Application of spatial modulation of magnetization (SPAMM) to children: the effect of image resolution on tagging pattern

BACKGROUND AND OBJECTIVE

Spatial modulation of magnetization (SPAMM) is a valuable magnetic resonance imaging technique for studying ventricular biomechanics. In order to track the intersection points of the stripes to calculate regional wall motion and strain, the stripe spacing should be at most half the wall thickness, yet sufficiently larger than the image pixel size in order that the stripes be well resolved. These conflicting requirements, that the grid spacing be much smaller than the wall thickness yet much larger than the pixel size, are relatively easy to meet in adult subjects but are difficult in children because of their small size. The purpose of this study was to delineate the effect of pixel size relative to SPAMM grid spacing on the stripe pattern produced by SPAMM with application towards its use in children and to present a new approach to the analysis of these images.

METHODS

We performed SPAMM imaging on a 1.5 Telsa Siemen's Vision MR system on a phantom, using an artificial ECG (R-R interval = 450 ms for triggering), holding the pixel size constant and varying the degree of stripe spacing. We used both square (1 mm) and rectangular (1 mm by 2 mm) pixels. We express the ratio of grid to pixel size as the ratio of the center-center spacing of the grid lines to the horizontal pixel size. We retrospectively reviewed the SPAMM images on 10 patients with a ratio of grid to pixel size approximately 4:1 and 10 with a ratio of grid to pixel size approximately 8:1. We further performed SPAMM imaging in four patients with different grid to pixel size ratios in the same patient. Finally, we tested a new algorithm to track the signal intense regions rather than the signal poor intersection points of the grid lines, which were compared on three ventricles with SPAMM tagging.

RESULTS

In a phantom, the effect of decreasing the separation between stripes while keeping the resolution of the image constant changed the stripe pattern from a series of two parallel lines perpendicular to each other to a "checkerboard" pattern. With a relative grid:pixel ratio of 8:1 as used with adult studies, the dark bands and the crossing points are well defined. As the ratio decreases from 8:1 to 6:1, the black band is less well resolved. When the resolution is reduced further to a grid:pixel ratio of 4:1, the image appears to be a checkerboard of white and dark squares. This occurred with both square and rectangular pixels. The effect in vivo is similar. When the ratio is approximately 8:1, all patients demonstrated a stripe pattern as a set of parallel lines perpendicular to each other. When the ratio was approximately 4:1, all patients demonstrated the stripe pattern as checkerboard. This was found to be the case in the same patient, whether varying the pixel size by changing the field of view or matrix or by changing the grid spacing. We also found that tracking the signal intense regions was equivalent to tracking the signal poor intersection points of the grid, and this approach was much easier to implement.

CONCLUSION

With decreasing ratio of grid spacing to pixel size, SPAMM stripe patterns change from a set of parallel lines perpendicular to each other to a "checkerboard" pattern. This effect has implications for tracking techniques to determine strain and wall motion. At smaller ratios, as is needed sometimes in children, it is easier to track the signal intense regions rather than the "intersection" points of the stripes. Both these approaches to tracking are equivalent.

Usefulness of branch pulmonary artery regurgitant fraction to estimate the relative right and left pulmonary vascular resistances in congenital heart disease

In postoperative congenital heart patients with pulmonary regurgitation, individual branch pulmonary artery regurgitant fractions estimate relative pulmonary vascular resistance independent of pulmonary blood flow distribution.

Brain versus lung: hierarchy of feedback loops in single-ventricle patients with superior cavopulmonary connection

BACKGROUND

CO2 vasodilates and O2 vasoconstricts the cerebral vascular bed; the opposite is true in the lungs. When the brain and lungs are connected exclusively in series, which feedback loop predominates is unknown. The circulation of the superior cavopulmonary connection (SCPC) provides a unique physiology to answer this question.

