University of Groningen
Computed tomography for the evaluation of the aortic valve and coronary arteries
Piers, Lieuw Hendrik
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to
cite from it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date:
2009
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Piers, L. H. (2009). Computed tomography for the evaluation of the aortic valve and coronary arteries s.n.
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the
author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the
number of authors shown on this cover page is limited to 10 maximum.
Download date: 18-06-2017
Introduction
Millions of people world wide are at risk of developing cardiovascular disease. In
the Netherlands, more than 350 per 100,000 people die annually from cardiovascular
disease.1, 2 Cardiovascular disease includes atherosclerosis of the coronary arteries
and sclerosis of cardiac valves. Cardiovascular disease is especially common in the
elderly population: about 25 percent of adults over 65 years of age have aortic valve
sclerosis,3, 4 and about 17 percent of patients over 60 years of age suffer from coronary
artery disease.5 The early stages of these diseases are characterized by inflammatory
cell infiltration and lipid deposition.4, 6, 7 Ensuing inflammation causes calcification
of the aortic valve leaflet or coronary artery wall. Even though both disease share
pathophysiological pathways and have common risk factors, a discrepancy in
coexisting prevalence exists between aortic valve sclerosis and coronary artery
disease indicating different disorders.8 As these unique disorders are associated with
significant morbidity and mortality, early detection and evaluation of its progression is
necessary.
Aortic valve sclerosis
The most common forms of aortic valve sclerosis are degenerative changes in a
congenitally bicuspid aortic valve and sclerosis of a normal trileaflet aortic valve. These
degenerative changes can lead to a decrease of the aortic valve orifice area. The
presence of aortic sclerosis, with or without demonstrable haemodynamic obstruction,
is associated with an increase of 50 percent in the risk of cardiovascular death.9 Aortic
valve replacement is the only possible therapy.
In clinical routine, transthoracic echocardiography is the gold standard for the
evaluation of aortic valve sclerosis. Using transthoracic echocardiography, the
degree of aortic valve sclerosis can be expressed in several ways. One way is to
assess the pressure deficit, the pressure gradient, across the valve, which has shown
to correlate well with invasive measurement.10, 11 Using the continuity equation it is
possible to calculate the functional aortic valve area.10, 11 However, the reliability of
transthoracic echocardiography measurements depends heavily on image quality,
which is influenced by aortic valve calcification and adequacy of the ultrasound
window, and on physiological characteristics like left ventricular function.12-14 As a
consequence of these limitations, invasive confirmation of the severity of aortic valve
sclerosis is often still necessary preceding valve replacement surgery. For this purpose,
cardiac catheterization evaluating aortic valve area by applying the Gorlin formula
is available.15 However, the reliability of this method also depends on the patient’s
cardiac function and presence of aortic regurgitation.16 Consequently, transthoracic
echocardiography and cardiac catheterization are influenced by physiological
characteristics of the patients. In addition, catheterization is an invasive procedure
that may be associated with serious complications.17
Coronary artery disease
Coronary artery disease is the main cause of death in Western countries. Coronary
artery plaques progress from fatty streaks without luminal narrowing to lipid, fibrous
or calcified plaques causing severe stenosis of the coronary artery and eventual
myocardial ischemia.6 In clinical routine there are several tests available for the
evaluation of coronary artery disease, i.e. exercise stress testing, myocardial perfusion
11
Introduction
single photon emission computed tomography, stress echocardiography and
magnetic resonance imaging. These techniques evaluate the presence of myocardial
ischemia by detecting hypoperfusion or systolic ventricular dysfunction.18 Conventional
invasive coronary angiography is the gold standard for the evaluation of coronary
artery disease.19 This technique allows visualization of coronary anatomy and stenosis,
while direct intervention is possible. However, there is a small associated risk for serious
complications.20
Computed tomography
Computed tomography allows non-invasive visualization of cardiac structures,
like coronary arteries and aortic valves.21 Cardiac calcifications, as an expression
of cardiovascular disease, can be quantified without the use of contrast agent,22
while contrast-enhanced scans can depict the cardiac anatomy.21, 23, 24 Therefore
computed tomography holds the possibility of evaluating coronary artery and aortic
valve calcification, next to visualizing the anatomy of the aortic valve and coronary
arteries.
Aim of this thesis
The aim of this thesis was to evaluate the usefulness of computed tomography for
the assessment of aortic valve and coronary artery sclerosis in daily clinical routine.
In the 1st chapter electron beam computed tomography and transthoracic
echocardiography were compared for determining aortic valve area. Using contrastenhanced electron beam computed tomography it is possible to identify the aortic
valve orifice area. Without the use of a contrast agent, the degree of aortic valve
calcification can be measured, next to the degree of coronary artery calcification.
We studied whether aortic valve area or calcification measured with electron beam
computed tomography was useful for the evaluation of aortic valve sclerosis. Therefore
we performed contrast-enhanced electron beam tomography and transthoracic
echocardiography in a cohort of patients under evaluation for aortic valve stenosis
(TOAST study: TOmographic assessment of Aortic valve STenosis).
In the 2nd chapter electron beam computed tomography was used to measure
aortic valve and coronary artery calcification in patients with chronic kidney disease.
Decreased renal function is known to increase cardiovascular risk. This chapter is
based on a prospective study in which patients with various degree of chronic kidney
disease were included (PARIS: Progression of Aortic valve sclerosis in Renal Insufficiency
Study). They underwent electron beam tomography for the evaluation of their aortic
valve and coronary arteries. In this study we tried to define subgroups of patients with
chronic kidney disease being at increased risk of cardiovascular disease.
The 3rd chapter discusses the role of coronary artery calcification within the diagnostic
process of patients with cardiac complaints. Many patients are referred to our tertiary
medical centre every year for the evaluation of cardiac complaints. A large cohort of
these patients underwent electron beam computed tomography for the measurement
12
Introduction
of coronary artery calcification, as well as tests to assess myocardial ischemia. Based
on the results of these tests a decision was made whether a coronary angiography had
to be performed. The presence of coronary artery calcification holds an increased risk
of significant coronary artery disease, so the results of an electron beam computed
tomography scan possibly influences the clinical decision process. In this cohort we
retrospectively observed the significance of the role of coronary artery calcification
score, next to conventional tests, within the diagnostic process.
The 4th chapter is based on a prospective study (CARDUCCI: Conventional coronary
Angiography veRsus DUal source Computed tomography for Coronary Imaging) in
which patients scheduled for a conventional coronary angiography also underwent
computed tomography coronary angiography for the evaluation of coronary artery
disease. Many studies have determined the accuracy of computed tomography
coronary angiography for detecting significant coronary artery disease. However, as
we sought to further identify the role of computed tomography coronary angiography
within the daily clinical process, we investigated the accuracy of computed
tomography coronary angiography based therapeutic decision-making, next to the
detection of significant coronary artery disease.
13
14