(Circulation. 1998;98:2873-2882.)
© 1998 American Heart Association, Inc.
Clinical Investigation and Reports* |
In Vivo Evaluation of Fontan Pathway Flow Dynamics by Multidimensional Phase-Velocity Magnetic Resonance Imaging
From the Departments of Cardiology (E.B., M.J.L., T.G.) and Radiology (T.C.), Children's Hospital; the Department of Radiology, Brigham and Women's Hospital (S.E.M.); and the Departments of Pediatrics and Radiology, Harvard Medical School, Boston, Mass.
Correspondence to Tal Geva, MD, Department of Cardiology, Children's Hospital, 300 Longwood Avenue, Boston, MA 02115. E-mail geva_t{at}a1.tch.harvard.edu
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Abstract |
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Background—Hemodynamic efficiency of Fontan circulation is believed to be a major determinant of outcome. Prior research on flow dynamics in different modifications of Fontan circulation used in vitro models and computer-based simulation. This study was designed to compare in vivo flow dynamics in the systemic venous pathway between patients with atriopulmonary anastomosis (APA) and those with total cavopulmonary connection (TCPC).
Methods and Results—Multidimensional phase-velocity magnetic resonance imaging (PV-MRI) studies were performed on 10 patients who had undergone a modified Fontan operation (5 with TCPC and 5 with APA) and were free of symptoms. The groups were comparable in terms of age and body surface area. The interval since surgery was longer for APA than for TCPC subjects. In each subject, the phase-velocity data sets were used to generate dynamic velocity-vector maps and to calculate quantitative flow indices describing the 3-dimensional blood-flow patterns throughout the cardiac cycle at the widest diameter of the Fontan pathway. Mean flow rate was comparable between groups. Velocity-vector maps showed areas of flow reversal, flow stagnation, and circular flow within APA but not TCPC pathways. Analysis of quantitative flow indices showed that compared with the APA group, flow velocities in the TCPC patients were significantly higher (mean velocity, 14±6 cm/s versus 5±3 cm/s; P=0.02), less variable (coefficient of variation, 19±2% versus 37±3.5%; P<0.0001), and more unidirectional (degree of unidirectionality, 89±7% versus 71±12%; P=0.03). APA pathways were significantly more dilated than were TCPC pathways (P<0.01) and showed a trend toward larger diameter with increased interval since surgery (R2=0.6, P=0.09). Fontan pathway dilatation correlated with flow velocity variability (R2=0.57, P=0.01) and inversely with flow unidirectionality (R2=0.75, P=0.001).
Conclusions—Blood flow patterns are more organized and uniform in TCPC than in APA pathways and are significantly influenced by pathway diameter. We speculate that TCPC may result in a more hemodynamically efficient circulation than APA because of differences in pathway dimension and uniformity.
Key Words: magnetic resonance imaging • blood flow • hemodynamics • Fontan procedure • heart defects, congenital
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Introduction |
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Since its inception in the early 1970s, the Fontan operation and its modifications have been used for a wide spectrum of congenital heart disorders in which a biventricular repair cannot be achieved.1 2 It has been speculated during the past decade that the hydrodynamic characteristics and energy efficiency of the Fontan circulation influence the medium- and long-term outcomes of these patients.3 Several reports indicated that progressive right atrial dilatation may lead to flow stagnation, thrombus formation, supraventricular arrhythmias, exercise intolerance, and low cardiac output.4 5 de Leval et al3 recognized the importance of minimizing energy losses across the Fontan pathway. They hypothesized that in a Fontan circuit with an atriopulmonary anastomosis (APA), disorganized, and thus energy-inefficient, venous flow patterns occur because of the variations in pathway diameter inherent to that surgical technique. Thus, Puga et al6 and de Leval et al3 advocated the creation of a total cavopulmonary connection (TCPC) by means of a prosthetic intra-atrial baffle of uniform diameter, postulating that this would result in a more streamlined, and thus energy-efficient, blood-flow pattern. To date, however, nonrandomized clinical studies comparing outcome for APA versus TCPC have yielded equivocal results.4 5 Recent studies performed on in vitro models7 and computer-based simulations8 demonstrated that energy loss is greater and flow is more disturbed in Fontan circulation with APA compared with TCPC. These in vitro studies, however, may not accurately reflect in vivo conditions, and any differences between APA and TCPC pathways in this regard still remain unknown.