METHODS AND RESULTS

To determine cerebral and pulmonary blood flow and to establish the hierarchy of cerebral and pulmonary feedback mechanisms, 12 intubated, ventilated, single-ventricle patients in SCPC physiology (age 2.2+/-0.5 years) underwent magnetic resonance imaging velocity mapping of their jugular veins and aorta in room air, hypercarbia, and 100% O2. Flows in these vessels and arterial blood gases were measured. With 22+/-6 torr CO2 (Pco2) increased from 40 to 63 mm Hg, P<0.01), flow to the brain and lungs increased (1.5 to 2.7 L/min per m2, P=0.0003), Po2 improved (48 to 60 mm Hg, P=0.0004), and cardiac index increased (4.3 to 5.4 L/min per m2, P=0.0003). The increased cardiac index accounted for the increased cerebral and pulmonary blood flow (R=0.73, P=0.02) and cerebral O2 transport increased by 80% (P=0.0005) while preserving body O2 delivery. Hyperoxia did not change cerebral and pulmonary blood flow; Po2 increased 94% (P=0.01).

CONCLUSIONS

The cerebral CO2 feedback loop predominates over the pulmonary one when they directly compete with each other. CO2 has a major impact on flow distribution whereas O2 has little impact. Increased CO2 improves cerebral oxygenation in SCPC patients. This may provide a clue in determining neurological sequelae in SC physiology and may influence timing of Fontan completion.

Is routine cardiac catheterization necessary in the management of patients with single ventricles across staged Fontan reconstruction? No!

With the advent of cardiac magnetic resonance imaging and high-resolution echocardiography, cardiac catheterization is unnecessary in clinical protocols in the "routine" single ventricle patient. Catheterization adds little to clinical care in these cases, and there are significant risks and costs associated with it. Catheterization should be reserved for cases in which noninvasive evaluations are equivocal, conflictory, demonstrate deterioration, or needed for intervention. This article delineates the role of noninvasive evaluations relative to cardiac catheterization in the routine single ventricle patient.

Physics-Driven CFD Modeling of Complex Anatomical Cardiovascular Flows?A TCPC Case Study

Recent developments in medical image acquisition combined with the latest advancements in numerical methods for solving the Navier-Stokes equations have created unprecedented opportunities for developing simple and reliable computational fluid dynamics (CFD) tools for meeting patient-specific surgical planning objectives. However, for CFD to reach its full potential and gain the trust and confidence of medical practitioners, physics-driven numerical modeling is required. This study reports on the experience gained from an ongoing integrated CFD modeling effort aimed at developing an advanced numerical simulation tool capable of accurately predicting flow characteristics in an anatomically correct total cavopulmonary connection (TCPC). An anatomical intra-atrial TCPC model is reconstructed from a stack of magnetic resonance (MR) images acquired in vivo. An exact replica of the computational geometry was built using transparent rapid prototyping. Following the same approach as in earlier studies on idealized models, flow structures, pressure drops, and energy losses were assessed both numerically and experimentally, then compared. Numerical studies were performed with both a first-order accurate commercial software and a recently developed, second-order accurate, in-house flow solver. The commercial CFD model could, with reasonable accuracy, capture global flow quantities of interest such as control volume power losses and pressure drops and time-averaged flow patterns. However, for steady inflow conditions, both flow visualization experiments and particle image velocimetry (PIV) measurements revealed unsteady, complex, and highly 3D flow structures, which could not be captured by this numerical model with the available computational resources and additional modeling efforts that are described. Preliminary time-accurate computations with the in-house flow solver were shown to capture for the first time these complex flow features and yielded solutions in good agreement with the experimental observations. Flow fields obtained were similar for the studied total cardiac output range (1-3 1/min); however hydrodynamic power loss increased dramatically with increasing cardiac output, suggesting significant energy demand at exercise conditions. The simulation of cardiovascular flows poses a formidable challenge to even the most advanced CFD tools currently available. A successful prediction requires a two-pronged, physics-based approach, which integrates high-resolution CFD tools and high-resolution laboratory measurements.

