unavailable.

METHODS

A representative sample of 318 Framingham Heart Study (FHS) Offspring participants free of clinically overt cardiovascular disease underwent CMR examination to determine LV end-diastolic and end-systolic volume (EDV and ESV, respectively), mass, ejection fraction (EF) and linear dimensions (wall thickness, cavity length). Subjects with a clinical history of hypertension or those with a systolic blood pressure > or =140 mm Hg or diastolic pressure > or =90 mm Hg at any FHS cycle examination were excluded, leaving 142 subjects (63 men, 79 women; age 57 +/- 9 years).

RESULTS

All volumetric (EDV, ESV, mass) and unidimensional measures were significantly greater (p < 0.001) in men than in women and remained greater (p < 0.02) after adjustment for subject height. Volumetric measures were greater (p < 0.001) in men than in women after adjustment for body surface area (BSA), but there were increased linear dimensions in women after adjustment for BSA. In particular, end-diastolic dimension indexed to BSA was greater in women (p < 0.001) than in men. There were no gender differences in global LVEF (men = 0.69; women = 0.70).

CONCLUSIONS

Cardiovascular magnetic resonance measures of LV volumes, mass and linear dimensions differ significantly according to gender and body size. This study provides gender-specific normal CMR reference values, uniquely derived from a population-based sample of persons free of cardiovascular disease and clinical hypertension. These data may serve as a reference to identify LV pathology in the adult population.

Assessment of left ventricular mass by cardiovascular magnetic resonance

Left ventricular hypertrophy is associated with significant excess mortality and morbidity. The study and treatment of this condition, in particular the prognostic implications of changes in left ventricular mass, require an accurate, safe, and reproducible method of measurement. Cardiovascular magnetic resonance is a suitable tool for this purpose, and this review assesses the technique in comparison with others and examines the clinical and research implications of the improved reproducibility.

Regression of left ventricular mass one year after aortic valve replacement for pure severe aortic stenosis

The aim of the study was to quantify a 1-year change in left ventricular (LV) mass index (MI) and systolic LV function in 30 patients with pure severe aortic stenosis by means of serial 3-dimensional (3-D) echocardiography. To assess the completeness of LVMI regression after 1 year, we compared the postoperative mass of patients with mass values of 30 normotensive control subjects without a history of cardiac disease. Ejection fraction increased from 64 +/- 14% before surgery to 69 +/- 8% at follow-up (p = 0.067), and functional class improved from 2.9 +/- 0.5 to 1.4 +/- 0.5 (p <0.05), with improvement in each patient. During the same period, LVMI regressed by 23.4% (p <0.001). Postoperative LVMI was related to preoperative LVMI (r = 0.82; p <0.001) and baseline ejection fraction (r = -0.5; p = 0.009). LVMI regressed into the normal range in 64% of patients at follow-up. Patients achieving normal mass values did not differ with respect to patient gender, valve type, or valve size. Patients with reduced preoperative LV function had larger volumes (p <0.01), larger mass values (p <0.01), and a trend toward more mass regression (p = 0.062) than patients with normal preoperative function. Although ejection fraction improved after 1 year in all of these patients (p <0.03), they were less likely to achieve normal mass values at follow-up (p = 0.01). Regression of LVMI in patients with pure aortic stenosis is a positive event that occurs in each patient and that is associated with improvement in functional status. LVMI regressed into the normal range in most patients with normal preoperative function. Preoperative LV function, but not patient gender, valve type, or size, was related to normalization of LVMI at follow-up in this selected study population.

LV volume quantification via spatiotemporal analysis of real-time 3-D echocardiography

This paper presents a method of four-dimensional (4-D) (3-D + Time) space-frequency analysis for directional denoising and enhancement of real-time three-dimensional (RT3D) ultrasound and quantitative measures in diagnostic cardiac ultrasound. Expansion of echocardiographic volumes is performed with complex exponential wavelet-like basis functions called brushlets. These functions offer good localization in time and frequency and decompose a signal into distinct patterns of oriented harmonics, which are invariant to intensity and contrast range. Deformable-model segmentation is carried out on denoised data after thresholding of transform coefficients. This process attenuates speckle noise while preserving cardiac structure location. The superiority of 4-D over 3-D analysis for decorrelating additive white noise and multiplicative speckle noise on a 4-D phantom volume expanding in time is demonstrated. Quantitative validation, computed for contours and volumes, is performed on in vitro balloon phantoms. Clinical applications of this spaciotemporal analysis tool are reported for six patient cases providing measures of left ventricular volumes and ejection fraction.

