“Vascular Age”

"A man is as old as his arteries." - Thomas Sydenham

 

Why look at the neck when you are interested in the heart?

The carotid arteries provide a "window" to the coronary arteries. Not only do they have similar risk factors, the relationship between the atherosclerotic burden in a carotid artery and a coronary artery is the same as between any two coronary arteries (1). Thus, carotid atherosclerosis measurements also reflect the degree of coronary and systemic arterial injury in a given individual. By examining the carotid artery wall rather than the lumen, risk prediction with carotid ultrasound identifies an earlier stage of atherosclerosis than standard Duplex carotid imaging. Using a high-resolution B-mode ultrasound transducer, the common carotid, the carotid bulb, and the internal carotid artery can be interrogated to identify the presence of non-occlusive plaques and to measure carotid intima-media thickness (CIMT), the combined thicknesses of the intimal and medial layers of carotid walls. CIMT is an independent predictor of future cardiovascular disease (CVD) events, including heart attacks, cardiac death, and stroke (2).

 

 

Rationale for Using CIMT-Derived "Vascular Age" in Clinical Practice

The American Society of Echocardiography consensus statement on use of carotid ultrasound to identify subclinical vascular disease and evaluate CVD risk recommends reporting CIMT values with their corresponding percentiles, based on the patient’s age, sex, and race (2). In our experience, communication of the results of CIMT studies to patients and clinicians can be facilitated by reporting “vascular age” (3-5). “Vascular age” represents the age at which a given CIMT values would be “normal” – that is, the age at which the patient’s CIMT value would be at the 50th percentile for their sex and race (3-5). For example, a 45-year black female with a composite CIMT of 0.593 mm would have a CIMT percentile of 50% and a vascular age of 45 years; however, a 45-year black female with a composite CIMT of 0.678 mm would have a CIMT percentile of 71% and a vascular age of 55 years, the age at which a composite CIMT value of 0.678 mm represents the 50th percentile. We and others have reported on this concept, and have described our techniques for extrapolating vascular age from normative CIMT databases derived from epidemiological studies (3-7).

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Use of Vascular Age in Clinical Practice - UW Experience

Since the UW Vascular Health Screening Program started in November, 2001, over 1000 patients have had carotid ultrasounds to measure CIMT and to look for carotid plaques. This screening program requires a physician order and includes comprehensive patient counseling after the ultrasound study. As part of the clinical report, vascular age is calculated and used as a communication tool to help patients and their physicians understand the meaning of their CIMT values and how they compare to others of the same sex and race.

Vascular Age ChartIn two research reports, we substituted “vascular age” for “chronological age” in the Framingham risk prediction model. In the initial group of 82 individuals (45 males, 37 females) who underwent CIMT screening at UW, the median chronological age was 56 years old and the mean Framingham 10-year coronary risk was about 9.5%, representing middle-aged patients who were at intermediate risk for a cardiovascular event (4). The average CIMT was 0.806 mm and the average "vascular age" was about 65 years, an average increase in this referral population of about 9.6 years above their chronological age. Substituting CIMT-derived "vascular age" for chronological age also led to changes in predicted coronary risk. A predicted increase in coronary risk was observed in approximately 46% of subjects and a reduction in predicted coronary risk was seen in 20% of subjects. Of intermediate risk individuals, 36% were reclassified as higher risk and 14% were reclassified as lower risk. That is, 50% of subjects at intermediate risk could be reclassified into a higher risk zone, for more aggressive therapy, or a lower risk zone, for less intensive intervention.

Vascular Age ChartIn a second report, we focused on 261 individuals who were not on lipid-lowering therapy (5). We found increased CIMT in 77 individuals (30%). Of the 97 subjects at "moderate" or "moderately high" risk, 56.7% changed risk classification.

In our practice, we report the CIMT-derived “vascular age” along with the absolute CIMT value and CIMT percentile range. This approach helps patients and their physicians understand abnormal results and improves communication. We do not recommend substituting vascular age for chronological age outside of research settings.

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How To Obtain the Vascular Age Algorithms for Use in Your Clinical Lab

The concept of determining "vascular age" using ultrasound is the intellectual property of the Wisconsin Alumni Research Foundation (WARF). The algorithms for determining vascular age have been licensed to Emageon (as part of their CIMT Screen software package) and to Siemens Medical Solutions. For licensing information, contact Jerry Shattuck, Licensing Manager.

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References

  1. Young W, Gofman J, Tandy R, Malamud N, Waters E. The quantitation of atherosclerosis III. The extent of correlation of degrees of atherosclerosis with and between the coronary and cerebral vascular beds. Am J Cardiol 1960;8:300-8.
  2. Stein JH, Korcarz CE, Hurst RT, Lonn E, Kendall CB, Mohler ER, Najjar S, Rembold CM, Post WS. Use of carotid ultrasound to identify subclinical vascular disease and evaluate cardiovascular disease risk: A consensus statement from the American Society of Echocardiography Carotid Intima-Media Thickness Task Force. Journal of the American Society of Echocardiography 2008; 21:93-111.
  3. Stein, JH. Carotid intima-media thickness and vascular age: You're only as old as your arteries look. J Am Soc Echocardiogr 2004;17:686-689.
  4. Stein JH, Fraizer MC, Aeschlimann SE, Nelson-Worel J, McBride PE, Douglas PS. Vascular age: Integrating carotid intima-media thickness measurements with global coronary risk assessment. Clin Cardiol 2004; 27:388-392.
  5. Gepner AD, Keevil JG, Wyman RA, Aeschlimann SE, Korcarz CE, Busse KL, Stein JH. Use of carotid intima-media thickness and "vascular age" to modify cardiovascular risk prediction. J Am Soc Echocardiogr 2006; 19:1170-1174.
  6. Junyent M, Zambon D, Gilabert R, Nunez I, Cofan M, Ros E. Carotid atherosclerosis and vascular age in the assessment of coronary heart disease risk beyond the Framingham Risk Score. Atherosclerosis 2008; 196:803-809.
  7. Grundy SM: Coronary plaque as a replacement for age as a risk factor in global risk assessment. Am J Cardiol 2001;88:8E-11E.

 

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Last updated September 19, 2008