Image-Derived Assessment of Left Ventricular Mass in Fetal Myocardial Hypertrophy by 4-Dimensional Echocardiography: An In Vitro Study.

OBJECTIVES: This study tested the accuracy of new 4-dimensional fetal echocardiography to evaluate left ventricular (LV) mass in an experimental model of fetal myocardial hypertrophy. METHODS: Ten fresh rabbit hearts were studied. Fetal myocardial hypertrophy was simulated by fixing different amounts of myocardial tissue to the LV epicardium. A small latex balloon was mounted on vinyl tubing and fixed within each LV cavity. The proximal end of the tube was attached to a pulsatile pump apparatus. The pump was calibrated to deliver stroke volumes of 2 and 4 mL at stroke rates of 60 and 120 beats per minute (bpm). Four-dimensional data were acquired and analyzed with quantification software. Reference values for LV mass were determined by the displacement method. RESULTS: Echo-derived measurements of LV mass showed good correlations with reference values at all stroke rates and stroke volumes: at 2 mL and 60 bpm, r = 0.95; at 2 mL and 120 bpm, r = 0.95; at 4 mL and 60 bpm, r = 0.93; and at 4 mL and 120 bpm, r = 0.95 (P< .01 for all values). There was also excellent interobserver (r = 0.98; mean difference of -0.32 g; -4.4% of the mean) and intraobserver (r = 0.98; mean difference of -0.28 g; -3.8% of the mean) agreement. CONCLUSIONS: In this controlled in vitro study, high-resolution 4-dimensional echocardiography was shown to accurately assess LV mass and have the potential to evaluate fetal myocardial hypertrophy.

Quantitative assessment of mitral inflow and aortic outflow stroke volumes by 3-dimensional real-time full-volume color flow doppler transthoracic echocardiography: an in vivo study.

OBJECTIVES: Noninvasive quantification of left ventricular (LV) stroke volumes has an important clinical role in assessing circulation and monitoring therapeutic interventions for cardiac disease. This study validated the accuracy of a real-time 3-dimensional (3D) color flow Doppler method performed during transthoracic echocardiography (TTE) for quantifying volume flows through the mitral and aortic valves using a dedicated offline 3D flow computation program compared to LV sonomicrometry in an open-chest animal model. METHODS: Forty-six different hemodynamic states in 5 open-chest pigs were studied. Three-dimensional color flow Doppler TTE and 2-dimensional (2D) TTE were performed by epicardial scanning. The dedicated software was used to compute flow volumes at the mitral annulus and the left ventricular outflow tract (LVOT) with the 3D color flow Doppler method. Stroke volumes by 2D TTE were computed in the conventional manner. Stroke volumes derived from sonomicrometry were used as reference values. RESULTS: Mitral inflow and LVOT outflow derived from the 3D color flow Doppler method correlated well with stroke volumes by sonomicrometry (R = 0.96 and 0.96, respectively), whereas correlation coefficients for mitral inflow and LVOT outflow computed by 2D TTE and stroke volumes by sonomicrometry were R = 0.84 and 0.86. Compared to 2D TTE, the 3D method showed a smaller bias and narrower limits of agreement in both mitral inflow (mean ± SD: 3D, 2.36 ± 2.86 mL; 2D, 10.22 ± 8.46 mL) and LVOT outflow (3D, 1.99 ± 2.95 mL; 2D, 4.12 ± 6.32 mL). CONCLUSIONS: Real-time 3D color flow Doppler quantification is feasible and accurate for measurement of mitral inflow and LVOT outflow stroke volumes over a range of hemodynamic conditions.

Real-time 3-dimensional echocardiographic assessment of ventricular volume, mass, and function in human fetuses.

OBJECTIVES: We sought to determine the feasibility and reproducibility of real-time 3-dimensional echocardiography (RT3DE) for evaluation of cardiac volume, mass, and function and to characterize maturational changes of these measurements in human fetuses. METHODS: Eighty pregnant women in the 2(nd) and 3(rd) trimesters (59 with normal fetuses and 21 with fetuses with congenital heart disease [CHD]) were enrolled. We acquired RT3DE images using a matrix-array transducer. RT3DE measurements of volume, mass, stroke volume (SV), combined cardiac output (CCO), and ejection fraction (EF) were obtained. Images were scored and analyzed by two blinded independent observers. Inter- and intraobserver variabilities and correlations between fetal cardiac indices and gestational age were determined. RESULTS: Fifty-two of 59 normal data sets (88%) and 9 of 21 CHD data sets (43%) were feasible for analysis. In normal fetuses, the right ventricle (RV) is larger than the left ventricle (LV) (P<0.05), but no difference exists between the LV and RV in mass, SV, CO, and CO/CCO. The EFs for the LV and RV were diminished; the RVSV/LVSV was reduced in CHD fetuses compared with normal fetuses (P<0.05). Fetal ventricular volumes, mass, SV, and CCO fit best into exponential curves with gestational age, but LVEF, RVEF, and RVSV/LVSV remain relatively constant. CONCLUSIONS: RT3DE is feasible and reproducible for assessment of LV and RV volume, mass, and function, especially in normal fetuses. Gestational growth of these measures, except for EF, is exponential in normal and CHD fetuses. CHD fetuses exhibit diminished LV and RV EFs.