Phase-velocity magnetic resonance imaging (PV-MRI) has recently been shown to be capable of noninvasively depicting flow direction and measuring flow velocity in 3 dimensions throughout the cardiac cycle.9 10 11 12 13 It has also been shown to allow for accurate site-specific quantification of flow rate.9 10 14 15 16 The present study, therefore, was designed to analyze and compare the in vivo 3-dimensional blood-flow patterns in APA and TCPC Fontan pathways by the use of PV-MRI.
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Methods |
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Patients
Patients who had previously undergone a Fontan-type operation were recruited from the outpatient clinic of the Boston Adult Congenital Heart program at Children's Hospital to undergo a voluntary MRI scan. Patients were excluded from the study if they had any contraindication to the performance of an MRI. The study protocol was approved by the institutional review boards of Children's Hospital and Brigham and Women's Hospital in Boston. Informed consent was obtained from each patient.
MRI Protocol
MRI was performed on a standard SIGNA 1.5-T whole-body unit with
software release 5.4 (General Electric). A wrap-around
radio-frequency coil was used in all patients. Prospectively ECG-gated
T1-weighted spin-echo images in coronal, transverse, sagittal, and,
when necessary, oblique planes were obtained so as to image the entire
Fontan pathway and to locate appropriate planes for subsequent velocity
mapping (echo time=20 ms, repetition time=R-R interval,
slice thickness=5 to 8 mm, image matrix size=256x128, field of
view=24 to 40 cm, number of excitations=2 to 4). Retrospectively
ECG-gated phase-velocity images, encoded for flow in the x-,
y-, and z-axis directions were then acquired in
coronal, sagittal, or oblique planes, and were intended
to include the caval, atrial, and pulmonary components
of the Fontan pathway in the imaging planes (echo time=13 ms,
repetition time=24 ms, image matrix=256x128, 20o
flip angle, 2 excitations per acquisition, 24 images per cardiac
cycle). Respiratory compensation was used to minimize motion artifacts.
The scan time for a single location was 
2 to 4 minutes, depending on
the patient's heart rate. No sedation or contrast material was used in
this study.
MRI Data Processing
Flow quantification and analysis were performed off line
on a SUN workstation with customized software (XPhase) developed by 1
of the authors (Dr Maier). The accuracy of the system for
measuring flow rate was validated by our group.14
This dedicated MRI flow analysis software automatically
correlates the x-, y-, and z-axis
velocity-vector components of each pixel of a 3-dimensional MRI
phase-velocity data set. The instantaneous x- and
y-axis velocity vectors are resolved into a single
"in-plane" velocity vector, which is depicted as a line vector on a
velocity-vector map. The origin of the line vector is indicated by a
dot located at the center of the relevant pixel. The length of the line
vector is proportional to the magnitude of the instantaneous in-plane
blood-flow velocity at that pixel, and the direction of the line vector
indicates the instantaneous direction of in-plane flow (Figure 1A
through 1D). The z-axis
(through plane) velocity component for each pixel is depicted as a
background color scale (Figure 1D). Gray represents zero
velocity, progressively darker red indicates progressively higher
instantaneous velocities out of the plane, and progressively darker
blue indicates progressively higher instantaneous velocities into the
plane. By superimposing the x-y flow-vector map
on a z-axis color scale, a depiction of instantaneous
3-dimensional flow is achieved. For each cardiac cycle, 24 sequential
instantaneous flow-vector maps are generated from each phase-velocity
data set. Both instantaneous and dynamic flow patterns can be reviewed
by either displaying each frame individually or by viewing the 24
frames as a continuous cine loop. This results in the depiction of
blood flow in terms of 5 dimensions: x, y, and
z spatial axes; velocity; and time.
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Because the amount of flow data generated by each vector map was
substantial, the mean velocity of each 2x2 or 3x3 group of pixels was
represented by a single line vector. This facilitated
graphic representation and data interpretation. In addition, we
found that when we analyzed flow patterns in which the
z-axis component was relatively static, overall flow
analysis was facilitated by the use of a background color scale
depicting the speed of blood, rather than the z-axis
velocity component (Figure 1C
). Speed, as opposed to velocity, is a
scalar quantity possessing magnitude but not direction. It is derived
from the x, y, and z velocity-vector
components by the following formula:
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Qualitative Analysis of Flow Patterns
The qualitative nature of 3-dimensional blood flow through the
Fontan pathways was assessed by inspecting the flow-vector maps. The 24
instantaneous maps comprising 1 cardiac cycle were inspected frame by
frame to identify the following flow patterns: (1) laminar flow
(characterized by parallel orientation of the velocity vectors
throughout the vessel or pathway), (2) disorganized flow (characterized
by velocity vectors that are simultaneously oriented in
different spatial directions), (3) circular flow (characterized by a
circular flow pattern within the pathway or vessel as seen by dynamic
vector mapping), and (4) stagnant flow (characterized by velocity
vectors 
5 cm/s). By viewing the 24 frames as a cine loop, the dynamic
nature of the blood-flow patterns could be appreciated.
