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Abstract

Thickening of the intima media (IMT) of the common carotid artery (CC) is an independent risk factor for the cardiovascular morbidity & mortality, and is considered an early marker for the development of atheroma. Atheroma is predominantly an intimal process, but current ultrasound imaging does not allow delineation of the intima from the media, despite the differential mechanisms involved in the thickening of these layers.

The aim of this study was to identify important factors influencing the CC IMT in untreated hypertensives with evidence of end organ change.

20 untreated hypertensive subjects (Median age 55 (range 41-66)yrs) were recruited from the Peart-Rose Clinic at St Mary's Hospital. Hypertension was confirmed using 24 ambulatory blood pressure monitoring (SpaceLabs 90207). Each subject underwent high-resolution examination of the right CC using a 7.5 Mhz ultrasound transducer (L 12-5 Scanhead, HDI 5000, ATL, USA). Each RCC was scanned in the 3 planes: anterior, anterolateral and posterior. Flow was recorded using pulse wave Doppler and local pressure assessed with applanation tonometry. Left ventricular mass was determined according to Penn convention and adjusted to body surface area.

IMT and luminal diameters (LD) were measured in diastole over a 1cm section proximal to the carotid bulb using a semi-automated edge detection package (AMS V6, Chalmers University, Sweden). The IMT and LD were identified as the median measure of the 3 image planes.

Associations were examined using linear regression and data are expressed as adjusted R2 and p values.

IMT was highly significantly associated with wall tension (T) (R2 =0.31, p=0.008) and also significantly with left ventricular mass index (LVMI) (R2 = 0.22, p = 0.02) but not any other parameter including shear stress.

Variation in IMT was best explained in a multiple linear regression model containing T, LVMI and triglycerides (adjusted R2 = 0.47, p = 0.01).

In this group of moderate to severe untreated hypertensives, the increase in IMT may represent an adaptive response to increased wall tension designed to normalise wall tensile stress. This implies that the predominant contribution to increased IMT is made by medial changes.

These findings should be taken into account when using IMT in the overall cardiovascular risk.

Intima Medial Thickness, Wall Tension, Untreated Hypertension
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© American Journal of Hypertension, Ltd. 2001
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