3D ultrasound measurement of large organ volume

Freehand 3D ultrasound is particularly appropriate for the measurement of organ volumes. For small organs, which can be fully examined with a single sweep of the ultrasound probe, the results are known to be much more accurate than those using conventional 2D ultrasound. However, large or complex shaped organs are difficult to quantify in this manner because multiple sweeps are required to cover the entire organ. Typically, there are significant registration errors between the various sweeps, which generate artifacts in an interpolated voxel array, making segmentation of the organ very difficult. This paper describes how sequential freehand 3D ultrasound, which does not employ an interpolated voxel array, can be used to measure the volume of large organs. Partial organ cross-sections can be segmented in the original B-scans, and then combined, without the need for image-based registration, to give the organ volume. The inherent accuracy (not including position sensor and segmentation errors) is demonstrated in simulation to be within +/- 2%. The in vivo precision of the complete system is demonstrated (by repeated observations of a human liver) to be +/- 5%.

In vitro simulation and quantification of temporal jitter artifacts in ECG-gated dynamic three-dimensional echocardiography

The image quality of dynamic 3-D echocardiography is limited by temporal jitter artifacts that result from the asynchronous acquisition of video frames with the cardiac cycle. This paper analyzes the source and extent of these artifacts using in vitro studies. Dynamic 3-D images of a myocardial motion phantom were reconstructed and analyzed for eight cardiac motion patterns. The extent of temporal jitter artifacts was quantified, first, from the images by computing temporal jitter maps and, second, predicted from the motion waveforms. Temporal jitter appeared as a pattern of streak artifacts converging at the axis of rotation of the imaging plane, for the rotational scanning approach used in our study. The results of the experimental analysis techniques were compared with the waveform analysis using linear regression analysis. The least squares line showed good correlation between the data (r > 0.9) and its deviation from the line of identity was calculated to be <9%.

[Comparative study of echocardiography and magnetic resonance imaging in the assessment of left ventricular mass]

AIM OF THE STUDY

Echocardiography is a widely applied technique for the estimation of left ventricular mass, although magnetic resonance is considered as a reference method for this purpose. Both techniques were compared in the present study and the usefulness of a simplified method of calculation by magnetic resonance was also tested.

METHODS

Left ventricular mass was determined in 42 patients by M-mode echocardiography by the application of two equations: the so-called Penn's convention and that proposed by the American Society of Echocardiography. Magnetic resonance studies were also performed, left ventricular mass being estimated from an anatomical method (summation of contiguous transverse ventricular slices) that was considered as a reference, and also by means of a geometrical method (planimetry on a single longitudinal view).

RESULTS

Echocardiographic studies were judged as technically inadequate in 3/42 (7%) patients, while magnetic resonance was performed in all cases. Comparison between each echocardiographic method and the anatomical method of magnetic resonance showed a coefficient correlation of r = 0.70 (Penn's convention formula), and r = 0.71 (American Society of Echocardiography), with an overestimation being observed, particularly with Penn's convention method. The geometrical method of magnetic resonance showed an excellent correlation with the anatomical technique (r =0.93).

CONCLUSIONS

Magnetic resonance is more applicable for the estimation of left ventricular mass than M-mode echocardiography, with the latter showing an overestimation when compared with magnetic resonance, particularly with the Penn's convention method. A simplified method of geometrical estimation of left ventricular mass by magnetic resonance is a reliable alternative to the anatomical method.

Three-dimensional echocardiographic measurement of left ventricular mass: comparison with magnetic resonance imaging and two-dimensional echocardiographic determinations in man

This study was performed to compare a novel three-dimensional echocardiography (3DE) system to clinical two-dimensional echocardiography (2DE) and magnetic resonance imaging (MRI) for determination of left ventricular mass (LVM) in humans. LVM is an independent predictor of cardiac morbidity and mortality. Echocardiography is the most widely used clinical method for assessment of LVM, as it is non-invasive, portable and relatively inexpensive. However, when measuring LVM, 2DE is limited by assumptions about ventricular shape which do not affect 3D echo.

METHODS

A total of 25 unselected patients underwent 3DE, 2DE and MRI. Three-dimensional echo used a magnetic scanhead tracker allowing unrestricted selection and combination of images from multiple acoustic windows. Mass by quantitative 2DE was assessed using seven different geometric formulas.

RESULTS

LVM by MRI ranged from 91 to 316 g. There was excellent agreement between 3DE and MRI (r = 0.99, SEE = 6.9 g). Quantitative 2D methods correlated well with but underestimated MRI (r = 0.84-0.92) with SEEs over threefold greater (22.5-30.8 g). Interobserver variation was 7.6% for 3DE vs. 17.7% for 2DE.

CONCLUSIONS

LVM in humans can be measured accurately, relative to MRI, by transthoracic 3D echo using magnetic tracking. Compared to 2D echo, 3D echocardiography significantly improves accuracy and reproducibility.