Quantitative Analysis of Flow Patterns
To facilitate meaningful statistical analysis of
differences in flow patterns between TCPC and APA pathways, we measured
flow through a standardized region of interest (ROI) in the center of
each Fontan pathway. The ROI was defined at the widest mid–right
atrial diameter, encompassing the entire width of the pathway between 2
parallel horizontal lines separated by a vertical (or
superior-inferior) distance of 10 cm (Figure 1B). Because
the z-axis dimension (ie, the imaging slice thickness) of
the ROI was standardized at 6 mm in each case and the
y-axis dimension was standardized at 10 cm, the ROI
represented a 3-dimensional volume in the mid-Fontan
pathway whose volume varied from patient to patient depending on the
degree of pathway dilation (ie, variation in the x-axis
dimension of the ROI). In TCPC patients with baffle fenestration, the
ROI included the systemic venous aspect of the fenestration. To
determine interobserver variability in determining the ROI, it was
traced by 2 investigators who were unaware of each other's
measurements. Simple linear regression analysis was used to
calculate the correlation of measurements by the 2 observers. The
absolute difference between observers' measurements was divided by the
mean value of measurements and expressed as a percentage. Interobserver
variability was expressed as the mean±SD of these percentages.
The mean, maximum, and minimum flow velocities through the entire ROI of each Fontan pathway during the course of the cardiac cycle were computed from the relevant x-, y-, and z-axis phase-velocity data sets. Instantaneous flow rates were calculated for each of the 24 phase-velocity maps by multiplying the mean flow velocity by the cross-sectional area of the pathway. Flow volume was then computed by integrating the flow rates throughout the cardiac cycle. Flow within the ROI was then analyzed in terms of 3 parameters that quantify the uniformity of flow velocity and direction.
- Temporal coefficient of variation (CV) of flow speed: To quantitatively express the degree of variation in flow speed throughout the cardiac cycle, the mean instantaneous flow speed through the ROI for each of the 24 flow maps (comprising 1 cardiac cycle) was determined. Subsequently, the mean and SD for the 24 resulting data points were computed and the CV of flow speed was derived and expressed as a percentage by use of the following formula:
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- Percentage unidirectionality of flow (PUF): To evaluate the degree to which blood flow was unidirectional, the 3-dimensional velocity vectors within the ROI for 1 cardiac cycle were combined into a single antegrade velocity vector (representing all antegrade velocity vectors) and a single retrograde velocity vector (representing all retrograde velocity vectors). The relative magnitudes of the antegrade and retrograde velocity vectors were expressed as the PUF, which was defined as follows:
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3. Vector angle (VA): In addition to the relative magnitudes of
the antegrade and retrograde flow vectors, the angle between the 2
vectors also quantifies an element of flow reversal. For an
antegrade-retrograde vector pair with a given PUF, a wider angle
between the 2 vectors implies a greater degree of flow reversal during
the cardiac cycle than does a narrower angle. The angle between the
antegrade (a) and retrograde (r) flow vectors, defining the VA, was
therefore calculated for each ROI by use of the following formula:
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Statistical Analysis
Data are reported as mean±SD for each group of measurements. A
2-tailed unpaired Student t test was used to compare
continuous variables between APA and TCPC groups. Potential
associations between continuous variables were examined by linear
regression analysis. Data analysis was performed with a
commercially available statistical package (StatView 4.1, Abacus
Concepts Inc). For all tests, P0.05 was considered
statistically significant.
