Correspondence

Carotid-Artery Intima and Media Thickness as a Risk Factor for Myocardial Infarction and Stroke

N Engl J Med 1999; 340:1762-1763June 3, 1999

Article

To the Editor:

Better predictors of stroke and myocardial infarction are clearly needed. The article by O'Leary and colleagues (Jan. 7 issue),1 which draws attention to the association between carotid-artery intima–media thickness and the risk of stroke and myocardial infarction in asymptomatic men and women who are 65 years of age or older, has made a contribution. However, the technology they used is complex and expensive, and the differences in carotid-artery intima–media thickness between patients at high risk and those at low risk are too small for common clinical use. The report by O'Leary et al. proposes the use of a sophisticated morphometric test of carotid structure as an additional screening test for vascular risk, to complement information about known risk factors. Is this test warranted in healthy older persons? Is it warranted when simpler functional tests (e.g., carotid tonometry, measurement of pulse pressure, or measurement of aortic pulse-wave velocity) may provide more information at a lower cost?

We believe that the primary ill effect is not the increase in carotid-artery thickness in itself, but rather the increase in the stiffness of the vessel that results from increased wall thickness and content. The increase in stiffness causes an increase in systolic and pulse pressure and, in persons over 60 years of age, a decrease in arterial diastolic pressure. The risk of stroke increases gradually with increasing pulse pressure and central arterial thickness.2 As the arteries become stiffer, the pulse-wave velocity increases, and the reflected pressure wave from the periphery returns in systole and thereby augments pressure (augmentation index) during ventricular contraction and ejection.3 This increase in pressure places an additional load on the left ventricle and leads to the development of ventricular hypertrophy, one of the most important risk factors for heart failure, ischemic heart disease, myocardial infarction, and sudden death. The results of carotid tonometry have shown a close, age-related association between systolic-pressure augmentation, left ventricular mass, and carotid-artery intima–media thickness.4 Aortic pulse-wave velocity is an established, well-known, and easily determined measure of aortic degeneration and left ventricular load.5

The technique of measuring carotid-artery intima–media thickness cannot separate intima from media and therefore cannot identify an increase in media thickness caused by premature degeneration of elastic fibers; this is the basis for increased aortic impedance and left ventricular load and hypertrophy with aging.2 As the authors also acknowledge, the technique cannot completely distinguish between thickening and early atherosclerosis within the intima itself. The measure is imprecise and nonspecific as well as expensive to obtain.

The measurement of carotid-artery intima–media thickness has become fashionable at the expense of functional measurements. Before it is accepted as a screening tool, all the above issues should be addressed.

Wilmer W. Nichols, M.D.
Carl J. Pepine, M.D.
University of Florida, Gainesville, FL 32610

Michael F. O'Rourke, M.D.
University of New South Wales, Sydney, NSW 2010, Australia

5 References

1. 1

   O'Leary DH, Polak JF, Kronmal RA, Manolio TA, Burke GL, Wolfson SK Jr. Carotid-artery intima and media thickness as a risk factor for myocardial infarction and stroke in older adults. N Engl J Med 1999;340:14-22
   Full Text | Web of Science | Medline

2. 2

   Bots ML, Hoes AW, Koudstaal PJ, Hofman A, Grobbee D. Common carotid intima-media thickness and risk of stroke and myocardial infarction: the Rotterdam Study. Circulation 1997;96:1432-1437
   Web of Science | Medline

3. 3

   Nichols WW, O'Rourke MF. McDonald's blood flow in arteries. 4th ed. New York: Oxford University Press, 1998.
   

4. 4

   Saba PS, Roman MJ, Pini R, Spitzer M, Ganau A, Devereux RB. Relation of arterial pressure waveform to left ventricular and carotid anatomy in normotensive subjects. J Am Coll Cardiol 1993;22:1873-1880
   CrossRef | Web of Science | Medline

5. 5

   Bramwell JC, Hill AV. The velocity of the pulse wave in man. Proc Soc Exp Biol Med 1922;93:298-306
   

Author/Editor Response

The authors reply:

To the Editor: We would like to make two points in response to Nichols et al. First, our article did not propose that measurements of carotid-artery intima and media thickness be used as a screening test. Second, although pulse-wave velocity is an interesting measurement, the work the authors cite was published in 1922.1 To the best of our knowledge, none of the simpler functional techniques have been evaluated with regard to the prediction of cardiovascular outcomes, although they have been with us for a long time. The idea of using ultrasonography to study carotid-artery intima–media thickness dates back to 1986.2 The ultrasound equipment used in our study was purchased in 1989. There have been 10 years of progress in imaging technology since then, which suggests that we would do even better if we were to initiate our study today. We are all in agreement that in the future noninvasive measurements of subclinical disease with the use of ultrasonography or other techniques may be important tools for predicting the risk of myocardial infarction and stroke in otherwise asymptomatic persons. Our article describes the results of a first step in this direction.

Daniel H. O'Leary, M.D.
New England Medical Center, Boston, MA 02111

Joseph F. Polak, M.D., M.P.H.
Brigham and Women's Hospital, Boston, MA 02115

Richard A. Kronmal, Ph.D.
University of Washington, Seattle, WA 98195

2 References

1. 1

   Bramwell JC, Hill AV. The velocity of the pulse wave in man. Proc Soc Exp Biol Med 1922;93:298-306
   

2. 2

   Pignoli P, Tremoli E, Poli A, Oreste P, Paoletti R. Intimal plus medial thickness of the arterial wall: a direct measurement with ultrasound imaging. Circulation 1986;74:1399-1406
   CrossRef | Web of Science | Medline

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