Noninvasive imaging of isolated persistent fifth aortic arch

Persistent fifth aortic arch was suspected by echocardiography and confirmed by magnetic resonance imaging (MRI) in an infant with a heart murmur. Selected images including three dimensional reconstruction from MRI demonstrating this very rare congenital anomaly are presented.

Flow volume asymmetry in the right aortic arch in children with magnetic resonance phase encoded velocity mapping

BACKGROUND

The right aortic arch is not uncommon in pediatrics. Flow dynamics in this type of aortic arch, which is important for cardiac energetics, organ perfusion, and Doppler flow calculations, have not been defined. Although there are complex secondary flow patterns, bulk axial flow makes up most of the energy use.

METHODS

We examined 14 children with a right aortic arch by using through-plane phase-encoded magnetic resonance velocity mapping in the ascending and descending aorta to determine flow volume symmetry and velocity. The aortic cross section was divided into 4 quadrants aligned along the long axis of the aorta. Significance was defined as a P value <.05.

RESULTS

In the ascending aorta, the posterior right quadrant demonstrated significantly greater blood flow than the other quadrants across the entire cardiac cycle (28% vs 23%-25%) and at the point of maximum flow (29% vs 22%-25%). Flow asymmetry was also present in the descending aorta; there was significantly more flow in the posterior quadrants than the anterior quadrants in total flow across the cardiac cycle (28% vs 21%-23%) and at the point of maximum flow (27%-28% vs 20%-24%). The time to maximum flow was significantly shorter in the ascending than the descending aorta (18% vs 24% of the cardiac cycle). In 10 of 14 patients, maximum velocity occurred in the right half of both the ascending and descending aorta. Flow reversal at end-systole was haphazard, occurring in all quadrants.

CONCLUSION

Flow volume asymmetry exists in the ascending and descending portions of the right aortic arch, which has implications for cardiac energetics, organ perfusion, and Doppler scanning flow calculations. This information may be useful in designing improved aortic surgical reconstructions in cases of congenital heart disease.

Use of ejection fraction (or lack thereof), morbidity/mortality and heart failure drug trials: a review

Ejection fraction (EF) is an ejection phase parameter used to assess the performance of the heart in normal individuals and pathologic states such as myocardial infarction, dilated cardiomyopathy, and congestive heart failure (CHF). It can be measured by radionuclide ventriculography, angiocardiography, echocardiography and magnetic resonance imaging. EF is dependent on the loading conditions of the heart as well as contractility of the myocardium which makes it a less useful measure of cardiac performance. Nevertheless, it has been widely utilized and discussed for years. EF has been used as an entry criteria for many trials in CHF and has been used to characterize the hemodynamic effects of various classes of drugs which are used in treating CHF. How predictive an increase in EF on therapy is of morbidity and mortality is a matter of debate. This review outlines the utilization (or lack thereof), of EF in various CHF drug trials, its relationship to symptomatic improvement and morbidity/mortality.

Mid-term follow-up of patients with transposition of the great arteries after atrial inversion operation using two- and three-dimensional magnetic resonance imaging

BACKGROUND

Older patients with transposition of the great arteries who have undergone an atrial inversion procedure (ATRIAL-INV) are difficult to image by echocardiography. The surgical baffles are spatially complex.

OBJECTIVE

To test the hypothesis that two- and three-dimensional MRI can elucidate the spatially complex anatomy in this patient population.

MATERIALS AND METHODS

Twelve patients with ATRIAL-INV, ages 16+/-4.5 years, underwent routine T1-weighted spin-echo axial imaging to obtain a full cardiac volumetric data set. Postprocessing created three-dimensional shaded surface displays and allowed for multiplanar reconstruction. Routine transthoracic echocardiography was available on all patients.

