1 Full Member of the Colégio Brasileiro de Radiologia e
Diagnóstico por Imagem (CBR), MD, Radiologist on the Hospital Santa Luzia,
Brasília, DF, Brazil.
2 MD, PhD, Radiologist on the Hospital Santa Luzia, Brasília,
DF, Brazil.
1 Full Member of the Colégio Brasileiro de Radiologia e
Diagnóstico por Imagem (CBR), MD, Radiologist on the Hospital Santa Luzia,
Brasília, DF, Brazil.
Summary
Summary
INTRODUCTION
Heart problems is the main explanation for loss of life worldwide, coronary artery
illness (CAD) accounting for half of all such deaths(1).
At the very least 25% of sufferers experiencing nonfatal acute myocardial infarction or sudden
loss of life had no earlier signs(2).
The identification of asymptomatic people at higher danger of experiencing
future cardiovascular occasions is prime for the implementation of preventive
methods.
“Total risk scores” are very helpful and must be used because the preliminary methodology of
stratification, though they can predict solely 65-80% of future
cardiovascular occasions (1,2). The Framingham danger rating is one
of probably the most extensively used(2).
The characterization of coronary-artery calcification by computed tomography exhibits
equivalence with the full coronary atherosclerosis load and the danger of
cardiovascular occasions(3).
This evaluate on the coronary artery calcium (CAC) rating addresses the next
matters: acquisition and quantification protocols; stratification of coronary danger
and correlation with different medical scores; use of the CAC rating in asymptomatic
sufferers, together with indications, interpretation, and prognosis; use of the CAC rating
in symptomatic sufferers; and use of the CAC rating in sufferers with diabetes.
ACQUISITION AND QUANTIFICATION PROTOCOLS
The CAC rating was initially studied by electron beam computed tomography, a great half
of the scientific literature then being primarily based on that approach(3). Nevertheless, multidetector computed
tomography subsequently grew to become the modality of alternative for CAC analysis. As a
consequence, electron beam computed tomography is now virtually unavailable.
The dedication of the CAC rating by computed tomography is predicated on axial slices,
with a thickness of three mm, with out overlapping or gaps, restricted to the cardiac
area, acquired prospectively in synchrony with the electrocardiogram at a
predetermined second within the R-R interval, normally within the mid/late
diastole(1), with out the
use of intravenous distinction medium.
The efficient dose of radiation is normally low, sometimes lower than 1.5
mSv(3), which is the
highest efficient dose beneficial to be used in picture acquisition, in keeping with the
Society of Cardiovascular Computed Tomography(1).
Calcification is recognized as areas of hyperattenuation of not less than 1
mm2-with > 130 Hounsfied items (HU) or ≥ 3 adjoining
pixels(4).
The principle programs for the quantification of the CAC rating are the Agatston
methodology(4), dedication of
the quantity of calcium(5), and
dedication of the calcium mass rating(6). The primary two are probably the most extensively used, particularly the
Agatston methodology, which is used as a reference for many inhabitants databases and
publications involving danger stratification and is subsequently the strategy most frequently
utilized in medical follow. The calcium quantity rating and calcium mass rating have
proven higher reproducibility(7).
Agatston methodology – The Agatston methodology makes use of the weighted sum of lesions
with a density above 130 HU, multiplying the realm of calcium by an element associated to
most plaque attenuation: 130-199 HU, issue 1; 200-299 HU, issue 2; 300-399 HU,
issue 3; and ≥ 400 HU, issue 4.
Subsequently, the slice thickness and the interval should comply with the unique protocols in
order to cut back the noise variation and, consequently, the utmost attenuation of
the plaques, permitting the unique printed scores to be reproduced.
Calcium quantity rating – The calcium quantity rating has confirmed to be the
most sturdy and reproducible methodology(8). It’s calculated by multiplying the variety of voxels with
calcification by the quantity of every voxel, together with all voxels with an attenuation
> 130 HU. Nevertheless, this methodology is especially delicate to the partial quantity
(particularly in plaques with excessive attenuation) and topic to variability between
checks, relying on the place of the plaque within the axial slice acquired.
Relative calcium mass rating – The relative calcium mass rating is
calculated by multiplying the imply attenuation of the calcified plaque by the plaque
quantity in every picture, thus lowering the variation brought on by the partial quantity. The
absolute calcium mass rating makes use of a correction issue primarily based on the attenuation of
water(8).
