Internal Carotid Artery Angle Variations are Poorly Explained by Vascular Risk Factors: The Northern Manhattan Study

The internal carotid artery (ICA) angle of origin may contribute to atherogenesis by altered hemodynamics. We aim to determine the contribution of vascular risk factors and arterial wall changes to ICA angle variations.

We analyzed 1,065 stroke-free participants from the population-based Northern Manhattan Study who underwent B-mode ultrasound (mean age 68.7±8.9 years; 59% women). ICA angle was estimated at the intersection between the common carotid artery and the ICA center line projections. Narrower external angles translating into greater carotid bifurcation bending were considered unfavorable. Linear regression models were fitted to assess the relationship between ICA angle and demographics, vascular risk factors, and arterial wall changes including carotid intima-media thickness (cIMT) and plaque presence.

ICA angles were narrower on the left compared to the right side (153±15.4 degrees versus 161.4±12.7 degrees, p<0.01). Mean cIMT was 0.9±0.1 mm and 54.3% had at least one plaque. ICA angle was not associated with cIMT or plaque presence. Unfavorable left and right ICA angles were associated with advanced age (per 10-year increase β=-1.6; p=0.01, and -1.3; p=0.03, respectively) and being Black participant (β=-4.6; p<0.01 and -2.9; p=0.04, respectively), while unfavorable left ICA angle was associated with being female (β=-2.8; p=0.03) and increased diastolic blood pressure (per 10 mmHg increase β=-2.1; p<0.01). Overall, studied factors explained less than 10% of the variance in ICA angle (left R²=0.07; right R²=0.05).

Only a small portion of ICA angle variation were explained by demographics, vascular risk factors and arterial wall changes. Whether ICA angle is determined by other environmental or genetic factors, and is an independent risk factor for atherogenesis, requires further investigation.