Intima media

Intima media


Juana M Plasencia Martínez et al

Carotid intima-media thickness and hemodynamic parameters

vascular risk factors. In a previous study whose sample

was classied in cardiovascular risk quartiles according

to IMT, minimal differences in magnitude moved pa

tients to distant quartiles. In that paper, being included

in the highest or the lowest quartiles depended on IMT

differences of just 0.3 mm [18]. Therefore, variability

of carotid ultrasound IMT magnitudes might make us

ing it as a biomarker of cardiovascular risk questionable.

Moreover, a recent large meta-analysis has questioned

the prognostic utility of IMT as a risk biomarker and has

argued that the extent of carotid plaque, when compared

to IMT, showed a greater accuracy for the prediction of

future coronary ischemic events [19]. In this scenario, the

analysis of carotid US agreements becomes relevant.

A number of previous papers have analyzed the re

producibility of manual and automatized carotid IMT

measurements [5,11,12,14,20,21]. However, only a few

made just a correlation analysis and agreement was not

actually assessed [11,12,20]. For other researchers, cor

relation based on coefcients of variation or difference

of means were acceptable [14,21] or very high [5], but

the interobserver agreement was not studied in the latter.

Unlike those studies, we assessed intra and interobserver

agreements with the intraclass correlation coefcient and

95% CI, and agreement, although overall acceptable, was

variable. IMTmean was always more reproducible than

IMTmax, probably because it is just one measurement,

it may be more variable than IMTmean [9]. IMTmax is

the normal approach in our department and has also been

the reference parameter in some studies [20]. However,

IMTmean (averaged three IMT measurements in the

distal CCA centimeter) is recommended by the ASE for

IMT manual quantication [9] and, as our results cor

roborate, less variable [15,21].

IMT agreement in this study was always better on

the left. Right-to-left thickness differences might be the

rst reason for agreement inconsistencies [5]. Though

not always the case [22], some reports have suggested

that atheromatosis might be more severe on the left CCA

[23-25]. Moreover, a stiffer and less elastic wall would

make it less variable during the cardiac cycle. In fact,

the effect of cardiac cycle on an IMT agreement can be

another possible source of variation [25]. Accordingly, a

thicker and less changing left carotid wall might allow

the operator to be more accurate when placing the cali

pers at the IMT edges. Further supporting that hypothe

sis, when reproducibility has been reported equal in both

sides, the consistence of measurements was higher on

the side where the carotid wall was thicker [5]. And lev

els of agreement were better bilaterally when IMT was

also bilaterally increased [11]. However, other authors

have reported a negative relation between agreement and

thickness [14,26] and taking into account that the higher

agreement on the left has been also reported with semi-

automated software [27], other factors than thickness

could inuence agreement and laterality. Accordingly,

the operators position on the left may change the angle

of insonation or the applied pressure [28,29]. And zoom

ing or experience might also have to be considered in the

background of inconsistencies. In our case, the operator

systematically enlarging the image also showed different

degrees of agreement and lower thickness values, which

is consistent with other reports [9]. On the other hand,

our results do not suggest an important impact regarding

the operator’s experience. Specic and fast training pro

tocols may improve IMT agreement even with inexperi

enced operators [30] suggesting that highly experienced

sonographers might not signicantly differ from less

trained operators. However, more dedicated designs are

required to achieve more reliable conclusions on zoom

ing or experience, even more considering that experience

has been previously related with disagreements [29,31].

Regarding the hemodynamic parameters, our intra

and interobserver agreements were slightly and clearly

worse, respectively, than others previously reported [32],

always with wide condence intervals. Intraobserver

concordance was higher with EDV than PSV, perhaps

related to the narrower range of EDV magnitudes. How

ever, we cannot easily explain why the interobserver was

better than the intraobserver agreement. Maybe, it was

partially an effect of the small sample, but, once again,

we cannot rule out the impact of those previously com

mented factors, related to technical, anatomical, physi

ological and pathological reasons, which, for the hemo

dynamic parameters, could be even more relevant.

Our study has several limitations. First, though we

wanted to involve more patients, their special character

istics and the number of examinations in different days

made it difcult to get a larger sample. As a result, the

small size lowers our statistical power. However, repro

ducibility studies may be attempted with at least 20 sub

jects [33,34] and, with that sample size, we can assume a

20% error margin [35], which is acceptable for the pre

liminary objective of this work. Moreover, a small sample

avoids the learning effect of successive carotid explora

tions identied in other studies [29]. Furthermore, our ef

fective sample size for a complete two time-point analy

sis was not signicantly different to other two time-point

agreement analysis in which the elderly with expected

cardiovascular disease were included [14,36]. Second, the

technical simplicity and the operators autonomy could

have introduced unpredictable sources of variability. The

foreseeable impact of subjectivity in manual quantica

tion makes reasonable thinking that automated techniques


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