RESULTS

Three-dimensional reconstruction enabled complete spatial conceptualization of the venous pathways, and allowed for precise localization of a narrowed region in the upper limb of the systemic venous pathway found in two patients. This was subsequently confirmed on angiography. Routine MRI was able to image the full extent of the venous pathways in all 12 patients. Routine transthoracic echocardiography was able to visualize proximal portions of the venous pathways in eight (67%), the distal upper limb in five (42%), and the distal lower limb in four (33%) patients, and it was able to visualize the outflow tracts in all patients.

CONCLUSION

Three-dimensional reconstruction adds important spatial information, which can be especially important in stenotic regions. Routine MRI is superior to transthoracic echocardiography in delineation of the systemic and pulmonary venous pathway anatomy of ATRIAL-INV patients at mid-term follow-up. Although transesophageal echocardiography is an option, it is more invasive.

Nonuniform flow dynamics in the aorta of normal children: a simplified approach to measurement using magnetic resonance velocity mapping

PURPOSE

To determine regional flow dynamics in the normal aorta (Ao) in children. Understanding flow dynamics in children is important in cardiovascular energetics, in designing improved aortic reconstructions by crafting the surgery to mimic normal aortic flow, and in Doppler flow calculations. The objective of this study was to determine regional flow dynamics in the normal Ao in children.

MATERIALS AND METHODS

We performed magnetic resonance velocity mapping on 13 subjects (ages 7.2 +/- 6.2 years) with normal Aos to determine flow dynamics in four equal quadrants in the ascending (AAo) and descending aorta (DAo) aligned along the long axis of the Ao. Statistical significance was set at P <.05.

RESULTS

In the AAo, the left posterior quadrant displayed significantly less blood flow (16% +/- 5%) than the other quadrants (26-29%) over the cardiac cycle. In the DAo, both anterior quadrants carried significantly less blood flow (20% and 21%) than the posterior quadrants (27% and 32%). At maximum flow (15% +/- 5% into the cardiac cycle for the AAo; 27% +/- 15% for the DAo), there was significantly more flow in the right posterior quadrant (28% +/- 2%) than other quadrants (22-23%) in the AAo. In the DAo, both posterior quadrants had significantly higher flow rates (27% and 30%) than the anterior quadrants (21% and 22%). Maximum velocity in both the AAo and the DAo occurred in the left posterior quadrant in 10/13 at 16-24% into the cardiac cycle. At end-systole, a short flow reversal was noted in the posterior quadrants in the AAo in 11/13; in the DAo, this occurred in the anterior quadrants in 10/13.

CONCLUSION

Flow dynamics in the normal Ao in children are not symmetrical; the flow distributions are asymmetric in both the AAo and the DAo throughout systole, including flow reversal related to the dicrotic notch. These results may help improve Ao surgery.

A simplified approach for assessment of intracardiac baffles and extracardiac conduits in congenital heart surgery with two- and three-dimensional magnetic resonance imaging

BACKGROUND

Intracardiac baffles and extracardiac conduits have been used in the reconstructive surgery of a broad spectrum of congenital cardiac malformations. Periodic evaluation of these structures may not lend itself readily to echocardiographic and angiographic imaging. The purpose of the study was to describe the experience of our institution with the use of magnetic resonance imaging (MRI) in evaluating conduits and baffles and to describe the simplified approach we developed to image these structures, which allows for grouping individual lesions into broad categories.

METHODS AND RESULTS

We retrospectively reviewed our MRI experience in visualizing these structures from 1989-1996. One hundred thirty-nine patients underwent MRI to visualize 144 structures (116 baffles, 28 conduits). The 116 baffles included 86 Fontan, 16 Mustard, 6 Senning, 6 left ventricle to aorta, 1 right ventricle to aorta, and 1 pulmonary vein to left atrium baffle. The 28 conduits included 15 right ventricle to pulmonary artery, 4 left ventricular apical to aorta, 2 left ventricle to pulmonary artery, 3 aorta to aorta, 2 inferior vena cava to left atrium conduits, and 2 aortic root replacements. Of the 3 aortic-aortic conduits, 1 was in conjoined twins. Both inferior vena cava-left atrial conduits were in a Baffes procedure. An infectious mass missed by echocardiography in a right ventricle to pulmonary artery conduit was visualized by MRI. With multiplanar reconstruction, contiguous images were stacked atop each other and resliced to define the salient points of the anatomy. Three-dimensional reconstruction further added to this delineation. All structures were visualized successfully, and an assessment of obstruction was made. Multiple examples of conduit and baffle narrowing were diagnosed by spin echo and cine MRI and were subsequently confirmed by catheterization and surgical inspection.

