Left ventricular function and geometry in fetuses with severe tricuspid regurgitation.

OBJECTIVE: Neonatal congenital tricuspid valve (TV) dysplasia and/or displacement (Ebstein's malformation) with severe tricuspid regurgitation (TR) is a challenging condition in which outcomes are frequently poor. Little is known about left ventricular (LV) function during the perinatal period in patients with congenital TV disease. The objective of this study was to evaluate LV function in fetuses with congenital TV anomalies associated with significant TR. METHODS: Serial fetal echocardiograms in 16 fetuses with congenital TV dysplasia and/or displacement (five neonatal survivors and 11 fetal or neonatal deaths) were reviewed. LV stroke volume, LV end-diastolic volume (LVEDV), LV end-diastolic dimension (LVIDd), the LV eccentricity index, thoracic and cardiac areas and the cardiothoracic area ratio (CTAR), the right atrium area index, and LV longitudinal strains were compared according to gestational age and clinical outcome. RESULTS: The gestational age-adjusted LVEDV (Z-score) was lower in late gestation (-1.2 ± 1.2 at last examination ≥ 28 weeks) than earlier in gestation (0.3 ± 1.5 at last examination < 28 weeks) and LV output was lower than reported late-gestation normal values. LV short-axis dimension correlated with LV volume and CTAR. LV mid-septal strain was lower than the normal average of fetal mid-septal strain and correlated with the LV eccentricity index. Among these parameters, only the LV eccentricity index differed between survivors and non-survivors. CONCLUSION: LV function and anatomy are abnormal in fetuses with severe congenital TV anomalies and may be important contributors to outcome.

A flexible method for simulating cardiac conduction in three-dimensional complex geometries.

In this article we present a method for creating a membrane-based computer model capable of representing a three-dimensional irregular domain. The spatial discretization of our model is based on the Finite Volume Method. In combination with a robust meshmaking tool, our method may be used to simulate conduction in an arbitrarily shaped, complex region. In this way, conduction in specific subregions of cardiac anatomy may be examined. The capabilities of this methodology are demonstrated through 3 examples. The first shows the influence of abrupt changes in tissue geometry on conduction parameters. The second highlights the ability of the model to incorporate interior boundaries and altered membrane properties. The final example shows the inclusion of a full description of the fiber architecture in a portion of the canine left ventricle. Future applications will make use of the model's capabilities to conduct investigations in complex regions including the atria.

A finite volume model of cardiac propagation.

This paper describes a two-dimensional cardiac propagation model based on the finite volume method (FVM). This technique, originally derived and applied within the filed of computational fluid dynamics, is well suited to the investigation of conduction in cardiac electrophysiology. Specifically, the FVM permits the consideration of propagation in a realistic structure, subject to arbitrary fiber orientations and regionally defined properties. In this application of the FVM, an arbitrarily shaped domain is decomposed into a set of constitutive quadrilaterals. Calculations are performed in a computational space, in which the quadrilaterals are all represented simply as squares. Results are related to their physical-space equivalents by means of a transformation matrix. The method is applied to a number of cases. First, large-scale propagation is considered, in which a magnetic resonance-imaged cardiac cross-section serves as the governing geometry. Next, conduction is examined in the presence of an isthmus formed by the microvasculature in a slice of papillary muscle tissue. Under ischemic conditions, the safety factor for propagation is seen to be related to orientation of the fibers within the isthmus. Finally, conduction is studied in the presence of an inexcitable obstacle and a curved fiber field. This example illustrates the dramatic influence of the complex orientation of the fibers on the resulting activation pattern. The FVM provides a means of accurately modeling the cardiac structure and can help bridge the gap between computation and experiment in cardiac electrophysiology.