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Results |
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Patients
Ten adult subjects, 5 with APA and 5 with TCPC, volunteered to participate in the study. Their diagnoses and demographic data are summarized in Table 1
. All subjects had
successfully undergone a Fontan procedure and were being monitored on
an outpatient basis. One of the APAs was accomplished via an
extracardiac conduit from the anterior free wall of the right atrium to
the left pulmonary artery (patient 8), and the other 4 via
anastomosis of the right atrial appendage to the main pulmonary
artery. In 4 patients, TCPC was performed by the creation of an
intra-atrial baffle connecting the inferior vena cava to
the cardiac end of the superior vena cava and an end-to-side
anastomosis between the superior vena cava and the right
pulmonary artery.5 In 1 TCPC patient, an
extracardiac conduit was placed between the inferior vena
cava and the pulmonary arteries (patient 2). In 4 of the TCPC
patients, a fenestration had been placed in the conduit/baffle. One
subject (patient 7) had recently undergone radiofrequency catheter
ablation of an intra-atrial reentrant tachycardia and
another subject (patient 8) was receiving diuretic therapy. No
patient exhibited signs or symptoms that suggested a failure of the
Fontan circuit that might indicate the need for reoperation. There were
no significant differences between groups with regard to age, gender,
weight, or body surface area. The interval between the date of Fontan
surgery and the MRI study was significantly longer for the APA group
(11.2±2.2 years) than for the TCPC group (1.8±1.2 years,
P<0.01).
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Anatomic Findings
The anatomy of the Fontan pathways and
pulmonary arteries was clearly imaged by spin-echo MRI in all
subjects and were shown to be unobstructed. Whereas TCPC pathways were
characterized by a relatively uniform diameter throughout their length
(Figure 2), the diameter of APA pathways
varied substantially from the cavae to the pulmonary arteries
and was maximal at the midright atrium (Figure 3 and 4).
Dilatation of systemic venous pathways in APA patients was not limited
to the Fontan pathway but was manifest in the superior and
inferior venae cavae of those patients with the most
dilated right atria (patients 8 and 10). The average midright atrial
diameter for APA pathways was 3 times wider than for TCPC pathways
(Table 2). Furthermore, in
patients with APA pathways, a trend between larger pathway diameter and
longer interval since surgery could be discerned but did not reach
statistical significance (R2=0.61,
P=0.09). No such trend was evident in the TCPC group.
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Analysis of Flow Patterns
Inspection of the cine-loop flow vector maps revealed that flow
through each of the 5 TCPC pathways was characteristically
unidirectional and, at any instant in the cardiac cycle, of relatively
uniform velocity throughout the pathway (Figure 2). During the course
of the cardiac cycle, flow was biphasically pulsatile, but with a
relatively small difference between the maximal and minimal velocities.
There were no areas of flow stagnation. In patients 1 to 3 and 5, in
whom a baffle fenestration was present, there was streaming toward
the fenestration without disturbance of the overall laminar
flow pattern. In 4 TCPC patients, flow through the
cavopulmonary anastomosis itself was laminar and of a similar
velocity to flow through the midbaffle. In these pathways, the
cardiac and cephalic ends of the cavopulmonary anastomosis were
offset from each other. Accordingly, blood from the superior vena cava
streamed preferentially to the right pulmonary artery and blood
from the inferior vena cava to the left pulmonary
artery, with the 2 oppositely directed streams producing an area of
circular flow between them. This was the only circular flow phenomenon
noted within TCPC pathways. In the patient with an extracardiac TCPC
conduit, a small area of turbulence occurred immediately after the
proximal anastomosis where the inferior vena cava and the
conduit had a 135o angle between them. There were
no other occurrences of turbulent flow within the Fontan pathways in
either subgroup.
Flow patterns in the APA group were far more varied than
those found in the TCPC patients. The APA patient with the narrowest
right atrial diameter (patient 9) demonstrated flow through the right
atrium that was consistently unidirectional throughout the
cardiac cycle. Blood velocity was maximal in the center of the pathway,
becoming progressively slower toward the periphery and almost stagnant
adjacent to the anterior wall of the right atrium (Figure 3). In
contrast to the TCPC pathways, flow accelerated markedly through the
APA. The flow velocities in this patient remained relatively constant
throughout the cardiac cycle and there were no areas of disorganized or
circular flow. In contrast to the flow pattern observed in the
narrowest APA pathway, the patient with the widest right atrial
diameter (patient 8) exhibited a complex and disorganized pattern of
very low–velocity flow (Figure 4). Flow within the markedly dilated
right atrium was characterized by large, slow, circular flow swirls
that gradually changed their location and velocity during the course of
the cardiac cycle. Areas of flow stagnation occurred intermittently at
multiple locations within the chamber. Flow at the points of Fontan
pathway inflow (the superior and inferior venae cavae) and
outflow (the APA) was characterized by periods of flow reversal
occurring in mid- to late ventricular systole. The
remaining 3 APA patients, each with intermediate degrees of right
atrial dilation, exhibited flow patterns intermediate to the 2
described above. An area of transient circular flow within the body of
the right atrium occurred in all 3 patients. Transient flow reversal
was noted within the inferior vena cava in 1 subject,
within the right pulmonary artery in a second, and within the
body of the right atrium in the third patient. All 3 exhibited areas of
flow stagnation toward the periphery of the right atrium, and 1 subject
demonstrated stagnation of flow within the body of the right
atrium.