CONCLUSION

MRI, with multiplanar and 3-dimensional reconstruction, is useful in examining the variety of baffles and conduits used in congenital heart surgery. MRI can add to the care of patients whose echocardiographic windows or whose angiographically overlapping structures do not allow adequate delineation of conduits and baffles.

Evaluation and follow-up of patients with left ventricular apical to aortic conduits with 2D and 3D magnetic resonance imaging and Doppler echocardiography: A new look at an old operation

BACKGROUND

Although the interposition of left ventricular apical to descending aorta conduits has diminished with the advent of the Ross-Konno operation, it remains a useful option. We reviewed our institutional experience imaging these conduits and tested the hypothesis that the gradient across the native left ventricular outflow tract (LVOT) by echocardiography correlated with the conduit gradient by cardiac catheterization. In a patient with an unobstructed conduit, no gradient should exist across the native LVOT.

METHODS

This was a retrospective review of the echocardiography, cardiac catheterization, magnetic resonance imaging (MRI) data, and history of 9 patients with these conduits over an 8-year period. In 7 of 9 patients, 8 conduit obstruction events were assessed by Doppler interrogation of the native LVOT and by cardiac catheterization. Five patients underwent 6 MRI scans.

RESULTS

In all cases of obstruction diagnosed by catheterization (56.3 +/- 21.9 mm Hg), Doppler echocardiography demonstrated gradients across the native LVOT (69.3 +/- 21.2 mm Hg, r = 0.67). Because 2D echocardiography could not visualize the entire conduit in any patient, 2- and 3-dimensional MRI was used successfully to evaluate anatomy and identify the site of obstruction. All patients manifested conduit obstruction. Four (44%) of 9 patients died, 3 underwent the Ross operation, 1 continues to live with his original conduit, and 1 was lost to follow-up.

CONCLUSIONS

A gradient by Doppler interrogation of the native LVOT is an indirect means of assessing conduit obstruction. MRI is a useful tool to complement anatomic diagnosis by echocardiography. Conduit obstruction is common, and late mortality rates appear to be high.

Diastolic biomechanics in normal infants utilizing MRI tissue tagging

BACKGROUND

Most of what is known about diastolic function in normal infants is derived from flow and pressure measurements. Little is known about regional diastolic strain and wall motion.

METHODS AND RESULTS

Magnetic resonance tissue tagging was performed in 11 normal infants to determine regional diastolic strain and wall motion. Tracking diastolic motion of the intersection points and finite strain analysis yielded regional rotation, radial displacement, and E(1) and E(2) strains at 3 short-axis levels (significance was defined as P<0.05). E(2) "circumferential lengthening" strains were significantly greater at the lateral wall, regardless of short-axis level, whereas E(1) "radial thinning" strains were similar in all wall regions at all short-axis levels. In general, no differences were noted in strain dispersion within a wall region or in endocardial/epicardial strain at all short-axis levels. At all short-axis levels, septal radial motion was significantly less than in other wall regions. No significant differences in radial wall motion between short-axis levels were noted. Rotation was significantly greater at the apical short-axis level in all wall regions than in other short-axis levels, and it was clockwise. At the atrioventricular valve, septal and anterior walls rotated slightly clockwise, whereas the lateral and inferior walls rotated counterclockwise.

CONCLUSIONS

Diastolic biomechanics in infants are not homogeneous. The lateral walls are affected most by strain, and the septal walls undergo the least radial wall motion. Apical walls undergo the most rotation. These normal data may help in the understanding of diastolic dysfunction in infants with congenital heart disease.

