Biomedical Engineering Reference
In-Depth Information
1
Introduction
There is high demand for patient-specific cardiovascular therapeutics, especially in
pediatric cardiology which is confronted with complex and rather unique congenital
diseases. The incidence of congenital heart disease (CHD) is about 75/1, 000 live
births, out of which dysfunctions of the aortic valve (AV) and the aorta is a major
subgroup that requires expert cardiologic care [
1
]. Aortic diseases are rarely
isolated disorders but rather occur in presentments of other birth defects. For
instance 50
%
of patients with aortic coarctation have a bicuspid AV, which is
also common in nongenetic aortic aneurysms. Marfan's patients, in addition to
aortic aneurysms, typically have both functionally abnormal aortic and mitral
valves as a consequence of their fibrillin gene defect. Without appropriate clinical
management the wall of the aorta can dissect or even rupture, which leaves little
hope for survival and usually results in sudden death.
In case of aortic aneurysm, the clinical state of the art is based on prompt
diagnosis of risk factors and subsequent onset of therapy as soon as the diameter
of the ascending aorta (AAo) has reached a predefined value [
2
]. However, aortic
diameter is an imperfect predictor of aortic dissection or rupture and the current
criterion of a diameter
50 mm misses 40
%
of dissections. Therefore, even today,
the burden of premature morbidity and mortality is profound. In contrast to aortic
aneurysm, coarctation of the aorta is a common discrete or sometimes tubular
congenital narrowing within the lumen of the aorta. Percutaneous balloon angio-
plasty and stent implantation have displaced surgery as primary therapy for native
and recurrent coarctation [
3
]. The state-of-the-art is balloon or stent enlargement of
the aorta no larger than the surrounding nondiseased aorta. However, this approach
is commonly associated with the development of early and late aortic dissection and
aneurysm formation or suboptimal clinical improvement [
4
]. Presently no guidance
exists to personalize percutaneous therapy to achieve an optimal therapeutic out-
come with the least initial and long term risk for the patient.
The influence of blood hemodynamics on disease progression and therapeutical
outcome has become increasingly acknowledged [
5
]. Over the past two decades
methods for blood flow measurements using 2D time-resolved (Cine) phase con-
trast (PC) MRI have continuously evolved [
6
]. Newest MRI systems enable today
3D Cine PC-MRI with three-directional flow encoding that can capture blood
velocities within a 3D volume of interest [
7
]. Using this technique [
8
], significant
variations in flow patterns where observed even for mild aortic pathologies. Never-
theless, 3D flow measurements are limited in resolution and cumbersome and time
consuming to acquire even in research settings. In addition, in vivo flow analysis
does not enable for the simulation and prediction of hemodynamic performance
related to specific cardiac procedures.
The potential of advanced disease analysis and therapy planning systems based
of computational fluid dynamics (CFD) has been illustrated in [
9
]. The optimal
treatment option for a Fontan patient with severe left pulmonary arteriovenous
malformation was determined by simulating multiple surgical scenarios with the
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