Quantitative Flow Analysis
The qualitative observations described above were corroborated by
the flow measurements performed within the ROI (Table 2).
Although the amount of blood flow through the 2 pathway types was
similar (mean flow, 28±7 versus 27±7 mL/s), there were marked
differences between APA and TCPC pathways with regard to the nature of
the flow. Compared with APA patients, flow velocities in TCPC pathways
were 2 to 3 times faster, 49% more uniform (CV, 19±2 versus 37±3.5;
P<0.0001), consistently more antegrade (PUF,
89±7% versus 71±12%; P=0.03), and with a smaller angle
between antegrade and retrograde velocity vectors (112±6° versus
135±20°, P=0.058). The diameter of the Fontan pathway
correlated negatively with mean (R2=0.58,
P=0.01), maximal (R2=0.5,
P=0.02), and minimal (R2=0.6,
P<0.01) flow velocities, and with PUF
(R2=0.75, P=0.001). A positive
linear correlation was found between pathway diameter , CV
(R2=0.57, P=0.01), and vector
angle (R2=0.47, P<0.03).
Interobserver Variability
The mean interobserver variability for ROI measurements was
2.3±7.2% (0.8±2 mm). The correlation coefficient by simple
linear regression analysis for measurements by the 2 observers
was 0.99 (P<0.0001).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The noninvasive application of multidimensional flow imaging by PV-MRI flow vector mapping allowed for in vivo visualization and quantitative analysis of flow dynamics in Fontan pathways. The results of this study demonstrate marked differences in flow patterns between APA and TCPC pathways. Flow through TCPC pathways was characteristically unidirectional and streamlined (as evidenced by a high PUF and a low VA, biphasic, and of relatively high velocity. In contrast, flow through APA pathways was significantly slower, more disorganized, and varied. Except for the narrowest APA (patient 9), flow patterns in dilated APA pathways were characterized by multiple circular, reversed, or stagnant flow systems within the right atrium. Stagnation of blood near the periphery of the right atrium was observed in all APA patients, even in the patient without significant chamber dilatation who exhibited a relatively organized flow pattern at the center of the pathway. The study found evidence of increased right atrial diameter as a function of the interval since surgery in the APA group. It also found strong correlations between indices of impaired flow profiles and pathway diameter.
The results of this study provide in vivo corroboration of the mounting evidence from in vitro and computer simulation studies indicating that flow dynamics in APA is inefficient. de Leval and his colleagues first studied hemodynamic and energy factors in an in vitro model of APA-type Fontan circulation.3 They found that the hydrodynamic design of the APA was relatively poor and that the presence of a large passive chamber between the systemic veins and the pulmonary circulation was a major cause of flow inefficiency. On the basis of the results of those experiments, they advocated the use of TCPC that was designed to produce a more streamlined flow pattern that should lead to less energy loss. Subsequent in vitro7 17 18 19 20 21 and computational8 18 19 studies confirmed those observations. The effect of progressive right atrial dilatation on energy loss and resistance to flow was recently studied by Lardo and associates20 in an in vitro flow model of explanted sheep hearts with APA-type Fontan pathways. Their experiment showed that progressive right atrial dilatation is associated with increased energy loss and resistance to flow, which were more pronounced at higher flow rates. Other investigators studied various geometries of TCPC, attempting to find the most efficient connection.7 8 18 19 21 22 Although these in vitro and computational experiments provided important information regarding isolated aspects of the Fontan circulation, they have not been validated in vivo.