Assessment of cardiac function by magnetic resonance imaging

Magnetic resonance imaging (MRI) is a unique and insightful tool for the assessment of physiology and function in congenital heart disease, in both the preoperative and postoperative state. MRI can accurately measure the volume and mass of unusual ventricular shapes, perform myocardial tissue and blood tagging, and can measure velocity and flow using phase-encoded velocity mapping. This has added new dimensions to research in pediatric cardiology. Newer techniques such as oxygen-sensitive MRI and echo-planar MRI promise further advances in the field. This article describes contemporary MRI studies of the physiology of complex congenital heart disease.

Regional wall motion and strain of transplanted hearts in pediatric patients using magnetic resonance tagging

Abnormal ventricular systolic torsion is present during histological rejection in adult cardiac transplant patients. Because biomechanical properties of transplanted hearts in the baseline state have not been studied in children, pediatric patients were evaluated to quantify ventricular wall motion and strain. Eight transplant studies and eight normal controls were evaluated. Magnetic resonance tagging was performed to determine radial shortening, twist, and strain in four ventricular anatomic areas at two short-axis levels. Controls had counterclockwise twist. Six transplant studies had clockwise twist, six had akinetic regions, and all had regions of no twist. One demonstrated paradoxical motion of the septum. A comparison between transplant patients and controls revealed strain to be similar in all regions except one (superior wall at the atrioventricular valve level) and strain distribution to be different only in two of eight regions. Pediatric transplant patients demonstrate regional wall motion abnormalities in the absence of rejection. Compared with normal controls, the transplanted left ventricle maintains normal strain in the presence of abnormal twist. This may be a compensatory mechanism and have clinical implications.

Caval contribution to flow in the branch pulmonary arteries of Fontan patients with a novel application of magnetic resonance presaturation pulse

BACKGROUND

A complete understanding of fluid mechanics in Fontan physiology includes knowledge of the caval contributions to right (RPA) and left (LPA) pulmonary arterial blood flow, total systemic venous return, and relative blood flow to each lung.

METHODS AND RESULTS

Ten Fontan patients underwent cine MRI. Three cine scans of the pulmonary arteries were performed: (1) no presaturation pulse, (2) a presaturation pulse labeling inferior vena cava (IVC) blood (signal void), and (3) a presaturation pulse labeling superior vena cava (SVC) blood. The relative signal decrease is proportional to the amount of blood originating from the labeled vena cava. This method was validated in a phantom. Whereas 60+/-6% of SVC blood flowed into the RPA, 67+/-12% of IVC blood flowed toward the LPA. Of the blood in the LPA and RPA, 48+/-14% and 31+/-17%, respectively, came from the IVC. IVC blood contributed 40+/-16% to total systemic venous return. The distributions of blood to each lung were nearly equal (RPA/LPA blood=0.94+/-11).

CONCLUSIONS

In Fontan patients with total cavopulmonary connection, SVC blood is directed toward the RPA and IVC blood is directed toward the LPA. Although the right lung volume is larger than the left, an equal amount of blood flow went to both lungs. LPA blood is composed of equal amounts of IVC and SVC blood because IVC contribution to total systemic venous return is smaller than that of the SVC. This technique and these findings can help to evaluate design changes of the systemic venous pathway to improve Fontan hemodynamics.