Assessment of interventricular dyssynchrony by real time three-dimensional echocardiography: an in vitro study in a porcine model.

BACKGROUND: Loss of synchronous contraction between or within the right and left ventricle (RV, LV) leads to adverse ventricular function. We used real time three-dimensional echocardiography (RT3DE) for evaluation of severity of interventricular dyssynchrony and function in a porcine heart model. METHODS: Six fresh in vitro porcine hearts were used to create a controlled model of LV and RV dyssynchrony using two sets of pulsatile pumps. Synchronized and dyssynchronized pump settings were used with two different dyssynchronized settings: LV filled first and RV filled first. RESULTS: There was good correlation between actual measurement and RT3DE for interventricular time difference (r = 0.95, P < 0.0001) and stroke volume (SV) for LV and RV (0.89, 0.85; P < 0.0001, respectively). RT3DE data showed a small but significant underestimation for actual volume (P < 0.05). The intra- and interobserver variabilities are 2.9 +/- 1.5% and 3.1 +/- 5.4% for LV and RV SVs, and 1.7 +/- 2.4% and 2.2 +/- 3.2% for time differences by RT3DE. There was significant difference in RV SV between synchrony and dyssynchrony when the RV filled first (P < 0.05), but not in other groups. The same pattern was found in RT3DE derived SVs (synchrony versus dyssynchrony with RV filled first, P < 0.05). CONCLUSIONS: There is no compromise in LV SV during interventricular dyssynchrony; but RV SV was significantly diminished when the RV filled first. RT3DE is a feasible, robust and reproducible method to identify interventricular dyssynchrony and to evaluate ventricular SVs.

Assessment of left ventricular radial deformation by speckle tracking imaging.

The left ventricular radial strain in the inner and outer layers was evaluated by using two-dimensional speckle tracking imaging (2DS). Twenty-five piglets were studied. The short axis views were acquired. Peak systolic radial strain was measured from 6 circumferential points related to 6 standard segments in the inner and outer layers respectively using 2DS methods. The peak positive first derivative (dp/dt) of left ventricular pressure was compared to the radial strain from 2DS. The inner band showed higher peak radial strain values as compared to the outer band at all of the segments (P<0.0001), but the differences had significance just in anteroseptal, posterior, inferior and septal segments (P<0.05). Good correlation could be found between radial strain of inner and outer layers and peak dp/dt (P<0.001). These preliminary results showed that the degree of local deformation or wall thickening of the ventricular wall in its inner layer was more obvious than its outer layer. It is suggested that the 2DS technique is useful and sensitive for better understanding the regional and global myocardial motion and its relationship to the complex architecture of myocardium.

The contribution of left ventricular muscle bands to left ventricular rotation: assessment by a 2-dimensional speckle tracking method.

BACKGROUND: Torsion is an essential component of left ventricular (LV) function. Systolic rotation, as a component of torsion, winds the heart muscle up like a spring, setting up recoil for early diastole. We used a new 2-dimensional speckle tracking strain method to study differences in twisting in subendocardial and subepicardial layers of the LV in open-chest pigs. Our aim was to identify the relative contributions of the inner or outer layers of the LV wall to rotation and, hence, systole. METHODS: A total of 23 juvenile pigs were imaged in the short axis, epicardially, to obtain images at a level just below the papillary muscles with high-frequency (14 MHz) ultrasound. Speckle tracking software using scanline files was used to measure the torsional contribution of septum, anterior, posterior, and inferior LV wall segments. Two zones on the septum were evaluated separately: one with apparent circumferential fiber orientation in the inner layer and one with a speckle pattern suggesting longitudinal fiber orientation on the right ventricular aspect of the septum. Pressure rate changes (dP/dt) during the cardiac cycle were measured as an index of LV function and correlated with the regional torsion. RESULTS: Mean peak rotations measured by speckle tracking echocardiography at the apex showed counterclockwise rotation of LV septal wall (10.68 +/- 2.67 degrees for the inner layer and 8.27 +/- 1.73 degrees for the outer layer). The time difference for time to peak rotation was 213.22 +/- 77.95 and 241.17 +/- 54.67 milliseconds for inner and outer layers, respectively. Significant differences were shown between the inner and outer layer of the LV for both rotation (P = .000) and timing of rotation (P = .02). The dP/dt measurements correlated well with the inner rotation magnitude of the LV and with the difference of short-axis rotation between inner and outer layers of the LV wall. CONCLUSIONS: Inner and outer layers of the LV wall, especially at the septum, have different rotational behaviors. When used with very high-resolution imaging, this method could contribute to the understanding of functional contributions of the LV wall and their relative contribution to cardiac segmental twisting.

Real-time 3-dimensional Doppler echocardiography for the assessment of stroke volume: an in vivo human study compared with standard 2-dimensional echocardiography.