Energy Considerations
The complex flow patterns observed in dilated APA pathways that
consisted of multiple circular, reversed, or stagnant flow systems
imply the presence of multiple planes of shear between adjacent fluid
flow systems. In the clinical context of Fontan circulation, friction
between these layers and at the interface with the walls of the pathway
may result in a loss of pressure energy. In an attempt to confirm the
hemodynamic advantage of TCPC over APA, several
researchers studied the magnitude of energy loss in simulated APA and
TCPC circuits.8 17 Their results, however,
predict that the losses of pressure energy due to increased friction
would be of very small absolute magnitude (<1 mm Hg for an APA
pathway).8 Our experience, too, has been that in
the absence of a significant anatomical stenosis even markedly
dilated Fontan pathways do not exhibit clinically measurable pressure
gradients across the right atrial chamber and APA at cardiac
catheterization.23 Consideration
of the principles of hydraulic energetics in light of the preceding
observations regarding Fontan pathway dilation, however, would suggest
an alternative explanation for the possible advantage of TCPC over APA.
Because total blood volume exerts a profound effect on myocardial
energetics, the tendency of APA pathways to dilate over time may,
therefore, cause a gradual increase in the myocardial energy
expenditure required to maintain normal cardiac output and blood
pressure. The possible protection against pathway dilatation afforded
by TCPC may thus be of significant long-term benefit in terms of
myocardial energy expenditure.
Clinical Implications
The findings of this study provide a link between fluid
dynamics and several clinical observations. Progressive right atrial
dilatation in APA has been linked to exercise intolerance, thrombus
formation, atrial arrhythmias, and increased systemic venous
pressure and its sequelae.3 5 24 We found that
blood velocities within APA pathways were significantly slower than
those in TCPC. In addition, blood velocity was less constant over time
and space, manifesting as a significantly higher speed CV for the APA
group than for the TCPC group. The dynamic 3-dimensional flow maps
confirmed this finding, revealing multiple areas of transient or even
constant flow stagnation within the most dilated APA pathways,
particularly toward the periphery of the chamber. These flow patterns
likely contribute to the substrate that may lead to thrombus formation
in some of these patients.
Study Limitations
The APA group was monitored for a significantly longer
period after the operation than the TCPC group. This limitation is
somewhat offset by the fact that the 2 groups showed no significant
differences in terms of demographics, body surface area, clinical
well-being, and Fontan flow rate. In addition, it is important to note
that acquisition of PV-MRI data was not gated to the respiratory cycle
and was acquired with patients in the supine position and at rest. Each
data set represents an average of multiple heart beats and
respiratory cycles. The effects of respiration, body position, and
exercise on the observed flow patterns require further study. Although
the results of this study demonstrate an association between pathway
diameter and flow patterns, it does not establish a cause and effect
relationship between these variables. A much larger number of
participants is required for such analysis.
Conclusions
PV-MRI mapping of Fontan pathways in a small group of patients
demonstrates in vivo that TCPC results in venous flow patterns that are
significantly more organized and uniform with higher flow velocities
than those occurring in APA pathways. The flow dynamics observed
in patients with APA connection is thought to be
hemodynamically inefficient and more thrombogenic. The
disadvantageous flow characteristics increase with pathway
dilatation.
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Acknowledgments |
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This study was funded in part by grant No. M01 RR02172 from the General Clinical Research Centers Program of the National Center for Research Resources, National Institutes of Health, Bethesda, Md. We thank Drs Andrew J. Powell and Steven D. Colan for their comments.
Received April 16, 1998; revision received August 20, 1998; accepted August 31, 1998.
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24.
Rosenthal M, Bush A, Deanfield J, Redington A.
Comparison of cardiopulmonary adaptation during exercise in
children after the atriopulmonary and total
cavopulmonary connection Fontan procedures.
Circulation. 1995;91:372–378.To evaluate flow dynamic
in Fontan pathways, phase-velocity magnetic resonance imaging was
performed on 10 patients: 5 with atriopulmonary anastamoses
(APA) and 5 with total cavopulmonary connection (TCPC).
Multidimensional flow-vector maps showed areas of flow reversal, flow
stagnation, and circular flow within APA but not TCPC pathways.
Quantitative parameters showed TCPC pathways to exhibit
significantly higher, less variable, and more unidirectional
blood-flow pattern than APA pathways. These parameters
correlated with the degree of pathway dilation. These data indicate
that TCPC may result in a more hemodynamically
efficient circulation than APA.
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