Cefazolin in chronic hemodialysis patients: a safe, effective alternative to vancomycin

Vancomycin use is common in hemodialysis patients, due in part to the ease of dosing, but can lead to the development of resistant organisms, including vancomycin-resistant enterococcus. Alternate antibiotics may be equally effective and allow similar dosing in the chronic hemodialysis population. A retrospective review of culture results from a 217-patient, non-hospital-based outpatient hemodialysis center was performed over a 7-month period. Wound and blood culture sensitivity to cefazolin, vancomycin, cefazolin plus gentamicin, and vancomycin plus gentamicin was analyzed. Cefazolin was equivalent to vancomycin for empiric treatment of clinically significant infections in a population with a low rate of methicillin-resistant Staphylococcus aureus infection. Cefazolin plus gentamicin was superior to vancomycin alone. The vancomycin plus gentamicin combination did provide minimally broader coverage than the cefazolin plus gentamicin combination. A prospective pharmacokinetic analysis of postdialysis cefazolin dosing was performed in anuric chronic hemodialysis patients dialyzed with polysulfone dialyzers. Peak, predialysis, and postdialysis cefazolin levels were obtained. Nondialysis clearance of cefazolin was sufficiently low (k(e), 0.027; t(1/2), 26.4 hours) and dialysis clearance sufficiently high (k(e), 0.254; t(1/2), 3.19 hours) to provide for safe and effective peak and trough cefazolin levels with postdialysis dosing in anuric hemodialysis patients. In conclusion, cefazolin alone or with gentamicin in an appropriate empiric antibiotic choice in chronic hemodialysis patients dialyzed in a nonhospital setting with low methicillin-resistant S. aureus infection rates. For infections with documented sensitivity to cefazolin, a 1 g intravenous dose postdialysis (750 mg in patients weighing <50 kg) is safe and effective.

Mechanics of the single left ventricle: a study in ventricular-ventricular interaction II

BACKGROUND

Left ventricular (LV) effects on right ventricular (RV) function are well known. Less is understood about the effect of the RV on systemic LV mechanics. To determine this interaction, we compared systemic LVs with and without an RV mechanically coupled to them.

METHODS AND RESULTS

MR myocardial tagging was used to examine 18 subjects with systemic LVs: 10 with functional single LVs (SLV) and 8 normal subjects (NL). Tracking the systolic motion of the intersecting stripes were used to determine regional twist and radial motion. Finite strain analysis was applied to derive principal strains at the atrioventricular valve (AVV) and apical short-axis levels and in 4 anatomic wall regions. Similar E1 (circumferential shortening) strain and heterogeneity of strain were noted between SLV and NL except in the septal wall. At the septal wall, NL displayed greater absolute strain (AVV=-0.16+/-0.02, apex=-0.17+/-0.02) and less heterogeneity of strain than SLV (AVV= -0.12+/-0.02, apex=-0.13+/-0.02). Similar E2 (wall thickening) strain and heterogeneity of strain were also noted between SLV and NL except again at the septal wall. At the septal wall, SLV displayed greater absolute E2 strain (AVV=0.17+/-0.08, apex=0.19+/-0.09) and less heterogeneity of strain than NL (AVV=0.07+/-0.07, apex=0.05+/-0.05). SLV twisted significantly less counterclockwise than NL in 6 of 8 wall regions and actually twisted clockwise at the AVV lateral wall. Although there was no significant difference between groups in radial wall motion, the septal and inferior walls of SLV demonstrated significantly less radial motion compared with other SLV walls.

CONCLUSIONS

A major influence of the RV on systemic LV strain and radial motion occurs in the septal wall, whereas absence of the RV causes marked differences in LV twist. These findings may yield clues to the long-term functioning of the SLV and be useful in determining strategies for RV augmentation of LV function.

Cardiac MR imaging in congenital heart disease

Magnetic resonance imaging is a unique and insightful tool for the assessment of structure and function in congenital heart disease. For anatomic assessment, the large field of view, lack of limitation by patient size, and ability to create three-dimensional surface displays from routine imaging acquisitions offer several advantages over other modalities. The ability of magnetic resonance imaging to assess the volume and mass of bizarre ventricular shapes accurately and myocardial tissue and blood tagging as well as phase encoded velocity mapping has enhanced research in pediatric cardiology. Newer techniques, such as oxygen-sensitive magnetic resonance imaging and echo-planar magnetic resonance imaging, promise even further advances in research and in clinical applications.