BACKGROUND: Invasive monitors and noninvasive 2-dimensional echocardiography are the standard clinical methods for stroke volume (SV) and cardiac output computation. We studied the use of real-time color Doppler 3-dimensional (3D) echocardiography (3DE) for the assessment of SV in human beings. METHODS: In all, 55 pediatric and adult patients with good transthoracic windows and a normal aortic valve were studied. Real-time 3DE color Doppler volumes incorporating the left ventricular outflow tract and aortic valve were taken. SV was calculated from the color Doppler data in the 3DE DICOM dataset. This was compared with 2-dimensional echocardiography SV calculation from the pulsed wave velocity through the aortic valve along with the left ventricular outflow tract diameter. RESULTS: Five patients were excluded because of mismatching of the 3D color Doppler segments in the 3D volume. The 3D Doppler volumes from the remaining 50 patients were analyzed. There was good correlation between the patients' averaged 3DE SV calculations and the 2-dimensional echocardiography pulsed wave SV estimation (y = 0.84x + 7.8, r2 = 0.90). CONCLUSION: Real-time 3D Doppler echocardiography can be used to accurately calculate SV and cardiac output, compared with conventional pulsed Doppler measurement, in pediatric and adult patients from transthoracic imaging.

A novel method for the assessment of the accuracy of computing laminar flow stroke volumes using a real-time 3D ultrasound system: In vitro studies.

AIMS: Laminar flow stroke volume (SV) quantification in the ascending aorta or pulmonary artery can provide a measure for determining cardiac output (CO). Comparing flows across different valves can also compute shunt volumes and regurgitant fractions. Quantification methods for 3D color Doppler laminar flow volumes have been developed using reconstructive 3D, but these are cumbersome and time-consuming both in acquisition and measurement. Our study evaluated newly developed color Doppler mapping with real-time live 3D echo to test velocity, spatial and temporal resolution for computing SV. METHODS AND RESULTS: Five rubber tubes (diameters=3.0, 2.25, 2.0, 1.9, 1.7 cm), a freshly dissected porcine aorta (Ao) and a pulmonary artery (PA) (both 2-3 cm diameter) were connected to a pulsatile pump in a water bath. Different SV, from 10 to 80 ml/beat, were studied at pump rates of 40-60 bpm in this phantom model with flow quantified by timed collection. The Nyquist limit was set between 43 and 100 cm/s and frame rate ranged from 14 to 23/s. ECG triggered 3D color Doppler volumes were acquired with a 2-4 MHz probe. The digital scan line data from the 3D volumes, with retained velocity assignments, was exported and analyzed offline by MatLab custom software. Close correlations were found between 3D calculated SV and reference data for all tubes (r=0.98, y=1.14x-1.69, SEE=2.82 ml/beat, p<0.0001). Both Ao and PA flows were also highly correlated with the reference measurements (PA: r=0.98, SEE=3.17 ml/beat; Ao: r=0.99, SEE=3.20 ml/beat). CONCLUSIONS: Real-time 3D color Doppler method could provide an efficient, accurate and reliable method for clinical evaluation and quantification of flow volumes in patients.

Risk of sudden cardiac death in young athletes: which screening strategies are appropriate?

Resources are not available to comprehensively evaluate all young athletes before participation in competitive sports. Therefore, the cardiovascular evaluation of young athletes needs to be targeted at high-risk areas and focus on the individuals who are at greatest possible risk: those who have suggestive, even if minor, symptoms, and those who have a family history of sudden death or premature cardiac disease.

Assessment of pulmonary artery stenosis using freehand "flock of birds" digital color three-dimensional echocardiographic reconstruction.

Pulmonary artery (PA) trunk or branch PA stenosis is commonly found in patients with congenital heart disease. The aim of the present study was to evaluate the freehand "Flock of Birds" color Doppler three-dimensional (3D) reconstruction on a modeled-segment imitating PA stenosis. First, a PA model was created from latex tubes to simulate the main PA and its main branches with baseline cross-sectional areas (CSA) of 0.7 cm2. A series of narrowed segments in the right and left PA were created. The cross-sections of the smallest area ranged from 0.13 to 0.59 cm2 and stenotic segmental length ranged from 0.17 to 1.80 cm. The dimensions of these elements mounted on to the model were verified by intravascular ultrasound (IVUS) imaging. Next, pulsatile flows at 60 beats/ min were generated through the system. A GE/VingMed System FiVe with magnetic locator system (Flock of Birds) on a 3.5 MHz transducer was used to acquire a freehand sweep for ECG gated 3D data acquisition of color Doppler flows through the model. The images were reconstructed by EchoPac 3D software and the morphology of the stenotic elements were determined. The results revealed that the narrowest CSA determined by the 3D color flow cast of the pulmonary artery were in excellent agreement with IVUS CSA (r = 0.98, p < 0.001, SEE = 0.04 cm2). The stenotic length estimated from 3D was also in good agreement with the IVUS (r = 0.98, p < 0.001, SEE = 0.03 cm). In addition, complex morphology of the stenosis was well visualized by this technique. As a result, the noninvasive free-hand digital color 3D echocardiography can be adopted for the accurate assessment of the severity and morphology of PA stenosis in patients with congenital heart diseases.