STRATIFICATION OF CORONARY RISK AND RELATIONSHIP OF THE CAC SCORE TO OTHER
CLINICAL SCORES – “calcium count”
The CAC rating performs a related position within the stratification of cardiovascular danger.
A number of research have proven that the CAC rating is considerably related to the
prevalence of main cardiovascular occasions (all-cause mortality, cardiac mortality,
and nonfatal myocardial infarction) within the medium- and long-term follow-up.
In an American School of Cardiology Basis/American Coronary heart Affiliation (ACCF/AHA)
consensus(9), information from six
massive research that collectively included 27,622 asymptomatic sufferers had been
aggregated and the relative danger of main cardiovascular occasions was calculated for
sufferers with a constructive CAC rating and for these with a CAC rating of zero. The
following outcomes had been obtained:
The CAC rating was studied in affiliation with different well-established conventional danger
rating programs, particularly the Framingham danger rating, displaying the next
benefits: unbiased added worth within the prediction of all-cause mortality and
mortality attributable to coronary illness in asymptomatic people(9); and reclassification within the
class of coronary artery illness risk-60% of atherosclerotic coronary occasions
happen in sufferers categorized as being at low or intermediate danger in keeping with the
Framingham danger rating. For example, amongst sufferers at intermediate danger in accordance
to the Framingham danger rating and with a CAC rating > 300, the annual frequency of
myocardial infarction or coronary loss of life can be 2.8%, which might place them in a
excessive danger class, the 10-year occasion frequency subsequently being roughly
28%(10).
The Framingham danger rating is a straightforward, low-cost methodology of cardiovascular danger
stratification that may be decided within the physician’s workplace and establishes the
10-year danger of CAD. The strategy takes into consideration age, gender, systolic blood
strain, ratio of whole ldl cholesterol to high-density lipoprotein fraction, smoking
standing, and the presence or absence of diabetes.
The CAC rating provides worth to the Framingham danger rating and to different strategies, offering
a considerable enhance within the accuracy of the danger stratification(1,11-13). It’s of notice
that the incidence of cardiovascular occasions reported for sufferers categorised as
being at intermediate danger by the Framingham danger rating and with an elevated CAC
rating is the same as or higher than that reported for sufferers categorised as being at
excessive danger by the Framingham danger rating and with a low CAC rating(1).
In america, only one% of girls between 50 and 59 years of age and 9% of males
between 60 and 69 years of age can be categorised as intermediate or excessive danger
in keeping with the Framingham standards. Nevertheless, the incidence of occasions in these
teams is ≤ 60% and ≤ 92%, respectively(14).
The CAC rating can also be an unbiased predictor of the danger of main cardiovascular
occasions, with demonstrated superiority over the Framingham danger rating, C-reactive
protein stage, and carotid intima-media thickness(11,13,15-18).
Varied research have used the receiver working attribute (ROC) curve
C-statistic-also often known as the realm beneath the curve-to evaluate completely different strategies of
predicting cardiovascular occasions. The ROC curve is a graph of sensitivity (fee of
true-positive outcomes) versus specificity (fee of false-positive outcomes) and
permits two or extra diagnostic checks to be in contrast. The world beneath the curve ranges
from 0.5 to 1.0, values > 0.7 being indicative of passable efficiency.
A research by Detrano et al.(19), who
adopted 6722 sufferers for a imply of three.9 years and in contrast medical danger elements
(age, gender, blood strain, serum ldl cholesterol, smoking, diabetes, household historical past
of CAD, serum triglycerides, serum creatinine, physique mass index, waist circumference,
and hip circumference), alone and together with the CAC rating, discovered space
beneath the curve values of 0.79 and 0.83, respectively. Different research(11-13,20) are quoted in
Desk 1.
THE CAC SCORE IN ASYMPTOMATIC PATIENTS: INDICATIONS, INTERPRETATION, AND
PROGNOSIS
USE OF THE CAC SCORE IN SYMPTOMATIC PATIENTS
A meta-analysis primarily based on articles printed between 1990 and 2008 analyzed the CAC
rating in symptomatic sufferers, correlating it with the prevalence of cardiovascular
occasions, the presence of great stenosis on angiography, the diagnostic accuracy
of the calcium rating for myocardial ischemia, and the detection of acute coronary
syndrome within the emergency room(30). These correlations might be mentioned beneath.