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UVMFLOWNET  August 2007

UVMFLOWNET August 2007

Subject:

Re: IMT

From:

"Johnson, Bill" <[log in to unmask]>

Reply-To:

UVM Flownet <[log in to unmask]>

Date:

Wed, 15 Aug 2007 12:53:24 -0700

Content-Type:

text/plain

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Parts/Attachments

text/plain (94 lines)

Bill Johnson, Kent, WA.
 
There does not appear to be an accepted criterion for IMT and it appears it would have to be a criteria (the plural), with consideration regarding age, sex, the presence of diabetes and possibly ethnicity.  
 
Since most studies utilizing IMT measurement have used it as a surrogate end-point for various drugs/treatments for atherosclerotic diseases, the concept o.  Instead of waiting for the patient to have a stroke, the end-point is reached with a defined increase in IMT.  In some studies the hope is to see a decline in IMT, or no increase.  Most of these studies can give some idea of what is considered "normal" in IMT, but were not designed to test the utility of IMT in overall risk assessment.  
 
There are studies that try to answer this question, many are very small studies and many do not consider the demographics of the patient population.  I have tried to condense the information from some of the best studies I have found, particulary with respect to demographics.  Please be aware the use if IMT as a risk assessment tool is somewhat controversial.
_________________________________________________________________________________________
 
6389 ( 55 years) subjects were included.  

 

To indicate no, mild, moderate, and severe thickening of the carotid wall, we divided the IMT into quartiles based on the population distribution, using cutoff points of 0.88, 0.99, and 1.12 mm, respectively.   

None < 0.88 

Mild 0.89 - 0.99 

Moderate 1.0 - 1.12 

Severe > 1.12

At the baseline (1990-1993) examination of the Rotterdam Study, a population-based cohort study among subjects age 55 years, carotid plaques and intima-media thickness (IMT) were measured by ultrasound, abdominal aortic atherosclerosis by x-ray, and lower-extremity atherosclerosis by computation of the ankle-arm index. In the present study, 6389 subjects were included; 258 cases of incident MI occurred before January 1, 2000. All 4 measures of atherosclerosis were good predictors of MI independently of traditional cardiovascular risk factors. Hazard ratios were equally high for carotid plaques (1.83 [1.27 to 2.62], severe versus no atherosclerosis), carotid IMT (1.95 [1.19 to 3.19]), and aortic atherosclerosis (1.94 [1.30 to 2.90]) and slightly lower for lower-extremity atherosclerosis (1.59 [1.05 to 2.39]), although differences were small. The hazard ratio for MI for subjects with severe atherosclerosis according to a composite atherosclerosis score was 2.77 (1.70 to 4.52) compared with subjects with no atherosclerosis. The predictive value of MI for a given measure of atherosclerosis was independent of the other atherosclerosis measures.

van der Meer IM, Bots ML, Albert Hofman A, et al. Predictive Value of Noninvasive Measures of Atherosclerosis for Incident Myocardial Infarction - The Rotterdam Study. Circulation. 2004;109:1089-1094.

1,288 eastern Finnish men

The study reports that a one-time measurement of the maximal common carotid arterial intima-media thickness greater than 1.0 mm was predictive of acute myocardial infarction over a 1-month to 3-year period (relative risk, 2.2 [CI, 0.7 to 6.7]). 

Salonen JT, Salonen R. Ultrasonographically assessed carotid morphology and the risk of coronary heart disease. Arterioscler Thromb. 1991; 11:1245-9

 

319 healthy subjects (154 men, 165 women; age range, 21 to 105 years) with no history of hypertension, diabetes mellitus, or atherosclerotic disease.

"...we found a linear correlation between mean CCA IMT and age..." 

 

This study contains a scattergram very helpful in understanding the effect of aging on IMT see figure 1 - Bill

 

Homma S, Hirose N, Ishida H, et al.  Carotid plaque and intima-media thickness assessed by b-mode ultrasonography in subjects ranging from young adults to centenarians. Stroke. <javascript:AL_get(this,%20'jour',%20'Stroke.');>  2001 Apr;32(4):830-5.

http://stroke.ahajournals.org/cgi/content/full/32/4/830 <http://stroke.ahajournals.org/cgi/content/full/32/4/830> 

 

 

The ARIC investigators have obtained data from well standardized measurements in a population-based study of 15,792 persons across four communities. 7,865 women and 6,349 men aged 45-64 years without prior stroke. The associations of IMT with potential stroke risk factors have already been firmly established (53-67). This analysis establishes the association of carotid IMT with incident ischemic stroke. After we accounted for the predictive value of other variables, having a mean IMT of 0.8-1.0 mm at baseline was associated with at least a twofold greater hazard rate of subsequent  ischemic stroke, and having a mean IMT above 1.0 mm was associated with a three- to fourfold greater hazard rate. To put these numbers into perspective, we note that the hazard rate ratios for hypertension, diabetes, and current smoking (relative to never smoking) were 2.1, 2.5, and 1.3, respectively. We conclude that mean carotid IMT is a useful noninvasive measure that can contribute to the risk stratification of free-living individuals regarding future occurrence of ischemic stroke.

 

http://aje.oxfordjournals.org/cgi/reprint/151/5/478 <http://aje.oxfordjournals.org/cgi/reprint/151/5/478> 

 

Chambless LE, Folsom AR, Clegg LX, et al.  Carotid wall thickness is predictive of incident clinical stroke: the Atherosclerosis Risk in Communities (ARIC) study.  Am J Epidemiol. 2000 Mar 1;151(5):478-87.

 

  

Aged 33 to 42 - mean maximum carotid IMT 

            Men  0.79  0.12mm - Cutoff 0.91

            Women 0.72  0.10 mm - Cutoff 0.81

Davis PH, MD; Dawson JD, Riley WA, et al.  Carotid Intimal-Medial Thickness Is Related to Cardiovascular Risk Factors Measured From Childhood Through Middle Age - The Muscatine Study. Circulation. 2001;104:2815.

271 type II diabetics, 285 control subjects.

 

See figure 5 for a scattergram showing the effects of diabetes on IMT - Bill

 

http://care.diabetesjournals.org/cgi/reprint/22/11/1851 <http://care.diabetesjournals.org/cgi/reprint/22/11/1851> 

Davis PH, MD; Dawson JD, Riley WA, et al.  Carotid Intimal-Medial Thickness Is Related to Cardiovascular Risk Factors Measured From Childhood Through Middle Age - The Muscatine Study. Circulation. 2001;104:2815.


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